Abiotic and biotic factors influence diapause induction in sexual and asexual strains of Trichogramma brassicae (Hym: Trichogrammatidae)

Somayeh Rahimi-Kaldeh,Nicolas Ris,Ahmad Ashouri,Alireza Bandani

doi:10.1038/s41598-018-35626-7

Abstract

The effects of some abiotic (maternal photoperiod and offspring developmental temperature) and biotic (host quality during both maternal and offspring generations) factors on diapause induction were investigated for two sympatric strains of Trichogramma brassicae Bezdenko (Hym: Trichogrammatidae) differing by infection status with regard to Wolbachia. The mode of reproduction, developmental temperature, maternal photoperiod and the quality of the host significantly affected diapause induction. The highest percentage of diapausing individuals were observed with the sexual strain reared at 14 °C using a “high quality” host and after a long photophase during the maternal generation. Environment-by-Environment, as well as Genotype-by-Environment interactions, was observed. All these patterns were discussed with the goal of providing relevant protocols for the commercial mass-rearing of such biocontrol agents. A successful diapause in beneficial insects could affect the efficiency of mass rearing by increasing the duration of storage conditions based on a high percent emergence and providing a large number of individuals at the appropriate time in the field season.

Highlights

Egg parasitoids of the genus Trichogramma are widely used as effective biocontrol agents against many Lepidopteran pests, mainly because of the early destruction of their host before any plant damage, the ease of mass-rearing, and their short life cycle[1]
The present study was aimed at investigating the influence of maternal photoperiod, the direct influence of rearing temperature, and the influence of host quality on the diapause induction of two strains of T. brassicae, an uninfected-sexual strain and a Wolbachia-infected asexual strain[17]
Our results showed that the proportion of diapausing progeny was significantly dependent on developmental temperature

Summary

Introduction

Egg parasitoids of the genus Trichogramma are widely used as effective biocontrol agents against many Lepidopteran pests, mainly because of the early destruction of their host before any plant damage, the ease of mass-rearing, and their short life cycle[1]. The presence of Wolbachia in Trichogramma species is not widespread with only 18 of 180 species tested known to be infected and while in some species Wolbachia infection is fixed at the population level (e.g. T_oleae and T. cordubensis)[5], infection frequencies are low for some species (e.g. 6–26% of T. kaykai females[6,7]). As a consequence, both sexual-uninfected and asexual-infected individuals can be observed in a single species. We have previously shown that both strains were able to overwinter in natural conditions (central Alborz Mountains) sexual T. brassicae has more overwintering ability in natural climatic conditions[18]

Methods

Results

Conclusion