Understanding host-acceptance behavior and larval feeding of the parasitic wasp Melittobia digitata (Hymenoptera: Eulophidae) to facilitate rearing on an artificial host

Abstract

A multifactorial design was used to test the effects of oviposition experience, mating, feeding, age, and foundress number on host-acceptance, number of offspring, and sex ratio in Melittobia digitata. The most important factor expediting oviposition was previous oviposition experience. All factors except for feeding experience affected the number of hours it took for a female to start laying eggs. Oviposition experience, mating, and age affected the number of eggs a female laid in the first 24 hours. The sex ratio was only affected by mating, and total numbers of offspring increased with an increase in mated females and foundresses. There were several complex interactions between various factors. Behavioral studies were conducted of M digitata on Apis mellifera pupae, pupashaped glass dummies, and flat glass to determine if females use shape to identify an object as a host worthy of oviposition. Results indicated that shape plays a major role in host recognition. In further experiments, M digitata was found to oviposit on artificial hosts, Parafilm(& domes containing artificial diet. It was determined that females preferred artificial hosts containing the agar-based diet to those containing only agar. Further testing ruled out the possibilities of a chemical ovipositional stimulant originating from the parafilm. Results suggest that females respond to the nutritional content of the host when considering an object for oviposition. Larval M. digilata mouthparts were examined in both dead and live specimens, using both light and electron microscopy. Newly hatched M digitata larvae were fed dyed wax and bee pupae to determine how larvae initially feed after hatching and to assess how larvae access food through the host cuticle. After 24 hours, larval guts contained dye, showing that upon hatching the larvae were capable of ingesting both wax and hemolymph fluids through the bee cuticle. Feeding damage was observed on honey bee larvae and pupae using microscopy, histology, and electron microscopy. Behavioral observations were made of feeding larvae under light and dissecting microscopes. This, along with the feeding damage seen in sections and with the electron microscope, suggests that larvae initially feed on the epicuticle, and subsequently suck fluids through the procuticle.