Australian populations of onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), are resistant to some insecticides used for their control

Abstract Onion thrips, Thrips tabaci Lindeman, is a major pest of Australian field onion Allium cepa Linnaeus with their control heavily reliant on a few insecticides. An earlier study after grower complaints of control failures did not detect resistance in three populations. After testing an additional nine populations via a Potter spray tower laboratory bioassay unequally against α‐cypermethrin, diazinon, dimethoate, λ‐cyhalothrin, malathion and methidathion, we document resistance in T. tabaci for the first time in Australia. The maximum difference in response (resistance) for each insecticide was detected by dividing the most resistant LC50 response by the least resistant LC50 response. Comparison of the most susceptible to the least susceptible population tested produced α‐cypermethrin and λ‐cyhalothrin resistance at 164‐ and 606‐fold, respectively. Diazinon and dimethoate resistance was also detected at 27‐fold and 5.2‐fold respectively although omethoate, malathion and methidathion resistance were not detected.