Erythmelus klopomor: First steps toward classical biological control of the oak lace bug Corythucha arcuata, a dangerous invader in the European oak forests

The North American oak lace bug (OLB), Corythucha arcuata (Say, 1832) (Hemiptera: Tingidae), is a very dangerous invasive pest of European oaks ( Quercus spp., Fagaceae). It was first detected in Europe in 2000 and currently occurs in 26 countries in the Palearctic region. Most Eurasian deciduous oaks are suitable host plants, therefore about 30 million hectares of oak dominated forests in Europe can facilitate its rapid spread. Its negative effects can be very diverse: decreasing photosynthetic activity, deteriorating health, decreasing acorn yield, negative effect on other oak herbivorous insects, and more. One of the main reasons for its rapid expansion is that native European predators, parasitoids and insect pathogens are unable to control it. The only feasible control option is a classical biological control program, the essence of which is to find and introduce a preferably specialist regulatory species that is effective in the pest’s native range. In July 2023 and in 2024, we collected oak leaves with OLB eggs from different locations in six states of the United States of America. All emerged egg parasitoids were preserved for later identification. Our initial observation was that collecting OLB eggs in the field proved to be more challenging than we first assumed. Overall, 23.7% of the samples contained parasitoids, with the average parasitism of 14.5%. Up to this point results indicate that the fairyfly Erythmelus klopomor Triapitsyn, 2007 (Hymenoptera: Mymaridae) is the only known egg parasitoid of OLB. Its host range is restricted to lace bugs, mainly Corythucha spp., and C. arcuata seems to be its preferred host. Our conclusion is that E. klopomor is a promising and only (at least so far) candidate for a classical biological control program, but further research efforts are unavoidable to clarify its life history parameters and minimize the risk of unintended non-target effects prior to a potential deliberate introduction to Europe.