Biological Control of Insect Pests

Biological Control of Insect Pests
CIHEAM- Mediterranean Agronomic Institute of Bari Biological Control of Insect Pests Prepared by: Hamid El Bilali and Vito Simeone

Contents Main non-pesticides control tools: micro-organisms, macro-organisms, natural products and semiochemicals; Definition of biological control; Biocontrol history; Basic biological control theories; Biological control objectives; Biocontrol approaches; Biological control agents: parasitoids, predators and pathogens.

Pests control in organic agriculture
In organic agriculture, crops protection is based first of all on a good deal of knowledge on agroecosystem (biocenocis and biotope) and information about the target pest, prevention, interactions plant- environment-pest and finally on the use of the allowed pesticides (Annex II-B of the E.C.R. N° 2092/91).

Pests management Knowledge of the pest: key pest, identification, bio-ethology and techniques of monitoring and sampling. Monitoring: Pheromone/chromotropic traps, sticky barriers… Prevention techniques. Biological control. Cultural management: Appropriate species and varieties: tolerant or resistant cultivars; Appropriate rotation programmes; Longer fallow period and more frequent grass rotation. Irrigation and fertilisation; Pruning, leaves removal… Mechanical practices: Use of mechanical barriers- insect-proof net; floating row covers; plastic tunnels, reflective mulches (aphids)… Use of authorised bio-pesticides. Mechanical barrier against Otiorrhynchus cribricollis

Prevention techniques
Site selection (climate and soil): Effective for nematodes and soilborne pathogens ( Armillaria, Fusarium, Plasmodiophora, Sclerotium, Verticillium, Phytophtora, Pythium and Rhizoctonia). Use of healthy material: Certified seeds (pathogen-free seeds) and propagation material (transplants). Use of forecasting model can help in the management of some diseases like fungal ones. Inoculum reduction: Crop rotations; Soil solarisation; Preventing the introduction of the inoculum by exclusion practices; Use clean pots, trays and potting mix; Inoculum eradication; Soil tillage….

Prevention techniques
Use of resistant varieties and root-stocks; Shifting the cropping period: Coordinate planting and harvesting dates to avoid pests. Field sanitation (roguing): Removal and destruction of diseased, dying and dead plants; Promoting crops aeration by canopy management practices: Effective against fungal diseases. Rational fertilisation (balanced in nitrogen) and irrigation (clean water at proper amount); Promoting beneficial insects. Use of indicator plants: Rose for grapevine powdery mildew.

Pests biological control
Release of reared beneficial predator and parasitoid arthropod, insects and mites, (inoculative, augmentative or inundative releases): Psyttalia (Opius) concolor against olive fruit fly, Bactrocera oleae. Mating disruption. Use of antagonist micro-organisms: bacteria, Bacillus thuringiensis against Lepidoptera, fungi Ampelomyces quisqualis against powdery mildew; Protozoa; nematodes; baculovirus and granulosis virus. Biological control of powdery mildew with: Orthotydeus lambi (Tydeidae mite), Bacillus (subtilis) sp., Trichoderma harzianum , Verticillium lecanii, Tilletiopsis sp. …

Trap plants: Phacelia tanacetifolia againt Frankliniella occidentalis, Tagetes sp. against nematodes (Meloidogyne spp.). Oilseed radish could be a potential trap crop for cyst nematode ( Heterodera spp.). Phacelia tanacetifolia

Bio-pesticides Advantages: Low mammalian toxicity; Minimal effect on beneficial insects; Fast action and breakdown so low environmental impact; High selectivity; Short pre-harvest interval; Low phytotoxicity. Limit: Contact products so adequate coverage is essential to have a good efficacy. Types: Naturally occurring substances; Substances of plant origin (botanicals); Substances of animal origin; Microorganisms-based bio-pesticides.

Types of bio-pesticides
Naturally occurring substances: Sulphur and lime sulphur (calcium polysulphide), copper (up to 6kg/ha/year); quartz sand.. Botanicals (plant origin): Azadirachtin (Azadirachta indica), rotenone (Derris spp., Tephrosia spp. and Lonchocarpus spp. ), pyrethrins (Chrysanthemum/ Tanacetum spp), Quassia amara extract, Nicotiana tabacum extract, Sabadilla (Schoenocaulon spp.), Hellebore (Veratum album), croton (Croton tiglium), Yam bean (Pachyrhizus erosus ), Ryania (Ryania speciosa), thunder god vine (Tripterygium wilfordii), Amur corktree (Phellodendron amurense), Heliopsis longipes..

Types of bio-pesticides
Plants oils: Mint, pine and caraway (Carum carvi ) linseed, hempseed, cottonseed, rapeseed (colza), castor bean (Ricinus communis), coconut, soybean, palm, corn... Substances of animal origin: beeswax, gelatine, hyrolysed proteins… Animal fats: Whale, fish (cod, herring, menhaden, sardine), degras (wool grease), lard, neatsfoot… Substances used in traps and/or dispensers: Diammonium phosphate, metaldehyde, pheromones, pyrethroids (Deltamethrin and Lambda-Cyhalothrin) Others: Paraffin and mineral oils, K-permanganate...

Use plant suppressive effects on diseases: Broccoli on Verticillium dahliae microsclerotia, cover crops like mustards and sudangrass on soilborne pathogens. Bio-fumigation: Use of compost and organic amendments (castor, neem and argan cakes) supressive properties due to their content in allelopathic substances to kill soil pathogens (nematodes and soil-borne pathogens).

Non-pesticides control
In “The Manual of Biocontrol Agents” (Copping, 2004) there are 373 entries of which: Micro-organisms: 112 entries (species/ isolates/ formulations). Macro-organisms: 126 entries (insects and mites, arthropods); Natural products: 57 entries (microorganism- and plant-derived products). Semiochemicals: 55 entries (sex, aggregation, and alarm pheromones); Genes: 19 entries (resistance to hrerbicides, insects, and viruses inducers).

Non-pesticides control
(Copping, 2004)

Natural products especially plant- and microorganisms- derived ones

Natural products use in biocontrol
(Copping, 2004)

Azadirachtin Source: Neem tree, Azadirachta indica ; Family: Meliacae;
Natural Habitat : South Asia, in particular India ; Extracted from seeds (Kernels);

Azadirachtin: active ingredients
Principal active ingredients: Azadirachtin A (AZA) (C35H44O16) with its 7 isomers and Azadirachtin B ; Mechanism of action: repellent, growth regulator, anti-oviposition, reduces adults fecundity and eggs vitality. Mode of action: Contact, ingestion with a systemic activity; Activity spectrum: Effective against at lesat 200 insect species, nematicide, acaricide with a certain fungicidal activity. Pre-harvest interval: 3 days;

Rotenone Derris elliptica Lonchocarpus sp.
Plants : Derris elliptica , mistica and malaccensis; Lonchocarpus utilis, urucu, nicou and chrysophyllus; Tephrosia macropoda, toxicaria, vogelii and virginiana; Family: Leguminosae; Extracted from roots; Derris elliptica Lonchocarpus sp.

