Sperm Production Is Reduced after a Heatwave at the Pupal Stage in the Males of the Parasitoid Wasp Microplitis rufiventris Kok (Hymenoptera; Braconidae)

Abstract

Simple Summary Biocontrol with natural enemies of insect pests needs an optimal reproduction of beneficial insects. Most insects are sensitive to heat, and many males suffer from sperm decrease when exposed to warmth during their development. It is dramatic in hymenoptera because males are issued from the development of unfertilized oocytes and only females develop from fertilized eggs. The sex ratio of populations then results from the availability of sperm for egg laying females. Microplitis rufiventris is a parasite of the cotton worm; this moth is a major pest for cotton fields in Egypt. Because the temperature is high in Egypt, reproduction of M. rufiventris must be studied to optimize its use in the fields. We conducted experiments to measure the sperm number of males after heat periods during their development. It shows that M. rufiventris males have less sperm than controls when they were exposed to 36 °C and 40 °C short periods during their development. Moreover, those males live shorter than males that were maintained at 25 °C. In conclusion, we found, males to be sensitive to heat waves, which results in lower fertility, resulting in a lower availability of sperm for females leading to a sex ratio bias. It may lead to a decrease of the efficacy of biocontrol in cotton fields. Abstract Understanding reproduction is essential for controlling pests and supporting beneficial insects. Among the many factors allowing optimal reproduction, sperm availability is key to sex ratio control in hymenopteran parasitoids since males are haploid and only females come from fertilization. Microplitis rufiventris (Hymenoptera; Braconidae) is a solitary endoparasitoid of some noctuids. This insect could be used for the control of the cotton leafworm Spodoptera littoralis. Under controlled conditions, sperm quantity was measured in virgin males at 1, 5, 10, and 15 days; it increases in adult males until the fifth day. Sperm stock of control males increased from 2500 at one day to 6700 at 15 days. With the control climatic condition being 25 °C, we tested the effects of a time-limited increase of temperature that can be found in Egypt (36 and 40 °C) during one day at the early pupal stage. Emerging males had 1500 and 420 sperm at 36 and 40 °C, respectively; both lived shorter than the control. The sperm potential of males is dependent on both age and temperature during the early pupal stage. It could have dramatic consequences on the sex ratio of M. rufiventris in natural and controlled populations.