CHARACTERIZATION OF MALATHION RESISTANCE IN A MEXICAN POPULATION OF RHIZOPERTHA-DOMINICA

Malathion resistance of a held-collected population of Rhizopertha dom inica (Coleoptera: Bostrichidae) from Mexico was evaluated and the res istance mechanisms were characterized both in vivo and in vitro. The M exican population showed a resistance level of 50-fold at LC50 as comp ared with that of a susceptible laboratory population. Malathion bioas says with the synergists triphenyl phosphate, piperonyl butoxide and d iethyl maleate suggested that esterases were likely to contribute to t he resistance whereas cytochrome P450 monooxygenases and glutathione S -transferases were not. In-vitro assays of esterases indicated that th e general esterase activity was 1.3-fold higher in the Mexican populat ion than in the susceptible population. However, the phosphotriesteras e activity in the resistant population was 3.7-fold higher than in the susceptible population. Significantly higher phosphotriesterase activ ity in the resistant population was further indicated by 3.4-fold incr ease of V-max in enzyme kinetics and higher frequency of individuals w ith high phosphotriesterase activity in this population. All these fin dings suggested that phosphotriesterases play a role in malathion resi stance in the Mexican population of lesser grain borer. (C) 1998 SCI.