Rotenone Principal active ingredients: Rotenone or Nicouline (Isoflavonoid, Alkaloid) ; Mechanism of action: Interference with respiration and with perpherical nervous system; Mode of action: Mainly by contact and sometimes via ingestion; Activity spectrum: Non-systemic selective insecticide (Diptera, Coleoptera, Lepidoptera, Hemiptera, Thysanoptera, Hymenoptera) with a secondary acaricidal activity. Pre-harvest interval: 10 days;

Pyrethrins Plant: Tanacetum (Chrysanthemum)
cinerariaefolium and T. cineum. Family: Compositae; Natural habitat: China, east of Africa and Japan; Extracted from flowers; Main active ingredient: Pyrethrin I; Mode of action: Contact and ingestion; Mechanism of action: Acts on peripherical and central nervous system causing an immediate insects paralysis; Activity spectrum: mainly an insecticide with a certain acaricidal activity; Pre-harvest interval: 2 days;

Pyrethrins: Active ingredients
There are six different active ingredients (pyrethrins) resulting from the combination of two acids and 3 alcohols Cathegory Acid Alcohol Active ingredients Pyrethrins Pyrethrins I Crysanthe-mic Pyrethrolone Pyrethrin I Cinerolone Cinerin I Jasmolone Jasmolin I Pyrethrins II Pyrethroic Pyrethrin II Cinerin II Jasmolin II

Semiochemicals: Reppelents, attractants and sex, alarm, and aggregation pheromones.

Semiochemicals use in biocontrol
(Copping, 2004)

Semiochemicals Sex pheromone:
Males locate and subsequently mate with females by following the trail or pheromone emitted by virgin females. The indiscriminate application of high levels of sex pheromone in traps and dispensers interferes with this natural process since a constant exposure to high levels of pheromone makes trail following impossible (habituation/adaptation phenomenon). The use of discrete source of sex pheromone released over time presents the male a false trail to follow (sexual confusion/ mating disruption). Control is subsequently achieved through the prevention of mating and consequently the laying of fertile eggs. Sex pheromone are species-specific.

Semiochemicals Aggregation pheromones:
Males and females locate host trees by following a plume of air enriched with a mixture of the odour of the host tree and the aggregation pheromone. Evaporation of pheromone vapours from dispensers attached to host trees attract both males and females of the insect pest to the baited trees and establiches conditions for mass attack of baited trees by the insect pests. The baiting of selected areas and trees reduces the number of attacks in the main orchard or forest areas. The baited trees and those trees closed to them should be felled before the progeny emerges from the infested trees. Aggregation pheromone can be also used in monitoring. They are effective in the case of beetles (Coleoptera). Attractants are used in traps for monitoring and time management decisions of pesticides applications.

Semiochemicals Alarm pheromones:
Alarm pheromones are released under natural conditions when the population in threatened or being attacked by a predator. The result of this release in an increase in the activity of phytophagous insects with the subsequent higher exposure to a co-applied pesticide. Alarm pheromones are often mixed with conventional pesticides (especially acaricide) and show an increase in the mortality of pests (mites). The alarmed pests (e.g. spider mites) feed less than undisturbed ones.

Semiochemicals Reppelent pheromones:
Reppelent pheromones are emitted naturally by some insect pests (e.g. beetles) when they reach a critical density in order to repel additional insects and, thereby to protect the food supply needed by these insects and their offspring. A slight chemical alteration can change an attractant to a reppelent (e.g., Seudenol which is an attractant of douglas fir and spruce beetles was transformed into 3-methyl-cyclohex-2-en-1-one which is a reppelent of the same species). The use of reppelent pheromone on healthy trees can be combined with the use of aggregation pheromone on dead or dying trees.

Mass trapping: Attract&Kill method
Attractant: Ammonium bicarbonate; Pheromone: Virgin female sex pheromone; Insecticide: Pyrethroids (Deltamethrin in Eco-trap or Lambda-Cyhalothrinin Agrisense). Agrisense Eco-trap 3030

Definition of biological control

Biological control definition
Biological control can be defined as the use of natural enemies to reduce the damage caused by a pest population. Biological control is an approach that fits into an overall pest management program, and represents an alternative to continued reliance on pesticides.

Biological control definition
One definition of biological control that is easy to use and to remember is that biological control is "three sets of three". The sets of three represent: The "who": The natural enemies themselves that is to say predators, parasitoids and pathogens. The "what": The objective to achieve which can be prevention, reduction or delay of infestation. The "how": The approach that is taken with the natural enemy to achieve the objective which can be conservation, augmentation or importation.

Biocontrol history

Biocontrol history Predation, parasitism and insect pathology have different histories; Predation has been more easily observed and recorded than parasitism and disease because of larger size of insect predators with respect to pathogens and parasitoids. Records from southern China indicate that weaver ant, Oecophylla smaragdina, nests have been gathered, sold, and placed in citrus orchards for approximately 2000 years. Date growers in Yemen placed colonies of predatory ants in date palms for insect control. The beneficial aspects of coccinellid predation has been recognized in Europe since the 13th century.

Biocontrol history Interpretation of insect parasitism and the development of insect pathology were dependent upon the invention of microscopy. The earliest recorded observations in western Europe of insect parasitism occurred during the 1600s. In 1602 Aldrovandi recorded observations of parasitic larvae of Apanteles (Cotesia) glomeratus exiting from cabbage butterfly (Pieris rapae) and spinning external cocoons. In 1670 Martin Lister correctly interpreted insect parasitism in a letter published in the Philosophical Transactions of the Royal Society of London.

Biocontrol history The importation of the vedalia ladybird beetle to California citrus orchards beetle to reduce the population level of cottony cushion scale can be considered as the beginning of the modern era of biological control. This importation project saved the developing citrus industry in California in the late 1800s and provided the impetus for biological control efforts within California. This spectacular biological control success in California was repeated in several other countries. Nowadays, many biological control agents are used with success for the containment of many pests in almost all the countries.

Basic biological control theories: populations dynamics, density-dependance and alternative theories.

Basic biological control theories
There is a high diversity and complexity of theories and models in biological control that try to understand the biology of natural enemies and their impact on host (prey) population dynamics. The process by which densities of populations are maintained in nature is referred to as "natural control". Natural control serves as the basis for biological control and other pest control tactics. Understanding the major concepts of natural control is key to understanding how natural enemies control pests and how they can be used in biological control programmes. Biological control has contributed significantly to the theoretical understanding of natural control..

Basic biological control theories: population dynamics
A population is a group of interbreeding individuals of the same species located in a defined area. Early history of the field of ecology reflected the interest of ecologists in determining a theoretical structure to explain the observed patterns of population dynamics in order to identify the relative role of factors responsible for causing population change. Understanding of natural control to which the majority of biological control specialists subscribe is that populations exists at a characteristic abundance, which is defined as the long-term expected numbers of individuals in a population.

