This guest post is by PhD Candidate Emily Meineke.
Parasitoid wasps are often effective at keeping pest populations below damaging levels. Five parasitoid species attack oak lecanium scale, one of the two most damaging pests on urban oak trees in the Southeastern US. Besides being lovely to look at, these parasitoids reduce the number of eggs oak lecanium scales produce, which means they help the trees.
Oak lecanium parasitoids are emerging right now in North Carolina. So are oak lecanium crawlers, which are more responsive to pesticide treatment than any other life stage. Our research shows one of the most effective parasitoid species, Encyrtus fuscus, is active right now on leaves. I observed them last week lapping up honeydew and oak lecanium crawlers.
Many studies show spraying when natural enemies are active can lead to pest outbreaks, which leaves us in a bit of a pickle when it comes to oak lecanium treatment. However, our research shows that on the hottest urban trees the parasitoids and other natural enemies are not keeping up with scale abundance. On these trees horticultural oil applications during crawler emergence could help reduce scale abundance without last effects on parasitoids and other natural enemies.