1. ROLES OF MICROBES IN BIOLOGICAL PEST CONTROL: A REVIEW 1Imam, T. S
ROLES OF MICROBES IN BIOLOGICAL PEST CONTROL: A REVIEW   1Imam, T.S.*, 2Abashe, S.A. and 3Sani, M. N.   1 Department of Biological Sciences, Bayero University, Kano, P.M.B.3011, Kano, Nigeria. 2 Department of Food Science & Technology, KUST, Wudil, P. M. B Kano, Nigeria. 3Department of Microbiology, Federal University, Dutse, Jigawa State, Nigeria * Corresponding Author’s GSM No:
Paper
1st INTERNATIONAL CONFERENCE ON DRYLANDS
8th-12th December, 2014
VENUE: Centre for Dryland Agriculture ,BUK

2. OVERVIEW
The term ‘microbial control’ was first used by Steinhaus (1949), to express the pest population management through disease causing microorganisms or their by-products in the control of pest species.
Although the use of biotic agents are more than 80 years old, their development depended largely on the accumulated knowledge of the biology of such pathogens like bacteria, viruses, fungi and protozoa.
Many countries have instituted more strict regulations on pesticides, manufactures, registrations and uses.
Therefore, the need for alternative pest control practices to reduce chemical pesticide use is evident (Hoy and Herzog, 1985).

3. MICROBES USED IN BIOLOGICAL CONTROL
Bacteria in Bio-controls of Pest:
These Include the Following:
Bacillus thuringiensis
Bacillus papillae
Serratia entomophila

4. Bacillus thuringiensis
Different varieties of Bacillus thuringiensis have been formulated to control certain insects. Granules are commonly seen in living sample under light microscopy.
The prominent insects controlled by B. thuringiensis include moth and butterfly caterpillers, as well as certain beetle and fly larvae.
Some variety of Bacillus thuringiensis specifically controls many caterpillar pests such as horn worms, cabbage worms, mosquito, black fly and gnat larvae.

5. Figure 1: Action of B. thuringiensis var Kurstaki on Caterpillars.

6. Effectiveness
Successful use of Bacillus thuringiensis formulations require application to the correct target species at a susceptible stage of development, in the right concentration,
At the correct temperature to ensure feeding, and before the pest enter the plant or fruit where they would be protected.
As with any microbial insecticide, determining when the pest is most susceptible is the key to getting the best results.

7. Bacillus papillae
Baciluus papillae are a naturally occurring bacteria that have been mass-produced for the control of many insect pests.
It was the first insect pathogen to be registered in the U.S. as a microbial control agent. When used as a pesticide, it is typically spread onto the turf so it can soak into the underlying soils (Smart,1995).
The Japanese beetle, Popillia japonica, is the specific insect that Bacillus papillae controls.
Other varieties of Bacillus papillae have been found to work on other beetles in the family Scarabeaidae,
which include the Japanese beetle, the chafers (a pasture pest) and the beneficial dung beetles

8. Figure 2: Bacillus papillae Infection: Infected larva (left) and Healthy larva (right) (Smart,1995).

9. Effectiveness
The treatment is most effective when applied on a region or statewide basis to reduce the overall levels of beetle infestation.
It is less effective when used by small landowners who may control larvae in their own turf only to have their plants eaten by beetles from neighboring properties.

10. Serratia entomophila
Serratia entomophila is commonly found in New Zealand pastures but has rarely been isolated elsewhere in the world.
Pathogenic and non pathogenic of both S. entomophila and S. proteamaculans are found in mixed populations in soil where larvae are present.
Selected strains of S. entomophila were safely tested for mammalian, non target and environmental effects, and registered as New Zealand’s first indigenous insect microbial control agent,
And the first in the world to be based on member of the Enterobacteriaceae (Jacson et al.,1992).
Pest controlled includes beetles, grass grub and Costelystra zealandica.

11. VIRURES IN BIOCONTROLS OF PESTS
The use of viruses as control agents against crop attacking insects is increasingly becoming popular.
Insect-specific viruses can be highly effective natural controls of several pests. (Mahr et al., 2008).
The following viruses are some of the most commonly used in pest control:
Ascoviruses
Nuclear Polyhedrosis viruses
Cytoplasmic Polyhedrosis viruses

12. Figure 3: Generalized life-cycle of insect viruses (Larcey et al

13. Ascoviruses
The ascoviruses (Ascoviridae) are a new family of DNA viruses, an interesting feature with these viruses is that transmission from host to host depend on vectoring by female endoparasitic wasps.
Ascoviruses are very difficult to transmit by feeding, with typical infection rates averaging less than 15% even larvae are fed thousands of vesicles in a single dose.
Pests controlled by ascoviruses includes cabbage looper, cotton bud worm, corn earworm and fall armyworm.

