The epigeal predatory arthropods in aubergine fields at South Sumatra (Indonesia) with regard to the plant cover and the use of insecticides Vorkommen der epigäischen Raubarthropoden in Auberginenfeldern Süd-Sumatras (Indonesien) unter Berücksichtigung der Pflanzenbedeckung und der Anwendung

For the first time, the predatory arthropods of aubergine fields in South Sumatra, Indonesia, were studied by pitfall trapping and by square flooding in two four-week periods; first, early after transplanting, and second, during harvest. Plant cover and insecticide use were very low in the first (I) and high in the second period (II). In 20 pitfall traps were caught (I) 3,794, and (II) 2,875 specimens of predatory arthropods. The high number in period I was mainly due to Pheidole sp. The frequency of two predator groups decreased significantly from period I to period II, and further six groups showed the same tendency of decrease. But the frequency of 12 other predator groups increased from period I to II. Concerning the ants Pheidole sp. and Tapinoma sp., square samples revealed that apparently the temperature on bare soil stimulated a high activity and also a high abundance. Both species were not negatively affected by the insecticide sprays. In all, the effects of the seven weekly insecticide sprays on the epigeal predators proved to be low, presumably mainly due to the plant cover. The average predator numbers per m2 were 18.1 (with 5.8 mg/m2) (period I), and 70 (with 13.7 mg/m2) (period II). Over both periods, spiders were represented in traps/squares with 23.2/25.9 % of all predators, ants with 59.3/46.1 % and gryllids with 10.5/15.3 %. All other predator groups shared less than 10 %. Ants (Formicidae) were represented with 17 genera, spiders (Araneae) with ten families. The results are discussed concerning the low effect of the insecticides on the epigeal predators, and the effects of plant cover of soil.