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The use of neonicotinoid insecticides in the United States has grown by about a factor of four since the mid-2000s. Seed treatments account for a significant fraction of overall insecticide application to crops, and a large proportion of major U.S. crops are now planted using seed treated with neonicotinoids. Neonicotinoid insecticidal seed treatments are primarily intended to protect crops against sporadic or minor early-season pests. A better understanding of factors that influence the risk of economic infestations and extent of crop damage by sporadic pests is needed to target neonicotinoid insecticidal seed treatments use based on expected pest pressure. In a series of papers, we review the distribution, ecology, and historical management of seed and seedling pests targeted by neonicotinoid seed treatments in U.S. corn (Zea mays), soybean (Glycine max), wheat (Triticum aestivum), and cotton (Gossypium hirsutum L.). This information is key to region-specific management practices that reduce the risks and increase the benefits of neonicotinoid seed treatments.

The use of insecticides at planting has been a common crop management practice in cotton for several decades. Historically, U.S. cotton growers relied on in-furrow applications of insecticides, such as aldicarb, to control early-season insect pests. In-furrow applications have largely been replaced with insecticide-treated seed. Since 2012, more than 60% of the U.S. cotton crop is planted with seed treated with insecticide, primarily the neonicotinoids imidacloprid or thiamethoxam. Several insects or insect groups are included on the labels of these neonicotinoids for use as seed treatments. An increased understanding of the risks associated with economically injurious populations of insect pests is needed to optimize use of early-season insecticides and reduce over-reliance on them in cotton, especially when initial decisions for insect control before planting have subsequent influence on future pest abundance. Existing literature pertaining to these early-season cotton insect pests was examined to identify factors favoring their distribution and abundance and the importance of insect control tactics used at planting. The relative importance of some of these pests is dependent on the cotton-growing region and impacted by local production practices. Thrips (predominantly Frankliniella spp.) (Thysanoptera: Thripidae) are the most prevalent early-season insect group in cotton across the United States and the primary target of initial insect control. Other targeted insects include the black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), aphids (predominantly Aphis gossypii Glover) (Hemiptera: Aphididae), plant bugs (Hemiptera: Miridae), and wireworms (Coleoptera: Elateridae).

Soybean faces potential economic damage from a wide variety of early-season invertebrate pests. The objective of this article was to determine the extent and intensity of nine early-season soybean insect pests targeted for control by insecticidal seed treatments in the United States and to identify various management options for them: bean leaf beetle (Cerotoma trifurcate Förster, Coleoptera: Chrysomelidae); grape colaspis, Colaspis brunnea (F.) (Coleoptera: Chrysomelidae); leafhoppers (Hemiptera: Ciccadellidae); seedcorn maggot, Delia platura (Meigen) (Diptera: Anthomyiidae); soybean aphid (Aphis glycines Matsumura, Hemiptera: Aphididae); threecornered alfalfa hopper, Spsistilus festinus (Say) (Hemiptera: Membracidae); thrips (Thysanoptera: Thripidae); white grubs (Coleoptera: Scarabaeidae); and wireworms (Coleoptera: Elateridae). Seedcorn maggot, white grubs, and wireworms have been limited to a relatively small proportion of soybean fields with readily defined factors regarding their risk. However, questions about the pest status of the other six pests were identified. Bean leaf beetle, which vectors Bean pod mottle virus to soybean, has been present across major soybean-production regions, but frequency and proportion of soybean fields that economically impacted is not adequately documented. The impact of threecornered alfalfa hopper and thrips on soybean productivity varied within regions, but specific reasons for the variation were unclear. Early-season management of grape colaspis and leafhoppers has been infrequent, but factors that promoted economic injury and the need for management in specific fields were undetermined. Although early-season management of soybean aphid has not proven feasible for individual fields, questions remain regarding its management in fields near overwintering stands and the possibility for areawide suppression.

A preventative insecticide treatment is a tactic compatible with an integrated pest management (IPM) strategy for a particular pest only when a rescue treatment is not a realistic option, and if there is a reasonable expectation of economic damage by that pest. Most corn, Zea mays L., planted in the United States is protected from several sporadic early-season insect pests by neonicotinoid seed treatments, usually without the knowledge of the threat posed in a given field. We undertook an extensive literature review of these sporadic pests to clarify the prevalence of economic infestations in different regions of the United States, and the agronomic, biotic, and abiotic factors that affect the likelihood of attack. The summaries of the prevalence and risk factors presented here should help farmers and consultants better assess the value of preventative protection of seedling corn under local conditions, and provide others with a better understanding of the complexities farmers face in assessing risks posed by potential pests. The profiles suggest that, in general, pressure from most sporadic pests on seedling corn is rare or local, seldom high enough to decrease yield. However, this is not true in all regions for all sporadic pests. An important issue exposed by the profiles is that the value of preventative insecticide protection of seedling corn depends on understanding the likely combined pressure from multiple species. While such risk may often still be negligible, there is a great need for robust methodology to assess the risk posed by multiple pests. This represents a significant challenge for future research.

The Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae); cereal aphids (Hemiptera: Aphididae); and wireworms (Coleoptera: Elateridae) are three common and important insect pests of seedling wheat, Triticum aestivum L., in the United States. Though less common as pests, false wireworms (Coleoptera: Tenebrionidae) may also be problematic in situations that favor wireworms. In addition, cereal aphids vector viruses that cause barley yellow dwarf, a serious and widespread wheat disease. Scientific journal publications, review articles, and management guidebooks on wheat insect pests were consulted to determine the extent and intensity that these pests impose on wheat production in the United States. Widespread outbreaks occur infrequently, but local outbreaks happen nearly every year for the three major pests and cause several millions of dollars in crop losses annually. Hessian fly perennially threatens wheat in the southeastern United States, and wireworms are persistent pests in northwestern wheat-production systems. Otherwise, the particular location and severity of outbreaks vary yearly and are largely unpredictable. However, particular agronomic practices can greatly reduce risk of infestation such as elimination of volunteer wheat and weedy hosts and planting wheat during periods of reduced pest abundance. In addition, resistant cultivars can limit Hessian fly and Russian wheat aphid (Diuraphis noxia [Kurdjumov]) damage in some areas, but virulent biotypes of each pest complicate their management. Although several preemptive tactics reliably suppress infestations and barley yellow dwarf severity, they are not compatible in all agricultural systems. Consequently, insecticides are necessary in certain areas and within particular production systems to manage major early-season insect pests of wheat.