Selective treatments,including combinations of pyrethroid and organophosphorus insecticides. For control of stored product Coleoptera at two temperatures

Selective treatments, appropriate to simulated storage conditions, reinfestation pressures and species or strains of insects present in the wheat, required less insecticide than any “blanket” or all-purpose treatment. In particular, the pyrethroids bioresmethrin, synergized bioresmethrin or synergized pyrethrins were especially effective where Rhyzopertha dominica and especially a strain resistant to organophosphorus insecticides, was the only species present. Conversly, the organophosphorus insecticides dichlorvos, malathion, fenitrothion and pirimiphos-methyl were especially effective against Tribolium and Sitophilus species. There was no antagonism between any of the pyrethroids and any of the organophosphorus insecticides when they were applied in combination, in that the period of protection given by combinations was the period of protection given by the pyrethroid component against R. dominica and the organophosphorus component against Tribolium and Sitophilus species. As an example of the data required for selective treatments, bioassays were conducted at 20 and 30°C and it was found that the net effect of the lower temperature in reducing toxicity but increasing persistence was to increase the period of protection given by insecticides in cooled storages. It is suggested that the amounts of insecticides applied to grain could be considerably reduced if more consideration was given to grain conditions, if reinfestation pressures were more carefully examined and if less attention were given to surviving adults under conditions where progeny do not develop.