2009 Annual Report
1a.Objectives (from AD-416)
The overall objective of this research is to develop effective and environmentally safe tools and sustainable strategies for the integrated management of livestock pests. Toward that goal our specific objectives for the next 5 years are to: .
1)Develop and improve methods of chemical control of horn flies and stable flies;.
2)Develop alternatives to classical chemical control of horn flies and stable flies; and.
3)Develop and evaluate control strategies to provide sustainable pest management practices.
1b.Approach (from AD-416)
Use in-vitro and in-vivo bioassays to evaluate new classes of chemical control agents against horn flies and stable flies. Develop and improve both conventional and controlled release chemical delivery systems to increase the effectiveness, improve efficiency, reduce the quantity of pesticide needed, and improve the safety of chemical control. Develop biological and physical control technologies for blood-feeding flies on cattle. Create and use simulation models to serve as a framework to guide both research and implementation of sustainable control programs. Develop and test sustainable horn fly and stable fly management strategies for pastured cattle. Develop computer assisted decision-aid programs for use by extension personnel and producers. Develop protocols for the selective breeding of cattle resistant to horn flies.
Research conducted over the past five years has contributed significantly to completion of the objectives originally established for this project. New control measures have been evaluated for controlling stable and horn flies, including novel insecticides (electron transfer inhibitors and novaluron) and two promising strains of entomopathogenic fungi, Beauveria bassiana and Metharhizium anisopliae. We have accumulated a significant genomic DNA database from over 200 cows which have been phenotyped for horn fly carrying capacity that will be used for gene mining. We have isolated and sequenced 75% of the stable fly sodium channel gene including the region in which mutations associated with pyrethroid resistance have been identified in the house fly and the horn fly. We have assembled a database of 12,590 stable fly ESTs representing genes expressed in embryonic, larval, pupal, and adult heads that represent genes that are involved in stable fly chemosensation, neurotransmission, reproductive behavior, and insecticide resistance, as well as genes that are similar to sex-determination pathway genes described in other dipteran insects. A senior scientist retired in 2008. Thus, some of the milestones related to the retired scientist's area of responsibility have not met completion.
Use of entomopathogenic fungi for the control of horn flies: Entomopathogenic fungi are naturally occurring fungi that infect a specific, limited group of host insects without negatively affecting the environment. Due to resistance problems and growing concerns over the environmental impact of synthetic insecticides, a need for more natural types of control for biting flies on cattle has emerged. Three strains of entomopathogenic fungi, Beauveria bassiana, Metarhizium anisopliae, and Paecilomyces fumosoroseus, were tested in the laboratory for control efficacy against horn flies. Laboratory studies showed that exposure to B. bassiana resulted in greater than 90% mortality of horn flies within seven days. M. anisopliae and P. fumosoroseus were not as effective. Recently, a new formulation of M. anisopliae was evaluated in the lab against horn flies and was found to be as effective and as fast-acting as B. bassiana. Both of these look promising for field application to control horn flies on pastured cattle.
Isolation and sequencing of the stable fly sodium channel gene: Resistance to pyrethroids, a commonly used class of insecticide, has been well-documented in horn flies and house flies. This phenomenon has been attributed to a sequence difference in the sodium channel gene, the target of pyrethroids, resulting in an insensitive target. Little is known about pyrethroid resistance in wild populations of stable flies, a significant pest of livestock in the U.S. We have isolated a portion of the stable fly sodium channel gene that corresponds with the region in which mutations associated with pyrethroid resistance have been identified in the house fly and the horn fly. This finding is significant because it will enable us to begin surveying natural populations of stable flies for sequence differences in this region that would indicate a likelihood of pyrethroid resistance. Further, this finding has facilitated the collaboration with a scientist at the University of Florida who is selecting in vitro for stable flies that are non-susceptible to pyrethroids. New control methods for stable flies, e.g., insecticide impregnated cloth targets, are being applied in the field, and this work will provide a tool to enable researchers to monitor field populations of stable flies for target site (sodium channel) sequence differences that may arise from such new control methods.
Development of a database of genes expressed by stable flies: Alternative technologies for controlling stable flies are desired because current methods are not cost-effective or highly efficient. Identifying molecules produced by the stable fly that can be targeted to interfere with a critical stable fly behavior, e.g., feeding, mating, would provide the basis for developing these alternative methods. To support identification of target molecules, we have assembled a database of 22,800 sequences that represent genes expressed by immature and adult stages of the stable fly. This database is significant because it will enable target identification and facilitate collaboration with other researchers within the fly community.
Evaluation of new insecticides for horn fly and stable fly control: The horn fly and the stable fly are two economically important pests of cattle and cause approximately $2 billion in losses per year to the US cattle industry. Resistance to currently used insecticides is a major problem for the control of the horn fly in the US. New insecticides with a different mode of action are needed in order to combat resistance problems. ARS scientists in the Biting Fly Research Unit in Kerrville, Texas, evaluated the toxicity of several new chemical insecticides through laboratory bioassays, and have identified two (electron transfer inhibitors) that have the potential to be further developed for biting fly control on cattle. This research will help the animal health industry develop new insecticide formulations for biting fly control.
Lohmeyer, K.H., Miller, J.A., Pound, J.M., Klavons, J.A. 2009. A sustained release gel formulation of Doramectin for control of Lone Star Ticks (Acari: Ixodidae) and horn flies (Diptera: Muscidae) on cattle. Journal of Economic Entomology. 102(2):804-808.
Li, A.Y., Lohmeyer, K.H., Miller, J.A. 2009. Dynamics and mechanisms of permethrin resistance in a field population of the horn fly, Haematobia irritans irritans (L.). Insect Science. 16:175-184.