Are egg parasitoids of the genus Trichogramma (Hymenoptera: Trichogrammatidae) promising biological control agents for regulating the invasive Box tree pyralid, Cydalima perspectalis (Lepidoptera: Crambidae)?

The Box tree pyralid, Cydalima perspectalis Walker (Lepidoptera: Crambidae), is an invasive species in Europe, not yet regulated by natural enemies. It is highly destructive to ornamental and native Buxus due to defoliation by larval feeding. The ability of eight Trichogramma species (T. brassicae Bezdenko, T. bourarachae Pintureau & Babault, T. cacoeciae Marchal, T. cordubensis Vargas & Cabello, T. dendrolimi Matsumura, T. evanescens Westwood, T. nerudai Pintureau & Gerding and T. pintoi Voegele) to parasitise and locate eggs of C. perspectalis was assessed in the laboratory. In direct observation tests, all species started to examine and oviposit into exposed eggs. Resulting egg parasitism was low and ranged between 4% and 20% for most of the parasitoid species after three days of exposure. Only T. dendrolimi parasitised significantly more host eggs with parasitism rates above 40%. On average, two to three progeny emerged from one host egg and the resulting sex ratio was female-biased, indicating suitability of the target host for progeny production. In subsequent cage tests on potted Buxus plants, again T. dendrolimi was the most efficient species in locating host eggs on foliage. We conclude that C. perspectalis eggs are attractive to various Trichogramma species. T. pintoi had the highest number of egg encounters and active females. T. dendrolimi females were most able to locate host eggs and to oviposit and produce successfully on them. Nonetheless, further study is needed to clarify the suspected role of potentially egg defensive mechanisms that may impede higher parasitisation in C. perspectalis.