RESISTANCE TO A RANGE OF INSECTICIDES IN THE PREDACEOUS MITE TYPHLODROMUS-PYRI (ACARI, PHYTOSEIIDAE) - INHERITANCE AND PHYSIOLOGICAL-MECHANISMS

Two strains of Typhlodromus pyri Scheuten were studied to investigate physiological and genetic patterns of resistance to several insecticid es. Results revealed resistance to a range of insecticides (carbamate, organophosphate, and pyrethroid). This species may thus have a promis ing future in integrated pest management programs in various crops. In heritance of resistance to an organophosphate using conventional techn iques (crosses/backcrosses) indicated polygenic resistance to parathio n methyl, a common phenomenon in laboratory-selected strains but rare in wild strains. Release of mites with polygenic resistance in the fie ld might lead to hybridization with susceptible migrants, thus making resistance mechanisms unstable. However, Fl females (hybrid females) w ere more resistant than R females and resistance levels in the 2 types of Fl females were different. Such higher resistance in hybrid female s could be explained by a heterosis effect (associated with a compleme ntation phenomenon). We used 2 synergists (DEF and piperonyl butoxide) to define the physiological mechanisms of resistance to parathion met hyl and fenvalerate. Results seemed to indicate that neither ester-lin k hydrolysis nor oxidative degradation of insecticides has a critical role in resistance to. parathion methyl. Tests done with fenvalerate s uggest that oxidative degradation and, to a lesser extent, hydrolytic reactions are partially involved in the mechanisms of resistance to th is pyrethroid. Overall results are discussed in terms of basic researc h (genetic) and agronomic applications (for example, improved resistan ce management, strain selection with resistance genes).