Interspecific Competition Between Callosobruchus Maculatus Fabricius And C. Chinensis L. (Coleoptera: Bruchidae)

Callosobruchus maculatus(Fabricius)and Callosobruchus chinensis(L.),which belong to Callosbruchus,Bruchidae,Coleoptera,are two important stored products insect pests and damage many kinds of stored beans.Callosobruchus maculatus,an alien species and a quarantine object in China,is often intercepted in many customs.This paper studied the interspecific competitions between C.s maculates and C.chinensis with mungbean as their food.The objectives are to explore the competitive results and mechanism of these two bruchids and provide academic supports for IPM of these two insect pests.1.Population competitions between C.maculatus and C.chinensisResults of population competitions between between C.maculatus and C.chinensis showed that C.maculatus population increased faster than C.chinensis when the two species existed separately with their initial density of 10 pairs.After 3 generations,at 30℃,C.maculatus population increased 20.93 folds,whereas,C.chinensis population increased just 14.60 folds.At 35℃,C.maculatus population increased 13.33 folds and C.chnensis increased 5.78 folds.When C.maculatus:C.chinensis were 15:5,10:10 and 5:15,C.maculatus increased its population consistently,but C.chinensis behaved differently.The 1^st generation of C.chinensis just increased its population number slightly and then decreased its numbers gradually.After 2-3 generations,C. maculates replaced C.chinensis completely.It occurred faster at 35℃than 30℃2.Oviposition competition between C.maculatus and C.chinensisThe results of oviposition competition between C.maculatus and C.chinensis indicated the male adult of one species could decrease the female oviposition of the other species.Especially for female C.chinensis,when male adults of C.maculatus existed,which proved male C.maculatus disturbed female C.chinensis more significantly.Two bruchids lay eggs with their preference.The C.maculatus oviposition order for bean state was as follows:mungbeans without any eggs, mungbeans with C.chinensis egg,and mungbeans with C.maculatus eggs.For C.chinensis,the oviposition order for bean state was as follows:mungbeans without any eggs,mungbeans with C. chinensis egg,and mungbeans with C.maculatus eggs.The oviposition differences of C. maculatus were not significant among the beans with C.chinensis eggs,with hatched C.chinensis eggs,and without any eggs.Meanwhile,the egg differences of C.chinensis were significant among the beans with C.maculatus eggs,with hatched C.maculatus eggs and without any egg beans,which meant C.maculatus and the larvae could affect the C.chinensis behavior significantly.3.Developmental competition between C.maculatus and C.chinensisWhen reared separately,two kinds of bruchids survived best at 30℃,where the generation survival were 86.34%and 76.67%for C.maculatus and C.chinensis.The immature stage for C. maculatus was the shortest(19.33d)at 35℃,whereas for C.chinensis was at 30℃(21.47d).The adult weights of C.maculatus for both females and males were heavier than that of C.chinensis. Under the conditions of more than 1 egg,the development of two species inhibited and hatching percentage and generation survival decreased,and the developmental stage increased.Under 30℃and 35℃,when two species coexisted on mungbeans,the generation survival for C.maculatus were 81.21%,73.00%,respectively,whereas 49.70%and 37.47%for C.chinensis.Developmental time for C.maculatus slightly lengthened and for C.chinensis significantly lengthened.The above concluded C.maculates was the dominant species in interspecific competition system between C.maculatus and C.chinensis,and C.maculates could replace C.chinensis in the end.