The insect growth regulator Altosid SR-10 was evaluated against larvae of the floodwater mosquito Aedes (Ochlerotatus) detritus Haliday, 1833 in a salt marsh in the Province of Grosseto, Italy. In laboratory tests, the LC50 LC90 values for Altosid SR-10 were 0.0009 and 0.0085 ppm respectively. Altosid SR-10 when applied at 30 g AI/hectare (0.026 lb AI/acre) to natural salt marsh pools yielded complete inhibition of adult emergence up to 4 days, while at 60 g AI/hectare (0.052 lb AI/acre) inhibition of emergence was complete for the duration of the test (8 days). At both rates used, diving beetles showed a tolerance and copepod population showed non-marked short-term reduction. The SR-10 formulation applied at the rate of 40 g AI/hectare (0.035 lb AI/acre) in a 4,550 m2 salt marsh provided complete control of A. detritus for 4 days after treatment; adult emergence inhibition did not drop below 50% until the 16th day. The residual properties of this microencapsulated formulation, offering a period of emergence inhibition of about two week, as found in these studies, are excellent for control of floodwater mosquitoes.