The occurrence of weeds and the composition and abundance of predatory arthropods in newly sown maize fields in the Central Province of Papua New Guinea

Weeds, epigeal predatory arthropods and their interactions were studied in two maize fields at Laloki/ Port Moresby, Papua New Guinea (PNG) with two methods: 1), 10 pitfall traps per field, which were emptied weekly, and 2), 10 squares of 0. 1 m(2) per field which were sampled for predatory arthropods at three dates. The biodiversity of epigeal predatory arthropods was determined in arable fields in PNG for the first time. The weed flora of the fields, three weeks after sowing, covered nearly 100 % of the soil surface and consisted mainly of seven weed species, Rottboellia exaltata (Poaceac) prevailing. 8,447 predatory arthropods were caught in 20 pitfall traps. Predatory beetles proved to be very rare in the traps (in contrast to Europe and other tropical fields, no carabids were found at all), while ants were significantly dominating with 89.9 %. Spiders were 6.8 %, while gryllids, earwigs and predatory bugs were rather rare. The weed cover, increasing during the study, influenced negatively the activity of the most common ant species (Oligomyrmex sp.). Per m(2), ants formed 65.2 % of all predators, and spiders 32.3 %. In total, 34 specimens of predatory arthropods occurred per m(2), with a dry bio-mass of 36 mg/ m(2). The results are discussed, concerning the necessity of weed control, and also the density and composition of predatory arthropods.