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Changes in malathion resistance with age in Anopheles stephensi from Pakistan |
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| Institution: | 1. Entomology program, Department of Agricultural Biotechnology, Seoul National University, Seoul 08826, Republic of Korea;2. Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Republic of Korea;1. College of Horticulture and Plant Protection, Yangzhou University, Yangzhou 225009, China;2. Joint International Research Laboratory of Agriculture and Agri-Product Safety of the Ministry of Education, Yangzhou University, Yangzhou 225009, China |
| Abstract: | Resistance to malathion in Anopheles stephensi from Pakistan was measured at intervals during the first week of adult life. LT50 values for homozygous resistant females decreased four-fold during the first 7 days of adulthood. A decrease in resistance with age also occurred in heterozygotes; the LT50 values of males and females fell sevenfold during the first 5 days of adulthood. The sensitivity to malathion of a susceptible strain increased with age. A biochemical basis for the declining resistance levels was investigated. Resistant and susceptible adults were homogenized at intervals during the first week of adulthood and soluble extracts were incubated with 14C]malathion. The rate of malathion metabolism to mono- and dicarboxylic acids was faster in resistant than in susceptible mosquitoes. The rate of malathion metabolism decreased with age in both strains. A decrease in carboxylesterase activity with age in resistant and susceptible mosquitoes is thus responsible for the increasing sensitivity to malathion. Implications for the monitoring of resistance in the field by diagnostic dosages and for the future use of malathion in mosquito control are discussed. |
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