Mortality of nontarget arthropods from an aerial application of pyrethrins.

Mortality of nontarget organisms from an ultra-low volume (ULV) aerial application of pyrethrins (Evergreen EC 60-6) was monitored by collecting arthropods from ground tarps placed at the interface of open and canopy areas. A larger number and greater diversity of arthropods were recovered from tarps in the ULV spray area. The observed mortality was approximately 10-fold greater than in the control area. Kruskal-Wallis tests revealed a significant difference in the abundance and diversity of arthropods collected at treatment and control sites at 1 and 12 h postspray. Arthropods, primarily insects, from the treatment area included representatives from 12 orders and > or = 34 families, as compared to 7 orders and 12 families in the control area. Chironomidae (midges) and Formicidae (ants) were the most commonly represented families, accounting for 61% of the arthropods collected from the treatment area; no large-bodied insects (>8 mm) were recovered. Mortality of sentinel mosquitoes in the treatment and control areas averaged 96% and <1%, respectively, at 24 h postexposure. This study supports previous work that the impact of a single ULV application of pyrethrins was limited to a variety of small-bodied arthropods.

Nontarget effects of the mosquito adulticide pyrethrin applied aerially during a West Nile virus outbreak in an urban California environment.

In August 2006, a pyrethrin insecticide synergized with piperonyl butoxide (EverGreen Crop Protection EC 60-6, McLaughlin Gormley King Company, Golden Valley, MN) was sprayed in ultralow volumes over the city of Davis, CA, by the Sacramento-Yolo Mosquito and Vector Control District to control mosquitoes transmitting West Nile virus. Concurrently, we evaluated the impact of the insecticide on nontarget arthropods by 1) comparing mortality of treatment and control groups of sentinel arthropods, and 2) measuring the diversity and abundance of dead arthropods found on treatment and control tarps placed on the ground. We found no effect of spraying on nontarget sentinel species including dragonflies (Sympetrum corruptum), spiders (Argiope aurantia), butterflies (Colias eurytheme), and honeybees (Apis mellifera). In contrast, significantly higher diversity and numbers of nontarget arthropods were found on ground tarps placed in sprayed versus unsprayed areas. All of the dead nontarget species were small-bodied arthropods as opposed to the large-bodied sentinels that were not affected. The mortality of sentinel mosquitoes placed at the same sites as the nontarget sentinels and ground tarps ranged from 0% to 100%. Dead mosquitoes were not found on the ground tarps. We conclude that aerial spraying with pyrethrins had no impact on the large-bodied arthropods placed in the spray zone, but did have a measurable impact on a wide range of small-bodied organisms.