Biological Control Strategies II Natural Enemies: An Introduction to Biological Control by Ann E Hajek   Cambridge University Press Insect Pest Management by David Dent  -   CABI Publishing

Augmentation

Bio-control Strategies Classical Biological Control Augmentation - Inundation - Inoculation Conservation Biological Control As we have seen, bio-control strategies can be classified in three main groups: Classical, augmentation and conservation biological control.

Augmentation Definition It is the periodical introduction of natural enemies to achieve pest control. Natural enemies used in augmentation do not establish and need to be introduced each time pest populations reach the threshold level.

Augmentation Release of reared natural enemies Temporary control Natural enemy should be adapted to focus area Easy to culture Preference for pest species Higher reproductive rate than pest Good response to pest density Nat.enem. Should not attack others Nat. enem.

Augmentation Begginings In England in 1895 the egg parasitoid Trichogramma became the first natural enemy to be reared and release to control arthropod pests. After this the techniques to rear natural enemies increase but it is only in the 1970s than mass rearing escalated correlating with the increase of their use in greenhouses.

When to use Augmentation? When natural enemies are absent or occur at low numbers When natural enemies appear late The term augmentation is used to imply that natural enemies are being added to areas that might already have them there. Keep in mind that augmentation also include adding natural enemies not present in the area of release (if you do add them without establishment as a goal). If you introduce a natural enemy with establishment as a goal, what kind of biocontrol do you have? If natural enemies against a particular pest tend to appear too late to save the crop in a particular area you can use augmentation for biocontrol. Extreme seasonal changes in weather or other abiotic and/or biotic conditions may allow natural enemies to thrive at a particular area only for a relatively short period of time.

Bio-control Strategies Classical Biological Control Augmentation - Inundation - Inoculation Conservation Biological Control As we have seen, bio-control strategies can be classified in three main groups: Classical, augmentation and conservation biological control. The augmentation biocontrol can be divided in inundation and inoculation.

Inundative Biological Control A lot of the agents used in inundative biological control involve pathogens. However, predators and parasitoids can also be used in this way. For example, lady beetles are used inundatively to control aphids and predatory mites are also used inundatively to control thrips. Natural enemies applied inundatively are often referred as biopesticides. However, I prefer the use of the term biopesticides when talking about biological products and not the organisms themselves (e.g., bt toxin, fungus toxins). If microbes are used (e.g. Bacillus thuringiensis) inundative bio-control is sometimes refer as microbial control and the bacteria or microbe used is referred as microbial pesticide. Microorganisms used to control weeds are sometimes refer as bioherbicides and if they are fungal in origin they are referred as mycoherbicides. Control agents do not reproduce For rapid biological control For low economic thresholds

Inoculation Control agents reproduce This technique provides longer term control and a relatively more self sustained control than inundation. The natural enemies involved in inoculative bio-control reproduce after they are released so innoculative control is characterized by fewer releases than inundative control. However, unlike classical biocontrol the released natural enemies do not establish and they die after the growing season. Because they die passed the growing season they need to be reintroduced if the pest problem appears again. Control agents reproduce Agent persist longer than in inundative control

Bio-protectants Plants can be attacked not only by herbivorous insects but also by pathogens. Plants can get sick due to viruses or bacteria infesting them. Antagonists or natural enemies of plant pathogens (usually other bacteria or pathogens) can be used as bio-protectants. These bioprotectancts impede plant pathogens from colonizing the plants, preventing plants from getting sick. More than one generation is needed to allow protective agents to colonize wounds, roots and potential vulnerable tissues so they protect the plant. Because they have short generation times we expect to find many generations of these bio-protectants in the wounds. Bio-protectants are commonly used innoculatively.

Products Used in Augmentation Macroorganisms Microorganisms Macroorganisms (macro means big) do not need to be registered in a governmental agency. Microorganisms (micro means small) do!! In other words, microorganisms are viewed as if they will be a chemical substance. The registration of microorganisms is way cheaper than the one required for chemical insecticides.

Why do you think pathogens are more common than parasitoids in augmentative control? Answer: Because it is usually less expensive to mass produce pathogens than parasitoids.

Microbes for biological control are often sold in formulations that look very similar to insecticide formulations. Most of them can be applied with the same equipment that insecticide applications use. This may explain part of their popularity among farmers that want to achieve control quick (as it is usually achieved with pesticides). Thus, because they look similar they think bioscides and insecticides are the same or share the same killing speed. From an environmental perspective though, microbial insecticides are preferred over insecticides.

