The Macro-arthropod Community of Sugarcane Fields and of Cyperus Immensus Stands

Arthropods associated with sugarcane seven to eleven months old, and with the sedge Cyperus immensus (C.B.CL.) were collected at two monthly intervals over a fifteen month period. The search was carried out in each of four regions in the sugar industry. This work formed part of a project designed to study the predators of the sugarcane borer Eldana sacckarina Walker. Generally greater number of arthropods were found on stools of C. immensus than on sugarcane. It is suggested that the lower numbers of arthropods associated with sugarcane may be related to agricultural practices. Of the twenty taxa identified, the Formicidae and Araneida were the m'ost abundant. These two taxa are considered to include the more important predators of E. saccharina primarily because of their abundance. In all regions the highest numbers of arthropods were collected in April 'or June. The recording of the highest numbers of arthropods in samples collected in these two months may be associated with peaks in a number of climatic factors recorded in preceding months. Sampling method Vacuum sampling was found to be cumbersome-and unsuitable because moderately sized arthropods could avoid capture. Hand sampling allowed the collection of large as well as small arthropods (of a few millimeters in size). A third technique was tested. A plastic tent was placed over a stool and a fumigant insecticide released beneath it. After a suitable period the tent was removed and the stool carefully examined for arthropods. However, this technique also was Introduction In a study of the insect pests d a crop, a knowledge of the arthropod cc~mmunity is important. The work reported here concerns an examination (of the arthropods present in two plant communities, those of sugarcane and of the sedge Cyperus immensus (C.B.CL.) . The sugarcane borer Eldana Sacch,arina Walker occurs in both communities, C. immensus being the preferred wild host (Atkinsonl and Carnegie and Smaill". This borer is currently the major pest of the South African sugar industry and causes severe damage to sugarcane stalks in certain regions. The surveys discussed below form part of a larger project in which natural predators of E. saccharina were examined. They were designed to answer the following questions : 1. What arthropods occur in the two communities ? 2. Are there any differences in the taxa recorded from the two communities ? 3. Are there any seasonal or geographical trends in arthropod distribution ? 4. Which arthropods recorded are potential predators of E. Saccharins ? Methods Surveys were conducted in four regions of the sugar industry. These were the Eastern Transvaal region, the North Inland region, the North Coastal region, and the South Coastal region (see Figure 1 ). The choice of sampling sites within each region was dictated by several factors, the most important of which was stool size. Stools of sugarcane having approximately fifteen stalks and ten to sixteen joints per stalk were sampled. Similarly C. immensus stools comprising twenty to thirty stalks were having these characteristics be FIGURE I Regions of the Sugar Industry from which samples of arrhrosampled efficiently. pods were collected. T R A N S V A A L