Natural predators and parasitoids of insect pests

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Farm Forum

Although this isn’t the ideal time of year to discuss insect pests, it is the season of pesticide applicator certification, and insect pests is one of the common topics covered in meetings. The entomology team members at SDSU Extension are big believers in taking advantage of natural predators in managing insect pests and working hard to educate farmers and crop advisors of their potential.

Unless their populations are reduced due to routine applications of insecticides, insect predators are usually common in many agricultural crops and natural habitats. They consume prey rapidly, at both immature and adult growth stages, and often consume prey in significant numbers. Insect predators usually also eat many different species of insect pests, are highly mobile, and very important in natural control.

One of the most well-known species of insect predators are lady beetles, which have voracious appetites for aphids. In one study, over a 24 hour time period, sevenspotted lady beetle females ate on average 115 soybean aphids, males ate 78, and third instars ate 105. Multicolored Asian lady beetle females ate 95 soybean aphids, males ate 54, and third instars ate 112. Although best known for consuming aphids, as with most insect predators, lady beetles feed on a variety of soft bodied insect pests. The larval stage of the lady beetle are often described as looking like miniature, black and orange alligators, much unlike the recognizable adult stage, and commonly mistaken for plant pests. There are about 5,000 different species of lady beetles, and while most of them are insect predators and highly beneficial, a few species feed on plants. The Mexican bean beetle and the squash beetle are two examples.

Pirate bugs are another insect predator, which with their piercing-sucking mouthparts, are efficient predators of aphids, spider mites, thrips and other soft bodied insect pests. Damsel bugs are very common in agricultural crop fields and generalist predators. Green lacewings, appropriately nicknamed, aphid lions, are considered great aphid predators and very abundant in wheat fields. Adult hover flies look like small bees and are actually not predaceous, but feed on flower nectar and pollen. The larval stage however, are predaceous, and tend to specialize on aphids.

Another group of insect predators are the parasitoids, which include certain flies and parasitic wasps. The adults are free-living, and lay their eggs inside the bodies of soft bodied insects each species specializing as predators of specific insect pests. The eggs hatch inside the insects’ bodies and the larvae consume their insides, after which time they emerge as adults. Species that specialize on aphids, will leave brown, inflated, papery-looking aphid mummies as evidence of their presence. This group of insect predators are very small, and unlikely to be seen or identified in the field.

Before making insecticide applications, scout to determine if the population of the pest species is at or above the economic threshold, and look for insect predators. If present in high enough populations, they can help keep the pest species under control and don’t charge for their services.