Role of volatile infochemicals emitted by feces of larvae in host-searching behavior of parasitoid Cotesia rubecula (Hymenoptera: Braconidae): A behavioral and chemical study

The role of volatile infochemicals emitted by feces of larvae in the host-searching behavior of the parasitoid Cotesia rubecula was evaluated during single- and dual-choice tests inside a wind tunnel. The following treatments were tested: feces produced by second and fourth instars of Pieris rapae (preferred host), second instars of P. brassicae (inferior host), second instars of P. napi (nonhost), and wet feces of second instars of P. rapae. During a single-choice situation females of C. rubecula oriented to all types of feces tested. When a preference was to be made, C. rubecula preferred feces of second instars of P. rapae over that of fourth, feces of P, rapae over that of P. brassicae, feces of P, napi over that of P, brassicae, and wet over normal host feces. No preference was exhibited between feces of second instars of P. napi and that of second instars of P. rapae. The relative importance of infochemicals from host feces versus plant damage caused by host larvae to the searching behavior of C. rubecula was also evaluated. Plant damage was more important to the searching females than host feces when feces were present in specific concentrations in relation to damage. The volatiles released by normal and wet feces of second instars of P. rapae, wet feces of fourth instars of P. rapae, and normal and wet feces of P. brassicae were collected and identified. Overall, 85 chemical compounds were recorded belonging to the following chemical groups: alcohols, ketones, aldehydes, esters, isothiocyanates, sulfides, nitriles, furanoids, terpenoids and pyridines. The blend of chemicals emitted by feces of different instars of P. rapae and different species of Pieris exhibited an instar and species specificity in both quantity and quality. Wetting of normal feces increased the amount of volatile chemicals released, and it was also responsible for the appearance of new compounds. The role of feces of larvae in the host-seeking behavior of C. rubecula is discussed.