Basic biological control theories: population dynamics
Presence of a characteristic abundance suggested that populations were being maintained around a given level (density) through the actions of factors found in the local environment. Reduction and maintenance of introduced pest populations following introduction of "exotic" natural enemies was seen as confirming both the existence of a characteristic abundance and the role natural enemies play in maintaining insect population densities.

Basic biological control theories: Density-dependance
Maintaining population density around a characteristic abundance required the action of factors that behaved in a density dependent fashion. The tendency for population to be maintained around a characteristic abundance via action of density dependent factor(s) is referred to as population regulation. A factor that acts in a density-dependent fashion increases its impact on the affected population as the density of the population increases. Thus, natural enemies whose percentages attack rate increases in response to host (prey) density increases are said to be acting in a density-dependent fashion.

Basic biological control theories: Density-dependance
The need to have density-dependent factor(s) regulating populations around a characteristic abundance was seen as necessary to counter the potential exponential growth rate that all populations possess. Without a factor(s) that acted in a density-dependent fashion, populations would eventually grow to the point where they consume their resource base and crash towards local extinction. The persistence of populations, and the relative lack of data for local extinctions, was seen as confirming evidence for the existence of density-dependence factors and the regulation of populations in nature. Other than natural enemies, factors that act in a density-dependent fashion are intra-and inter-specific competition and territoriality.

Basic biological control theories
Illustration of natural control: the population number is fluctuating over time it is bounded within a range. The population's "characteristic abundanc“, the long term expected number of individuals in the population, is represented by the yellow. Example of a factor that acts in a density-dependent fashion (

Basic biological control theories: Alternative theories
Historically, the major challenge to the "density-dependent school" came from those who felt that the evidence for population stability in nature was not proved, and that the numbers of individuals in a population was largely determined by the time available for population growth. Population control can be accounted for via vagaries in environmental limits that are not related to density per se. Whereas followers of the density-dependent school saw populations existing in a characteristic abundance, those of the density-independent school saw populations in flux, with extinctions common and the long-term expected number of a population only a statistical, not biological, reality. The abundance and distribution of populations reflected adaptation to local conditions that are limited as to the nature, magnitude and direction of change.

Populations track environmental change, expanding in favourable times and contracting during unfavourable periods. Population control was seen to have elements of maintenance within boundaries ("control") and return to equilibrium ("regulation"). Extinction of populations happens and the imposition of density- dependence occurs for only relatively short time periods. For the most part, it is a combination of so-called "imperfect density-dependent" factors (including natural enemies) and density-independent factors (primarily weather) that influence population dynamics.

"Conditioning factors" uninfluenced by density, will control or set the framework of environment upon which density dependent factors act. At lower densities, either density-independent factors "relax" or the population goes extinct. At higher densities, the only "perfect" density-dependent factor, intra-specific competition prevents continued population growth and causes the population to decline to lower levels. Uunderstanding of the role of natural enemies in the natural control of insect populations has evolved over time: Originally seen as acting as so-called "perfect" density-dependent agents regulating populations, more synthetic theories place the impact of natural enemies within a context of overall environmental impact on population dynamics.

Biological control objectives: reduction, prevention or delay of infestation

Infestation reduction
Reduction of a pest population after it occurs at a damaging level It approximates the use of pesticides. A biological control agent is used after the pest population has exceeded the economic threshold, with a goal of sufficiently reducing pest density and maintaining a lower density over a long period of time. The pest is not eradicated but simply reduced to non-pest status. This has been the historical approach for importing natural enemies against exotic pests: Vedalia ladybird beetle against cottony cushion scale.

Infestation prevention
The objective is to keep the population of a potential pest from reaching a high, or economic, level. Prevention requires early intervention, before a pest build-up occurs. The action of a natural enemy early in the life cycle of the potential pest can keep the population from reaching pest status. Infestation delay This objective is similar to prevention, in that both require early intervention, before a population exceeds a threshold. However, delay means that the population will eventually build up to a high level, but it does so at a time when the species is no longer considered a pest.

Biocontrol approaches: The tactical approach taken to achieve the objectives, which may be conservation, augmentation or importation.

Conservation Conservation biological control basically means keeping alive and enhancing the effectiveness of those natural enemies that are already present. Many conservation approaches are easily integrated into production regimens and can be very effective. Reduction of pesticides use is one of the most important tools in conservation approach: Use of fewer applications of pesticides, Altering the timing or formulation of the pesticides, Use of "soft" pesticides such as those based on natural products, which may be less persistent and also less toxic to natural enemies. Integration of other control measures like agronomical ones.

Conservation Often, providing a missing requirement can make the difference for a natural enemy: Non-prey food sources, such as flowers that might produce nectar or pollen. Nesting sites for social insects (wasps) can lead to increased population persistence and, as a result, greater predation against certain pest species. Wood lots moderate temperature for some beneficial insects especially parasitoids.

Habitat management or farmscaping
Protection of natural enemies by incorporating beneficial practices (alternative food sources, over-wintering sites, shelter, alternative preys/hosts) and avoid harmful practices (insecticides, inappropriate ploughing , irrigation and burning of crop residues). Hedges with native plant species that are easily attacked by alternative preys and that produce nectar, pollen and fleshy fruits… Preserve dry walls, old and high trees, flowering borders, hedges and perennial habitats and non-crop habitats Diversified cropping systems: double cropping, strip cropping, cover cropping, and intercropping. Till the soil leaving some areas temporarily with weeds ; Keep fields covered in winter (cover-crops and natural weeding); Install artificial nests for insectivorous birds and bats.

Key considerations in drafting a farmscaping plan
Ecology of pest and natural enemies and their movement behaviour, Timing ; Identification of strategies for increasing farm biodiversity; Insectary establishment. Indicators for evaluating a farmscaping strategy Vegetation types and biodiversity; Prey/host abundance; Availability of complementary resources (nectar, pollen); Ratio of crop to interplanted land and spatial arrangement of interplanted vegetation.

Principles for conserving and/or enhancing agricultural biodiversity
Adoption of diversified farming systems: Diversification in time (crop rotation, sequences), space (polycultures, agroforestry, mixed farming, intercropping..). Recycling and conservation of soil nutrients and organic matter: use of plant and animal biomass and favours recycling of nutrients and on-farm natural resources. Integrated pest management and biological control. Conservation and regeneration of natural resources: germoplasm conservation; beneficial fauna and flora, soil health, water… Enhance soil biodiversity: farming practices that minimise soil disturbance, minimum or no-tillage, crop rotation, organic amendments (manure, compost), recycling of plant residues…

Principles for conserving and/or enhancing agricultural biodiversity
Application of agroecological principles; Active participation and empowerment of native and indigenous small farmers and the protection of their rights; Adaptation of practices to local agroecological and socio-economic conditions; Conservation of local animal and plant genetic resources; Reforming genetic research and breeding programs towards more respect of agrobiodiversity; Creating a supportive policy environment.

