Chemical control of nuisance midges in the Santa Ana River basin, southern California.

Granular formulations of temephos and Dimilin® [1-(4-chlorophenyl)-3 (2,6-difluorobenzoyl)-urea] were applied to flowing water by using a simple method of containment in burlap sacs for control of chironomid midges in water spreading basins and flood control channel in the Santa Ana River Basin, southern California. Larvae of the genera Chironomus, Tanytarsus , and Procladius were predominant in the various water spreading structures studied. Temephos, at the rate of 0.28-kg AI/surface ha in the spreading basins, produced excellent control (4–5 weeks) of larvae of Chironomus spp. and Tanytarsus spp. but did not affect Procladius spp. Dimilin evaluated at the rate of 0.11-kg AI/surface ha in the spreading basins and in the flood control channel was highly effective on all 3 genera. This IGR in the shallow (water depth <1-m) flood control channel yielded excellent control of midges for 4–5 weeks but produced mediocre control (3–4 weeks) in the deeper (water depth 1–2 m) basins. Dimilin treatments caused significant larval mortality in the basins and in the channel.