The isolation and inheritance of dieldrin resistance in the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae)

Abstract

AbstractFour geographical strains of Ceratitis capitata (Wiedemann) were subjected as third-instar larvae to mass selection with dieldrin. Two strains, SOUTH and COSRIC, responded well but continued to show substantial heterogeneity in tolerance to the insecticide after 21 and 25 generations of selection, respectively. The technique was altered to single family sib selection, resulting in the isolation from the SOUTH strain of a dieldrinresistant strain (73) showing a more homogeneous response to the insecticide. By the same technique, a dieldrin susceptible strain (72/3) was isolated from the COSRIC strain. A decline in resistance was observed in the 73 strain between generations three and four, but the level subsequently increased again, without selection, reaching 68-fold in generation seven. It remained high for the next two years. No significant change was observed in susceptibility to dieldrin of strain 72/3; it remained highly susceptible. Resistance to solutions of technical dieldrin (96%) was shown to be mainly under the control of a single major autosomal gene, intermediate in dominance but with a modifying effect of the genetic background on the expression of the resistance gene. The resistance heterozygotes, segregating in backcrosses to susceptible individuals, were shown to be more resistant than expected, while in backcrosses to resistant ones they were more susceptible. A dose of 11 p.p.m. dieldrin was found to discriminate almost completely between heterozygous and homozygous-susceptible individuals among backcross progeny. In tests using a purer form of the insecticide (99·7%), a similar pattern of resistance was observed. The implications for genetic sexing in C. capitata are discussed.