Location: Crop Protection and Management Research2012 Annual Report
1. Pest tradeoffs in technology. Reduced damage by caterpillars in Bt cotton benefits aphids. The rapid adoption of genetically engineered plants that express insecticidal Cry proteins derived from Bacillus thuringiensis (Bt) has raised concerns about their potential impact on non-target organisms. Particular concern lies with the possibility that herbivores insensitive to the Bt toxin might develop pest status in Bt crops, and a number of studies have now reported increased levels of non-target pests in Bt crops which threatens to compromise the sustainable use of the transgenic varieties. We show that, because of effective suppression of Bt sensitive lepidopteran herbivores, Bt cotton contains reduced levels of induced terpenoid aldehydes and changes in the overall level of these defensive secondary metabolites are associated with improved performance of a Bt-insensitive herbivore, the aphid Aphis gossypii, under glasshouse and field conditions. This study helps explain non-target pest outbreaks in Bt crops and will improve management of resistance development in the target pest populations.
2. Release from competition with Bt-susceptible pest species may contribute to increased stink bug populations in Bt cotton. Competitive interactions through differences in growth rates between the two stink bug species, Nezara viridula and Euchistus servus, and the Bt-susceptible pests Heliocoverpa zea and Heliothis virescens caterpillars had equivalent effects on resource availability, but distinctly different effects on stink bug growth rates. Fourth instar H. zea reduced growth rates of both stink bug species by 60% when caged on a single cotton boll and reduced growth rates of only E. servus by 36% when caged on a cotton branch. In contrast, H. virescens had no effect on stink bug growth rates. Resource competition was apparent in the interactions between H. zea and E. servus, but interference competition (i.e. direct aggressive interactions between individuals that interfere with foraging, survival, reproduction or by physical prevention of establishment in a portion of the habitat) may also have contributed to the interactions. Competitive release as a contributing mechanism of stink bug population increases in Bt cotton is possible, and is more likely for E. servus than for N. viridula.
3. Deterrence and facilitation of stink bugs through induced responses in cotton. Herbivory often induces systemic plant responses that affect subsequent herbivores feeding preference. Understanding the mechanisms of feeding preferences provides insight into the potential ecological significance of preference. Preference responses of two fruit-feeding stink bug species, Nezara viridula and Euschistus servus to herbivory by two caterpillar species, Helicoverpa zea and Heliothis virescens was investigated on cotton plants. Prior H. zea feeding inhibited, whereas H. virescens feeding facilitated, E. servus feeding on damaged plants. Caterpillar feeding did not affect N. viridula feeding behavior. Caterpillar herbivory caused an overall reduction in phenolic concentration with a particularly strong reduction in chlorogenic acid in bolls from plants damaged by H. virescens. Euschistus servus preference was strongly influenced by host selection and host edibility but phenolics did not likely influence plant choice.
4. Effects on stink bugs of field edges adjacent to woodland. Stink bug responses to crop edges in fields of corn, peanut, cotton and soybean adjacent to woodland were found most often to be random with respect to the woodland edge of all crops examined. The exception occurred mainly in corn fields, where more stink bugs were found at the crop edge when flowering alternative hosts were present in the woodland edges. In 113 fields of four major crops grown in this area, the woodland edge was not a major source from which stink bugs colonized these crops. These results suggest that edge-specific control measures should not be concentrated at those field edges adjacent to woodlands, thereby reducing insecticide applications and management and environmental costs.
5. Threshold detection of boar taint chemicals using parasitic wasps. The need for threshold chemical detection, rather than simple detection of absence/presence of a chemical applies to many food quality issues, including the detection of spoilage or pest damage in crops or stored foods. Surgical castration has been long used to prevent consumers from experiencing taint in meat from male pigs, which is a large problem in the pig husbandry industry. Due to obvious animal welfare issues, Europe now wants an alternative for castration, suggesting an urgent need for novel methods of boar taint detection. The wasp, Microplitis croceipes showed both compound and concentration specific responses to the boar taint compounds, skatole, androstenone and indole. Also tested was the wasps’ ability to discriminate between known concentrations of indole, skatole and androstenone in real boar fat samples at room temperature. The wasps were also successful in reporting low, medium and high concentrations of indole, skatole and androstenone in boar fat at room temperature. Application of the wasp biosensor for the commercial detection of boar taint at threshold and higher concentrations appears to have high potential.
6. Food provision for natural enemies. Many natural enemies of agricultural insect pests require food, such as nectar or pollen, to live and reproduce. However, in many agricultural systems, food resources for natural enemies are lacking. Stink bug parasites and insect pollinators were observed feeding on nectar of milkweed near cotton. Parasitism of the southern green stink bug and the green stink bug was 3-5 times higher in cotton when this nectar resource was present than in cotton without this resource. In conclusion, providing food for natural enemies of stink bugs can increrase their ability to kill stink bugs in cotton.
Scully, B.T., Nagata, R.T., Cherry, R.H., Nuessly, G.S., Trenholm, L.E., Kenworthy, K.E., Schwartz, B.M., Unruh, J.B. 2012. Registration of "Ultimate" Zoysiagrass. Journal of Plant Registrations. 6(1):71-74.