A laboratory study of competition betweenTribolium castaneum(Hbst.) (Coleoptera, Tenebrionidae) and three moth species

Abstract

Laboratory studies were undertaken to find out if the increased degree of infestation by certain moth species,Cadra cautella(Wlk.),plodia interpunctella(Hb.) andCorcyra cephalonica(Stnt.) following the chemical control of beetles includingTribolium castaneum(Hbst.) in stacks of groundnut (Arachis) in Nigeria could be due to relaxation of inter-specific competition.All test insects were reared and studied at a constant temperature of 25.5°C. and 70 per cent. ralative humidity. All experiments were conducted on shelled nuts (or germs of nuts) in specimen tubes, crystallising dishes or jam jars. The survival and development of the immature stages of the moth species was studied and the numbers of eggs laid by the adults recorded in the presence of adults ofT. castaneum;the reciprocal effects of moth larvae onT. castaneumwere also briefly studied.The most important harmful effects ofT. castaneumwere on copulating moths and on moth eggs. Adults were frequently disturbed and sometimes killed or, if they survived, laid fewer eggs; eggs were also eaten, especially those laid loose in the medium. Adults ofT. castaneumalso attacked and killed moth larvae and pupae, but this was considered to be of minor importance. The silk produced by moth larvae was inimical to larvae ofT. castaneum, but the effect on the population ofT. castaneumwas probably offset by the beneficial effect of moth cocoons, which provide shelter for larvae ofT. castaneumfrom cannibalism.It is conculaded that as a result of competition for food and/or space betweenT. castaneumand the moth species the moth populations are likely to be exterminated despite their apparently higher intrisic rate of increase.