Location: Southern Insect Management Research2012 Annual Report
1a. Objectives (from AD-416):
The objective of this cooperative research project is to conduct risk assessment research for Lepidopterous pests of Bt-crops. This research should enhance Bt-resistance management strategies which are designed to delay the onset of resistance development in target insects.
1b. Approach (from AD-416):
This agreement will determine the effect of Bt crop production on the population genetics of bollworm, tobacco budworm, and fall armyworm. Specific issues will be: 1) a better overall understanding of gene flow and population structure for the pests, 2) Bt-resistance allelic frequency estimates over time, 3) the impact of changing refuge strategies and dynamic agroecosystems on managing resistance to Bt, and, 4) the impact of Bt-suppressed population densities on insecticide resistance, e.g. the recent pyrethroid resistance in bollworm. The cooperator will be actively involved in all phases of this research including the collection of test insects from across the U. S. Cotton Belt. Pyrethroid resistance assays will be conducted in cooperators laboratory. Insect tissue will then be sent to the USDA-ARS for use in genetic marker analysis and carbon isotope analysis. Other technologies (e.g. secondary plant chemical detection in insect tissue and oxygen and nitrogen isotope analysis) will be used as they become available to further understand the population ecology of the pests in relation to Bt resistance management.
3. Progress Report:
An experiment was conducted to measure bollworm survival on silks from non-Bt field corn and VT3P field corn. Bollworm survival on silks from non-Bt field corn averaged 89.0%. In contrast, bollworm survival averaged 39.2% on silks from VT3P field corn. This experiment demonstrated that while dual-gene Bt field corn silks reduced bollworm survival, a significant number of small larvae were capable of surviving exposure to the Bt toxins present in VT3P field corn. These results suggest that selection with Bt toxins in field corn could potentially impact bollworm survival in subsequent generations infesting Bt cotton. The influence of dual-gene Bt corn hybrids on bollworm susceptibility to dual-gene Bt cottons was measured in field and laboratory experiments in 2011. Late instar larvae were collected from Genuity VT3P corn and from non-Bt corn throughout Mississippi. Inbred and reciprocal crosses were made with each population, and the offspring were subjected to dose-mortality bioassays using lyophilized Bollgard II cotton tissue. Offspring from the inbred cross with bollworms collected from VT3P corn had a higher LC50 than offspring from the inbred cross with bollworms collected from non-Bt field corn. Additionally, the reciprocal cross that used females from VT3P hybrids produced offspring with an elevated LC50. These results, if confirmed, could impact the utility of non-Bt corn refuges in the southern U.S. Experimental dual-gene cottons were evaluated in 2011 for efficacy against heliothines. Results confirmed that these experimental lines were as good, or better, than current dual-gene cotton varieties that are currently available commercially.