Preliminary experiments in the greenhouse on the control of the greenhouse whitefly, Trialeurodes vaporariorum (Westw.) showed that sprays of wettable 'Maneb' and 'Zineb' are insecticidal to larvae and adults of this insect. Subsequent experiments and observations carried out in a controlled-temperature, plant-growth room indicated that these fungicidal compounds probably have a toxic action different from most insecticides. 'Perthane' and 'Malathion, conventional insecticides which were also used in these experiments, killed the majority of the larvae affected by them within three days and after seven days all such larvae were desiccated and shrivelled. In contrast, larvae affected by 'Maneb' or 'Zinebusually did not die until one to three weeks after treatment. During this post-treatment period the affected larvae did not moult; however, they grew to the extent of cuticular limitations and became bloated and globular. When they were teased off the leaf, movements of the styli could be detected. Larvae that were not affected by 'Maneb' or 'Zineb' moulted similarly to those in check treatments and retained their normal appearance. Table 1. RELATIVE TOXICITIES OP 'PERTHANE', 'MANEB' AND'ZINEB' TO GREENHOUSE WHITEFLY Slope of LD50 grams 5 %Material regression of actual fiducial line toxicant limits per litre of spray 50% wettable'Perthane' 2-3310-166 0-275 0-249 0-304 70% wettable 'Maneb' 1-7610-161 0-338 0-241 0-471 65% wettable'Zineb' 2-7450-185 1-511 1-381 1-654 Table 1 shows the relative toxicities of sprays of 50 per cent wettable 'Perthane', 70 per cent wettable 'Maneb', and 65 per cent wettable 'Zineb' to a mixed population of first and second instar larvae of T. vaporariorum.Further work is being done to learn more about the mode of action of ethylene frisdithiocarbamates on insects.