Stink Bug Pests: When Should We Expect Their Appearance in Kentucky Soybeans?

PRINCETON, KENTUCKY

   Stink bugs are one of the most common insect pest groups attacking soybeans worldwide and probably the most important pest of soybeans in the USA. Given their economic damage, many aspects of the life history, management methods, and distribution of endemic species is known. As with many other insects, stink bugs can display physiological adaptations allowing them to persist or even colonize new environments.

   Common Stink Bugs in Soybeans

   Stink bugs are common pests in soybeans, which has made farmers adopt several management strategies to reduce their damage (cultural practices, insecticide application, insecticide seed treatment, and resistant cultivars, etc.). In Kentucky, soybean growers deal every year with the attack of three stink bug species: green stink bug (Chinavia hilaris); brown stink bug complex (Euschistus spp.); and brown marmorated stink (BMSB) bug (Halyomorpha halys), the new invasive species now colonizing the largest soybean growing area in west Kentucky. Green stink bug and brown stink bug are found from southern Canada to northern Mexico (Figure 1), whereas brown marmorated stink bug is widely distributed in northwestern, midwestern, and northeastern states; BMSB is not established in the southern states (around the Gulf of Mexico) and reports are only of hitchhikers (a well-known behavior of this species).

   When Stink Bugs Can Appear

   According to different studies in North America, populations of these three stink bug species tend to be present in soybeans from mid-May to mid-October, but numbers vary among latitudinal regions, depending on the time of planting and developmental stages of soybean plants. In Kentucky, BMSB overwinter as adults in home and other buildings, as well as wooded areas; they become active in the spring with warmer temperatures. Throughout their range, stink bugs can be observed in the field beginning in early April.

   Scouting for Stink Bugs

   As preventive treatments are not recommended or economical, soybean farmers in Kentucky should begin weekly scouting their fields once they reach reproductive stages (R1-R6) and treat only in case economic thresholds are reached. Past research has shown that stink bug number can increase rapidly when beans reach R3 and R4. Stink bugs are sampled with sweep nets and the economic thresholds for treatment are:

• 9 stink bugs/100 sweeps for the R1-R3 (it may occur from May to end of June); or
• 36 stink bugs/100 sweeps for R4-R6 (it may occur from July to September).

   Increase in Stink Bug Issues Likely

   The issues with stink bugs in soybeans are likely to increase due to the new invasive species increasing in number in western Kentucky, as well as the fact that global temperature increases may get cause stink bug problems to worsen. In this regard, some scientists predict key pests may expand their host range, distribution, and most likely increase their development rates. For example, about a decade ago soybean farmers in southern regions of the United States started to face attacks from the invasive redbanded stink bug, Piezodorus guildinii (Figure 1). Although this species is common in the neotropical region, it became established in the southern region of the U.S., and populations continue to expand northward with increasing temperatures (Figure 2). The distribution expansion of stink bugs (and most likely other pests) in North America will certainly impact the production of legumes and other crops in the future. Therefore, it is critical that researchers design and growers adopt IPM strategies to minimize impacts of climate change on economic returns. ∆

   Armando Falcon-Brindis, Entomology Research Analyst, and Raul T. Villanueva, Entomology Extension Specialist, University of Kentucky