Examples of hedge species planted in organic orchards
Mastic Tree, Evergreen Pistache: Pistacia lentiscus Gum arabic tree: Acacia spinosa Inula viscose Jujube berries: Zizyphus sativa

Hegde species and beneficial insects
Family: Santalacee; Scientific name : Osyris alba L.; Common name: Poet's Cassia (Ginestrella Comune in Italian). Poet’s Cassica hosts many beneficial insects against olive moth (Prays oleae) like Chelonus eleaphilus. Furthermor, they are also some alternative preys of this beneficial insect living on Poet’s Cassia.

Augmentation Augmentation biological control basically means adding natural enemies, either where they are not present, or are present at small numbers. Augmentation has been used more extensively in greenhouse and interior settings than in crop settings, but there are examples of successful use in nearly all settings. Two different approaches to augmentation: Inoculation of small numbers of natural enemies, or inundating with large numbers.

Augmentation: Inoculation and Inundation
With inoculation, one begins with a small number and allows the natural enemy populations to increase over time. In this case, the pest population does not decrease quickly but can either be prevented from reaching pest status or the population increase is delayed. With inundation, one introduces a large number of natural enemies, with the intention of reducing the population quickly. Inundation has a greater associated cost, as the large number of natural enemies either must be purchased or reared.

Importation Importation biological control means to introduce a new exotic natural enemy from one environment to a new setting, hence "importing" it. This approach is often called "classical" biological control. Some biological control practitioners consider this the only "true" biological control approach.

Biological control agents: parasitoids, predators and pathogens.

Macro-organisms use in biocontrol
(Copping, 2004)

Phytophagous biocontrol agents
(Copping, 2004)

Parasitoids

Parasitoids Parasitic insects (also known as parasites and parasitoids) are insects whose immature stages (larvae) develop by feeding on or in the bodies of their host arthropods, which are usually other insects. Host: The organism attacked and used as a food source by the parasite. The recipient of the protagonist's action. Equivalent to a prey used by a predator. Unlike true zoological parasites, parasitic insects kill their hosts. Parasitic insects are unique, because it is the immature stages that kill the host. Nearly all parasite immatures develop on or in a single host.

Parasitoids Parasites are holometabolous, having complete development (egg, larval, pupal and adult stages). Adult parasites are free living; some species will feed on hosts (predators), in addition to ovipositing in or on the hosts. In the world of parasites, only females are significant players, as they are the ones that find and attack hosts. For some species, males are not known to exist. The number of species of parasites is unknown and speculative, ranging from an estimate of 800,000 to as many as 25% of all insects.

Parasitoids types Parasitoids are usually defined by:
Where the egg is laid (inside the host = endoparasite; outside the host = ectoparasite). The feeding habit of the immature stage (egg, larval, pupal parasite, etc.). Whether one or more parasite progeny emerge from the host (solitary vs. gregarious). Host-parasitoid interactions.

Parasitoids types The feeding habit of the immature stage:
Egg parasite: Parasite adult attacks the host egg, and the parasite progeny emerge from the egg. Egg-larval parasite: Parasite adult attacks the host egg, but the parasite progeny emerge from the larva. Larval parasite: Parasite adult attacks the host larva, and the parasite progeny emerge from the larva. Larval-pupal parasite: Parasite adult attacks the host larva, but the parasite progeny emerge from the pupa. Pupal parasite: Parasite adult attacks the host pupa, and the parasite progeny emerge from the pupa.

Parasitoids types Place of oviposition:
Ectoparasite (External Parasite): Parasite develops externally on the host with its mouthparts inserted into the host's body. Endoparasite (Internal Parasite): Parasite larva develops inside the host's body. Number of parasites’ progenies that emerge from the host : Parasite species load: The number of parasite species that usually attack a host species. Hosts range: The number of host species that are usually attacked and utilized successfully by a parasite species.

Parasitoids types Number of parasites’ progenies :
Gregarious parasite: Multiple parasite eggs are deposited, the larvae feed together on a single host, and multiple parasite offspring emerge. Solitary parasite: Only one parasite egg is deposited per oviposition event and generally only one progeny emerges from the host. Polyembryonic parasite: Many (up to several thousand) parasites emerge from a host, having arisen from asexual division of one or two parasite eggs. Restricted to four families of parasitic Hymenoptera (Braconidae, Dryinidae, Encyrtidae, Platygastridae).

Parasitoids types Number of parasites’ progenies :
Multiparasitism: A single host is attacked by more than one species of parasites, and the second parasite species feeds on the original host, not the other parasite species. Superparasitism: Several females of one species of parasite attack the same host, or one female oviposits more than one egg, with only one egg laid at a time. Often, only one progeny will survive. This is not the same as gregarious parasitism, where a single female lays many eggs in one oviposition bout.

Parasitoids types Host-parasite interactions:
Primary parasite: The parasite attacks and develops in or on a host, and that host is not another parasite. Cleptoparasite: A parasite that requires a host to be parasitized already. Facultative hyperparasite: Can develop either as a hyperparasite in a host already parasitized by a primary parasite, or it can develop as a primary parasite in an un-parasitized host. Heteronomous parasite (Autoparasite and Adelphoparasite): Females develop as primary parasites of homopterans (whiteflies, scales), but males develop as a hyperparasite of female primary parasites of homopterans. Heterotrophic parasite: The female is a primary parasite of homopterans, but the male is an obligate parasite of a completely different host, such as eggs of Lepidoptera.

Parasitoids types Host-parasite interactions:
Idiobiont parasite: Parasite prevents continued growth by the host. Hosts are often paralysed. Often egg, pupal, and adult parasites. Koinobiont parasite: Parasite allows continued growth and development of the host. Host not paralysed. Egg-larval, larval-pupal parasites, and larval parasites. The parasite larva either suspends development as a first instar, or the parasite larva avoids feeding on vital organs until late in development. Obligate hyperparasite: The hyperparasite can only develop as a parasite of a primary parasite. Secondary parasite (Hyperparasite): The parasite attacks a host that is another parasite.

Parasitoids taxonomy Although parasitism is found in several insects orders, primary orders of parasites are Hymenoptera and Diptera. The greatest diversity of parasites is found in Hymenoptera. The most important parasitic families within Hymenoptera order are: Dryinidae, Bethylidae, Chrysididae and wasps. Several Diptera families have members that are parasitic: Acroceridae, Bombylidae, Cecidomyiidae, Cryptochetidae, Phoridae, Pipincluidae, Tachinidae, and Sarcophagidae. Rare representative taxa are also found in the Coleoptera, Lepidoptera and Neuroptera. Strepsiptera are true zoological parasites, as they do not kill their hosts.

