Removal sampling of male mosquitoes from field populations by sound-trapping

Abstract

A 1x2.5-m black cloth was wrapped around the base of a 0.7-m high tripod to attract male mosquitoes, and 2 or 4 sound traps were hung above the cloth at 0.7 and 1.5 m. At dusk, 370 Hz sound waves at 100 dB were emitted for 5-s periods at 15-s intervals by each speaker to trap Culex tarsalis and C. tritaeniorhynchus. The trapped mosquitoes were mostly 3- and 4-day-old males. The standard deviation of their age was much smaller than that of resting males. Removal sampling of males of C. tarsalis by 3 or 6 sets of 12 sound traps from a stand of marsh fleabane ( Pluchea purpurascens) in California over a period of 2 weeks may have led to the reduction that occurred in the insemination rate of the unfed resting female population from 22% to zero, while the insemination rate remained unchanged at 55% in an untreated area. The removal of sound-sensitive males by this technique may prove more efficient for mosquito control than other male manipulation techniques. ADDITIONAL ABSTRACT: In California, sound traps were placed above an artificial swarm marker consisting of a 0.7-m high black cone. The sound traps were switched on 15-20 min after sunset and emitted 370 Hz at 100 dB SP for bursts of 5-s duration with 15-s intervals. The traps captured males, mainly 3-4 days old, of Culex tarsalis and Cx. tritaeniorhynchus. After 2 weeks' sampling the traps had captured 3349 Cx. tarsalis males. During the same period the proportion of inseminated Cx. tarsalis females collected in sweep nets in the locality declined from 36% to 14%. This decline was even more pronounced among unfed females, for which the proportion inseminated dropped from 22% to 0%. Meanwhile the proportion of inseminated females in a control area remained unchanged at 55%. The authors suggest that the sound traps may have selectively removed the more fecund males from the study area, thereby suppressing the insemination rate. Ludvik Gomulski