Preference of Bt‐resistant and susceptible Busseola fusca moths and larvae for Bt and non‐Bt maize

Abstract

The sustainability of genetically engineered insecticidal Bacillus thuringiensis Berliner (Bt) maize, Zea mays L. (Poaceae), is threatened by the evolution of resistance by target pest species. Several Lepidoptera species have evolved resistance to Cry proteins expressed by Bt maize over the last decade, including the African maize stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae). The insect resistance management (IRM) strategy (i.e., the high‐dose/refuge strategy) deployed to delay resistance evolution is grounded on certain assumptions about the biology and ecology of a pest species, for example, the interactions between the insect pest and crop plants. Should these assumptions be violated, the evolution of resistance within pest populations will be rapid. This study evaluated the assumption that B. fusca adults and larvae select and colonize maize plants at random, and do not show any preference for either Bt or non‐Bt maize. Gravid female B. fusca moths of a resistant and susceptible population were subjected to two‐choice oviposition preference tests using stems of Bt and non‐Bt maize plants. Both the number of egg batches as well as the total number of eggs laid on each stem were recorded. The feeding preference of Bt‐resistant and susceptible neonate B. fusca larvae were evaluated in choice test bioassays with whorl leaf samples of specific maize cultivars. Although no differential oviposition preference was observed for either resistant or susceptible female moths, leaf damage ratings indicated that neonate larvae were able to detect Bt toxins and that they displayed feeding avoidance behaviour on Bt maize leaf samples.

Larval Migration Behaviour of Busseola fusca (Lepidoptera: Noctuidae) on Bt and Non-Bt Maize under Semi-Field and Field Conditions

“…Based on results obtained from the laboratory experiment, where larvae showed significant Bt avoidance behaviour (by ballooning off plants), it was expected that a greater number of plants would exhibit whorl damage symptoms in the Bt maize than non-Bt maize plots under greenhouse and field conditions. This hypothesis was also developed by Visser et al [27], following the results from choice-test experiments that indicated that both Cry1Ab-resistant and susceptible larvae avoided feeding on MON810 and MON89034 leaf samples. However, the results of the greenhouse and field experiments did not support this hypothesis.…”

“…Busseola fusca egg batches were obtained by rearing field-collected populations according to the methods described in [27]. The egg batches were placed in 50 mL plastic containers with mesh-infused lids, which was then kept in a glass desiccator (30 cm diameter) with the RH maintained at 70 ± 5% by means of a potassium hydroxide solution [38].…”

“…The methods used to confirm the status of resistance/susceptibility of the VAA16-R and HAR18-R populations are described in Visser et al [27]. The B. fusca population in the Vaalharts area is known to be resistant to Cry1Ab maize [36,39,40].…”

“…Such effects of the presence of Cry proteins in Bt crops have been demonstrated for several pest species including the following noctuids: Helicoverpa zea (Boddie), Heliothis virescens (Fabricius), and Spodoptera frugiperda (J.E. Smith) [27]. When a host plant is not preferred by larvae, foraging and migration within and between plants is likely to continue [28].…”

Plant Abandonment by Busseola fusca (Lepidoptera: Noctuidae) Larvae: Do Bt Toxins Have an Effect?

“…It is therefore possible that the presence of Bt-toxins in maize leaf tissue can be detected by foraging larvae and that this may affect their feeding and migration behavior. When a host plant is not preferred by larvae, foraging and movement within and between plants is likely to continue [41,42]. Refuge design should therefore aim to mitigate the selection pressure on migrating larvae.…”