Seasonal abundance and diversity of sorghum panicle-feeding Hemiptera in South Africa

Abstract

During the past two decades, panicle-feeding Hemiptera have become pests of sorghum in West and Central Africa, and particularly in Mali, where this is a staple food crop. Of the more than 100 sorghum insect pests reported in Africa, 42 species were found to be panicle-feeding pests. Prior to this study, no research had been done on the panicle feeding Hemiptera in South Africa. The objectives of the study were to determine the abundance and diversity of panicle-feeding Hemiptera on sorghum. A check list was compiled and the temporal distribution of different Hemiptera species determined during the different panicle stages of development. In addition, the effect of insecticide application on Hemiptera numbers was evaluated and the correlation between grain mould severity and Hemiptera feeding damage was investigated. To determine the abundance and diversity of Hemiptera on sorghum panicles, surveys were conducted between November 2004 and June 2006 at 26 sites in four provinces of South Africa. Two methods of collection were used viz. the plastic bag and D-Vac methods. The total number of the adults and nymphs collected during this study was 23 798. Forty-three different herbivorous Hemiptera species were collected. The most abundant family was the Miridae (41 %), followed by the Lygaeidae (17 %). Eurystylus spp., Calidea dregii, Campylomma sp., Creontiades pallidus, Nysius natalensis and Nezara viridula were the most abundant species and also occurred widely in the sorghum production area. Infestation levels of these species were low compared to that in other parts of Africa and it cannot be concluded that they have pest status in South Africa. There was no clear distinction between the stages during which panicles were infested by different species. The general tendency was that nearly all species were present from the flowering stage onwards and that numbers declined when grain hardened. In general, Campylomma sp. and C. pallidus numbers peaked during the flowering stage and Eurystylus spp. and N. natalensis during the milk stage. Hemiptera feeding damage resulted in an increase in incidence of seeds with discoloured germ, therefore contributing significantly to reduction in grain quality.