Developing a decision-making framework for insect pest management: a case study using Aphis glycines (Hemiptera: Aphididae).

BACKGROUND: The profitability of farming varies based on factors such as a crop's market value, input costs and occurrence of resistant pests, all capable of altering the value of pest management tactics in an integrated pest management program. We provide a framework for calculating expected yield and expected net revenue of pest management scenarios, using the soybean aphid (Aphis glycines) as a case study. Foliar insecticide and host-plant resistance are effective management tactics for preventing yield loss from soybean aphid outbreaks; however, pyrethroid-resistant aphid populations pose a management challenge for farmers. We evaluated eight scenarios relevant to soybean aphid management in Iowa with varying probabilities of aphid outbreaks and insecticide-resistant aphids occurring. RESULTS: Our equation suggests that insecticide use is profitable when the probability of an aphid outbreak is ≥29%, and soybean production will become more costly with increasing probability of pyrethroid-resistant aphids. If farmers continue to use pyrethroids, they will not experience financial consequences from pyrethroid-resistant aphids until the chance of insecticide resistance is 48%. Aphid-resistant varieties provided consistent yield and offered the highest net revenue under all conditions. CONCLUSION: This framework can be used for other crop-pest systems to evaluate the profitability of management tactics and investigate how resistance impacts revenue for farmers. Including the cost of resistance in crop budgets can help farmers and agronomic consultants comprehend these impacts and enhance decision-making to increase revenue and curb resistance development.

Evaluating Soybean Aphid-Resistant Varieties in Different Environments to Estimate Financial Outcomes.

Farmers face many choices when selecting seed for soybean (Glycine max (L.) Merr.) production, including highly desired herbicide tolerance traits. Despite the convenience of herbicide tolerance, resistant weeds and technology fees may reduce utility and profitability of these varieties, especially when commodity prices are low. Sporadic outbreaks of soybean aphid (Aphis glycines Matsumura, Hemiptera: Aphididae) that require insecticide use for optimal yield can be a further complication for farmers in Iowa. Soybean aphid-resistant varieties are commercially available, but in limited genetic backgrounds without herbicide tolerance. We hypothesized yield and value of resistance traits will vary based on the environment. We established plots at two locations with different risks of soybean aphid outbreaks and used two planting dates at each location to mimic different yield environments. In 2016 and 2017, we planted four varieties that varied in their susceptibility to soybean aphids and glyphosate, and applied insecticides if aphid populations reached an economic threshold. Regardless of genetic background, aphid-resistant varieties prevented populations from reaching the economic threshold at all environments. We observed no significant difference in yield between resistant and susceptible varieties, revealing this trait is as effective at protecting yield as an insecticide application on susceptible varieties at the high-risk location. We also explored the value of each variety in different environments. Resistant varieties produced greater potential net revenue than susceptible varieties at the high-risk location, while the opposite occurred at the low-risk location. Resistant varieties with herbicide tolerance, if made available, would be the most valuable across all environments.