Culex erythrothorax (Diptera: Culicidae): Activity periods, insecticide susceptibility and control in California (USA).

Allen T Esterly,John Busam,Theresa L Shelton,Ryan J Clausnitzer,Benjamin Rusmisel,Joseph W Huston,Eric J Haas-Stapleton,Dereje Alemayehu,Tina Sebay,Nayer Zahiri,Ahmed Ibrahim Hasaballah

doi:10.1371/journal.pone.0228835

Abstract

The mosquito Culex erythrothorax Dyar is a West Nile virus (WNV) vector that breeds in wetlands with emergent vegetation. Urbanization and recreational activities near wetlands place humans, birds and mosquitoes in close proximity, increasing the risk of WNV transmission. Adult Cx. erythrothorax abundance peaked in a wetland bordering the San Francisco Bay of California (USA) during the first 3 hours after sunset (5527 ± 4070 mosquitoes / trap night) while peak adult Culex tarsalis Coquillett abundance occurred during the subsequent 3 h period (83 ± 30 Cx. tarsalis). When insecticide resistance was assessed using bottle bioassay, Cx. erythrothorax was highly sensitive to permethrin, naled, and etofenprox insecticides compared to a strain of Culex pipiens that is susceptible to insecticides (LC50 = 0.35, 0.71, and 4.1 μg/bottle, respectively). The Cx. erythrothorax were 2.8-fold more resistant to resmethrin, however, the LC50 value was low (0.68 μg/bottle). Piperonyl butoxide increased the toxicity of permethrin (0.5 μg/bottle) and reduced knock down time, but a higher permethrin concentration (2.0 μg/bottle) did not have similar effects. Bulk mixed-function oxidase, alpha-esterase, or beta-esterase activities in mosquito homogenates were higher in Cx. erythrothorax relative to the Cx. pipiens susceptible strain. There was no difference in the activity of glutathione S-transferase between the two mosquito species and insensitive acetylcholine esterase was not detected. Larvicides that were applied to the site had limited impact on reducing mosquito abundance. Subsequent removal of emergent vegetation in concert with larvicide applications and reduced daily environmental temperature substantially reduced mosquito abundance. To control Cx. erythrothorax in wetlands, land managers should consider vegetation removal so that larvicide can efficiently enter the water. Vector control agencies may more successfully control adult viremic Cx. erythrothorax that enter nearby neighborhoods by applying adulticides during the 3 h that follow sunset.

Highlights

Culex erythrothorax Dyar (Diptera: Culicidae), commonly known as the tule mosquito, is endemic to the western southwestern states of the United States [1]
The nocturnal bloodmeal-seeking by female Cx. erythrothorax was similar to Cx. tarsalis, Cx. pipiens and Anopheles gambiae [7, 28, 29] and correlated with nighttime roosting of waterfowl in the marsh
A CDC bottle bioassay was used to assess permethrin susceptibility of Cx. erythrothorax that were collected from a marsh habitat that supports diverse wildlife

Summary

Introduction

Culex erythrothorax Dyar (Diptera: Culicidae), commonly known as the tule mosquito, is endemic to the western southwestern states of the United States [1]. The larvae breed in heavily vegetated regions of shallow ponds and can be highly abundant in marsh habitats that contain dense clusters of Schoenoplectus spp (common tule), Typha spp. Unlike many species of mosquitoes, adult Cx. erythrothorax do not disperse distantly from where they emerge [3, 5, 6]. The time of host-seeking for Culex tarsalis Coquillett, another mosquito species found in marsh habitats, occurs 1–4 h after sunset [7, 8]. Larvicide applications to constructed marsh habitats can markedly reduce the abundance of adult Cx. erythrothorax [9]. We describe the impact of larvicide applications and removing emergent vegetation on Cx. erythrothorax abundance

Methods

Results

Conclusion