Nontarget Effects of the Mosquito Adulticide Pyrethrin Applied Aerially During a West Nile Virus Outbreak in an Urban California Environment

Abstract

In August 2006, a pyrethrin insecticide synergized with piperonyl butoxide (EverGreenH 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.

Toxicity and risk of permethrin and naled to non-target insects after adult mosquito management

“…The results for permethrin are different from those of Tietze et al (1996), who found that ULV applications of malathion caused significant mortality of sentinel crickets. However, the results of our study are supported by Davis and Peterson (2008), Kwan et al (2009), Boyce et al (2007, and Hill et al (1971), showing little to no impact on medium-to large-bodied common terrestrial arthropods after single and multiple ULV applications.…”

“…The risks to medium and large-bodied insects after aerial applications are most likely lower than those estimated here because concentrations deposited on the ground are generally lower than truck-mounted ULV applications (Schleier III et al 2008), which is supported by Boyce et al (2007) and Kwan et al (2009) who observed no significant mortality of these size classes after aerial applications of synergized pyrethrins. The results for permethrin are different from those of Tietze et al (1996), who found that ULV applications of malathion caused significant mortality of sentinel crickets.…”

“…Flying insect populations, though, recovered within 48 h after the initial application. Aerial ULV applications with pyrethrins and PBO had no significant impact on caged medium-to large-bodied insects within the spray zone, but researchers observed an impact on smaller-bodied insects (Boyce et al 2007). Davis et al (2007) found that the exposures to mammals, birds, and aquatic vertebrates and invertebrates most likely would not result in risks that exceed regulatory levels of concern after truck-mounted ULV applications.…”

Effects of Aerial Applications of Naled on Nontarget Insects at Parris Island, South Carolina

“…Other studies of mosquito control impacts have had similar results to ours. For example, Boyce et al (2007) saw no effect on caged sentinel insects (dragonßies, spider, butterßies, and honey bees) but found some small-bodied insects declined after sprays. Likewise, Davis and Peterson (2008) found few impacts of pyrethroid sprays on terrestrial nontarget insects.…”

“…For example, avian breeding in salt marshes could be impacted if invertebrates decline when juveniles are feeding. Conversely, mosquito control could beneÞt birds by reducing arbovirus transmission within their populations (Boyce et al 2007). This suggests that there might be both positive and negative ecological effects if spray impacts are consistent and large enough to affect ecosystem processes.…”