Acceptance and suitability of the box tree moth Cydalima perspectalis as host for the tachinid parasitoid Exorista larvarum

A laboratory bioassay and anatomical and histological studies were conducted to evaluate the acceptance and suitability of an exotic insect, the box tree moth Cydalima perspectalis (Walker) (Lepidoptera Crambidae), as host for the native parasitoid Exorista larvarum (L.) (Diptera Tachinidae). The factitious host Galleria mellonella (L.) (Lepidoptera Pyralidae) was maintained as control. In the bioassay, C. perspectalis and G. mellonella mature larvae were separately exposed for 3 hours to E. larvarum mated females. Box tree moth larvae were accepted by E. larvarum females, but a lower number of eggs were laid on them than on G. mellonella. 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 the exotic species was unsuitable as host for E. larvarum. The mortality following the parasitoid larval activity (independently of successful parasitization) 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.