2012 Annual Report
1a.Objectives (from AD-416):
Objective 1: Innovate new and established chemical approaches for management of
imported fire ants in order to create new and more effective ways to control them.
Sub-objective 1A: Search for new fire ant toxins from defensive chemicals in other ants.
Objective 2: Develop improved formulations and new products for more effectively
controlling floodwater mosquitoes using biological control agents and natural products.
Sub-objective 2A: Determine key physiological processes in the embryonating and embryonated eggs that may suggest new ovicidal targets or markers.
Sub-objective 2B: Discover biopesticides with ovicidal activity.
Sub-objective 2C: Develop effective formulations of selected biopesticides/natural products with demonstrated ovicidal effects to enhance penetration and lethality.
1b.Approach (from AD-416):
Despite the effort in developing alternative control technologies, management of fire ants and mosquitoes has continued to have challenges associated with effectiveness, application strategy, and cost. New environmentally friendly biopesticides would make product handling easier, improve public acceptance, and potentially provide more effective control. For fire ants, we will search new toxins from defensive chemicals produced by other ants and develop double-stranded ribonucleic acid (RNA) toxins. New toxins will be used in bait, mound drench and immersion treatment. Floodwater mosquitoes have evolved a reproductive strategy in which females deposit their eggs in damp soil of flood prone areas. The temporary separation of eggs from water may provide an opportunity to control eggs without applying control agents directly into the water, thereby reducing their impact on non-target aquatic organisms. An effective ovicide would also make it possible to treat floodwater mosquitoes over a longer period of time before emergence, greatly improving the practicality of community based control programs. Our research on mosquitoes focus on discovering biopesticides with ovicidal activity by studying key physiological processes in the embryonating and embryonated eggs and on identifying new naturally occurring substances and pathogenic microorganisms which can disrupt those processes. A correct formulation will greatly enhance the penetration of biopesticides into insect eggs. By selecting the right adjuvant group and optimizing hydrophile-lipophile balance (HLB) numbers, the improved biological formulation should be able to attack the eggs of the targeted mosquitoes.
Progress has been made in the following three areas: (1) Identification of ants with defensive chemicals which are lethal to fire ants; (2) Literature and database searches for expressed embryonic genes in floodwater mosquitoes; (3) Collecting natural products, extracts and fungi for toxicity bioassay on mosquitoes; and (4) Relationship of hydrophilic-lipophilic balance (HLB) of a surfactant to its impact on mosquito larvae and pupae. In addition to ants collected in the USA, two ant species from China were also analyzed for their defensive compounds. Compounds in Nylanderia spp. were identified and their toxicity was evaluated against red and black imported fire ants. Synergism among defensive compounds was also investigated. For mosquito research, no Aedes (Ae.) vexans colonies were established. Research has focused on the salt marsh mosquito, Ochlerotatus (O.) taeniorhynchus. An Animal Plant and Health Inspection Service (APHIS) permit was obtained to authorize receipt of O. taeniorhynchus eggs from Center for Medical, Agricultural, and Veterinary Entomology (CMAVE), Gainesville, Florida. Shipments of O. taeniorhynchus eggs were received from CMAVE. Target genes were sought and identified from related Culicid species, which can be used as developmental markers and to predict physiological function. Natural products, extracts, and fungi have been collected and tested on eggs of O. taeniorhynchus. How HLB affects the impact of surfactants on O. taeniorhynchus larvae and pupae was also investigated.
Control of mosquito larvae with polyoxyethylene tridecyl ether. Surfactants have been used in soft bodied arthropod control for years, but little is known about the mechanism. ARS scientists in Biological Control of Pests Research Unit at Stoneville, MS, found that the combination of both the surfactant chemistry and its specific hydrophilic–lipophilic balance (HLB) number can create the best insecticidal activity against mosquito larvae and pupae. This is the first time to show how chemistry and HLB number can interact with each other and be of great importance for mosquito control. These research results will also be instrumental in formulating new products for controlling other pest insects.
Formic acid and its esters for fire ant control. Synthetic pesticides cause public concern about health and environmental problems. Safe alternatives are desired. ARS scientists in Biological Control of Pests Research Unit at Stoneville, MS, found that formic acid and several formats are highly toxic to fire ants. This research has resulted in a peer reviewed publication and it will potentially lead to a new fire ant control product.
Zhao, L., Jones, W.A. 2012. Expression of heat shock protein genes in insect stress responses. Invertebrate Survival Journal. ISJ 9:93-101,2012.
Macgown, J. A. First record of the tramp ant Cardiocondyla obscurior (Hymenoptera: Formicidae) for Mississippi. Midsouth Entomologist. 5(1):9-10. 2012.