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Pesticide Compatibility: Is It Really Possible?

Pesticide Compatibility With Natural Enemies: Is It Really Possible?

There is a plethora of information pertaining to the release of biological control agents or natural enemies such as parasitoids and predators in conjunction with the use of pesticides (in this case, insecticides and miticides). Although this appears to be a “sound management strategy,” there are numerous factors that need to be considered before actually attempting to incorporate natural enemies along with making pesticide applications. Furthermore, there are currently existing misconceptions associated with implementing both pest management strategies together.

Pesticides, in general, known to be directly and indirectly harmful to natural enemies should not be used in greenhouses where biological control is being implemented. However, there has been research associated with the prospect of using natural enemies in conjunction with alternative pesticides such as insect growth regulators, insecticidal soaps, horticultural oils, feeding inhibitors, and microbial agents including entomogenous bacteria and fungi, and related micro-organisms. The thought is that alternative pesticides are more compatible with natural enemies compared to conventional pesticides in the chemical classes [1]; organophosphate, carbamate, pyrethroid, and neonicotinoid because alternative pesticides are active on a narrow range of insect and mite pests, and have very diverse modes of action.

Well, it has been demonstrated that alternative pesticides are actually harmful to certain natural enemies both directly (immediate mortality) and indirectly (sublethal effects). Not only will wet sprays directly kill natural enemies regardless of the pesticide (conventional or alternative) but dried residues may be indirectly toxic to natural enemies. In general, the harmful effects of pesticides on natural enemies may be due to direct contact, host elimination, residual activity, and/or sublethal effects:

Direct Contact:

Directed sprays of pesticides may kill natural enemies or in the case of parasitoids they are killed while developing inside the insect pest (host).

Host Elimination:

Pesticides may kill hosts, which may result in natural enemies dying or leaving because they are unable to locate additional hosts.

Residual Activity [2]:

Although spray applications of pesticides may not directly kill natural enemies, any residues may have repellent activity thus affecting the ability of parasitoids or predators to locate a food source.

Sublethal Effects:

Pesticides may not directly kill a natural enemy, but they may affect development or reproduction such as sterilizing females, reducing the females’ ability to lay eggs or impact the sex ratio (number of females to males). In addition, the foraging behavior may be modified thus influencing the ability of a parasitoid or predator to locate a host. Also, those parasitoids that host-feed such as the greenhouse whitefly parasitoid, Encarsia formosa [3] may inadvertently consume residues on hosts after a spray application. Any residues on potential hosts may make them unacceptable to a parasitoid or predator.

Furthermore, any differences in natural enemy susceptibility to pesticides may be associated with factors such as 1) whether the natural enemy is a parasitoid or predator, 2) natural enemy species, 3) life stage (egg, larva, pupa, and adult) sensitivity, 4) host development stage, 5) application rate, 6) timing of application, and 7) type or mode of action of pesticide used. The bottom line is that depending on the situation actually using natural enemies and pesticides together may be inefficient, difficult, and/or more time-consuming than using either pest management strategy alone.

About the Author: Dr. Raymond A. Cloyd is an Associate Professor and Extension Specialist in Ornamental Entomology and Integrated Pest Management for the Department of Entomology at Kansas State University (KSU). He is both knowledgeable and approachable.

Additional Resources

Here are additional resources that may compliment this article.

1. Learn more about chemical classes (wikipedia.org).
2. See residual as defined in our glossary (this site).
3. Learn more about Encarsia formosa (this site).

More: Also see this related 2007 Bug Blog article (this site).

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