The relative abundance of maize stem borers and their parasitoids at the Tshiombo irrigation scheme in Venda, South Africa

Abstract

Maize is an important resource in many small-scale farming areas in South Africa and especially on irrigation schemes in the Limpopo Province where this crop is cultivated under irrigation in sub-tropical conditions. The aim of this study was to determine the moth flight patterns, species distribution, infestation levels and parasitism levels of maize stem borers at the Tshiombo irrigation scheme in Venda. Moth flight patterns were monitored by means of sex pheromone traps over a 2.5-year period. The incidence of damaged plants and infestation levels were monitored by means of destructive sampling at 4–6 week intervals over a 15-month period. Moth flight patterns were erratic and although peaks were observed, the period of peak activity differed between seasons. The stem borer population was dominated by Chilo partellus which made up between 65–99% of the total number of larvae collected at each planting date. Busseola fusca and Sesamia calamistis made up between 0–16% and 0–31% of the population respectively. The most important parasitoid was Cotesia sesamiae and the average level of parasitism over species was 10%. The average level of parasitism ranged between 0–34, 0–7 and 0–3% for C. partellus, B. fusca and S. calamistis respectively.