Reduced reproductive effort in male field crickets infested with parasitoid fly larvae

Some populations of the field cricket Teleogryllus oceanicus are parasitized by the phonotactic fly Ormia ochracea. Flies locate crickets by their song and deposit larvae onto them. The larvae develop inside the cricket for 1 week before killing the host Upon emergence. The reproductive compensation hypothesis predicts that parasitized crickets should increase their reproductive effort during the initial stages of infestation to offset the loss of fitness resulting from their shortened life span. An alternative hypothesis predicts that parasitized crickets will decrease reproduction, either because they are unable to reproduce or because selection acting on the parasitoid favors decreased host reproduction. In laboratory experiments, parasitized male crickets had reduced reproductive effort (spermatophore production, calling, mating activity, and mass allocated to reproductive tissue) compared to unparasitized males. Parasitized males fed ad libitum showed no evidence of allocating a greater proportion of their resources to reproduction. Parasitized and healthy males did not differ significantly in resting or maximal metabolic rates, although this may have been due to the substantial contribution of larval respiration to the metabolic rate of the host-parasitoid complex. These results are consistent with previous studies and suggest that T. oceanicus males parasitized by O. ochracea do not increase their reproductive effort. We discuss potential reasons that crickets do not increase reproductive effort in response to fly larvae and address difficulties in demonstrating altered life-history patterns in response to parasitism.