Hymenoptera parasitic families
(Copping, 2004)

Parasitoids-hosts interactions
All parasites go through a series of processes by which they find, attack and utilize their hosts. In order to understand better parasitoids-hosts interactions it is very important to analyse the following main precesses: Habitat selection, host location, host acceptance, host suitability, and host regulation. It is important to remember that there is a great overlap between processes, and that some of the processes are less important for particular parasites or in some settings. Each process is mediated by a multitude of cues (signals).

Parasitoids-hosts interactions: Habitat selection
Habitat selection is the first of the processes that affect host utilization. The importance of habitat selection cues to biological control is that they serve to get the parasite to the appropriate habitat in which they may find the target pest, and thus have a greater chance of successfully controlling the target pest. Parasites that respond to specific habitat cues also will show some degree of habitat fidelity. The fidelity to particular habitat types means that the parasites will not be likely to attack non-target species that may be found in other habitats.

Many parasites use cues from the habitat itself, independent of whether hosts are present or not. The habitat selection cues are linked to the female's reproductive state, as it has been seen that, before the female parasite's eggs are mature, she is repelled by the same chemicals from the same plants (habitats). Numerous examples exist of parasites being attracted to the habitat of their hosts. These cues serve to get the parasite into an appropriate habitat, in which hosts might be likely to be found.

Cues serve to orient a parasite to a habitat, so most known habitat-related cues are long distance. Cues used for habitat selection are usually visual, or volatile odours: Visual cues: Drill-and-sting strategy in which the parasitoid drills its ovipositor through the stem of a grass, ovipositing into an enclosed lepidopteran pupa. Volatile odours or chemical cues: Chemicals existing in a certain habitat give some indications about the presence of the parasitoid host that emitted them.

Parasitoids-hosts interactions: Host location
In this process, the parasite is responding to cues that indicate the presence of a host, but only after the parasite is in the appropriate habitat. The cues serve to get the parasite from the "neighbourhood" of the host (the habitat), to the specific location of the host. These cues tend to be more specific, intimate, and shorter distance than habitat cues. Host-location cues can be chemical odours, visual (including movement), sound (or vibration), or radiation.

The cues can be from the host itself, by-products from the host, plants or other habitats used by the host, or even from other host-associated organisms. Host’s cues: Sex/aggregation pheromones, sound, vibrations from the enclosed hosts, movement, or the increase of habitat temperature induced by host’s emitted radiation. Host by-products: By-products of host feeding or other behaviour are often used as host-finding cues by a variety of parasites. Examples include frass produced by corn earworm and stemborers, including sugarcane borer, and honeydew produced via homopteran insects feeding.

Host-plant cues: Examples include terpenes released by pines, but only when being fed on by the host, specific damage induced by the host (but not by artificial damage), hosts that reaches the stage in which they are normally attacked by the host. Other associated organisms: Parasites respond to cues produced not by the hosts, but by other organisms that are found in association with the host. The utility of these cues depends on how intimate are the other organisms with the parasite's host.

Parasitoids-hosts interactions: Host acceptance
Host acceptance is the yes-or-no decision made by the parasite once it has found a host. The cues used include chemicals on the host surface or in the hemolymph; and size, shape, age, or texture of the host. Often, it is a series of cues, both physical and chemical, that lead to acceptance. Several egg parasites (Trichogrammatidae and Scelionidae) are sensitive to size and shape of their egg hosts while Ichneumonids are attracted to 3-dimensional cylindrical shapes, but only after responding to chemical odours.

Parasitoids-hosts interactions: Host acceptance
Host-movement cues indicating acceptability of hosts are seen in a variety of parasites. For several Trichogrammatids the movement of the developing embryo within the egg signals the age (and unsuitability) of the host. Some Ichneumonids will not attack immobilized hosts, suggesting that movement is required to tell hosts from non-hosts.

Parasitoids-hosts interactions: Host suitability
Once hosts are found and accepted, they still must be physiologically and nutritionally suitable for the parasite progeny to develop successfully. Hosts must provide the parasite progeny with a safe, nutritious place to develop. Host size will affect parasite development, often larger hosts may produce larger parasites, because of an abundance of food for the progeny and to quicker progeny development. Hosts too small to provide parasites with sufficient nutritional resources will lead to the death of parasite progeny.

Parasitoids-hosts interactions: Host suitability
Idiobiont parasites are limited to the resources the host provides when attacked while koinobiont parasites are not limited by the size or even the stage of the host attacked. Host age will also affect suitability. Eggs and pupae that have already developed somewhat may be less suitable for development, simply because of the difficulty for the parasite to metabolise their tissues. Hosts, often, are protected by a variety of defences, such as the immune system response of encapsulation of parasite progeny that should be overcome by the parasitoid.

Parasitoids-hosts interactions: Host regulation
The host's immune response must be overcome to prevent the host from killing the parasite eggs or larvae. This process overlaps with host location especially host defences such as the immune response. The parasite must be able to regulate the host's development and immune systems. The parasite must control moulting of larval host, so that it doesn't pupate before the parasite completes development.

Predators

Predators Predation can be defined as a trophic level interaction in which one species derives energy from the consumption of individuals of another species. A predator is considered an entomophagous species that generally consumes more than one prey individual to complete its development. Some parasitoids host-feed as adults which could be considered a type of predation. Over 16 orders of insects contain predaceous members, in approximately 200 families. Including spiders and mites, there are probably in excess of 200,000 species of arthropod predators. Many crops contain a rich assemblage of predators, and it is not uncommon to find species of predators in a given crop.

Predators Among the non-insect arthropods, spiders (Araneae) represent the largest, most diverse group. Spiders have been little utilized in biological control. Mites (Acari) have a number of predaceous members, most found in the family Phytoseiidae. Mites have been used in a number of biological control projects. Monophagy: A highly specialized prey range, the predator may feed on one or a very limited number of species within the same genera. Oligophagy: A semi-restricted prey range of a predator. For example, aphidophagous predators feed primarily on aphids preys, or, genera of coccinellids feed primarily on whiteflies or scales. Polyphagy: A broad prey range, may include plant materials (fluids, nectars, pollen), insects and fungi, a generalist predator.

Predators’ characteristics
Generally speaking the most common features of insect predators are: kill and consume more than one prey organism to reach maturity; Relatively large size compared to prey; Predaceous as both larvae and adults; Larvae are active with sensory and locomotory organs; Except for predatory wasps that store prey for immature stages, prey are generally consumed immediately. Frequency of individual prey items in the diet may be influenced by: Prey environment; Prey preferences; Competition with other predators; Suitability of prey.

