Abstract. Arthropod predators and parasitoids provide valuable ecosystem services in agricultural crops by suppressing populations of insect herbivores. Many natural enemies are influenced by non-crop habitat surrounding agricultural fields, and understanding if, and at what scales, land use patterns influence natural enemies is essential to predicting how landscape alters biological control services. Here we focus on biological control of soybean aphid, Aphis glycines Matumura, a specialist crop pest recently introduced to the north-central United States. We measured the amount of biological control service supplied to soybean in 26 replicate fields across Michigan, Wisconsin, Iowa, and Minnesota across two years (2005)(2006). We measured the impact of natural enemies by experimentally excluding or allowing access to soybean aphid infested plants and comparing aphid population growth over 14 days. We also monitored aphid and natural enemy populations at large in each field. Predators, principally coccinellid beetles, dominated the natural enemy community of soybean in both years. In the absence of aphid predators, A. glycines increased significantly, with 5.3-fold higher aphid populations on plants in exclusion cages vs. the open field after 14 days. We calculated a biological control services index (BSI) based on relative suppression of aphid populations and related it to landscape diversity and composition at multiple spatial scales surrounding each site. We found that BSI values increased with landscape diversity, measured as Simpson's D. Landscapes dominated by corn and soybean fields provided less biocontrol service to soybean compared with landscapes with an abundance of crop and non-crop habitats. The abundance of Coccinellidae was related to landscape composition, with beetles being more abundant in landscapes with an abundance of forest and grassland compared with landscapes dominated by agricultural crops. Landscape diversity and composition at a scale of 1.5 km surrounding the focal field explained the greatest proportion of the variation in BSI and Coccinellidae abundance. This study indicates that natural enemies provide a regionally important ecosystem service by suppressing a key soybean pest, reducing the need for insecticide applications. Furthermore, it suggests that management to maintain or enhance landscape diversity has the potential to stabilize or increase biocontrol services.

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Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), reached damaging levels in 2003 and 2005 in soybean, Glycine max (L.) Merrill, in most northern U.S. states and Canadian provinces, and it has become one of the most important pests of soybean throughout the North Central region. A common experimental protocol was adopted by participants in six states who provided data from 19 yield-loss experiments conducted over a 3-yr period. Population doubling times for field populations of soybean aphid averaged 6.8 d +/- 0.8 d (mean +/- SEM). The average economic threshold (ET) over all control costs, market values, and yield was 273 +/- 38 (mean +/- 95% confidence interval [CI], range 111-567) aphids per plant. This ET provides a 7-d lead time before aphid populations are expected to exceed the economic injury level (EIL) of 674 +/- 95 (mean +/- 95% CI, range 275-1,399) aphids per plant. Peak aphid density in 18 of the 19 location-years occurred during soybean growth stages R3 (beginning pod formation) to R5 (full size pod) with a single data set having aphid populations peaking at R6 (full size green seed). The ET developed here is strongly supported through soybean growth stage R5. Setting an ET at lower aphid densities increases the risk to producers by treating an aphid population that is growing too slowly to exceed the EIL in 7 d, eliminates generalist predators, and exposes a larger portion of the soybean aphid population to selection by insecticides, which could lead to development of insecticide resistance.

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yellow, and even drop. Other symptoms of direct feeding damage include plant stunting, poor pod fill, reduced Since 2000, the soybean aphid (Aphis glycines Matsumura) has pod and seed counts, smaller seed size, and nutrient become a major pest of soybean [Glycine max (L.) Merr.] in North America. In the USA, there are currently no commercial soybean deficiencies resulting in overall yield and quality reduccultivars with aphid resistance and there are no reported resistance tion (DiFonzo and Hines, 2002). Significant yield loss sources in early maturing soybean germplasm. The objectives of this (8-25%) occurs when the soybean plants are heavily study were to identify sources and types of resistance to soybean aphid infested by the aphid during the early reproductive stage from early maturing soybean germplasm. Over a 2-yr period, 2147 (DiFonzo and Hines, 2002). Honeydew, a sticky subsoybean accessions from maturity group (MG) 0 to III, originally stance excreted by soybean aphids onto the leaves, leads from northern China, were evaluated for aphid resistance in a greento the development of sooty mold, which affects photohouse and in field cages. The plants were hand-inoculated and aphid synthesis and results in yield loss (Baute, 2004). During populations were evaluated 10 d after inoculation. A damage index the feeding process, soybean aphids are capable of trans-(0-100%) was calculated for each accession. After 2 yr of evaluation mitting viruses including Alfalfa mosaic virus, Soybean and confirmation in choice tests, four MG III accessions from Shandong province, PI 567543C, PI 567597C, PI 567541B, and PI 567598B, mosaic virus, and Bean yellow mosaic virus. These viwere found to be resistant to the soybean aphid. Two of these acces-ruses commonly occur together and form a disease comsions, PI 567541B and PI 567598B, possessed antibiosis resistance,plex that leads to plant stunting, leaf distortion and preventing the aphids from reproducing on the plants in a no-choice mottling, reduced pod numbers, and seed discoloration study. PI 567543C and PI 567597C possessed antixenosis resistance.