# Dual Effects of Cold Storage and Stored Host Eggs of Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) on the Reproductive Capacity of Telenomus remus Nixon (Hymenoptera: Scelionidae)

## TL;DR

Cold storage affects the reproductive capacity of the parasitoid Telenomus remus when reared on stored or fresh eggs of its host, Spodoptera frugiperda.

## Contribution

The study identifies optimal cold storage conditions for T. remus parasitoids reared on stored and non-stored S. frugiperda eggs.

## Key findings

- S. frugiperda eggs can be stored at 10 °C for five days for T. remus rearing.
- T. remus pupae stored at 13 °C for 15 days show no reproductive capacity loss when reared on non-stored eggs.
- Optimal cold storage for T. remus parasitizing stored eggs is 7 °C for 5 days in the larval stage.

## Abstract

Spodoptera frugiperda is an invasive pest that causes serious damage to many economically important cereal crops worldwide. Telenomus remus is one of the most important egg parasitoids against S. frugiperda. Insect storage at certain conditions that temporarily halt development would facilitate effective commercial rearing and transportation, limiting the usual problems of hatching or emergence during shipping and aiding the inundative release of the parasitoids. We hypothesized that when parasitoid parasitizing host eggs are subjected to cold storage, their reproductive capacity would be affected by both the host quality and the cold storage. To confirm this hypothesis, the effects of cold storage on the reproductive capacity of T. remus reared on stored/non-stored S. frugiperda eggs and the hatching rate of S. frugiperda larvae were investigated. The results indicated that S. frugiperda eggs could only be stored at 10 °C for five days to be suitable for rearing T. remus. Telenomus remus pupae in non-stored S. frugiperda eggs were stored at 13 °C for 15 days without affecting the reproductive capacity of the parasitoid. However, the optimum cold storage conditions for T. remus parasitizing stored eggs were 7 °C for 5 days in the larval stage. The maximal shelf lives of T. remus parasitizing fresh and cold-stored S. frugiperda eggs were 15 and 10 days (including the storage duration of host eggs), respectively. Our study revealed that cold storage affected host eggs, thus further affecting the reproductive capacity of the parasitoid. Different storage conditions should be used when mass-rearing egg parasitoids on stored and non-stored eggs to reduce costs and obtain high-quality parasitoids.

Spodoptera frugiperda is the preferred host of the parasitoid Telenomus remus. Cold storage can preserve a sufficient quantity of parasitoids and their hosts in a laboratory colony for mass release. First, the effects of cold storage on the reproductive capacity of T. remus reared on non-stored S. frugiperda eggs and the hatching rate of unparasitized S. frugiperda eggs were investigated. Further, the dual effects of cold storage and stored S. frugiperda eggs on the reproductive capacity of T. remus were studied to determine the optimal storage conditions and the maximal shelf life for both the host and the parasitoid. The emergence rate, the number of adults produced, and the female proportion of T. remus were affected by cold storage factors. Pupae stored at 13 °C for 15 days is optimum for T. remus reared on non-stored S. frugiperda eggs. Spodoptera frugiperda eggs could only be stored at 10 °C for five days to be suitable for rearing T. remus. The optimum cold storage conditions for T. remus parasitizing stored eggs were 7 °C for 5 days in the larval stage. The maximal shelf lives of T. remus parasitizing cold-stored S. frugiperda eggs were 10 days. Cold storage affected the hatching rate of S. frugiperda eggs, thereby further affecting the reproductive capacity of T. remus. The findings suggest that different storage conditions should be used when mass-rearing T. remus on stored and non-stored eggs. Telenomus remus should be reproduced using fresh laid S. frugiperda eggs for maximum shelf life.