2013 Annual Report
1a.Objectives (from AD-416):
To test new mosquito and fly repellent, inhibitor and control products, and application strategies such as assessing the efficacy of perimeter treatments of
bifenthrin and ultra-low-volume (ULV) applications of other insecticides to control Culex tarsalis adults in a desert environment.
1b.Approach (from AD-416):
Weather stations will be established in the study area to closely monitor
environmental parameters. In initial studies, suitable field sites within these
habitats will be selected for small scale experimental plots consisting of military tents protected with novel mosquito inhibitors and nursery-obtained plants treated with residual application of bifenthrin formulations. Later, large - scale plots, consisting of naturally - occurring vegetation will be identified. Mosquito populations will be monitored with C02 - baited traps and human landing counts (when IRB approvals are obtained). Bioassays will be conducted to determine the longevity of the spray applications and the breakdown products of the insecticides. Periodically during the project, leaves and other vegetation will be collected and shipped to USDA-Agriculture Research Service Mosquito and Fly Research Unit at the Center for Medical, Agricultural and Veterinary Entomology (MFRU-CMAVE) in
Gainesville, Florida for gas chromatography-mass spectrometry (GC/MS) analysis to determine the amount of residual pesticide on the vegetation. Appropriate statistical methods will be applied. To achieve small droplet size, future studies will be made with specialized ground and aerial ULV application equipment. Insecticides will be applied in a concentrated form or technical grade and at very low volumes such as 1 oz per acre. Typically, aerial applications produce insecticide spray droplets of 30 to 50 microns measured as mass median diameter (MMD), with <2.5% of the droplets exceeding 100 microns. Ground ultra-low-volume (ULV) applicators produce droplets of 8 to 30 microns, with no droplets >50 microns MMD. Droplets will be collected on rotating teflon-coated glass slides and measured. Adult mosquito mortality will be measured primarily with the use of caged mosquitoes positioned at varying distances from the insecticide release point. Other new repellent and control products such as spatial inhibitors intended for use in military tents are being developed by the DWFP program in CMAVE and will be tested in this cooperative research project. Novel larval bio-control compounds are being developed and formulated for future testing. An overarching goal is to assess the efficacy and longevity of new mosquito control products in a desert environment under hot, dry, dusty, windy, and strong sunlight and high ultraviolet (UV) conditions.
This research relates to in-house Objective 3: Conceive and test new methods of managing vector and pest populations through the use of behavior-altering chemicals, including repellents, attractants, and inhibitors.
Aerial Ultra Low Volume pesticide application is an established strategy for adult mosquito control in hot humid tropical or temperate environments. However, not enough is known regarding the efficacy of aerial applications in hot-arid desert environments similar to those encountered by U.S. military personnel where mosquito and sand fly disease vectors of human diseases such as malaria, dengue, encephalitic and hemorrhagic arboviruses, and leishmaniasis pose significant threats to force health. ARS researchers at Gainesville, FL, placed colony-reared mosquitoes in sentinel cages across a grid of poles positioned across open and vegetated habitat in the Naval Air Facility El Centro parachute range located in a hot-arid desert borderland area of southern California. Poles were set in separate grids of placement in open sandy areas or placement directly in low desert vegetation, with sentinel cages attached to poles at the center of creosote bush shrubs. Synergized permethrin was applied in three trials using an aerial spray platform aboard a USAF C-130 at ~100 feet altitude at the Environmental Protection Agency label rate, and we recorded mosquito mortality in treatment and untreated control areas. In all three trials across open sandy areas and in two of the three trials across vegetated areas, mortality was generally 80-100% at 10 minutes post-spray. In one trial over a vegetated area with no offset, mortality was zero in the majority of cages and ~50% in only two cages. However, with a slight upwind offset a later trial over a vegetated area resulted in 80-100% mortality similar to that observed over open ground regardless of offset. Impact on non-target insect species was not observed. Results indicate that aerial application can be effective and targeted in a hot-arid environment against mosquitoes, but that even low sparse vegetation may provide refuge from the effects of the pesticide spray.