Resistance to a Range of Insecticides in the Predaceous Mite Typhlodromus pyri (Acari: Phytoseiidae): Inheritance and Physiological Mechanisms

Abstract

Two strains of Typhlodromus pyri Scheuten were studied to investigate physiological and genetic patterns of resistance to several insecticides. Results revealed resistance to a range of insecticides (carbamate, oregano phosphate, and pyrethroid). This species may thus have a promising future in integrated pest management programs in various crops. Inheritance of resistance to an oregano phosphate using conventional techniques (crosses/backcrosses) indicated polygenic resistance to parathion methyl, a common phenomenon in laboratory-selected strains but rare in wild strains. Release of mites with polygenic resistance in the field might lead to hybridization with susceptible migrants, thus making resistance mechanisms unstable. However, F1 females (hybrid females) were more resistant than R females and resistance levels in the 2 types of F1 females were different. Such higher resistance in hybrid females could be explained by a heterosis effect (associated with a complementation phenomenon). We used 2 synergists (DEF and piperonyl butoxide) to define the physiological mechanisms of resistance to parathion methyl and fenvalerate. Results seemed to indicate that neither ester-link hydrolysis nor oxidative degradation of insecticides has a critical role in resistance to parathion methyl. Tests done with fenvalerate suggest that oxidative degradation and, to a lesser extent, hydrolytic reactions are partially involved in the mechanisms of resistance to this pyrethroid. Overall results are discussed in terms of basic research (genetic) and agronomic applications (for example, improved resistance management, strain selection with resistance genes).