Erin W. Hodgson

Economic Threshold for Soybean Aphid (Hemiptera: Aphididae)

Abstract 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.

Probability of Cost-Effective Management of Soybean Aphid (Hemiptera: Aphididae) in North America

ABSTRACT Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is one of the most damaging pests of soybean, Glycine max (L.) Merrill, in the midwestern United States and Canada. We compared three soybean aphid management techniques in three midwestern states (Iowa, Michigan, and Minnesota) for a 3-yr period (2005–2007). Management techniques included an untreated control, an insecticidal seed treatment, an insecticide fungicide tank-mix applied at flowering (i.e., a prophylactic treatment), and an integrated pest management (IPM) treatment (i.e., an insecticide applied based on a weekly scouting and an economic threshold). In 2005 and 2007, multiple locations experienced aphid population levels that exceeded the economic threshold, resulting in the application of the IPM treatment. Regardless of the timing of the application, all insecticide treatments reduced aphid populations compared with the untreated, and all treatments protected yield as compared with the untreated. Treatment efficacy and cost data were combined to compute the probability of a positive economic return. The IPM treatment had the highest probability of cost effectiveness, compared with the prophylactic tank-mix of fungicide and insecticide. The probability of surpassing the gain threshold was highest in the IPM treatment, regardless of the scouting cost assigned to the treatment (ranging from

Biology of the Soybean Aphid, Aphis glycines (Hemiptera: Aphididae) in the United States

0.00 to

Management Recommendations for Soybean Aphid (Hemiptera: Aphididae) in the United States

19.76/ha). Our study further confirms that a single insecticide application can enhance the profitability of soybean production at risk of a soybean aphid outbreak if used within an IPM based system.

Alate Production of Soybean Aphid (Homoptera: Aphididae) in Minnesota

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a significant insect pest of soybean in the north-central region of the United States and southern Canada, and if left untreated can reduce yield value by

Drought impact on crop production and the soil environment: 2012 experiences from Iowa

2.4 billion annually. The soybean aphid is native to eastern Asia, where soybean was first domesticated, and was first detected in the United States in 2000. It quickly spread within 4 years of its discovery across 22 states and three provinces of Canada. Heavy infestations can result in a covering of sooty mold, yellow and wrinkled leaves, stunted plants, and aborted pods leading to significant yield loss of 40% or more. It can also transmit plant viruses such as Soybean mosaic virus and Alfalfa mosaic virus. The soybean aphid has a complex life cycle that involves different physical forms, sexual stages, and two host plant species-soybean and buckthorn (the overwintering host). Plant nutrition, natural enemies, climate, and weather all affect population growth rate, but the typical population doubling time is ≈6-7 days. Though at present management is primarily through broad-spectrum insecticides, biological control has a significant impact on soybean aphid population growth, and aphid-resistant soybean varieties are becoming increasingly available.

Effects of the insect growth regulator, novaluron on immature alfalfa leafcutting bees, Megachile rotundata

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is the primary pest of soybean, Glycine max L., in the north central region. After more than a decade of research and extension efforts to manage this pest, several consensus management recommendations have been developed for sustainable and profitable soybean production. A summary of integrated pest management (IPM) tactics for soybean aphid are discussed, including cultural, genetic, economic, and chemical controls. To date, sampling and timely foliar insecticides are routinely recommended to protect yield and delay genetic resistance to insecticides. Host plant resistance is a new tool that can regulate populations and reduce the reliance of insecticides to control soybean aphid. A combination of these management tools also will reduce overall production costs and minimize negative environmental effects such as human exposure, and mortality of beneficial insects and other animals.

