Intra-specific variations of the susceptibility to insecticides in Chironomus yoshimatsui

Abstract

Toxicities of four insecticides, fenitrothion, fenthion, ethofenprox and fenobucarb, to Chironomus yoshimatsui fourth and first instar larvae collected at 8 localities in Japan were investigated. The population collected in Yumoto Nikko-shi Tochigi-ken, was most sensitive to all insecticides and seems to be a wild type. The other populations had acquired resistance to insecticides; their LC_<50>s rose several tenfold to several hundredfold. Sensitivity depended on the age of larvae; first instars were always more sensitive than fourth instars, although the difference was always less than several tenfold.