Sex-specific dispersal by a parasitoid wasp in the field

Although parasitoid wasps are important regulators of herbivorous insect populations, very little is known regarding their movement under field conditions. Here, we examined the vertical and cardinal directionality of dispersal by Binodoxys communis (Gahan) (Hymenoptera: Braconidae: Aphidiinae), an exotic Asian parasitoid released as a biological control agent of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae: Aphidinae), in North American soybeans, Glycine max (L.) Merr. (Fabaceae). The patterns are consistent with time-dependent, sex-specific dispersal strategies; whereas males show flight that is devoid of vertical or cardinal directionality, females consistently move at or above soybean canopy height toward the east and north. Male capture rates also appear to be more correlated with local conditions than those of females. These results suggest that females actively cross the flight boundary layer (the space above which insect flight is largely wind-driven as opposed to self-directed) and follow air currents away from soybean fields, whereas males engage in more localized movement. The data also suggest differing response potentials of the sexes to changing local resource conditions (host availability, female availability, host plant cultivar). We discuss the implications for sex-specific movement on the basic biology of introduced parasitoid species, and their applied role as potential agents in importation biological control programs.