Spatial Processes in the Evolution of Resistance in Helicoverpa zea (Lepidoptera: Noctuidae) to Bt Transgenic Corn and Cotton in a Mixed Agroecosystem: a Biology-rich Stochastic Simulation Model

Abstract

A simulation model is developed to examine the role of spatial processes in the evolution of resistance in Helicoverpa zea populations to Bt corn and Bt cotton. The model is developed from the stochastic spatially explicit Heliothis virescens model described by Peck et al. (1999), to accommodate a spatial mix of two host crops (corn and cotton), and to reflect the agronomic practices, as well as the spatial and temporal population dynamics of H. zea, in eastern North Carolina. The model suggests that selection for resistance is more intense in Bt cotton fields than in Bt corn fields. It further suggests that local gene frequencies are highly dependent on local deployment levels of Bt crops despite the high mobility of the adult insects. Region-wide average gene frequencies depend on the region-wide level of Bt deployment, so incomplete technology adoption slows the rate of resistance evolution. However, on a local scale, H. zea populations in clusters of fields in which Bt use is high undergo far more rapid evolution than populations in neighboring clusters of fields in which Bt use is low. The model suggests that farm-level refuge requirements are important for managing the risk of resistance. The model can be used as an aid in designing plans for monitoring for resistance by suggesting the appropriate distribution of monitoring locations, which should focus on areas of highest Bt crop deployment. The findings need to be placed in the context of the input parameters, many of which are uncertain or highly variable in nature, and therefore, a thorough sensitivity analysis is warranted.

Boundaries of sustainability in simple and elaborate models of agricultural pest control with a pesticide and a non-toxic refuge

“…It effectively assumes one synchronized generation per year, and that year comprises just five discrete processes: random mating and reproduction, density-dependent attrition, density-independent selection, exchange between crop and refuge, and mutation. The big model is described in Appendix 2 and is identical to the deterministic version of the model of Bantle et al [6], which is very close to the model of Sisterson et al [32], and is in the same class as the models of Peck et al [26], Caprio [7] and Storer et al [33]. Following Sisterson, its many parameters are tuned to represent pink bollworm (Pectinophora gossypiella) on Bt cotton in Maricopa, Arizona.…”

Dynamically optimal strategies for managing the joint resistance of pests to Bt toxin and conventional pesticides in a developing country

“…Earlier work demonstrated that Bt cotton could control about 80-95 per cent pests on average in the Yellow River Valley (Wu, 2002;Li et al, 2004). Based on these studies (from China) and empirical studies in the United States (Caprio, 1998;Burd et al, 2001;Storer et al, 2003;Livingston et al, 2004), we assume that the mortality rate of pests with double susceptible genes to Bt toxin is 0.90 in Bt cotton fields. As assumed in Livingston et al (2004Livingston et al ( , 2002, we also assume that the mortality rate of pests with double resistant genes to Bt toxin, the so-called 'fitness cost', is 0.05.…”

Characterization of Chimeric Bacillus thuringiensis Vip3 Toxins

“…However, the prolonged application of B. thuringiensis formulations and the widespread planting of transgenic crops with B. thuringiensis endotoxins have raised concerns over the development of insect resistance (1,12,13,17,23,24,25,26). Thus, alternative insecticidal proteins that do not share a mode of action identical with that of B. thuringiensis endotoxins are highly desirable for the development of the next generation of transgenic insect-resistant crops.…”