Increased long-flight activity triggered in beet armyworm by larval feeding on diet containing Cry1Ac protoxin.

Xing Fu Jiang,Lei Zhang,Jian Chen,Li Zhi Luo,Thomas W Sappington

doi:10.1371/journal.pone.0063554

Abstract

Evaluating ecological safety and conducting pest risk analysis for transgenic crops are vitally important before their commercial planting. The beet armyworm, Spodoptera exigua, a long-distance migratory insect pest, is not a direct target of transgenic Cry1Ac-expressing cotton in China, but nevertheless it has recently become an important pest. Migrants leaving their natal field arrive in other appropriate habitat far away in a short time, often followed by larval outbreaks. S. exigua has low susceptibility to Cry1Ac. However, our results from laboratory experiments identified (i) sublethal effects of Cry1Ac protoxin on larval development rate, larval and pupal weight, and adult lifetime fecundity, and (ii) increased long-flight behavior triggered by Cry1Ac which may contribute to larval outbreaks elsewhere. No significant differences in larval mortality, pupation rate, adult emergence rate, longevity, pre-oviposition period, or oviposition period were observed between controls and larvae fed on artificial diet incorporating a low concentration of Cry1Ac protoxin. The negative sublethal effects on some developmental and reproductive traits and lack of effect on others suggest they do not contribute to the observed severity of S. exigua outbreaks after feeding on Cry1Ac cotton. Interestingly, the percentage of long fliers increased significantly when larvae were reared on diet containing either of two low-dose treatments of Cry1Ac, suggesting a possible increased propensity to disperse long distances triggered by Cry1Ac. We hypothesize that negative effects on development and reproduction caused by Cry1Ac in the diet are offset by increased flight propensity triggered by the poor food conditions, thereby improving the chances of escaping adverse local conditions before oviposition. Increased long-flight propensity in turn may amplify the area damaged by outbreak populations. This phenomenon might be common in other migratory insect pests receiving sublethal doses of Bt toxins and warrants further study.

Highlights

Transgenic crops that produce toxins from Bacillus thuringiensis (Bt) for insect control have become an important component of pest management worldwide [1]
No significant differences in larval mortality, pupation rate, adult emergence rate, longevity, pre-oviposition period, or oviposition period were observed between controls and larvae fed on artificial diet incorporating a low concentration of Cry1Ac protoxin
No significant differences in larval mortality were observed between larvae fed on the lower concentrations of 25 and 50 mg g21 Cry1Ac protoxin and those fed on protoxin-free control diet (Fig. 1A, P.0.05)

Summary

Introduction

Transgenic crops that produce toxins from Bacillus thuringiensis (Bt) for insect control have become an important component of pest management worldwide [1]. Bt crops can significantly suppress the target pest population, resulting in a reduction of chemical pesticide applications and increased crop productivity. Because of their compatibility with the environment, they are being approved for planting in more and more countries [2,3]. Bt cotton expressing the Cry1Ac toxin has been planted in northern and eastern China especially to control the target pest Helicoverpa armigera [5]. This widespread planting of Bt cotton has been accompanied by concerns of its sustainability and ecological safety. Characterizing Bt toxicity to non-target pests and their effects on population dynamics have become an important avenue of research in recent years

Methods

Results

Conclusion