Preys location and capture
Strategies used by predators to locate and capture preys include the following: Random searching: The predatory bug, Podisus maculiventris, searches bean plants without using cues, but did not search areas repeatedly once a prey was found. Directed searching: Supposing a certain capacity of orientation to objects in the microhabitat. Movement may be guided by features of the environment that increase chances for encountering prey. Active searching: Use of visual cues and other stimuli to orient to prey at a distance. Ambushing: Waiting for prey to approach within a striking distance then with their raptorial legs (praying mantids) they clasp their preys. Trapping: Neuropterans prepare conical pits in loose sand, larvae wait at the bottom with large sickle shaped jaws. Attracting: Lightning bugs, flashing of one species to attract males of another. Females then consume males.

Predators groups (Copping, 2004)

Predatory insect groups
The major groups of predaceous insects belong to the following orders: Coleoptera, Dermaptera, Diptera, Hemiptera, Hymenoptera, Mantodea, Neuroptera, Orthoptera and Thysanoptera. Coleoptera: Coleoptera (beetles and weevils) is the largest order in the class Insecta. Many Coleoptera species are herbivores, others live on fungi but many beetles are predators. There are even few parasitic beetles. The most important Coleoptera predaceous families are the following: Carabidae (ground beetles); Cicindelidae (tiger beetles), Staphylinidae (rove beetles); Lampyridae (fireflies); Cantharidae (soldier beetles) and Coccinellidae (ladybird beetles).

Dermaptera: Members of the order Dermaptera are recognized by pincers at the tip of the abdomen. These structures are used to hold prey while it is being consumed. The predaceous species feed on soft bodied insects (e.g. aphids, leaf hoppers, larvae of Coleoptera and Lepidoptera). The most important Dermaptera predatory families are: Forficulidae (spine tailed earwigs); Labiduridae (striped earwigs) and Labiidae (little earwigs).

Diptera: Some flies are predators of other arthropods (e.g., robber flies), but most of them are external parasites (e.g., mosquitoes and deer flies). Families that contain predaceous species are: Asilidae (robber flies), Empidae, Dolichopodidae (longlegged flies), Rhagionidae, Tabanidae, Tipulidae, Chamaemyiidae, Cecidomyiidae (midges), and Syrphidae (hover flies). Species in the later three families have been used in biological control. Hemiptera: Hemiptera is a large, cosmopolitan order of insects, comprising some 67,500 known species in three suborders: Auchenorrhyncha, Sternorrhyncha and Prosorrhyncha.

Hemiptera: The most relevant Hemiptera predatory families are: Miridae (plant bugs); Nabidae (damsel bugs), Anthocoridae (insidious flower bugs), Reduviidae (assassin bugs), Phymatidae (ambush bugs), Lygaeidae and Pentatomidae (stink bugs). Hymenoptera Hymenoptera is one of the larger orders of insects, comprising sawflies, wasps, bees, and ants. Females of Hymenoptera typically have a special ovipositor for inserting eggs into hosts or otherwise inaccessible places, often modified into a stinger. The most important Hymenoptera predaceous groups are: Sphecidae (sphecid wasps); Vespidae (paper wasps, yellow jackets); Eumenidae (mason and potter wasps) and Formicidae (ants).

Neuroptera: The insect order Neuroptera includes the lacewings, mantidflies, antlions, and their relatives. The order contains some 4000 species. The adults of this order possess chewing mouthparts, and most are predatory. The most important Neuroptera predaceous species belong to the following families: Chrysopidae (green or common lacewings), Hemerodiidae (brown lacewings), Mantispidae (mantid-flies), Coniopterygidae (dusty wings) and Myrmeliontidae (antlions). Orthoptera: The Orthoptera order includes the grasshoppers, crickets and locusts. The most important Orthoptera predaceous species are included in Gryllidae (tree crickets) which are Omnivorous on soft bodied insects, aphids and scales.

Thysanoptera: Most species of Thrips feed on plant tissues (often in flower heads), but some have been reported to feed on phytophagous mites, thrips, whiteflies, and lepidopteran eggs. The most important Thysanoptera predatory families are: Phlaeothripidae and Aelothripidae (Banded thrips). Mantodea: Mantids have elongate bodies that are specialized for a predatory lifestyle: long front legs with spines for catching and holding prey, a head that can turn from side to side, and cryptic coloration for hiding in foliage or flowers. The most important predaceous family is Mantidae (praying mantid).

Predator-prey interactions
The sequence of behaviours used by predators to locate prey is similar to that for parasitoids. In general, behaviours are not as clearly defined for predators as for insect parasitoids. Prey habitat location: For predators associated with ephemeral habitats (e.g. agricultural crops), adults must locate habitats with prey through seasonal movements into and out of cropping systems. Olfactory and visual cues are likely used by adult predators to locate suitable habitats. Volatile kairomones and synomones are known to be used as attractants by selected insect predators. For some predatory species, a blend of compounds, including volatiles from the plants in the habitat as well as prey volatiles, are involved. This blend is called synergistic mixture of plant and prey derived cues.

Prey location: Physical and chemical cues are used by many predatory species to locate prey. Vision may be important for ambush type predators or other predators of slow-moving prey. Kairomones can be used for short range perception of prey. Larval predators have evolved various means of locating and recognizing their prey through phototactic and/or geotactic responses, vision, olfaction, sound or vibration detection, or physical contact. Some larval predators switch from linear movement to area-intensive searching after they contact prey. A predator's previous experience (learning) can influence its searching behaviour, as well as the type and proportion of prey taken within an area.

Prey acceptance: Once a prey item is contacted, the behaviour used to initiate and continue feeding on prey. Generalist predators attack, subdue and consume a wide range of prey species they encounter. The following may influence prey acceptance: size of prey, anti-predator behaviours of prey, and composition of cuticle. Morphological and physiological factors can influence prey acceptance. Size, shape, movement, and external and internal chemical cues of prey are factors that can be used as stimuli to induce prey acceptance. Many insect predators are stimulated to bite or taste a prey following antennal or palpal contact.

Prey acceptance: One underlying physical factor that influences prey acceptance is the size of prey relative to the predator. Prey integumentary chemicals (e.g., waxes) may serve as kairomones or phagostimulants for some predatory species. Another aspect of prey acceptance involves prey behaviours and defences. Some prey (e.g. aphids) kick, run, drop, or fly away, or exude noxious chemicals when predators approach them. Prey preference: The consumption of a prey species in greater proportion than its relative abundance among possible prey items. Prey specificity: Properties of a predator which limit types of prey attacked, may involve behavioural, spatial, and temporal aspects.

Prey suitability Prey suitability can be considered as the influence of the nutritional composition of the prey on the development, survival, and reproduction of a predator. If prey are not suitable (i.e., they have low nutritional quality), the predator may reject the prey, or it may continue feeding, but with detrimental effects. The negative effects may include reduced rates of development, reproduction (fecundity) or survival. Prey suitability may or may not be the same for immature and adult stages of a predatory species. Lack of information on prey suitability explains why relatively few insect predators can be mass-reared successfully, and even fewer can be reared on artificial diets.

