Influence of time of day and insecticide treatment on the abundance of Culiseta melanura (Diptera: Culicidae) in resting boxes.

Frequent use of resting boxes by Culiseta melanura (Coquillett) during the day-time may offer the opportunity for use of these artificial resting sites as delivery substrates for insecticides to manage populations of this eastern equine encephalitis virus (EEEV) vector. In field studies at EEEV-endemic foci in southwestern Michigan, abundance in black-painted resting boxes of adult male and female Cs. melanura varied within the 24-h diel cycle, by whether the interiors of the boxes were treated with a microencapsulated formulation of lambda cyhalothrin (Demand CSTM), and from before to after treatment of boxes at field sites. Abundance was highest at noon, diminished to nil at midnight, and increased by noon the following day. Abundance of Cs. melanura was lower in insecticide-treated boxes compared to untreated boxes, and declined at field sites sampled after treatment of boxes with microencapsulated lambda cyhalothrin, compared to before treatment and to control sites. This population suppression effect lasted at least 30 days and exceeded 90% reduction. Field-caught Cs. melanura males and females experienced high mortality when exposed to lambda cyhalothrin-treated bottles in bottle bioassays and in overnight exposures to treated boxes set in the laboratory. Prolonged daily visits to resting boxes, resulting in exposure to residual insecticide, may explain the sustained, diminishing effect on abundance of field populations of Cs. melanura. Results support use of insecticide-treated boxes distributed into wooded upland edges of natural larval habitats as an intervention against EEEV transmission.