Distribution of Populations of Chironomus yoshimatsui (Diptera: Chironomidae) Susceptible or Resistant to Fenitrothion, an Organophosphorus Insecticide

Abstract

Susceptibility of populations of the midge Chironomus yoshimatsui (Diptera: Chironomidae) to fenitrothion was investigated at 32 sites. Resistance (48h-LC₅₀>1,000 μg/l) to the insecticide was found in populations on 23 sites, nine of which had no records of fenitrothion use. Susceptible populations (ranging from 6.7 to 17.7 μg/l of the 48h-LC₅₀) were found on 6 of 9 sites in Hokkaido, but only two of 23 sites in other districts. However, a susceptible population was found in Yumoto, while the population in Tokorono (30 km from Yumoto) where there are neighboring rice fields, comprised both susceptible and resistant individuals; no susceptible individuals were found in Honshu districts, except for Yumoto and Shirahone.