14. Ascoviruses
After being ingested, the virus enter the insect body through the gut.
They replicate and can disrupt components of an insect’s physiological function, interfere with the insects feeding, egg laying and movement.
After the insect dies, it will dissolve and leave viral particles on the foliage for other insects to consume.

15. Nuclear Polyhedrosis viruses
These viruses are known from a wide range of insect orders, but have been most commonly reported by far from lepidopterous insects, from which well over 500 isolates are known.
NPVs replicate in the nuclei of cell, generally causing an acute fatal disease.
The NPVs of lepidopterous insect infect a range of host tissues, but those of other orders are typically restricted to the midgut epithelium.
Nuclear Polyhedrous virus controls alfalfa looper, corn earworm, cabbage worm, cotton bullworm, cotton leafwom, tobacco budworm, armyworms, european corn borer, almond moth, spruce budworm, Douglas fir tussock moth, pine sawfly and gipsy moth.

16. STRAINS OF NUCLEAR POLYHEDROUS VIRUSES TYPES OF CROPS INFESTED
Table 1: Strains of Nuclear Polyhedrous Viruses and Pest Controlled.
STRAINS OF NUCLEAR POLYHEDROUS VIRUSES
PESTS CONTROLLED
TYPES OF CROPS INFESTED
1. Cabbage army worm Nuclear polyhedrous virus
Cabbage moth, American bollworm, diamondback moth, potato tuber moth, and grape berry moth
Cabbage, tomato, cotton,
2. Spodoptera littoralis Nuclear polyhedrous virus
Spodoptera littoralis
Cotton, corn, tomato
3. Helicoverpa zea Nuclear polyhedrous virus
Tobacco bud worm Helicoverpa zea, and cotton bollworm Heliothis virescens
Cotton and vegetable
4. Spodoptera exigua Nuclear polyhedrous virus
Beet armyworm (Spodoptera exigua)
Vegetable crops and green house flowers
5. Anagrapha falcifera Nuclear polyhedrous virus
Celery looper (Anagrapha falcifera)
Vegetables
6. Autographa californica Nuclear polyhedrous virus
Alfalfa looper (Autographa californica)
Alfalfa and other crops
7. Orgyia pseudotsugata Nuclear polyhedrous virus
Douglas fir tussock moth (Orgyia pseudotsugata)
Forest habitat, lumber
8. Lymantria dispar
Gypsy moth (L. dispar)

17. Cytoplasmic Polyhedrosis viruses
The cytoplasmic polyhedrosis viruses (family Rioviridae) are occluded double stranded RNA viruses with a genome divided into 9 or 10 segments of RNA.
CPVs are typically easy to transmit by feeding to species that belong to the same family of the host from which they were isolated, and thus the host range of this virus is quite broad (Mahr et al., 2008).
Some of the pests controlled include mosquitoes, black flies and midges.
Infection in early instars retards growth and development, extending the larval phase by weeks.
In advanced stages of disease, the infected midgut is white rather than translucent brown, because of large numbers of accumulated polyhedral.

18. FUNGI IN BIO-CONTROLS OF PESTS
Deliberate use of fungal pathogens as biological control against pests was first considered in the latter part of nineteenth century, with the insect pests as targets, the early attempts mostly failed.
Most fungi used for the control of insect pests belong to the group hyphomacetes.
Some species have been as commercial products because of their ability to be mass produced..

19. Some of the most commonly encoutered groups of fungi used in microbial pest control include the following:
Entomophthorales fungi
Hyphomycetes
Coelomyces

20. Entomophthorales fungi
These fungi comprises a large order of the Class Zygomycetes that contains numerous genera, many species of which are commonly found parasitizing insects and other arthropods.
Pests controlled includes aphids, leafhoppers, grasshoppers, flies, beetle larvae and caterpillars.
The fungi usually infects by active penetration through the cuticle. The typical life cycle begins when a spore either a motile spore or a conidium, lands on the cuticle of an insect.

