Consider the presence of natural enemies, such as the brown lacewing, when making pest application decisions Photo credit: Dan Mahr

Generally speaking, the beneficial natural enemies of pests are more susceptible to broad spectrum insecticides than are the pests themselves. Therefore, when we treat a field with a broad spectrum material, we generally do significant harm to natural enemies.

When natural enemy populations are greatly reduced, they are often not adequate to control the pests, either those that were the original target of the insecticide applications, or other pest species that may not have reached economically-damaging levels before their natural enemies were eliminated. When a target pest population rapidly rebounds after initial control by an insecticide, this is called pest resurgence. When a non-pest species greatly increases in numbers after a pesticide application used to control another species, this is termed a secondary pest outbreak. Both are common phenomena.

There has been much research on the effects of insecticides on natural enemies. Generally, the older, broad-spectrum insecticide classes, such as organophosphates, carbamates, and synthetic pyrethroids, are highly toxic to beneficials. Many of the newer insecticide groups are considered “reduced-risk” products because they have less negative effects on humans and the environment. In some cases, reduced-risk insecticides also present less risk to natural enemies.

Some of the newer reduced-risk insecticides are more expensive to use and therefore are not as widely used on crops such as soybean. However, if the use of a broad spectrum insecticide for aphid control results in a spider mite outbreak that necessitates one or more miticide applications, then the cost of the more selective products may be more tolerable.

Pest management decisions are based both on economics and on biology. Entomologists in the Midwest are conducting research on the impacts of both conventional and reduced-risk soybean aphid insecticides on natural enemies. The results will help growers make informed decisions about the best soybean aphid insecticides to use on their farms.

Research Updates

Kraiss, H. and E.M. Cullen. 2008. Efficacy and non-target effects of reduced-risk insecticides on Aphis glycines (Hemiptera: Aphididae) and its biological control agent, Harmonia axyridis (Coleoptera: Coccinellidae). Journal of Economic Entomology 101: 391-398. Read abstract»

Kraiss, H. and E.M. Cullen. 2008. Insect growth regulator effects of azadirachtin and neem oil on survivorship, development and fecundity of Aphis glycines (Hemiptera: Aphididae) and its predator, Harmonia axyridis (Coleoptera: Coccinellidae). Pest Management Science 64: 660-668. Read abstract»

Potential impact of soybean rust disease management on soybean aphid populations
Karrie A. Koch and David W. Ragsdale. Presented at the Annual Meeting of the Entomological Society of America 2007 Symposium: Soybean Aphid in the North Central US: Implementing IPM at the Landscape Scale. Results»

W. J. Ohnesorg, M. E. O’Neal, and K. D. Johnson, Iowa State University. Effects of Reduced-Risk Insecticides on the Soybean Natural Enemy Community -
2005 Field Study Results»

Effects of Reduced-Risk Insecticides on the Soybean Natural Enemy Community - 2006 update

The Soybean Entomology Laboratory at Iowa State has completed 2 years of field testing of several insecticides that may have a limited impact on imported natural enemies. The products tested included two seed treatments (Gaucho, Cruiser) comprised of unique active ingredients (imidacloprid, thiomethoxam respectively), and two foliar insecticides (Fulfill, Trimax) also comprised of two unique active ingredients (pymetrazione, imidacloprid respectively). These products were selected based on their mode of contact (systemic) and their selectivity for aphids.

All of these products have a reduced impact on aphid natural enemies, allowing a greater abundance and faster recolonization of predators then plots treated with Warrior (lambda-cyhalothrin). Of the products tested, two (Fulfill and Trimax) performed very well against soybean aphids, lowering populations to the same level as that of broad-spectrum insecticides like Lorsban and Warrior.