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THE GENETICS OF DACUS OLEAE. IV. RELATION BETWEEN ADULT ESTERASE GENOTYPES AND SURVIVAL TO ORGANOPHOSPHATE INSECTICIDES

The main bulk of adult esterases in the olive fruit fly Dacus oleae (Gmel) is controlled by two autosomal and independent genes, gene A and gene B. Gene A synthesizes an acetylcholinesterase and gene B a pseudocholinesterase or a lipase. Both genes are highly polymorphic in natural populations. More than 15 active alleles plus one silent allele have been found for gene A; more than 10 active alleles plus one silent in gene B. (Zouros et al., 1968; Zouros and Krimbas, in press; Krimbas and Tsakas, in press.) Most of the Dacus populations in olive orchards in Greece have been under control for the last few years with an organophosphate insecticide, dimethoate. It is generally accepted that organophosphate esters kill insects by inhibition of their cholinesterases (for a review of the "cholinesterase hypothesis" see O'Brien, 1960). Since both esterase enzymes controlled by genes A and B are cholinesterases or related to them it seemed interesting to investigate the action of dimethoate, acting as a selective agent, on genes A and B polymorphisms. Laboratory experiments dealing with this question are reported below.