The biology of Lysiphlebus fabarum (Braconidae, Aphidiinae) following cold storage of larvae and pupae

Abstract

Cold storage is a one means of preserving parasitoids prior to release in augmentation biological control programs. This study examined the feasibility of storing larval and pupal stages of a sexual population of Lysiphlebus fabarum Marshall (Braconidae: Aphidiinae) at 6.0 and 8.0 °C (± 1.0 °C), 50–60% RH, and 14L:10D photoperiod. These life stages were stored for periods of 1, 2 and 3 weeks under fluctuating thermal regimes (2.0 h daily at 21.0 ± 1.0 °C). Generally, pupae gave better results than larvae, 6.0 °C was better than 8.0 °C, and were better than constant, considering wasp survival, wasp size (tibial and antennal lengths), egg load and egg size. The best results were obtained with pupae stored for two weeks under a fluctuating temperature regime at 6.0 °C. Females emerging from this treatment did not differ from controls (developing directly at 21.0 °C) in body size, egg size, or progeny sex ratio and suffered less than 20% mortality. Egg loads were reduced in these wasps, but the reductions were substantially less than occurred in other two week storage treatments. Wasps stored in this manner successfully parasitized similar numbers of aphids as controls and produced similar progeny sex ratios. These results reveal a suitable set of low temperature conditions that can be used to delay the development of L. fabarum for two weeks with minimal impacts on wasp fitness.