Competitive release and outbreaks of non‐target pests associated with transgenic Bt cotton

Abstract

The adoption of transgenic Bt cotton has, in some cases, led to environmental and economic benefits through reduced insecticide use. However, the distribution of these benefits and associated risks among cotton growers and cotton-growing regions has been uneven due in part to outbreaks of non-target or secondary pests, thereby requiring the continued use of synthetic insecticides. In the southeastern USA, Bt cotton adoption has resulted in increased abundance of and damage from stink bug pests, Euschistus servus and Nezara viridula (Heteroptera: Pentatomidae). While the impact of increased stink bug abundance has been well-documented, the causes have remained unclear. We hypothesize that release from competition with Bt-susceptible target pests may drive stink bug outbreaks in Bt cotton. We first examined the evidence for competitive release of stink bugs through meta-analysis of previous studies. We then experimentally tested if herbivory by Bt-susceptible Helicoverpa zea increases stink bug leaving rates and deters oviposition on non-Bt cotton. Consistent with previous studies, we found differences in leaving rates only for E servus, but we found that both species strongly avoided ovipositing on H. zea-damaged plants. Considering all available evidence, competitive release of stink bug populations in Bt cotton likely contributes to outbreaks, though the relative importance of competitive release remains an open question. Ecological risk assessments of Bt crops and other transgenic insecticidal crops would benefit from greater understanding of the ecological mechanisms underlying non-target pest outbreaks and greater attention to indirect ecological effects more broadly.

Prevalence, damage, management and insecticide resistance of stink bug populations (Hemiptera: Pentatomidae) in commodity crops

“…The reasons for the decline in N. viridula and increase in E. heros and Dichelops populations have not been unveiled yet, although this phenomenon can be attributed to several factors. Among them, adaptability of these insect pests to soybean as a result of the availability of large areas with this host plant (Panizzi & Corrêa‐Ferreira, ; Husch et al ., ), global climate changes that favour species adapted to warmer conditions (Robinet & Roques, ; Saluso et al ., ), multiple cropping systems that affect host weeds (Smaniotto & Panizzi, ), inter‐specific competition among pentatomids, competitive release of nontarget pest outbreaks (stink bug populations) associated with Bt‐crops (Zeilinger et al ., ) and indeterminate soybean genotypes with longer pod filling stages. In addition, not adopting tillage practices may have mainly favoured Dichelops species that require sheltered conditions under crop stubble (Panizzi, ; Panizzi & Lucini, ).…”

Genetically modified soybean expressing insecticidal protein (Cry1Ac): Management risk and perspectives

“…The emergence of secondary pests is a possibility that can not be discounted, especially for plants such as soybeans that are targets of different insect species (Zeilinger et al 2016;Marques et al 2017). The relevant question here is as follows: how are we going to address this possibility?…”

Complex Outcomes from Insect and Weed Control with Transgenic Plants: Ecological Surprises?

“…Crops usually have numerous target pests, or potential target pests, some of which may be minor due to various reasons; this does not mean that they do not have the potential to cause large damagetheir damage potential is only suppressed by the dominating pest species. Change the density of this major pest, and these other potential pests may quickly respond due to competitive release (Zeilinger et al, 2016).…”