Colonization of cultivated and indigenous graminaceous host plants by Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) under field conditions
Stem borers are generally polyphagous, attacking cultivated as well as wild host plants. Two field trials, incorporating four cultivated cereal crops and two grass species, were conducted to study colonization of cultivated crops and grasses by stem borers. The first trial consisted of maize (Zea mays L.), sorghum (Sorghum bicolor (L.) Moench), sweet sorghum (Sorghum bicolor (L.) Moench), pearl millet (Pennisetum glaucum (L.) R. Br.), Hyparrhenia tamba (Steud) (blue thatching grass) and, Panicum maximum (Jacq.) (Guinea grass). During the following two seasons P. maximum was replaced by Pennisetum purpureum (Schumach) (Napier grass). In the second trial P. purpureum was replaced by P. maximum. Plots (5 x 5 m) were arranged in a 6 x 6 Latin square design. Natural infestation by stem borers was allowed to take place. The stem borers found on host plants were Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) and Busseola fusca (Fuller) (Lepidoptera: Noctuidae). The incidence of whorl damage, dead heart and stem damage observed indicated that all host plants were susceptible to stem borer attack. Cultivated host plants showed higher incidences of whorl and stem damage than the grasses. The low incidence of whorl damage on the grasses may be ascribed to larval antixenosis at the feeding site. Quicker larval development as well as increased size was observed on cultivated crops than on the grasses. The results of this study indicated better colonization of cultivated crops by the stem borers compared with the grasses.