Reduced caterpillar damage can benefit plant bugs in Bt cotton

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.

Reduced Mythimna separata infestation on Bt corn could benefit aphids

“…However, some other factors might be involved since increased populations of non‐target insects were also reported, for example from cotton when no chemical insecticides were applied on both Bt and non‐ Bt crops (Wilson et al ., 1992). This triggered additional studies to elucidate the potential ecological mechanisms underlying the effect of Bt crops on non‐target herbivore species including the importance of plant‐mediated indirect interactions among herbivores (Hagenbucher et al ., 2013; Wang et al ., 2018; Eisenring et al ., 2019).…”

“…Such plant‐mediated indirect interactions can have a strong effect on the interspecific interactions among herbivores (Kaplan & Denno, 2007; Poelman & Dicke, 2014). For example, feeding damage by larvae of Spodoptera exigua , Helicoverpa zea or Heliothis virescens (all Lepidoptera: Noctuidae) on cotton negatively affected plant‐sucking herbivores, such as Lygus hesperus (Hemiptera: Miridae) (Zeilinger et al ., 2011; Eisenring et al ., 2019) and Aphis gossypii (Hemiptera: Aphididae) (Hagenbucher et al ., 2013). In both cases, the effect was apparently caused by the increased terpenoid content in caterpillar‐damaged plants.…”

“…Considering the plant‐mediated interspecific interactions of different herbivorous species described above, it could be expected that reduced damage on insect‐resistant Bacillus thuringienis ( Bt ) crops may affect the population of non‐target herbivores. Previous studies with cotton where sucking pests benefited from reduced caterpillar damage on Bt ‐transgenic plants have confirmed this hypothesis (Hagenbucher et al ., 2013; Eisenring et al ., 2019). In contrast, reduced damage by the target pest Chilo suppressalis (Lepidoptera: Crambidae) to Bt rice caused a decrease in populations of rice planthoppers, Nilapavata lugens (Hemiptera: Delphacidae) (Wang et al ., 2018).…”

Arthropod food webs associated with cotton: Does Bt cotton mediate community stress?

“…Nonetheless, assessments exploring direct and indirect species interactions indicating potential community‐level stress are lacking, except for recent related efforts on maize (Zuim et al., 2021). This is important not only because Bt cotton may shift the dominance of prevailing pest species, as suspected with the US cotton plant bugs (Eisenring et al., 2019), but also because the suppression of cotton pest caterpillars may lead to bottom‐up effects on associated natural enemies in the area (Guedes et al., 2016, 2017).…”

“…The use of such a tool is timely, as the current stacking of Bt proteins in cotton may provide even more drastic effect on the target caterpillars, while mitigating the evolution of their resistance to individual proteins (Liu et al., 2019; Siegfried & Jurat‐Fuentes, 2016; Xiao & Wu, 2019). As a consequence, other secondary species may erupt (Eisenring et al., 2019). However, the Neotropical region presents a different peculiarity—the Bt cotton‐targeted pest species are secondary in importance, and the technology is not effective against the main pest species, noticeably the boll weevil ( Anthonomus grandis grandis ), whitefly ( Bemisia tabaci MEAM1 and MED) and the cotton aphid ( Aphis gossipy ).…”