July 24, 2013
As part of our green initiative at the Greater Des Moines Botanical Garden, we release beneficial insects to control our pest problems, including mealybugs, spider mites, white flies, fungus gnats and thrips. Though they do good, these beneficial avengers of plant health use some truly vicious methods of attacking their prey.
Implementing a beneficial insect control regimen requires a thorough understanding of the pests you have. This might be trickier than you think. For example, if you’re looking to control aphids, there are over 30 potential species that could be present in a greenhouse setting. Once you know what type of insect you’re fighting, you can begin implementing a routine to effectively control it.
Here at the Botanical Garden, we began our program with controlled releases of various insects and also implemented a spray regimen using sprays that are safe to the beneficials. The sprays themselves have interesting modes of action. One particular spray we use is merely a suspended solution of fungal spores that when applied to living insects, germinates on the surface of their body and parasitizes them from the inside out. If that sounds wicked, just wait until you hear about the insects.
As beneficial insects go, there are generally two separate classes of killers—predators and parasites. The difference between predators and parasites is simple enough—predators hunt down their prey and eat them, whereas parasites find their prey and use them as a nesting site to reproduce.
One of the most gruesome predators we use isAphidoletes aphidimyza. This is a bug you definitely don’t want to be around if you’re an aphid. Aphidoletesare small midges, almost like a miniature mosquito in appearance, and the adults fly around and lay their eggs next to colonies of aphids. When these hatch, the larvae crawl around until they find an unsuspecting aphid, bite its leg joints and inject it with a poison. This doesn’t kill, but rather immobilizes the aphid. Once paralyzed, theAphidoleteschow down on the still-living aphids. Gross, but very cool.
Another aphid killer,Aphidius matricariae, attacks aphids by parasitizing them. When released, they fly around looking for colonies of aphids in which to inject their eggs. The eggs then begin to grow, as does the aphid, until the eggs begin to pupate. At that point, the aphid swells up and hardens as theAphidius feeds on its innards. After five days of feeding, theAphidius reaches maturity, chews a hole in the aphid carcass and hatches to start the process over. Vicious.