Variability in development of the striped rice borer, Chilo suppressalis (Lepidoptera: Pyralidae), due to instar number and last instar duration.

Guang-Hua Luo,Jing Yao,Qiong Yang,Zhi-Chun Zhang,Ji-Chao Fang,Ary A Hoffmann

doi:10.1038/srep35231

Abstract

The striped stem borer, Chilo suppressalis (Walker), is an important insect pest of rice which shows substantial variation in developmental duration among individuals. This variation is currently poorly characterized but it is important from a control perspective because pesticides can only target early sensitive instars. It is unclear whether there are key stages that determine the length of developmental duration of individuals and/or whether variation in instar number contributes to this variation. In this study, a laboratory population and a population recently established from the field were used to test variation in development time across instar stages. The duration of developmental time of C. suppressalis started to diverge from the 5th instar onward. Individuals pupated at the 5th, 6th, 7th or even 8th instar stage. In both populations, both the instar at which the larva pupated and the duration of the last larval instar stage determined total developmental time of an individual. There was little impact of the developmental time of early instars on total developmental duration or on instar number prior to pupation. Sex influenced the number of instars but not development time within this number. The biological and applied significance of uneven development in C. suppressalis are discussed.

Highlights

In insects, the number of larval moults and the duration of larval instars can be influenced by environmental factors such as temperature, photoperiod, nutrition, and carbon dioxide anaesthesia1–6
Some C. suppressalis exhibit prolonged developmental times, suggesting a high level of inter-individual variation15. It is unclear whether this variation is due to key instar stages that determine the length of individual developmental time and/or variation in instar numbers as well as sex
We found a high level of variability in developmental duration which was strongly associated with the number of instars at the larval stage as well as variation in the final instar stage before pupation regardless of instar number

Summary

Introduction

The number of larval moults and the duration of larval instars can be influenced by environmental factors such as temperature, photoperiod, nutrition, and carbon dioxide anaesthesia. As well as varying with environmental conditions, instar numbers can vary among insects reared under the same constant conditions, suggesting that there is inherent variation in instar development not necessarily connected to environmental responses. This instar variation may be partly due to sex: sexual size dimorphism is common in insects, and by having a higher number of instars females may be able to develop to a larger size on emergence. Some C. suppressalis exhibit prolonged developmental times, suggesting a high level of inter-individual variation. Some C. suppressalis exhibit prolonged developmental times, suggesting a high level of inter-individual variation15 It is unclear whether this variation is due to key instar stages that determine the length of individual developmental time and/or variation in instar numbers as well as sex

Objectives

Methods

Results

Conclusion