Pathogens

Pathogens Associations between Microorganisms and insects range from mutualistic associations to those where the microorganism causes fatal disease in the insect host. Infectious insect diseases, usually causing deleterious effects in the invaded host, occur frequently in insects and often act as important natural control agents. Insect pathogens are most often viewed as microbial insecticides. It is very important to distinguish between diseases of insects caused by pathogens, those that are caused by non-infectious agents and also to distinguish between pathogenic and non-pathogenic micro-organisms that live in symbiosis with insects.

Pathogens Entomogenous: Organisms growing in or on the bodies of insects; usually connotes a parasitic or other intimate symbiotic relationship. Entomophagous: Insectivorous; the consumption of insects and their parts. Entomophilic: Associations between insects and other organisms, e.g. plant, microorganisms, Protozoa, and nematodes. Horizontal transmission: Transmission of a pathogen from infected individuals to conspecific individuals within a generation or overlapping generations in a season. Vertical transmission: Transmission of a pathogen from one generation of host to the next. Transovarial (or transovarian) transmission: Transmission from one generation to the next via the egg. The pathogen is transmitted within the ovary of the infected female and usually is found in the cells of the embryo.

Pathogens Transovum transmission: Transmission from one generation to the next via the egg. The pathogen can be on the surface of the egg and ingested upon hatch of the neonate host, or can be within the host embryo (transovarial transmission). Transovarial transmission is a special case of transovum transmission. Invasion/Infection: Invasion is the entry of a microorganism into the host body. Primary invasiveness is a property of pathogenic microorganisms. Infection implies that the pathogen enters the body of the host, usually the cells, and be able to reproduce to form new infective units. Simply ingesting a pathogen does not imply infection. Latent infection: Unapparent infection; the pathogen is in a non-reproductive phase and a pathogen-host equilibrium is established. Pathogenicity and virulence: Pathogenicity is the ability of an organism to invade the host and cause disease.

Non-pathogenic organisms & insects associations
Technically, the living together of dissimilar organisms regardless of the result of such an association is called symbiosis. Every insect/microorganism association is a symbiotic association and this would include all associations discussed within the subject area of biological control. When examining insects and diagnosing insect diseases, non-pathogenic organisms are often encountered and may be confused with true insect pathogens. There are mainly two kinds of insect/non-pathogenic organisms associations: Casual and mutualistic associations.

Non-pathogenic associations
Casual associations: Insects harbour microorganisms that occur in their immediate environment. Bacteria, fungal conidia, free living Protozoa and other organisms adhere to the cuticle of insects and may pass through the digestive tract. Such associations are largely accidental and are usually neither harmful nor beneficial to either insect or microorganism. Mutualistic associations: Most groups of organisms (viruses, bacteria, fungi, and Protozoa) have mutualistic associations with insects. These associations may be either intracellular or extracellular and are usually associated with insects that have some nutritional difficulty. The microorganisms provide a required nutritional compound or an enzyme necessary for converting an unusable into a usable food product. Although there have been attempts to manipulate mutualistic associations as a means of biocontrol, the potential of this approach appears limited at this time.

Non-infectious diseases of insects
Generally speaking we can distinguish between non-infectious diseases caused by abiotic agents and infectious diseases caused by pathogens. It is of paramount importance to be able to distinguish between these two kinds of infections that can cause insects death in order to assess accurately and precisely the efficiency of biological control means. Physical injuries, chemical injuries, nutritional deficiencies, genetic abnormalities, and neoplasms may result in a disease state. With the exception of sterility, non-infectious diseases are seldom considered a component of a biological control program. When evaluating individual insects or a population of insects for the underlying causes of disease, researchers should be aware of several possibilities other than infectious diseases.

Physical injuries: Insects are naturally somewhat protected from injury by the cuticle, tracheal system, and physiological adaptations. Injuries occur and include distension (blockage), trauma such as abrasions/contusions/ concussions/crushing, and open wounds. These injuries may include blood loss, tissue changes, and exposure to pathogens. Extreme cold and heat, as well as solar radiation and drought, can harm insects, often figuring strongly in the increase or decline of insect populations. Chemical injuries: Chemically poisoned insects can have the appearance of pathogen-infected insects.

Chemical injuries: Plant secondary compounds can poison non-adapted hosts, as can toxins produced by microorganisms. Toxins are sometimes a factor in the virulence of entomopathogens. Insecticides may be physical poisons, protoplasmic poisons, metabolic inhibitors, hormone mimics, stomach poisons, or neuroactive agents. Most synthetic insecticides are neurotoxins. Genetic diseases: All hereditarily transmitted biochemical, physiological, and morphological characters which are harmful for the organism are genetic diseases.

Genetic diseases: Genetic diseases may be classified as: Lethal factors: mutants or deficiencies. Sterility factors, usually chemical or irradiation mutations of males, have been used successfully in biological control programs. Structural alterations include any malformations such as winglessness, deformed body parts, supernumerary appendages, etc. Tumors. Gynandromorphs are inter-sex mutants that are usually sterile. Neoplasms: They are abnormal masses of tissue, the growth of which exceeds and is uncoordinated with that of normal tissue and persists in the same excessive manner after cessation of the stimulus that evoked the change. Etiologies may include carcinogens, inflammation, trauma, and viruses.

Biological agents: Predators that don't kill insect prey outright may leave wounds for which the same responses occur as for other physical injuries. Parasites may cause irritation and destruction of tissues, resulting in mechanical injury, for example, piercing of the host integument by female parasitoids, and surface feeding or feeding on (usually non-vital) tissues. Emergence of endoparasites usually causes death of the host. Parasitoids may also cause paralyzation and other physiological injury due to competition for nutrients, or parasite castration. Nutritional diseases: Deviations from basic conditions needed for attraction to and survival on a food source can lead to nutritional disease.

Nutritional diseases: Improper balance of nutrients, amino acids, proteins, fats, carbohydrates, vitamins, inorganic ions, etc. can cause various symptoms of nutritional disease. Limited feeding reduces growth, development, and reproduction. When insect populations outbreak, over-utilization of the food source can result in starvation of not only the outbreak species but also of other species utilizing the same food sources. Symptoms in larvae include severely affected growth rates and development. Often adults have deformed wings, and mating and egg production may be seriously affected.

Infectious diseases of insects
Infectious agents are living units that must invade the insect host in order to initiate an infection. Unlike parasites and predators, pathogens do not always kill the hosts. Infection usually involves reproduction of the agent. Invasion of the host may be dermal, body opening, oral by feeding/drinking, or introduced by stings of contaminated or infected parasites. The specific characteristics of the infective stages of pathogens greatly influence how they contact and infect their hosts. The infectious agents responsible for transmission of the pathogen are susceptible to many environmental factors: Few can survive more than a few hours of direct sunlight. Others may be particularly susceptible to dry conditions, high temperatures, freezing, and many chemicals. Survival of the infective stage of insect pathogens outside the host is a major factor in the development of microbial insecticides.