21. Entomophthorales fungi (CONTD)
Under suitable conditions, the spores germinate, producing a germ tube that grow and penetrates down through the cuticle in the hemocoel.
Once in the hemolymph, the fungus colonize the insect. Hyphal bodies bud off from the penetrant hyphae,
and either continue to gow and divide in a yeast-like manner or elongate, forming hyphae that grow throughout the insect body.

22. Figure 4: A typical life cycle of Entomophthorales Fungi (Larcey et al

23. Hyphomycetes
The fungi hyphomycetes belong to fungal subdivision Deutromycotina (imperfect fungi)
This group contains the fungal species that most workers consider to have the best potential for development as microbial insecticides,
These species have very broad host ranges and probably are capable of infecting insects of most Orders (Macoy, 1988).

24. Hyphomycetes (contd)
Pests controlled by this group of fungi include beetle larvae, plant hoppers, whiteflies and locusts.
During invasion and colonization, some fungal species produce peptide toxin that quicken host death .
The spore of B. bassiana will attach it self to the pest and begin to grow until the pset has been fully consumed.

25. Coelomyces
Coelomyces are aquatic fungi, and produce zoospore during reproduction.
The are the largest genus of insect- parasitic fungi, that has been reported worldwide from numerous mosquito species, many of which are vectors of important disease such as malaria and filariasis.
In some of these species, Anopheles gambiae in Africa, for example, epizootic caused in some areas by Coelomyces kill greater than 90% of the larval populations.
Such epizootics led to efforts to develop several species as biological control agents (Macoy, 1988).

26. Coelomyces (contd)
Coelomyces mainly attack mosquito larva and cope- pod.
The sexual phase parasitizes a microcstacean host, typically a cope – pod, whereas in the asexual generation develops, wit rare exception, in mosquito larvae. in the life cycles, a biflagellate zygosporre invades the hemocoel of a mosquito.
Where it produced a saprophyte that colonizes the body and forms resistant sporangia.the larva dies and subsequently the sporangia undergo meisosis. producing un-flagellate meiospores, that invade the hemocoel of a copepod host, where a gametophyte develops.
At maturation, the gametophyte cleaves, forming thousands of uniflagellate gametes. Cleavage results in death of the copepod and escape of the gamete.

27. PROTOZOA IN BIO- CONTROLS OF CROP PEST
The protozoa subphyla Sporozoa and Cnidospora contain numerous entomophilic protozoan and most promising examples in biological insect pest suppression programmes.
The effects of protozoa infection are chronic rather than acute and they may affect their hosts over a fairly long time period.
Because of this, disease is often manifested in the host insect only by reduction vitality, fecundity and life span (Sun et al., 2004).
The naturally occurring epizootics of protozoan disease in insect pest like European corn borer, some Lepidoptera, several species of flies, aquatic dipteral including mosquitoes and grasshopper.

28. PROTOZOA IN BIO- CONTROLS OF CROP PEST (Contd)
The notable protozoan worthy of mentioning, in term of microbial pest control are microsporidias (Phylum Microspore). They are the most common and best studied of the protozoan that cause important diseases of insects.
Microsporidia have been most commonly described from insect of the order Coleoptera, lepidoptera, dipteral, and orthoptera, but they are also known from other orders and probably occur in all.
The epizootics in insect populations caused by protozoa are usually due to microsporidia are obligate intracellular parasites and are unusual in that they lack mitochondria. in addition,

29. PROTOZOA IN BIO- CONTROLS OF CROP PEST (contd)
They produce spore that are distinguished from the spores of organisms of all other known types by the presence of polar filament, a long coiled tube inside the spore to infect hosts with the sporoplasm (Shanks 1990).
The typical microporidian life cycle begins with the ingestion of the spore by a sesceptible insect.
Once inside the midgut, the polar filament everts, rapidly injecting the sporoplasm into host tissue.

30. PROTOZOA IN BIO- CONTROLS OF CROP PEST (contd)
Pests controlled are mainly arthropods of the classes Celeoptera, Lepiddoptera, Hemiptera and Diptera.
The sporoplasm is unicellular but maybe uni or binucleate. Upon entry into the cytoplasm of a host cell (e.g., the fat body in many species of insects),
The sporoplasm forms a plasmodium (merot), which undergoes numerous cycles of vegetative growth (merogony).

