Interactions between the box tree moth Cydalima perspectalis (Walker) and the tachinid parasitoid Exorista larvarum (L.)

Cydalima perspectalis (Walker) (Lepidoptera Crambidae), native to East Asia, was first recorded in Europe in 2007. In Italy, it was detected in 2010 in Veneto and it is now distributed in other regions. This exotic species represents a threat to Buxus plants in European parks and gardens, as well as in natural environments, i.e. spontaneous formations of southern France and northwestern Italy. In Europe, only two parasitoids, including the tachinid Pseudoperichaeta nigrolineata (Walker), have so far been found to attack C. perspectalis in nature, at a very low rate. In the areas of origin, the parasitoid complex of the box tree moth is wider and comprises other tachinid species, including Exorista spp. A stock colony of Exorista larvarum (L.), a larval parasitoid native to the Palearctic region, is currently maintained in the laboratory of Entomology of the University of Bologna, using Galleria mellonella (L.) (Lepidoptera Pyralidae) as a factitious host. Both biological bioassay and anatomical and histological examinations were carried out to evaluate the possibility of adaptation of this indigenous tachinid species to C. perspectalis. In no-choice experiments, box tree moth larvae were accepted by E. larvarum females, though a lower number of eggs were laid compared to G. mellonella, maintained as a control. Most eggs hatched, as also shown in the anatomical and histological studies, but no puparia formed in any accepted C. perspectalis larva. Two out of six first instar E. larvarum larvae penetrated the body of a box tree moth larva and were encapsulated. The encapsulation response turned into the formation of the respiratory funnel by two parasitoid larvae, similarly to what happens in G. mellonella. The results obtained in this study showed that C. perspectalis was unsuitable as host for E. larvarum. The mortality following the parasitoid larval activity (independently of successful parasitism) was, however, not significantly different between C. perspectalis and G. mellonella. The overall results suggest that the mortality of C. perspectalis larvae due to the partial development of E. larvarum may be useful to regulate the populations of this invasive pest in a context of conservative biological control.