Biochemical mechanisms associated with methiocarb resistance were examined in laboratory-selected and field populations of the western flower thrips, Frankliniella occidentalis (Pergande). Seven populations were examined and they differed in their susceptibility to methiocarb by 30 times. Including the synergists piperonyl butoxide, a cytochrome P-450 monooxygenase inhibitor, or S,S,S-tributylphosphorotrithioate, an esterase inhibitor, in the methiocarb bioassays partially suppressed resistance in the most resistant populations. In vitro assays of general esterase, glutathione S-transferase, and acetylcholinesterase activities showed increased activity in some of the resistant populations and increased activity of the enzymes after methiocarb selection on one of the populations. Assays of acetylcholinesterase sensitivity to inhibition by methiocarb, dichlorvos, and eserine suggested insensitive acetylcholinesterase in two of the resistant populations. These results indicate that methiocarb resistance in F. occidentalis was polyfactorial and involved detoxification and altered target site. None of the biochemical assays showed interpopulation enzymatic differences strongly correlated with the level of methiocarb resistance. The possibilities for developing rapid biochemical diagnostic assays to detect methiocarb resistance in F. occidentalis are discussed.

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As part of the World Health Organisation (WHO) initiative to update the current requirements for BCG vaccine a collaborative study was carried out to establish the robustness, reproducibility and the suitability of the modified ATP assay. This assay was developed by Statens Serum Institut, Denmark, as a potential replacement of the method for detection of viable counts of BCG vaccine which is routinely used as a quality control test for lot release. Two BCG preparations, of same strain but different production methods, were tested. For each preparation, two different storage conditions of -20 or 37 degrees C were used in order to establish the suitability of this assay for testing heat-treated BCG vaccine as in the temperature stability test. The lyophilised BCG samples were tested using the ATP reagents from the same source and same principle of testing but some procedural modifications were allowed to accommodate different equipment and resource availability in different laboratories. Data from four laboratories showed that the heat-treated BCG samples contained significantly lower ATP content per sample than the untreated control stored at -20 degrees C. Three laboratories gave consistent mean ATP contents, especially for control samples, even with variations in testing protocol. The present study showed that this modified ATP assay is very robust and can be reproducible. Once the correlation of cultural viable count and ATP content of a BCG vaccine product has been established, this rapid alternative assay may be used to monitor BCG viable count. Due to the fact that this study was small, further investigation is planned. A collaborative study will be carried out using this modified ATP assay in parallel with the cultural viable count method in the establishment of the replacement of the WHO International Reference Preparation of BCG vaccine.