Location, acceptance and suitability of Spodoptera littoralis and Galleria mellonella as hosts for the parasitoid Exorista larvarum

The location, acceptance and suitability of the phytophagous Spodoptera littoralis (Boisduval) by the tachinid larval parasitoid Exorista larvarum (L.) was studied in the laboratory. A test was conducted in a cage environment to assess whether E. larvarum displays a difference in locating and accepting the laboratory host Galleria mellonella (L.) vs. S. littoralis and whether the host plant plays a role in host location by the parasitoid. Inexperienced E. larvarum females were similarly attracted to, and accepted, G. mellonella and S. littoralis larvae, but weakly responded to S. littoralis larvae feeding on a bean leaf. Since the latter were apparently less mobile compared to the other two targets, the results may support the hypothesis that, at close range, tachinid females use visual cues and, in particular, motion signals in host location. Host acceptance and suitability of S. littoralis vs. G. mellonella by E. larvarum were then further compared. Based on the time needed to obtain the oviposition of 4-6 eggs per larva, acceptance was not significantly different between the two host species. Puparia were however obtained from 1.3% of S. littoralis larvae vs. 75% of G. mellonella larvae. Despite the low successful parasitization, in parasitized S. littoralis larvae mortality was higher compared to control (unparasitized) larvae. This result suggests that E. larvarum may be a candidate for biological control of S. littoralis.