Pan trapping for soybean aphid (Homoptera: Aphididae) in Minnesota soybean fields

Abstract The soybean aphid, Aphis glycines Matsumura, is a serious pest in Midwestern soybean, Glycine max L. Merrill, and has the potential to colonize a large geographic range throughout a single growing season. Our objectives were to describe colonization patterns on a statewide spatial and temporal scale, examine the changing proportion of winged forms throughout a season, and assess photoperiod as a potential trigger for alate production. In Minnesota, we define initial colonization as the period of time during the early vegetative growth when alates were present and alatoid nymphs were absent on soybean. Initial colonization during 2002 and 2003 was ∼2 wk. On average across Minnesota, summer migrants were first produced when most fields were at the initial flowering stages in 2002. In 2003, an outbreak year, initial detection of summer migrants occurred earlier during vegetative stages before flowering. The significant increase in the proportion of all potential migratory forms (i.e., alatoid nymphs and adults) occurred during the beginning of seed set for both years. During seed set, the mean proportion of alate A. glycines was 0.15 ± 0.04 (SE) in 2002 and 0.16 ± 0.06 in 2003. The mean proportion of alatoid nymph A. glycines was 0.14 ± 0.04 in 2002 and 0.29 ± 0.04 in 2003 during seed set. The total mean proportion of migratory forms was higher when the critical L:D photoperiod was 14.5:9.5 h/d. A regression analysis also indicated the proportion of winged A. glycines increased with decreasing photoperiod.

Abundance of Soil-Borne Entomopathogenic Fungi in Organic and Conventional Fields in the Midwestern USA with an Emphasis on the Effect of Herbicides and Fungicides on Fungal Persistence

Enormous challenges were presented by the 2012 drought. Poor water availability and high temperatures resulted in significant stress during critical phases of corn (Zea mays L.) and soybean (Glycine max L.) development. These stress factors lead to management challenges with insects, diseases, and reduced nutrient availability and uptake by plants. The drought triggered soil changes, particularly in conventional tillage systems, such as increased fracturing, crusting, and deterioration of soil structure and aggregation. All this reinforced the need for soil conservation planning, especially its necessary role in buffering against unpredictable conditions and the impacts of dry and wet events on production and soil quality. In 2011, the USDAs National Drought Mitigation Center reported that 43% of Iowa experienced moderate-drought conditions and nearly 10% experienced severe-drought conditions. In 2012, 100% of Iowa experienced severe-drought conditions, while 65% experienced extreme-drought conditions by October. This article addresses several effects of drought on soil and crop production and lessons learned that will help develop appropriate drought mitigation strategies for future soil and crop management practices. The 2012 drought created unfavorable soil conditions for plant development and growth and changes in soil structure in many areas in the Midwest. These changes in soil structure included fracturing…

Evidence for Soybean Aphid (Hemiptera: Aphididae) Resistance to Pyrethroid Insecticides in the Upper Midwestern United States

Abstract Alfalfa leafcutting bees, Megachile rotundata F. (Hymenoptera: Megachilidae), are the most common pollinators of alfalfa in the Pacific Northwest. Reports from users of M. rotundata in Idaho, Utah and Colorado have indicated exceptionally poor bee return from fields treated with novaluron to control Lygus spp. Our goal was to evaluate novaluron toxicity to immature M. rotundata using two different possible mechanisms of exposure. One goal was to assess immature mortality via treating nectar-pollen provisions and adults with novaluron. Immature M. rotundata mortality in all novaluron provision dosing treatments was significantly higher than the water or blank controls, providing evidence that novaluron is toxic to progeny in nest cells. The mean cumulative frequency showed that more eggs and 1st–2nd instars died compared to older instars. Female M. rotundata nested similarly in field cages during the field cage experiment; however, there was greater immature mortality in cages where females were fed sugar-water + novaluron compared to sugar-water only. Although females provided adequate provisions, there was a low percentage of egg hatch and larval development when females ingested novaluron before mating and nesting. Novaluron was also present in egg provision of bees collecting resources from novaluron-sprayed plants. At least 84% of progeny died when the females were allowed to mate and nest 24 hours after a novaluron application. Novaluron could be contributing to poor bee return in alfalfa grown for seed. Timely insecticide applications to suppress Lygus spp. is an important consideration to improve ongoing bee health.