Update:
Analysis showed that, within a field, larger diameter soybean plants are more likely to be infested with Dectes Stem Borer (DSB) than smaller diameter plants. After correcting for differing plant size, feeding by DSB larvae causes a 10% reduction in yield of individual soybean plants, even in the absence of lodging.
Our samples found that sweeping for adult beetles is a much more effective way to detect adult beetles than visual counts. We also found that adults are present in soybean fields over an extended period of time with no apparent synchrony in emergence. Adults appear to emerge from overwintering larvae and pupae over an extended period of time, which contributes to their prolonged presence in soybean fields. Populations did begin to dwindle in early August, and very few adults were captured after the first week of August.
We tested generic long-horned beetle sex pheromones for activity in adult DSB, and found limited activity of generic compounds using a trap designed for tree-feeding long-horned beetles. The Millar lab was able to isolate two known beetle pheromones from an adult male DSB, and we plan to test these compounds using an updated trap design in 2018. If effective, these pheromones may be a useful tool for timing insecticide treatments for this insect.
Older studies of DSB found that fall tillage could inflict significant mortality on overwintering DSB larvae. However, this tillage may also disrupt overwintering parasitoids and other natural enemies that could attack different stages of DSB. Results of our field experiment show fewer parasitic wasps emerge from fields that were chisel plowed the previous fall when compared to no-till and planting cover crops. However, we found no evidence of any mortality inflicted by parasitoids in the DSB larvae reared in the lab.
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Feeding by Dectes Stem Borer larvae causes a 10% reduction in yield of individual soybean plants, even in the absence of stem lodging. Adult DSB emerge from overwintering larvae over an extended period of time contributing to their prolonged presence in soybean fields. DSB populations begin to dwindle in early August. Development of a DSB trap that uses DSB pheromones may prove to be a useful tool for timing insecticide treatments for this insect. Chisel-plowing fields in the fall may reduce the numbers of overwintering parasitoid wasps compared to no-till and planting cover crops, potentially decreasing a biological control agent for DSB.