Microorganism Mass Production Some microorganisms are very easy to mass-produce (e.g. Bacillus thuringiensis). Others are a little bit more challenging to mass-produce. Things such as the fermentation environment, the right balance between nitrogen and carbon in the growing media and the right amount and kind of nutrients sometimes need to be carefully chosen for the pathogen to grow properly and in large numbers. Although a lot of microorganisms can be produced without the need of live organisms some require live hosts. As with macro organisms, quality control is important for microorganisms mass production operations. Quality control issues in mass produced microorganisms involve: - Assurance that cultures have not become contaminated. Specially by microbes pathogenic to humans Assurance that virulence to target species has not declined Assurance that active unit numbers (e.g. spores) are being produced as it is stated for the product

Microorganisms Release Same equipment used for insecticide applications can be used to release microorganisms. Care should be taken in placing microorganisms close to the target since their ability to move is not as great as the one of macro organisms. To protect certain microorganisms from abiotic factors they are usually sprayed in formulations that protects them until infection from dangers such as desiccation and UV light. Microorganisms can also be aided by adding materials to the formulations that make infection easier.

Microorganism Storage and Transport It is not difficult to store microorganisms for a year. Some might need to be refrigerated. Some microorganisms are only able to be stored for up to a couple of months though. This storage problem is one of the major drawbacks of biopesticides.

Macroorganism Mass Production Keep in mind that, generally, to produce one macroorganism species for release you need to mass rear at least two species: The natural enemy and its hosts. Because this and the short shelf life of many natural enemies, macro-natural enemies for release usually cost more to produce than insecticides. In mass rearing quality control is extremely important. We need to make sure that no adaptation to rear conditions have occurred and that inbreeding depression is not a problem. What is inbreeding depression?

Macro organism Releases Factors influencing successful macro organism releases shared a lot of common factors with successful insecticide applications: Application rate, timing (including time of day) synchrony with the pest’s susceptible stage, coverage, severity of rainfall after application, and number of applications will all influence successful releases of macro organisms and successful insecticide application as well. While several microorganisms can be released using the same kind of equipment used for insecticide applications, macro-organisms are usually released manually.

Macroorganism Storage and Transport In case you were wandering, inbreeding depression refers to the decrease of fitness in organisms that reproduce among relatives (or genetically related individuals). So when rearing insects for control one needs to make sure that they do not reproduce among relatives all the time. Introducing fresh field populations in the mass rearing effort is a way to prevent inbreeding depression. One needs to make sure insects do not die during rearing or transportation due to overheating or cannibalism. To prevent cannibalism some macroorganisms are packed with buckwheat hulls, paper, or vermiculite to provide hiding places or refuges.

Seasonal Inoculative Releases Greenhouses For natural enemies that do not tolerate cold weather Seasonal inoculative releases are used when persistence of the natural enemy in the release area is shortened due to seasonal effects. In greenhouses each time harvest is over and the season of the crop is completed the introduced natural enemies will be eliminated during greenhouse cleanout practices.

Steps for Augmentative Releases Identification of a market Identification of right strain Develop a method for mass production Develop of storage methods Develop of methods for transport Develop release methods and dosages The market refer to enough demand for the product to be profitable when selling it. Right strain refers to a strain that will be effective against the pest and at the same time cost effective to produce. After the right market has been identified and the right strain chosen we need to develop a way to mass produce the natural enemies, store them transport them and release them in the right dosage. If you were wandering, the parasitoid in the picture is the famous Encarsia formosa, used inoculatively in green houses to control whiteflies.

Macroorganism Strain The strain of the organisms used might make a big difference when it comes to performance in the field.

Microorganism Strain Knowing the strain of the natural enemy we are dealing with is extremely important with microorganisms. It is important to corroborate results from the lab in the field. Same as with macroorganisms. Do not be mislead by their small size. These living organisms depend on abiotic and biotic conditions as much as their macro counterparts. The slide shows an example of a fungal pathogen (Verticillium chlamydosporium) that attacks nematode eggs that live on galled tomato roots. Different strains of this fungal pathogen differ in their ability to live in the root area. So picking the right strain is really important. A strain that attacks the nematode eggs in the lab might perform extremely poor out there in the real world if it is unable to live in the roots of the plants. In this particular case even the varieties of tomatoes involved (i.e. the host-plant variety), affected particular strains performance. Remember living organisms do not only interact with one but with many factors. The ecological niche is a multidimensional space.

Although mostly used in greenhouses augmentative bio control is also practiced in the field. For certain species of pests augmentative control in the field works well. Thricogramma spp parasitoids, for example, are released to control certain lepidopteran pests in field situations. More research and improvements in regulation policies and marketing could make augmentative biocontrol a more widespread practice.

Next class we will study conservation biological control!