Effects of Weeds on the Diversity and Abundance of Insects in Soybeans1

Abstract

Sweep-nel sampling and pilfalllrapping were used 10 survey insects in weedy and weedfree soybean habitals. Weedy soybean habitats consisted of (I) grassy soybeans; (2) soybeans with broad leaf weeds; and (3) soybeans with broadleaf weeds and grasses. Insect species diversity was greater in weedy soybean habitats than in weed-free soybeans. Greatest diversity of species occurred in Ihe mixed-weed soybean habitat. The most imponant phytophagous insect on soybeans in Indiana, the Mexican bean beetle, Epilachlla varivestis Mulsant, was mOSI abundanl in weed-free soybeans. Predators were mosl ahundanl in weedy soybeans. Coit'omeKilla marl/lata (DeGeer) was mllsl abundant in weedy soybean habitats, whereas Orius insidiosus (Say) and Nabis spp. were most abundant in soybean habitats with grasses and mixed weeds. In the pitfall trapping study, Harpalus spp. were more abundant in soybean habitats with grasses and mixed broad leaf and grass weeds. I 1 IAnnual weeds arc often a major component of soybean fields, yet little is known of insect-weed interactions in soybeans. Several studies indicated that weeds increase the diversity and abundance of insects in soybeans. Balduf (1923) surveyed thc in~cct fauna of soybeans and surrounding vegetation in Ohio. He reported that most of the 209 species collected were associated with weeds. In Minnesota, Kretzschmar (1948) reported that weedy soybeans had a larger and more diverse insect fauna than weed-free soybeans. In Arkansas, Tugwell et al. (1973) made sweep-net collections in soybeans and a weed host, Desmodium sp., growing adjacent to the soybeans. Of 133 species collected from Desmodium sp., 93 were also collected on soybeans.Although plant species diversity is generally associated with a diverse insect fauna, monocultures sometimes support a greater herbivore load than diverse plantings. Pimental (1961) and Smith (1976) found that colonizing aphids were more attracted to weed-free brussels sprouts, Brassica oleracea L., than sprouts grown with weeds. Tahvanainen and Root (1972) suggested that diverse vegetational communities exude so many different chemicals that herbivores may be confused and consequently seek simpler floral systems.This study was conducted to determine how annual weeds affect the diversity and abundance of insects in soybeans. Materials and MethodsResearch was conducted in southern Indiana during the summers of 1978 and 1979. The study area was a 5.7-ha field which had been in continuous soybeans for several years. The field was divided into 12 plots (30.5 by 30.5 m), with each of the four treatments (weed-free, broadleaf weeds, grass weeds, and mixed weeds) rep-' licated three times in a randomized complete block design.TrifJuralin (1.75 liters/ha) was applied preplant to broadlcaf-weed plots to control grasses, and metribuzin (0.83 kg/ha) was applied preplant to grass-weed plots to control broadleaf weeds. Weed-free plots and border areas were kept virtually weed free by preplant application of metribuzin and trifJuralin at the rate above, ...

Weed Management in Soybean — Issues and Practices

“…Overall, monoculture areas tend to present higher mites and pest infestation and reduced biological diversity when maintained free of weeds. At the same time, weeds help insect diversity and natural biological control [46]. Mites, important arthropods in agricultural systems, currently constitute themselves key pests for soybeans in regions of hot and dry weather.…”

Ocorrência de insetos na parte aérea da soja em função do manejo de plantas daninhas em cultivar convencional e geneticamente modificada resistente a glyphosate

“…Vários autores mencionam que o controle adequado de plantas daninhas pode afetar a abundância de artrópodes pragas (SHELTON & EDWARDS, 1983;BUNTIN et al, 1995;LAM & PEDIGO, 1998). SHELTON & EDWARDS (1983) verificaram que na soja livre de plantas daninhas ocorreu maior número de pragas e na presença destas plantas predominaram espécies predadoras.…”

Effect of soil management on the white grub population and damage in soybean

“…However, in some cases, these organisms were associated with the occurrence of a specific type of weed (Shelton & Edwards, 1983). The majority of these studies did not mention increases in economic damage, caused by arthropods in soybean fields where soil conservation practices were adopted (Stinner & House, 1990).…”