Potential Influences of Agricultural Pesticide Use on Biological Control of Non-Agricultural Weeds with Insects.

Weeds such as floating aquatic water hyacinth, the riparian giant grass known as arundo, and the arid rangeland invader yellow starthistle frequently consume or otherwise threaten water and soil resources.  These and many other invasive plants typically occupy vast areas in natural ecosystems, but often must also be controlled in terrestrial or aquatic habitats adjacent to agricultural production systems. Biological control with non-native, intentionally introduced arthropods (insects and mites) or native (or, rarely, introduced) phytopathogens is often the only environmentally and economically feasible approach for large-scale management of these invasive weeds. Little is known about the effects of agricultural pesticide use on the success of biological control of non-agricultural weeds, besides the obvious incompatibilities (direct off-target application of insecticides or herbicides kills the biocontrol agents and/or their weedy host plant). More subtle effects, such as those arising from low-dose pesticide drift on weeds and their biocontrol agents, sublethal phytotoxicity of insecticides and adjuvants to weeds, and insecticide-related reduction of native predators in crops, are largely unstudied. Suggested avenues of research to improve understanding of these interactions include: determination of insecticide, herbicide and adjuvant dose-response curves for well-established and widespread arthropod biological control agents of weeds; determination of drift-based pesticide exposure levels on weeds targeted for biocontrol that are growing near crop systems; quantification of sublethal phytotoxic effects on key plant nutrient and defense systems relevant to insect herbivores; and studies of predation on weed biocontrol agents occurring adjacent to conventional in comparison to organic/sustainable crop production systems.