TOXICOLOGICAL STUDIES OF THE CARBAMATES METHOMYL AND BENDIOCARB IN THE BULB MITE RHIZOGLYPHUS-ECHINOPUS (ACARI, ACARIDAE)

Methomyl was 15 and 31.3 times more toxic than bendiocarb to bulb mite s at the LC50 and LC90 90 values respectively. However, methomyl (pI(5 0) 3.0) was at least 126 times less active than bendiocarb (pI(50) 5.1 ) as an inhibitor of bulb mite cholinesterase in vitro. The disparity between the high toxicity of methomyl and its extremely low activity a s an inhibitor of mite cholinesterase in vitro indicated that another mechanism was likely involved in its toxic action. Pharmacokinetic stu dies of methomyl and bendiocarb showed that penetration and metabolism were rapid and that there were no substantial differences in the inte rnal levels of the respective parent carbamates during the 24 h test p eriod. However, volatile radioactive material(s), some of which was ca rbon dioxide, was produced in appreciably greater amounts from methomy l than from bendiocarb. We speculate that the production of volatiles, such as carbon dioxide, acetonitrile and/or methylamine, may contribu te to the toxicity of methomyl to bulb mites. (C) 1998 Chapman & Hall Ltd.