31. Other Protozoans that can be used in microbial pest control are shown in the table below: Table 2: Protozoa species and Pest Controlled.
S/N
Protozoan
Pest controlled 1.
Mettasia grandis
Cotton boll weevil 2.
Mettasia progodermae
Khapra beetle 3.
Nosema locustae
Grasshopper and locust species

32. HELMINTHES IN BIO-CONTROL OF PEST Nematodes in Bio-controls Crop Pest
Nematodes are live microscopic organisms (non- segmented round worms) that occur naturally in soil through the world. They are parasitic to insect pests that typically have a developing (larval or pupal) stages of adults, nymphs and larvea.
Nematodes are considered to be one of the most lethal parasites known to kill plant pests.
Nine families of nematodes (Allantone-matidae, Diplogasteridae, Heterorhabditidae, Mermithidae Neotylenchidae, Rhabditidae, Sphaerulariidae, Steinenematidae and Tetradonematidae,)
Include species that attack insects and kill or sterilize them, or alter their development (UN-LN, 2003).

33. Nematodes in Bio-controls Crop Pest (contd)
Heterorhabditis bacteriophora NC strain was applied, and it provided more than 70 percent control soon after treatment and was still providing that same level of control a year later (Shanks 1990).
Many nematode-based products are currently available . They are formulated from various species of Steinernema and Heterorhabditis.
Some of the products found in various countries are ORTHO Bio-safe, BioVector, Sanoplant, Boden-Ntitzlinge, Helix, Otinem, Nemasys, and so forth (Smart, 1995).

34. Nematodes in Bio-controls Crop Pest (contd)
A fairly recent development in the control of slugs is the introduction of “Nemaslug,” a microscopic nematode (Phasmarhabditis hermaphrodita) that will seek out and parasitize slugs, reproducing inside them and killing them.
They are used to control insect pests that typically have a developing (larval or pupal) stage of life in the soil;
however, they have been known to also parasitize above ground stages of adults, nymphs and larvae of Grubs, Fleas, Fungus Gnats and Over 200 other pests that develop in the soil.

35. Table 3: Nematode species and Pest Controlled.
S/No
Variety of Nematodes
Pest controlled 1.
Steinernema carpocapsae
Fleas, caterpillars, cutworms, armyworms, sod webworms, fly larvae, worker/soldier ants and worker/soldier termites 2.
Steinernema feltiae
Fungus gnats, ticks, thrips, leaf miners, onion maggots, root maggots, subterranean termites 3.
Phasmarhabditis hermaphrodita
Slugs 4.
Heterorhabditis bacteriophora
Various pest species

36. Integrated Pest Management
A great deal of research attention has devoted to the impact of conventional pesticides on natural enemies so that topic will be reviewed only briefly here in relation to the interactions of pesticides with host plant resistance and biological control.
Host plant resistance may make pests more susceptible to insecticides by slowing their growth such that they are smaller and less well developed or less well nourished at any given time.
Such an effect may be especially powerful when penetration of plant tissue by boring or mining pests is delayed (Kvedaras and Keeping, 2007).

37. Integrated Pest Management (contd)
An increase in pest susceptibility may also allow the use of an insecticide concentration that is low enough to allow many natural enemies to survive whilst still conferring a high level of mortality of the pest (van Emden, 1990).
Such a relationship between host plant resistance, biological control and dose-adjusted pesticide use would allow the application of a product to bring a pest outbreak under control,
whilst maintaining the within-crop of natural enemies to persist and provide ongoing protection from future pest establishment (Gurr and Kvedaras, 2010).

38. Figure 5: Biological Control Conceptualized as the Function of Integrated Pest Management and Illustrating some of the Positive Interactions with Other Pest Management Approaches. Adapted from Van Driesche And Bellows (1996). Biological Control, Chapman and Hall, New York, p.297.

39. conclusion
Based on the benefits of the use of microbes in controlling pests, the process helps in reducing environmental and public safety hazards of chemicals.
The method also is more economical alternative to some chemical insecticides.
Most of the microbes involved in the practice of pest control usually does not harm non target organisms found in the environment.
However, the use of these microbes require detailed knowledge of the pest’s biology and population dynamics, as well as natural enemies associated with the pests and their impact.
It is noteworthy that integrated pest management would be preferred method of pest control, because of its multi-focal approach.

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