Arthopoda predator penghuni permukaan tanah di pertanaman kedelai: kelimpahan, pemangsaan,dan pengaruh praktek budidaya tanaman

Abstract

Penelitian dilakukan pada pertanaman kedelai di Kecamatan Ciranjang, Kabupaten Cianjur pada MT 1997 dan 1998, dan di Kecamatan Lemahabang, Kabupaten Karawang pada MT 2000. Penelitian bertujuan untuk menentukan komposisi dan kelimpahan artropoda predator penghuni permukaan tanah dan tekanan pemangsaannya, dan mengkaji pengaruh beberapa praktek budidaya tanaman seperti mulsa jerami dan aplikasi insektisida dan herbisida. Kelimpahan predator diamati menggunakan lubang perangkap, dan tekanan pemangsaan dievaluasi menggunakan larva dan pupa Spodoptera litura (F.) sebagai mangsa umpan. Hasil penelitian menunjukkan bahwa pada permukaan tanah di pertanaman kedelai ditemukan lebih dari 15 jenis artropoda predator. Dua jenis yang paling dominan di Cianjur adalah laba-laba serigala Pardosa pseudoannulata (Boes. & Str.) (Araneae: Lycosidae) dan kumbang tanah Pheropsophus occipitalis (MacLeay) (Coleoptera: Carabidae), sedangkan di Karawang hanya jenis yang disebut pertama yang dominan. Demikian juga tekanan pemangsaan di Cianjur sekitar 9 kali lipat lebih tinggi daripada di Karawang. Perbedaan dominasi dan tekanan pemangsaan ini diduga berhubungan dengan perbedaan struktur lansekap dan intensitas penggunaan insektisida di kedua tempat tersebut. Kelimpahan artropoda predator penghuni permukaan tanah di Cianjur pada MT 1997 lebih rendah dibandingkan MT 1998, demikianjuga halnya dengan. detritivor seperti colembolan dan tungau.

Cianjur during the two soybean growing seasons of 1997 and 1998, and in the sub district of Lemahabang, Karawang during 2000. The objectives were to determine the composition and abundance of ground surface dwelling predatory arthropods and their predation pressure, and to evaluate the effects of some cultural practices, i.e. straw mulching, and insecticide and herbicide applications. Ground surface dwelling predatory arthropods were monitored using pitfall traps, and their predation pressure was evaluated using larvae and pupae of Spodoptera litura (F.) as baits. Our research revealed more than 15 species of ground-dwelling predators. The most dominant predators in Cianjur were wolf spider Pardosa pseudoannulata (Boes. & Str.) (Araneae: Lycosidae) and ground beetle Pheropsophus occipitalis (MacLeay) (Coleoptera: Carabidae), whereas in Karawang only the first mentioned species. Predation pressure in Cianjur was 9 times higher than those in Karawang. The differences in species dominance and predation pressure were thought to be related to differences in landscape stuctures and intensity of pesticide uses between the two locations. Abundance of ground-dwelling predators in Cianjur during 1997 growing season was much lower compared to those during 1998, and the same with the detritivores such as collembolans and mites. Predation pressure on lepidopteran larvae placed on soil surface reached 18 individuals per 2 hours which was mostly caused by ground beetles, whereas on pupae 10 individuals per 2 hours caused by shrew. Predation pressure on larvae at distance of 1 m from field bunds were 5 times higher than those placed at 5 m. Predation occurred mostly during the night. Some of the predators climbed the soybean canopy to prey the larvae. Predation pressure decreased with the increasing size of canopy. Incorporation of straw mulch onto soil surface inreased abundance of wolf spiders, dwarf spiders, and ants. The increase of predator population generally occurred several days following mulching. Conversely, burning of straw caused deleterious effects on predators. Immediatelly after burning, abundance of wolf and dwarf spiders, ants, and rove beetles decreased 66 up to 100%, but then they recovered due to recolonization. The negative impacts will last longer if burning covers large areas.