Reduced caterpillar damage can benefit plant bugs in Bt cotton

Michael Eisenring,Angelique Abbott,Jörg Romeis,Michael Meissle,Sven Bacher,Steven E Naranjo

doi:10.1038/s41598-019-38917-9

Michael Eisenring, Angelique Abbott + Show 4 more

Open Access

https://doi.org/10.1038/s41598-019-38917-9

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Abstract

Bt cotton was genetically modified to produce insecticidal proteins targeting Lepidopteran pests and is therefore only minimally affected by caterpillar damage. This could lead to reduced levels of inherent, systemically inducible defensive compounds in Bt cotton which might benefit other important cotton herbivores such as plant bugs. We studied the effects of plant defense induction on the performance of the plant bug Lygus hesperus by caging nymphs on different food sources (bolls/squares) of Bt and non-Bt cotton which were either undamaged, damaged by Bt tolerant caterpillars, or treated with jasmonic acid (JA). Terpenoid induction patterns of JA-treated and L. hesperus-damaged plants were characterized for different plant structures and artificial diet assays using purified terpenoids (gossypol/heliocide H1/4) were conducted. Nymphs were negatively affected if kept on plants damaged by caterpillars or sprayed with JA. Performance of nymphs was increased if they fed on squares and by the Bt-trait which had a positive effect on boll quality as food. In general, JA-sprayed plants (but not L. hesperus infested plants) showed increased levels of terpenoids in the plant structures analyzed, which was especially pronounced in Bt cotton. Nymphs were not negatively affected by terpenoids in artificial diet assays indicating that other inducible cotton responses are responsible for the found negative effects on L. hesperus. Overall, genetically engineered plant defenses can benefit plant bugs by releasing them from plant-mediated indirect competition with lepidopterans which might contribute to increasing numbers of hemipterans in Bt cotton.

Highlights

The cultivation of insect-resistant genetically engineered crops producing Cry proteins from Bacillus thuringienis (Bt crops) helps to control a range of key lepidopteran and coleopteran pest species while reducing the amount of chemical insecticide applications[1,2]
Using L. hesperus as a model species we hypothesized that plant bugs benefit from reduced caterpillar damage in Bt cotton as they might profit from reduced levels of caterpillar-induced cotton defenses
This hypothesis was tested in the greenhouse, were we studied L. hesperus performance on Bt and non-Bt cotton subjected to different induction treatments

Summary

Introduction

The cultivation of insect-resistant genetically engineered crops producing Cry proteins from Bacillus thuringienis (Bt crops) helps to control a range of key lepidopteran and coleopteran pest species while reducing the amount of chemical insecticide applications[1,2]. Increases of sucking bugs in Bt cotton can mainly be attributed to a reduction in broad-spectrum insecticide applications as many insecticides against pest Lepidoptera incidentally control other herbivore species[7,14]. Best studied is a set of biosynthetically related non-volatile terpenoids (e.g. gossypol, heliocides, hemigossypolone) that are stored in subepidermal pigment glands[20,21] These terpenoids are systemically induced in response to plant damage by tissue feeders[22,23,24]. Using L. hesperus as a model species we hypothesized that plant bugs benefit from reduced caterpillar damage in Bt cotton as they might profit from reduced levels of caterpillar-induced cotton defenses This hypothesis was tested in the greenhouse, were we studied L. hesperus performance on Bt and non-Bt cotton subjected to different induction treatments. In further greenhouse and laboratory experiments we elucidated induction patterns of defensive cotton terpenoids in different plant structures that L. hesperus feeds on and studied their potential as explanatory factors affecting L. hesperus performance

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