Deposition of pyrethrins and piperonyl butoxide following aerial ultra-low volume applications in the Coachella Valley, California.

Data on adulticide deposition were collected during studies optimizing aerial ultra-low volume applications and droplet size in the desert environment of the Coachella Valley, Riverside County, California. Pyrenone 25-5 and BVA Spray 13 oil were applied by a single-engine, fixed wing aircraft equipped with 2 Micronair AU5000 atomizers. Data recorded by a portable weather station documented that weather conditions were suitable for application. Adulticide residue was collected using 24-cm-diameter filter papers positioned along 2-3 transects, with 3 positive controls held outside of the treated zone. The trace amounts of 2 major insecticidal components (pyrethrin I and II) and the synergist piperonyl butoxide (PBO) were detected from samples near the center of the spray zone by high-performance liquid chromatography (HPLC); pyrethrin deposition was highest at the center, 156 microg/m2, and it was not detectable 60 m beyond the center of the transect, whereas PBO deposition was 5,000 microg/m2 at the center but was not detectable beyond 150 m. Droplet diameters on spinning Teflon slides were larger than expected for the rated output of the atomizers. For these single swath trials, the lack of swath overlap due to drift resulted in low mortality in sentinel mosquitoes. Detection of residues was limited to the centroid of droplet densities on spinning glass slides and with mortality among sentinel mosquitoes, indicating HPLC may be useful in detecting postspray residues.

Field evaluation of controlled release pellet formulation of methoprene against chironomid midges in man-made lakes.

The duration of the efficacy of 4% methoprene pellets against emergence of chironomid midges, Chironomus stigmaterus Say, Goeldichironomus amazonicus (Fittkau) and Tanypus imperialis Sublette, in man-made lakes supplied with tertiary effluent water in Palm Desert, California, was dose dependent. For C. stigmaterus and T. imperialis, the rate of 4.5 kg/ha of the controlled release pellet formulation of 4% methoprene yielded > 90% control for 3 wk and 75% control in the 4th week, the rate of 3.4 kg/ha provided > 90% control for 2 wk, and the rate of 2.25 kg/ha provided control for 1 wk. Goeldichironomus amazonicus was under 90% control for 2 wk at the rate of 4.5 kg/ha and 1 wk at the rates of 3.4 kg/ha and 2.25 kg/ha.

Diel patterns of oviposition and influence of agitated water surface in Chironomus anonymus (Diptera:Chironomidae).

A series of experiments was carried out in a 0.5-ha lake at Portola Country Club, Palm Desert, CA, to study the oviposition habits of Chironomus anonymus. Egg masses were collected by floatable polypropylene ropes attached to the 1.5-m-long stakes placed in the lake. In the diel experiment, ropes were changed every 2 h to determine the preferred oviposit on periods of C. anonymus. The peak of oviposition was between 1900 and 2100 h. For the interruption of oviposition experiment, ropes were placed in the still and agitated portions of the lake for 24 h. A significantly higher number of egg masses, according to applied t-test, was collected from the ropes placed in the still portion of the lake.

Occurrence of Culex (Melanoconion) erraticus (Diptera: Culicidae) in California.

Culex erraticus is added to the 52 currently recognized mosquito species from California. Four females and one male were collected in a CO2 trap on August 29, 1994, at the Imperial Wildlife Refuge, Wister Unit, Imperial County, CA. Additional specimens were collected on October 24, and larval habitats were located on October 31, 1994. Possible routes of introduction are discussed.

Mode of existence and seasonality of midge larvae (Diptera: Chironomidae) in man-made lakes in the Coachella Valley, southern California.

Over the past 2 decades, numerous man-made ponds and lakes constructed in country clubs and on golf courses in the Coachella Valley have become ideal habitats for various chironomid species. Large numbers of adult midges emerging from these water bodies pose nuisance and economic problems. During 1992 and 1993 we initiated comprehensive studies on the nature and scope of the nuisance midge problem in the valley. We sampled on a biweekly basis 2 lakes supplied with well water, 2 supplied with tertiary effluent water, and one supplied with a mixture of these 2 sources, to determine the midge larval fauna and the mode of existence, seasonal abundance, and population trends of these midges. Climbers, clingers, portable sand tube builders, and tube builders on plants predominated in well-water habitats with submerged vegetation and detritus bottoms. Tube builders and burrowers predominated in the tertiary water, which characteristically had a detritus bottom, devoid of vegetation. Habitats holding a mixture of the 2 water types with sandy bottoms supported midge larvae known to be sprawlers.