The IGR Dimilin and its formulations against mosquitoes.

Wettable powder (25), flowable concentrate (2) and granular (0.5) formulations of the insect growth regulator Dimilin® [1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl) urea] were evaluated under field conditions against various species of mosquitoes. In irrigated alfalfa hay fields, all 3 formulations applied at 0.0025 and 0.005 lb AI/acre, produced almost complete control of a synchronous floodwater mosquito Psorophora confinnis (Lynch-Arribalzaga). The granules were slightly less effective than the wp formulation and there was no marked difference between the wp and Fc formulations. The effective dosage of this IGR, therefore, is in the range of 0.0025–0.005 lb AI/acre against this species. The 3 formulations at 0.025 lb/acre were studied in freshwater ponds against Culex tarsalis Coquillett and Anopheles franciscanus McCracken, 2 asynchronous species of mosquitoes. Marked reduction in larval density was noted during the post-treatment period of 5–21 days. A. franciscanus experienced earlier and prolonged decline than C. tarsalis . Pupal populations almost disappeared from all treated ponds during the 5–16 days post-treatment period. Low numbers of pupae prevailed in treated ponds as compared to checks during the 27-day period after treatment. At this rate of application, all 3 formulations produced almost complete inhibition of emergence for more than 27 days.