Pest Status of Whitegrub Species (Coleoptera: Scarabaeidae) Attacking Commercially GrownAcacia mearnsiiSeedlings and Its Management Implications in KwaZulu-Natal Plantations, South Africa

Abstract

The abundance and distribution of whitegrub species that attacked black wattle seedlings during their establishment were assessed to determine their pest status and their contribution to the whitegrub species community structure patterns. Ten trials were planted on previous wattle sites. Monthly collections of whitegrubs that attacked seedlings were conducted during the first year of seedling growth. Very stressed or dying wattle seedlings and their surrounding roots were dug out and the soil was assessed to collect any whitegrub pests that caused seedling mortality. A multivariate analysis was used to rank the average abundance of the various whitegrub species that attacked wattle. The individual contribution of whitegrub species to the average similarity within a community and the dissimilarity between communities were tested with similarity percentages comparisons. The best two-dimensional (2-D) model obtained for each species pattern of distribution and relative abundance had a good ordination (stress value: 0.07). From a complex of 13 whitegrub pests found, six whitegrub species (Pegylis sommeri, Schizonycha affinis, Adoretus ictericus, Schizonycha fimbriata, an undescribed Maladera sp. 2 and an unknown species M8), with an average cumulative abundance of 96.4 %, were confirmed to have a high pest status. They accounted for the community structure pattern in the black wattle growing areas of KwaZulu-Natal. The remaining seven species, Heteronychus licas, undescribed Maladera sp. 1, and M5, M10, M11, M12 and M13 (all unknown species), contributed only 3.6 % to the average cumulative abundance and were considered to be minor pests within the whitegrub community structure.