Laboratory and field host preferences of introduced Cotesia spp. parasitoids (Hymenoptera: Braconidae) between native and invasive Pieris butterflies

In laboratory tests, Cotesia glomerata (Hymenoptera: Braconidae) exhibited a clear preference in small cage tests for first or second instars of the native butterfly Pieris napi oleracea (Lepidoptera: Pieridae) vs larvae of the invasive non-native species Pieris rapae (Lepidoptera: Pieridae), under both choice and no-choice test designs. Under the same conditions, Cotesia rubecula (Hymenoptera: Braconidae), either showed no preference (no-choice test) or preferred P. rapae (choice test). These laboratory data predict that both of these Cotesia species should attack P. napi oleracea and thus under modern biological control protocols, both should be rejected as candidate biological control agents (if they were being currently considered for introduction, rather than as is the case, already introduced, in North America). The predicted attack by C glomerata on P. napi oleracea under field conditions was confirmed by field choice tests in which C glomerata attack rates on P. napi were found to be fivefold greater than on P. rapae. In contrast, in the same field-based choice tests, attacks on P. napi by C rubecula were never observed, even when and where attacks on P. rapae were consistently observed. This lack of attack on P. napi oleracea is unexplained at present and suggests a need for better understanding of the influences present in laboratory tests that are able to affect estimates of parasitoid host ranges. Such improvements are critical for future enhancement of safety in classical biological insect control. (C) 2003 Elsevier Science (USA). All rights reserved.