The Alydidae (Broad-Headed Bugs) of Virginia and Their Pest Management in Edamame

Edamame, also known as edible soybean, is a crop with growing demand in the United States. Currently much of the edamame consumed in the United States is imported, but it has potential to be grown domestically, in Virginia and other mid-Atlantic states. With the introduction of a new crop, however, comes new challenges, such as novel pests. The broad-headed bugs (Hemiptera: Alydidae), a relatively insignificant pest of conventional soybean, have been observed in high numbers on edamame in Virginia. Their piercing-sucking feeding may produce dark marks on edamame beans that could result in economic losses. However, little research has been conducted on the pest status or management of these bugs in edamame. This study aims to determine their pest potential to edamame by investigating their distribution throughout the state, damage to the crop, and avenues for chemical control.

An important element in determining the pest potential of an insect is its distribution throughout an area. The distribution of broad-headed bugs in Virginia was last thoroughly investigated in 1975, and the research has scarcely been updated since. With advances in technology, however, it is now possible to crowd-source data from citizen scientists to supplement museum and field collection data. The first portion of this study explores the species of broad-headed bugs present in Virginia, and their distribution throughout the state. This was achieved using museum specimens, field-collected specimens, and photographs from the social network iNaturalist. By manually checking iNaturalist identifications of broad-headed bugs using a key, I was able to determine that iNaturalist is 96% accurate at identifying North American broad-headed bugs to species. Through the combination of museum, field, and iNaturalist data, I also found evidence of two species of broad-headed bug at elevations never before seen in Virginia, the first broad-headed bug ever found on the Eastern Shore of Virginia, as well as the first documented sighting of Hyalymenus tarsatus Fabricus in Virginia.

The level of injury that broad-headed bugs cause to edamame is presently unknown. The second portion of this study compares the density-damage relationship of broad-headed bugs on edamame to that of the brown marmorated stink bug (Halyomorpha halys Stahl), a known pest of edamame. Through a cage study conducted in Whitethorne, Virginia, I found that broad-headed bugs cause significant damage to edamame at densities of 10 insects per plant, but still less damage than that of brown marmorated stink bugs. Currently, no economic injury thresholds exist for broad-headed bugs, or brown marmorated stink bugs on edamame. Determining the density-damage relationship of these insects on edamame may contribute to the creation of these thresholds in the future.

The third portion of this study is the first attempt at evaluating chemical control of the broad-headed bugs on edamame. I performed a bioassay evaluation of four commercial selective insecticides including the following: flupyradifurone and sulfoxaflor, both with a mode of action similar to neonicotinoids, but with reduced non-target effects; the diamide cyclaniliprole, and a novel venom-like peptide insecticide, GS-omega/kappa-Hxtx-Hv1a. Each of the insecticides caused significant mortality of Alydus eurinus (Say) adults.

This thesis serves as a starting point in evaluating the potential threat of broad-headed bugs to Virginia's edamame production.