Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 14, 2001
Publication Date: N/A
Interpretive Summary: The horn fly, Haematobia irritans (L.), is an economic pest of cattle and has been controlled primarily by the application of insecticides. Due to the biology and behavior of the species, populations of the horn fly have the potential to develop resistance rapidly to various classes of insecticides. In order to prolong the use and effectiveness of the various chemicals it is important to understand how the horn fly becomes resistant, and to develop diagnostic tools for detecting and managing the development of resistance. One metabolic mechanism that horn flies utilize to detoxify insecticides is a class of enzymes known as esterases. It is possible to measure esterase activity in samples of a population and look for elevated esterase activity as an indicator of developing resistance. To statistically compare different populations it is necessary to have knowledge of the variability of esterase activity within populations. Thus, in this study we evaluated variation of esterase activity within female and male samples of a horn fly population that has not been exposed to insecticides for the past 8 years. We found considerable variation within our samples. Due to this inherent variation only large differences in population means can be compared. As subtle differences in esterase activity may be very important, the measurement of general esterase activity has a limited value as a disgnostic tool. Therefore, our findings further support the importance of continued identification of resistance mechanisms, the isolation of the specific enzymes involved, and the design of biochemical or molecular assays for their activity. These tools would provide resistance managers with meaningful information for use the mitigation of insecticide resistance.
Technical Abstract: Control of the horn fly, Haematobia irritans (L.), is dependent upon chemical insecticides. However, the biology and behavior of the horn fly favors rapid development of insecticide resistance. In order to prolong the effectiveness of various classes of insecticides, it becomes increasingly apparent that information is required regarding the various mechanisms of insecticide resistance. Metabolic hydrolysis of insecticides by esterases is recognized as a detoxification mechanism in various insect species. Thus, it would appear that measurement of general esterase activity within populations of horn flies may provide a diagnostic tool for resistance management. In this study we evaluated the amount of variation in general esterase activity within female and male horn fly samples from a population of horn flies that was not intentionally exposed to insecticides for 8 years. We found considerable variation in general esterase activity within samples of each sex, with females demonstrating the greater variation. The observed variation is thought to be the result of age-structure dynamics within the population. The amount of inherent variation documented would make it difficult to measure small mean differences between populations, limiting the utility of general esterase assays. Thus, the data support identification of specific detoxification enzymes, their purification, and the design of assays either biochemical or molecular in order to effectively use them as diagnostic tools in the mitigation of insecticide resistance.