Emesis or regurgitation? Crop response to the ingestion of insecticide‐bait blends in Anastrepha ludens

Abstract

Regurgitation is a phenomenon that is part of the digestive process in insects that have a crop organ. It is basically stimulated by liquid food concentration and viscosity. However, it has been proposed that regurgitation can be a defensive barrier to poisoning, and then it would be considered as emesis. We tested the regurgitation response of the Mexican fruit fly, Anastrepha ludens (Loew) (Diptera: Tephritidae), to sublethal doses of the insecticide malathion in sugar or protein–sugar solutions (i.e., insecticide baits) with varying sugar concentrations. By feeding flies with six sugar concentrations (1–50%) without insecticide, we determined that they regurgitated more when feeding on a 20% than when feeding on a 50% sugar solution. By feeding flies with six malathion concentrations in a 20% sugar solution, we determined two sublethal doses. Flies fed with those sublethal doses in protein (4%)–sugar (20 and 50%) solutions over-regurgitated about 2× more than those fed with controls, i.e., protein–sugar and sugar solutions. The over-regurgitation did not prevent a reduction in survival and fecundity in flies feeding on sublethal doses of malathion. It seems that regurgitation is provoked by the noxious substance, in addition to the food (sugar) concentration. The overresponse may be separated from the normal regurgitation used to process a meal and may be considered as emesis.