Temperature-dependent parasitism, development, and reproduction of Microplitis manilae (Hymenoptera: Braconidae) on Spodoptera litura (Lepidoptera: Noctuidae).

Abstract

The braconid wasp Microplitis manilae (Hymenoptera: Braconidae) is a solitary, koinobiont endoparasitoid of young Spodoptera litura (Fabricius) larvae and one of its most crucial natural parasitic enemies. The establishment of a stable and sufficient population of M. manilae by rearing them in a laboratory is the cornerstone of field release management. However, when reared in a laboratory, M. manilae is affected by temperature. Here, we attempted to optimize the rearing temperature of M. manilae for parasitizing second-instar S. litura larvae by examining the effects of rearing at 5 temperatures: 16 °C, 20 °C, 24 °C, 28 °C, and 32 °C. Our results suggest that the development of the parasitoid progeny speeded up with shorter durations of the egg-larval, pupal, and preadult stages with the increase in temperature from 16°C to 32 °C. The parasitism rate and fecundity of M. manilae upon parasitizing second-instar S. litura larvae increased with rearing temperature from 16°C to 24 °C, with the peaks at 24 °C reaching 52.90% and 111.70 eggs/female, respectively, and then decreased at 28 °C to 32 °C. At 24 °C, the sex ratio (0.22) was the lowest, whereas the emergence rate (68.54%) did not differ significantly compared with those at other temperatures. Meanwhile, at 28 °C, the parasitism rate, fecundity, and emergence rate approached the levels at 24 °C, whereas the sex ratio was higher (0.29) than at 24 °C. These findings suggest 24 °C to 32 °C is the most appropriate temperature range for M. manilae mass rearing under laboratory conditions.