Efficacy of six grain protectants applied alone or in combination against three species of Coleoptera

Laboratory experiments were carried out to establish whether there were synergistic or antagonistic interactions in combination treatments of certain grain protectants, Six protectants were applied alone, or in combination, against Rhyzopertha dominica (F.) in stored maize and wheat, and Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) in stored wheat. There were four organophosphorus (OP) insecticides (fenitrothion, chlorpyrifos-methyl, pirimiphos-methyl and methacrifos), one juvenile hormone analogue (methoprene) and one synergised pyrethroid (deltamethrin + piperonyl butoxide); and combination treatments consisted of either methoprene or synergised deltamethrin plus an OP insecticide. Based on the levels of control of adult progeny and periods of protection, there were no interactions between protectants. The results show that there is no need to alter field application rates to compensate for antagonism or to take advantage of synergism, They also support the view that application rates for combination treatments can be estimated from experiments on individual protectants using target species or strains. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.