DISTRIBUTION AND SAMPLING OF CHILO-PARTELLUS (LEPIDOPTERA, PYRALIDAE)IN MAIZE AND SORGHUM ON THE KENYA COAST

The seasonal occurrence and spatial distribution of the crambine stem borer, Chilo partellus (Swinhoe) were investigated in maize, Zea mays, and sorghum, Sorghum bicolor, fields at the Kenya coast. During the v egetative growth stage, small-sized larvae were typically found behind leaf sheaths and in whorls in maize and sorghum. In reproductive and senescent maize, small-sized larvae were also found feeding in ears. L ater immature life stages were located predominantly in stems in sorgh um, and in the stems and ears in maize. Density and variance estimates of small, medium-, and large-sized larvae and pupae in maize and sorg hum were fitted to Taylor's power law which provided significant regre ssions in all cases. The between-plant distribution was aggregated in all life stages. In maize, the distribution remained aggregated throug h the larval and pupal life stages, but in sorghum the distribution be came progressively less aggregated as insects aged. The relationship o f C. partellus density to the proportion of plants infested also sugge sted aggregation. Optimal sample sizes were determined for both binomi al and enumerative sampling plans at two levels of precision, and a di scussion is included on the relationship of optimal sample sizes to ec onomic injury levels. Additionally, a presence/absence sequential samp ling plan is proposed.