Infectious diseases of insects
All insect pathogens have a physiological host range in which they can potentially survive and reproduce. Some pathogen species may be very host specific, while others may be able to infect a wide range of insect species. The host range of a pathogen is especially important when considering a non-indigenous pathogen for introduction into a new habitat. Sub-lethal infections are not uncommon and these may include behavioural and developmental changes as well as a decrease in the fecundity of infected adults. Insects are infected by an incredibly large number and diversity of pathogen species. Most insect pathologists believe that there are actually more species of insect pathogens than there are species of insects. The major pathogen groups containing species that infect insects are: viruses, bacteria, fungi, protozoans, microsporidia, and nematodes.

Use of pathogens in insect biocontrol
Insect pathogens are used in biological control in at least three different ways: inundative applications, inoculative releases, management of naturally occurring pathogens, and introduction of exotic pathogens as classical biological control agents. Inundative applications: They are those in which insect pathogens are applied in large quantities with the goal of killing as many individuals of the pest population as quickly as possible. Pathogens used in this manner are called microbial insecticides. Replication of the pathogen in the host and production of additional infectious propagules may be desirable, but is not usually required for microbial insecticides to be effective.

Inoculative applications: Inoculative applications are those in which small quantities of insect pathogens are applied or released into an insect host population. The goal is to produce infections in at least a few hosts, which will, in turn, produce numerous infectious propagules that will infect many more susceptible hosts. Introduction of exotic pathogens as biocontrol agents: Hundreds of exotic parasitoids and predators have been introduced into different countries as classical biological control agents however few exotic species of pathogens have been intentionally introduced. Difficulties in identifying and isolating insect pathogens, along with regulatory uncertainties, have contributed to the under-utilization of insect pathogens as exotic biological control agents.

Management of naturally occurring pathogens: Insect pathogens are important components of the natural enemy complex of many insect species, including pest species. Some groups of pathogens, such as microsporidia, may not always maintain host insect densities below economic thresholds, but they suppress the rapid increase of pest populations. Insects pathogens and are often responsible for the decline of populations that have exceeded the economic threshold. In most cases the major goal for managing naturally occurring insect pathogens is to elicit an epizootic earlier in the season, before the host densities have exceeded the economic threshold. This can be accomplished by inoculative releases of the pathogen or by changing cultural and phyotosanitary practices to promote an epizootic.

Micro-organisms use in biocontrol
(Copping, 2004)

Types pathogens Insect viruses:
Viral diseases have been found in 13 insect orders and most likely occur in all orders. Viruses that are primarily or exclusively found in insects are currently placed in 12 families (Miller, 1998): DNA Viruses: Baculoviruses (Nuclear polyhedrosis viruses- NPV and Granuloviruses-GV), Ascoviruses, Iridoviruses, Parvoviruses, Polydnaviruses and Poxviruses. RNA Viruses: Reoviruses (Cytoplasmic polyhedrosis viruses), Nodaviruses, Picorna-like viruses and Tetraviruses. Bacterial pathogens: They can be divided into two broad categories, non-spore-forming bacteria and spore-forming bacteria. Although most of the species isolated from diseased insects are non-spore-forming, spore-forming bacteria in the genus Bacillus are the most important from the standpoint of biological control.

Types pathogens Fungal pathogens:
Entomopathogenic fungi are able to invade their insect hosts by penetrating directly through the cuticle. The fungal spore first adheres to the cuticle. Under appropriate conditions the spore germinates, penetrates the cuticle of the host and enters the hemocoel. Fungal reproduction occurs in the hemocoel of the insect host. As the hemocoel becomes filled with hyphal bodies, the insect usually dies and the fungus continues to develop saprophytically. After the body of the dead insect is filled with mycelia, fruiting structures emerge from the cadaver and produce infectious spores. Dead insect has the consistency of a moist loaf of bread and, depending on the colour of the spores or conidia, may appear white or some darker colour.

Types pathogens Fungal pathogens:
Tanada and Kaya (1993) listed 8 classes, 13 orders and 57 genera that contain entomopathogenic species of fungi. There are five major groups of fungi: the Flagellate fungi or Chytridiomycetes, the Oomycetes (also flagellate but also not true fungi), the Zygomycetes, the Ascomycetes, and the Basidiomycota. The Zygomycota and the Ascomycota contain common insect pathogens that are also useful in biological control programs. Microsporidia: Microsporidia are important primary pathogens of insects. Their best use will probably be as augmentatively released or classical biological control agents, not as pesticides.

Types pathogens Microsporidia:
The only microsporidian ever registered as a microbial pesticide (in the USA) is Nosema locustae, a pathogen of grasshoppers. Two other microsporidian species that are known to control populations of pest insects: Nosema fumiferanae and Nosema pyrausta. Protozoa: Protozoa are the most taxonomically diverse group of insect pathogens. Protozoa range in their interactions with insects from commensualists and mutualists, to plant and animal pathogens vectored by insects, to acute insect pathogens.

Types pathogens Protozoa:
Of some 14,000 described species of Protozoa, about 500 are pathogens of insects. Many are chronic pathogens that may debilitate a host without producing obvious disease symptoms but some species are extremely virulent, causing stunted growth, slow development, and early death. Entry into the host is typically by ingestion, but some can invade through the cuticle. Some species may be transovarially transmitted from infected females to their offspring. Species that invade the cells of the host are usually found in the cell cytoplasm and are typically more pathogenic than extracellular species. Some protozoans exhibit tissue tropism, infecting only certain tissues or organs, others are systemic.

Types pathogens Protozoa:
No toxins have been found to be associated with protozoa in insects. Death or debilitation of infected hosts may be, for example, the result of competition for metabolites, disruption of normal cell and tissue function, or blockage of the gut or other organs by extracellular species. The insect-pathogenic Protozoa are currently recorded from four major groups: Amoebas, Gregarines, Flagellates and Ciliates. Nematodes: Some entomogenous nematodes have characteristics that allow them to be considered with the pathogens. The most important insect pathogenic nematodes for biological control are very small and use mutualistic bacteria to kill the host.

Types pathogens Nematodes:
Although nematode species in at least 20 families are primary or facultative parasites of insects, those in the order Rhabditida have been most exploited as biological control agents. Species in the genera Steinernema and Heterorhabditis (Steinernematidae and Heterorhabditae, respectively), are particularly amenable to mass production and application in a variety of pest systems. Entomopathogenic nematodes enter the host via natural body openings or through the cuticle. Some species utilize an anterior stylet or a tooth to rasp the cuticle and gain entrance into the hemocoel. Others ingress by ovipositing on the host food source and the eggs hatch in the host midgut. Effects of nematode parasitism on the hosts can be sterility, reduced fecundity, reduced mobility and life span, behavioural and morphological changes, and death.

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Biological Control of Insect Pests

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