NCR - 125 Arthropod Biological Control
State Reports for 2004
| Iowa - project reports |
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Project Title: The Effect of Perennial Cover Crops on Natural Enemy Communities in Corn and Soybeans Investigators: Nicholas Schmidt1, Jeremy
Singer2, Keith Kohler2, Jarrad Prasifka3,
Richard Hellmich3, Matthew O’Neal1 Contact: Matthew O’Neal (oneal@iastate.edu) Project Description: Annual cropping systems are often unfavorable environments for natural enemies due to limited habitat suitability. Cover crops can diversify the agroecosystem, enhance the survival of natural enemies, and improve their efficiency as pest control agents. We determined the impact of two perennial forages, alfalfa (Medicago sativa) and kura clover (Trifolium ambiguum), used as a cover crop for corn and soybeans on arthropod natural enemies. Replicated plots (4 replications each, 20 m long and 4 m wide) of corn and soybean were planted within both alfalfa and kura clover and as a check planted without a cover crop, in a split-plot design, with cover crop as the split factor. In addition, we included treatments of each forage crop planted alone, for a total of 32 plots. We monitored the natural enemy community from mid-June to mid-October, 2004 with pitfall traps and yellow sticky traps; both traps deployed for 72 hours every 4 weeks. From the June and July samples we observed a significant impact on ground beetle and spider abundance, with greater densities found in corn and soybean planted within a cover crop. In addition, greater sentinel prey (European corn borer pupae) was removed when annual crops were grown with a cover crop. Future research questions include: do forage cover crops enhance soybean aphid natural enemies, and can the inclusion of a cover crop reduce soybean aphid establishment and populations growth? Project Title: Natural enemy community in soybeans and their response to insecticides applied for soybean aphid management. Investigators: Nicholas Schmidt, Kevin Johnson, Matthew O’Neal; Department of Entomology, Iowa State University, Ames Iowa. Contact: Matthew O’Neal (oneal@iastate.edu) Project Description: Natural enemies can play a key role in suppressing soybean aphid populations both in the US and in their native range of China. Iowa soybean fields contain many aphid predators, yet large populations of aphids (> 1,000/plant) have occurred in two of the past four years. In 2004, we began sampling the natural enemy community within soybean plots while monitoring for soybean aphids. We conducted weekly and monthly surveys using a variety of sampling methodologies (yellow sticky traps, pitfall traps, sweep-net sampling, whole plant counts and destructive plant samples) to determine natural enemy diversity and density from planting (May) to post-harvest (October). Although we collected data on several taxa, identifying these to family and genus when possible, our focus is on lacewings, coccinellids, and Hemiptera (Orius insidiosus) that can be a significant source of aphid predation. This variety of methods is focused on both actively foraging predators (adult coccinellids, adult syrphids, etc) as well as more sedentary natural enemies of soybean aphids (O. insidiosus, coccinellid larvae). In 2004, we observed a diverse community, with lacewings being the most frequently encountered natural enemy. From linear regression models, variation in the abundance of green lacewings (Chrysoperla spp.) explained the greatest amount of variation in soybean aphid densities (r2 = 0.86). Although lacewing eggs were abundant, larval and adult stages were not observed, suggesting some degree of intra-guild predation. After lacewings, O. insidiosus and Harmonia axyridis were the two most common species collected, with all life-stages present. We did collect a species of parasitoid wasp, although these were limited to heavily infested plants (500+ aphids/plant) with low levels of parasitism (>1%). A single application of lamda cyhalothrin (Warrior, Syngenta) on 8 August reduced the total natural enemy abundance by 43% + 0.08 (average total abundance +SEM) of the total collected in untreated controls. Project Title: Pupal survival of Galerucella spp. (Coleoptera: Chrysomelidae): effects of soil moisture on eclosion. Investigators: Bethzayda Matos1 and
John J. Obrycki2 Contact: Bethzayda Matos (bmatos@iastate.edu) Project Description: Several studies have suggested that flood regimens, landscape features, and predatory fauna have inhibited the success of Galerucella spp. released for biological control of purple loosestrife (Lythrum salicaria). In the field, we observed varying numbers of Galerucella in wetter vs drier areas of purple loosestrife infestations. Our objective was to determine if soil moisture affects pupal survival and adult emergence of Galerucella spp. We chose three treatments, 0, 30, and 60% soil moisture. We used 18 paper cups (16 oz, Sweetheart®) with 32 ± 0.7 g (mean SD) of potting soil mix. Each container had 5 pupae (6 cups of 5 pupae), which were placed at 2 cm deep. The paper cups were covered with clear plastic cups that were placed upside down to prevent adults from escaping. All the cups were placed in a growth chamber at 24 ±1° C temperature and 16:8 (L:D) photoperiod. The experiment was replicated 3 times. Soil moisture was determined using with a ThetaProbe® Soil Moisture Sensor (Delta-T Devices LTD). More than 50% of the pupae survived (adults eclosed from the soil) at 0 and 30% soil moisture. No adults emerged from the 60% soil moisture treatment. Soil moisture is one factor that may influence generational survival of Galerucella spp. in the field. Back to top of web page |
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