Site-Specific Integrated Pest Management Impact on Development of Esfenvalerate Resistance in Colorado Potato Beetle (Coleoptera: Chrysomelidae) and on Densities of Natural Enemies

Abstract

Maintenance of unsprayed refuges within fields has often been suggested as a mechanism for managing pesticide resistance and conserving natural enemies. Site-specific integrated pest management (IPM) can create unsprayed refuges that are temporally dynamic by limiting pesticide applications to areas within a field based on maps of pest densities within that field. We tested the impact of site-specific IPM on the development of insecticide resistance and densities of natural enemies in commercial potato fields. Three 1.2-ha fields were managed with site-specific IPM. These site-specific IPM fields were divided into 0.04-ha management blocks, each of which was treated with esfenvalerate plus piperonyl butoxide (PBO) only if that block was above the economic threshold for Colorado potato beetle, Leptinotarsa decemlineata (Say). The site-specific IPM treatment was compared with a standard IPM treatment in 3 additional 1.2-ha fields, in which esfenvalerate plus PBO was applied to the entire field when the mean exceeded a threshold. Malathion was applied to both treatments on a whole-field basis when mean potato leafhopper densities exceeded thresholds. The treatments resulted in variation in the amount and spatial pattern of selection pressure. The occurrence and degree of resistance was related to the degree of selection pressure applied to the population at both the whole-field and within-field scale. All standard IPM fields showed a significant increase in Colorado potato beetle resistance from preseason to postseason. In contrast, there was little to no change in resistance from preseason to postseason in an unsprayed control and in 2 of the 3 site-specific IPM fields. At the end of the season, significant within- field variation in resistance also occurred in fields treated with site-specific IPM. Densities of hymenopterous parasitoids and 3 taxa of generalist predators tended to be greater in site-specific IPM than in standard IPM fields. This demonstrates that site-specific TPM has the potential to slow the development of insecticide resistance and conserve natural enemies.