Comparative studies on the fecundity, egg survival, larval feeding, and development of Chilo partellus and Chilo orichalcociliellus (Lepidoptera : Crambidae) on five grasses

Chilo partellus (Swinhoe) and Chilo orichalcociliellus Strand (Lepidoptera: Crambidae) are gramineous stem borers that occur sympatrically in the sout hern coastal area of Kenya. Evidence over a 30-yr period indicates that the indigenous stem borer, C. orichalcociliellus, is being gradually displaced by the exotic stem borer, C. partellus. Comparative laboratory studies wer e conducted in several large-stemmed grasses to examine factors that may be involved in the displacement of C. orichalcociliellus, and to examine othe r possible effects of the invasion of C. partellus into Kenya. C, partellus had a higher fecundity than C. orichalcociliellus at 25 and 28 degrees C, but not at 31 degrees C. In addition, more C. partellus than C. orichalcoci liellus eggs survived to the first instar. C. partellus larvae developed fa ster than C. orichalcociliellus in maize and sorghum. In this shorter devel opmental time, C. partellus consumed more maize than C. orichalcociliellus, but both species consumed equal amounts of sorghum. On a daily basis, C. p artellus consumed more maize and sorghum than C. orichalcociliellus. A few C. orichalcociliellus survived to the pupal stage in napier and guinea gras ses, whereas no C. partellus survived. The shorter developmental period of C. partellus may give this species a competitive advantage over the slower developing C. orichalcociliellus. However, the ability of C. orichalcocilie llus to complete development in two native grasses in which C. partellus di d not survive may provide a refuge that has allowed C. orichalcociliellus t o escape extirpation from the coastal area of Kenya.