Evaluation of Pyrethrin Aerial Ultra-Low Volume Applications for Adult Culex Tarsalis Control in the Desert Environments of the Coachella Valley, Riverside County, California

Abstract

Eliminating infected female mosquitoes by aerial applications of ultra-low volume adulticides is the intervention strategy currently recommended to interrupt the epidemic transmission of encephalitis viruses, including West Nile. The current research optimized pyrethrin formulations and evaluated their efficacy in the desert environment of the Coachella Valley, Riverside County, California. After seven trials during 2004, a 1:2 by volume mixture of Pyrenone 25-5 in BVA oil optimized particle size, droplet descent to ground level, and kill of sentinel mosquitoes. Three subsequent experiments used 3 aerial applications of the 1:2 Pyrenone 25-5:BVA oil mixture on alternate nights to suppress Culex tarsalis Coquillett host-seeking abundance over a 1-square-mile target area. Mortality patterns among caged sentinel mosquitoes varied among sites and replicate sprays, indicating variable particle dispersion at ground level within the target area. In addition, mortality was observed for sentinels up to 1 mile downwind from the target area, indicating considerable particle drift. Geometric mean abundance of host-seeking Cx. tarsalis females collected at dry ice-baited traps within each of 3 sprayed and 2 unsprayed negative control strata varied similarly over time, indicating that our sprays minimally impacted the target population or that drift combined with other factors led to widespread area control. Experiments during March and June when recruitment rates were minimal showed general area-wide suppression of abundance following spray, whereas an experiment during September when recruitment rates were high from newly flooded marshes failed to prevent an area-wide increase in abundance. Clearly additional research is needed to standardize the efficacy of aerial applications of pyrethrins in hot dry desert environments.

Intensive Early Season Adulticide Applications Decrease Arbovirus Transmission Throughout the Coachella Valley, Riverside County, California

“…Ground applications were done by a truck-mounted Pro-Mist ® ultra-low volume (ULV) fogger (Clarke Mosquito Control Products, Inc., Roselle, IL) using undiluted LOTHROP ET AL. 478 was diluted at a ratio of 1:2 with BVA Spray 13 ® oil (BVA Inc., Wixom, MI) to minimize evaporation and aid in droplet descent (Lothrop et al 2007b). Ability of the CVMVCD to effectively disperse spray droplets into the target treatment area by ground and aerial ULV applications was assessed by bioassay during 2005 using replicated sentinel cages (Townzen and Natvig 1973) NW 9 65a 55a 18a 46a Mid 6 26a 47a 0a 24b SE 12 59a 41a 34a 49a Mean 27 59a 47a 21b 43a Means followed by the same letter were not significantly different (p Ͼ 0.05) using a Fisher's LSD test, n ϭ number of cages in each cluster.…”

Impact of Phlebotomine Sand Flies on United State Military Operations at Tallil Air Base, Iraq: 6. Evaluation of Insecticides for the Control of Sand Flies

“…This phenomenon has been observed when ULV applications of pyrethrins in desert environments in California failed to reduce populations of Culex tarsalis Coquillett (Lothrop et al 2007). Although sand ßies are generally believed to be weak ßyers traveling only short distances (Alexander 2000), several studies have reported marked sand ßies traveling distances up to 1,000 m (Mutinga et al 1992), 2,200 m (Killick-Kendrick et al 1984, or 4,000 m (Strelkova and Kraglov 1985).…”

Spatio-temporal impacts of aerial adulticide applications on populations of West Nile virus vector mosquitoes

“…Similarly, previous estimates have varied, in part because Mulla's formula cannot fully capture spatio-temporal nuances of mosquito population dynamics. For example, Lothrop et al [20] observed 73% increases in Cx. tarsalis abundances postspraying despite observing mortality in caged sentinel mosquitoes and large reductions during previous spray events.…”

“…We were also unable to account explicitly for drift outside the target zones during sprays, as has been previously described [20]. Our use of a continuous variable to measure spray coverage within the 5kmradius collection areas surrounding each trap partially accounts for this effect.…”