Host preference and suitability in the endoparasitoid Campoletis chlorideae is associated with its ability to suppress host immune responses

Abstract

Abstract The endoparasitoid wasp Campoletis chlorideae Uchida attacks many noctuid species which vary in their suitability but the host association of this wasp species is poorly understood. In this study, three sympatric noctuid species were chosen, Helicoverpa armigera (Hübner), Mythimna separata (Walker), and Spodoptera exigua (Hübner), to study host preference and suitability of C. chlorideae, examining the immunological compatibility between the parasitoid and the three host species. Campoletis chlorideae parasitised all three species, but showed a much higher preference for H. armigera and M. separata than for S. exigua. In H. armigera, the young wasps developed perfectly and none was encapsulated. In M. separata, about 50% and 10% of them were encapsulated in single and double parasitisation experiments, respectively, and the cocoons were significantly lighter than those from parasitised H. armigera and S. exigua. In S. exigua, 84.8% of the young wasps were encapsulated. In double parasitisation experiments, the phenoloxidase activity, the number of total haemocytes, and the number of plasmatocytes and granulocytes significantly decreased in the haemolymph of H. armigera and M. separata, but not in S. exigua. These results indicate that H. armigera is the most suitable host, M. separata is moderately suitable, whereas S. exigua is an unsuitable host for C. chlorideae. The suitability of the parasitoid to three host species was closely related with the capacity of the wasp to inhibit the host immune system. This study sustains the optimality theory and also evidences the correlation of host‐selection behaviour of the parasitoid wasp and its immunosuppressive ability.