Ectoparasitoid Dinarmus basalis causes greater offspring loss to the winged morph of Callosobruchus maculatus

The pest cowpea weevil Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) exhibits polymorphism with flight and flightless forms that differ in morphology and life-history. Flight forms are generally dispersers with lower fecundity that increase in frequency when population density and intraspecific competition are both high. Callosobruchus maculatus larvae can cause important damage to stored grains and the solitary ectoparasitoid Dinarmus basalis (Rondani) (Hymenoptera: Pteromalidae) is considered to be a good candidate biological control agent. However, whether morphs differ in the likelihood of their offspring surviving attack is unknown. Understanding this has implications for the pest status of the cowpea weevil following biological control. We found that attack by D. basalis lowered the number of emerging offspring produced by both morphs. The ectoparasitoid was most effective at reducing survival of larvae produced by flight morph parents, suggesting that there may be a further cost of dispersal for C. maculatus. Parental morph type did not influence D. basalis behavior or development when foraging, so the biological mechanism resulting in this difference remains unclear. Nevertheless, our study shows that D. basalis affects the offspring of both weevil morphs, as required for an effective biocontrol agent. These results contribute to our understanding of how intraspecific variation, including polymorphism, influences species interactions among biological control agents and their target insect pests.

Automated summary

The pest cowpea weevil, Callosobruchus maculatus, has flight and flightless forms that differ in morphology and life-history. The flight forms are dispersers with lower fecundity and increase in frequency when population density and intraspecific competition are high. The larvae of C. maculatus can cause significant damage to stored grains, and the ectoparasitoid, Dinarmus basalis, is a potential biological control agent. Our study found that attack by D. basalis reduced the number of emerging offspring produced by both morphs, with a greater impact on the flight morph. This suggests that there may be an additional cost of dispersal for C. maculatus.