Methoprene tolerance in Aedes nigromaculis in Fresno County, California.

Methoprene, a juvenile hormone analogue, has been used for at least 20 years as the primary insecticide to control the pasture mosquito Aedes nigromaculis in Fresno County, California. First reports of apparent methoprene control failures were noted in a pasture west of Fresno in September 1998. Insufficient control was noted in 12 different pastures the following season from April to September 1999. In September of 1999, field trials were conducted to better ascertain the level of control. Results based on pupal counts from different methoprene formulations and rates of application indicated that in some pastures low levels of control were achieved with Altosid (Liquid Larvicide) and Altosid XR-G. Control with Altosid Pellets was reported at 52-99%.

Potential for resistance to pyriproxyfen: a promising new mosquito larvicide.

An organophosphorus-resistant strain of Culex quinquefasciatus was pressured with pyriproxyfen for 17 generations. Egg viability began declining in the F7 generation and became lower as the selection process continued; by the F17 generation egg viability was too low to proceed further. Susceptibility tests on larvae of the F5, F10, F15, and F17 generations showed no indication of increased tolerance to pyriproxyfen.

Studies on the environmental persistence of S-31183 (pyriproxyfen): adsorption onto organic matter and potential for leaching through soil.

Analytical methods were developed to allow the extraction and analysis of S-31183 (pyriproxyfen), 2-[1-methyl-2-(4-phenoxyphenoxy)ethoxy]pyridine, in organic matter from animal waste-water lagoons. Analysis of water and organic debris from a treated lagoon showed that the active ingredient readily adsorbed onto organic matter. S-31183 persisted on organic matter for over a 2-month period, during which time the concentration decayed at an exponential rate. In leaching trials with four different soil types, over 50% of the active ingredient applied remained in the upper 6 cm of a 30-cm soil column; there was no indication of a rapid potential for downward migration. The use of S-31183 for treating wastewater lagoons at doses which are effective for mosquito control did not result in any apparent problems of environmental incompatibility.

ETOC and lambdacyhalothrin: new pyrethroid mosquito adulticides.

Two new pyrethroids, ETOC and lambdacyhalothrin, showed considerable promise against organophosphorus-resistant adults of Culex tarsalis in laboratory tests. In field trials using nonthermal aerosols, applications of both compounds resulted in effective swaths of up to one-half mile. At the highest concentrations evaluated, residues on alfalfa foliage were less than 0.2 ppm at 1 h. Residues declined greatly by 24 h and could not be detected at 48 or 72 h.

Efficacy of a juvenile hormone mimic, pyriproxyfen (S-31183), for mosquito control in dairy wastewater lagoons.

Pyriproxyfen (S-31183) was applied to dairy wastewater lagoons, during 1988, at 0.1 kg (AI)/ha in single and multiple applications which resulted in control of Culex spp. larvae for periods of 7 to 68 days. Length of the control period appeared to be related to water quality, with greater residual efficacy in more polluted sources. The AI apparently adsorbed onto organic debris where efficacy remained high in the lagoon even after water was pumped from the lagoon and replenished with untreated wastewater. Alternating treatments with control agents having a different mode of action is suggested to avoid selection of insecticide resistance.

Aerial adulticiding for the suppression of Culex tarsalis in Kern County, California, using low-volume propoxur: 1. Selection and evaluation of the application system.

Propoxur applied aerially at 4.7 liters/ha was an effective adulticide against organophosphate resistant Culex tarsalis. Applications by fixed-wing and helicopter underslung spray systems equipped with hydraulic nozzles provided good coverage of test areas as indicated by the mortality patterns of sentinel mosquitoes. However, the propoxur wettable powder in larvicide oil formulation was dispersed in a very broad particle range. The fixed-wing (Ayres Thrush) aircraft treated 260 ha (640 acres) in 45 min and could carry a full load of 1500 liters (400 gal) at temperatures in excess of 38 degrees C. In contrast, the helicopter (Bell UH-1) with an underslung spray system (Simplex Model 6800) required over 2 hrs to treat the same area at lower temperatures and could not carry a full load of 570 liters (150 gal) at temperatures greater than 38 degrees C.