Cereal stem borer (Lepidoptera) assemblage structure in a sub-tropical agro-ecosystem, Eastern Cape Province, South Africa

Abstract

Insect pests, especially lepidopterous stem borers, cause significant losses to cereal production at local and global scales. The borer species associated with cultivated grain cereals and alternative wild host plants were identified at three elevation gradients in the former Transkei area of the Eastern Cape Province, South Africa. Stem borer sampling was undertaken during maize crop and non-crop seasons in Port St Johns (PSJ), Mthatha and Elliot, sites that differ in elevation above sea level, annual precipitation and temperature. Morphologically identical borers retrieved from each sampling unit were recorded, processed and reared to adult stage for identification at an ambient temperature range of 25–28°C and a relative humidity range of 65–80%. Specimens were sorted first into morphospecies (MS1–MS6) based on external morphological characteristics. Six stem borer species (Busseola fusca, Sesamia calamistis, Eldana saccharina, Chilo orichalcocili, Chilo sacchariphagus and Chilo partellus) were collected during the survey. E. saccharina and C. orichalcocili were absent in PSJ; in Elliot, E. saccahrina occurred in very low numbers whereas C. partellus was absent. Busseola fusca was more abundant at high altitude (i.e. Elliot). Borer community structure in the study showed similarity between Mthatha and Elliot. Species richness and abundance across study sites were not statistically significant (P > 0.05). The study provides information on borer species occurrence in the study area, and techniques to identify larval stages for effective control by local farmers and extension workers. When designing strategies for borer control, elevation may not be a major concern at this spatial scale.