VARIABILITY IN RESISTANCE TO ORGANOPHOSPHOROUS INSECTICIDES IN FIELD-COLLECTED COLONIES OF AMBLYSEIUS-FINLANDICUS (OUDEMANS) (ACARI, PHYTOSEIIDAE)

Five colonies of Amblyseius finlandicus (Oudemans) were collected from Finnish apple orchards and tested for tolerance to two organophosphor ous insecticides (OPs), dimethoate and azinphosmethyl. Slide-dip bioas says demonstrated clear differences between the five colonies. The LC5 0 value for the most resistant colony was about five times the value o f the most susceptible colony for both pesticides. Colonies from orcha rds with previous OP treatments were more tolerant than the colonies f rom non-treated areas. Existing variation indicates it may be possibil e to increase resistance levels using laboratory selection.