Functional response ofTrichogramma chilonistoGalleria mellonellaandChilo sacchariphaguseggs

Abstract

AbstractA biological control programme using inundative releases ofTrichogramma chilonisIschii (Hymenoptera: Trichogrammatidae) reared onGalleria mellonellaL. (Lepidoptera: Pyralidae) is currently underway to reduce infestations ofChilo sacchariphagusBojer (Lepidoptera: Crambidae) in sugarcane,Saccharumspp., on Réunion Island. To assess the potential of the parasitoid as an inundative biocontrol agent, the functional response of threeT. chilonisstrains was tested withG. mellonellaand one strain withC. sacchariphagushost eggs in glass tubes in the laboratory. The shape of the functional response (type II or III) was determined using logistic regression, and attack coefficients and handling times (Th) were determined using non‐linear least‐square regression. The behaviour of all three strains withG. mellonellahost eggs corresponded to a type III response. The St BenoîtT. chilonisstrain had a significantly shorter estimate of Ththan the St Pierre strain (P<0.05) and may, therefore, be more appropriate as a biocontrol agent. The functional response withC. sacchariphagushost eggs was a type II with the St BenoîtT. chilonisstrain. MoreT. chiloniswasps developed per host egg from the largerC. sacchariphagushost eggs (2.9) relative toG. mellonella(1.1). Superparasitism at low host egg densities was, therefore, likely to have been less frequent withC. sacchariphagus. Black eggs were chosen as an estimate of number of eggs parasitized, although they represent the number of eggs where parasitism led to complete pupal development. The low rate of detected parasitism at low host densities withG. mellonellaeggs may be due to incomplete pupal development due to superparasitism rather than lack of parasitism, thus explaining the type III functional response.