Optimizing Photoperiod, Exposure Time, and Host-to-Parasitoid Ratio for Mass-Rearing of Telenomus remus, an Egg Parasitoid of Spodoptera frugiperda, on Spodoptera litura Eggs.

Wanbin Chen,Xiaoyu Jing,Qingfen Weng,Hongzhi Zhang,Mengqing Wang,Lisheng Zhang,Rui Nie,Yuyan Li,Jianjun Mao

doi:10.3390/insects12121050

Abstract

Telenomus remus (Nixon) is a dominant egg parasitoid of the destructive agricultural pest Spodoptera frugiperda (J. E. Smith), and so is used in augmentative biocontrol programs in several countries. An optimized mass-rearing system is essential to produce biological control products in a timely and cost-effective manner. In this study, the photoperiod, host egg:parasitoid ratio, and exposure time were evaluated to identify the optimal rearing conditions for T. remus on the alternative host Spodoptera litura (Fabricius) eggs. Results showed that increasing photoperiod above 12L:12D remarkably improved parasitoid progeny yield and life table parameters. Overlong photoperiods shortened female longevity, but within acceptable limits. There was a significant negative correlation between parasitism rate and host egg:parasitoid ratio under exposure times of 12 and 36 h, but not 24 h. Percentage of female progeny increased significantly along with increasing the host egg:parasitoid ratio. A significant negative relationship between the number of emerged adults per egg and the host egg:parasitoid ratio was observed at an exposure time of 36 h. It was concluded that T. remus may be mass-reared most efficiently on S. litura eggs using a photoperiod of more than 12L:12D, a 14-20:1 host egg:parasitoid ratio, and an exposure time of 24 h. These findings can be used to produce T. remus more efficiently and at lower costs.

Highlights

In order to achieve the best production levels that satisfy the needs from the field at lower costs, this study aimed to measure the effect of photoperiod, exposure time, and the host egg:parasitoid ratio on the parasitism rate, emergence rate, percentage of female progeny, and other biological parameters of T. remus reared on S. litura eggs
Mean fecundity of T. remus under constant dark conditions (0L:24D) was lowest, which was significantly lower than all photoperiods tested in this study
Our results revealed that the biological characteristics of T. remus on S. litura eggs depend closely on photoperiod: The all-dark photoperiodic condition caused the worst performance, and increasing illumination time positively affected the total number of parasitized eggs

Summary

Introduction

By September 2020, it had spread to 27 provinces (autonomous regions and municipalities) across the country [6]. Such invasive insects have considerable negative influences on their new environments, damaging indigenous plant species and becoming major agricultural pests [7]. The economic losses caused by invasive insects, in general, are estimated to be about US$1.3 trillion per year worldwide [8], and S. frugiperda is widely agreed to be one of the major devastating invasive pests [3,9,10]. In Africa, this pest has been calculated to cause annual yield losses in corn of 21–53%, with the financial losses estimated at approximately US$2.48–6.19 billion [9]

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