High levels of azinphosmethyl resistance, ca × 10 of a laboratory stock, were discovered in a field population of Aphytis lingnanensis Compere (Hymenoptera: Aphelinidae) parasitizing the California red scale, Aonidiella aurantii (Maskell) (Homoptera: Diaspididae), in a heavily sprayed citron orchard. Nine selections for increased resistance led to an initial loss of variability with no significant gains in resistance. Eight additional selections increased resistance to ca 4 times that of the source population, and variability to an extent indicating potential for further progress.
Additional selections of this stock by the male selection method resulted in further improvement and field releases of the resistant strain.
Initial levels of permethrin tolerance were ca 1.9 times higher than those of the susceptible population. LC50 values were only marginally increased by 13 selections, but a marked increase in the proportion of highly resistant individuals pointed to potential for further progress.
Exposure to the insecticides had no observable sub‐lethal after‐effects on rates of progeny production by survivors and on the sex ratio and developmental period of offspring.
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