Tri-trophic interactions and the minimal effect of larval microsite and plant attributes on parasitism of Sphenella fascigera (Diptera: Tephritidae)

Parasitoid insects are important natural biocontrols of insect herbivores. How parasitoids choose particular hosts among many larvae on different plants is not fully understood. Our study system was the coastal plant Senecio lautus and its tephritid herbivore Sphenella fascigera parasitised by an undescribed parasitoid wasp Pteromalus sp. We located S. fascigera larvae in the field and reared pupae to investigate factors that might promote variation in parasitism: host larval location on the plant (stem gall versus flower head), plant density and quality, host larval density, and presence of other insect herbivores. The overall rate of parasitism of S. fascigera was 25%. There was no significant effect of larval location, or any other recorded variable, upon parasitism. One explanation could be the evolution of an efficient search strategy by Pteromalus sp. Future research on whether S. fascigera larvae on congeneric plants experience different rates of parasitism could contribute to understanding the larger web of interactions involving these species.