Larval host plant influences male body size and mating success in a tephritid fruit fly

In phytophagous insects, the larval host plant may have a profound effect on the biology of the adult stage. This influence has been most widely studied in females, where larval diet may affect their fecundity and survival. Males have been less well studied, with focus on host plant effects on (1) male size and the consequences of variable male size on male mating success, ejaculate, and/or nuptial gifts, or (2) male-produced chemical signals important in sexual communication. The melon fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae), is a world-wide agricultural pest that infests plants of the family Cucurbitaceae primarily but also attacks hosts in other unrelated families. The objective of the present study was to investigate whether larval host influenced female choice in Z.cucurbitae and, in particular, test for random mating using adults (Z flies) whose larvae fed on a cucurbit host (zucchini, Cucurbita pepo L.) and adults (P flies) whose larvae fed on a non-cucurbit host (papaya, Carica papaya L., Caricaceae). In field tent trials, both Z and P females mated more often with Z males than P males, and in no-choice laboratory cage trials, mating latency was generally shorter for Z than for P males. Wing vein measurements, made both within and between generations, showed that Z males were consistently larger than P males. Further observations of fly trios one female plus one large and one small male revealed that large males dominated in aggressive encounters and exhibited wing fanning (signaling) more often than their smaller counterparts. Although olfactory signals associated with wing fanning were not investigated in the present study, the observed host-mediated difference in male size is, if not solely responsible, certainly an important determinant of the mating patterns described.