Heteromorphosis associated to host-exploitation in an atypical parasitoid, Mallophora ruficauda (Diptera: Asilidae)

In this work, we provide morphological illustration and descriptions of the immature stages of the ectoparasitoid robber fly Mallophora ruficauda. Additionally, we studied the ecological aspects of its life cycle through the correlation between the morphology and function performed in each phase of the consumption of their host, the white grub Cyclocephala signaticollis. For the morphological description and quantification of length and width of the egg and larval instars I–II, images were used through optical and scanning electron microscopy. Individuals from larval instars III–V were weighed and measured with digital calibre directly. Finally, images were taken of the cephalic structures of the larval instars and through the use of image processing software we measured in each instar the size of cephalic structures. In addition, the changes in the width of cephalic capsule and the relative size of the maxillary palps and labrum with respect to the width of cephalic capsule were studied for each larval instar through GLMs, to relate the morphology of the cephalic structures with the function they perform. We found that the cephalic structures of the larva undergo changes when moulting to the next instar, according to their relationship with the host, matching with the stage of development where the processes of orientation to the host and attachment to its cuticle take place. These observations reveal, for the first time in a parasitoid asilid larva, the correlation between cephalic morphology and ecological function during the parasitism process and host use.