STINK BUG POPULATIONS AND ENEMIES IN GEORGIA

Summary

The purpose of this project is to characterize the activity of stink bugs and their natural enemies in various crops (corn, cotton, peanuts, and soybeans) in Georgia in an effort to understand how stink bug populations move and develop in the landscape and how much mortality is inflicted by natural enemies on the stink bugs. We are also seeking to determine if there might be opportunities to improve the effectiveness of important enemies or possibly to import more effective enemies from elsewhere to effect greater biological control. Plot studies support earlier studies that peanuts and cotton are not particularly attractive to stink bugs for colonization, but may serve as adequate to good feeding hosts until better food resources are available. Reproduction in peanuts and cotton appears to be limited. In contrast, stink bugs colonize soybeans readily, with brown stink bugs attacking young to middle aged pods (R3/R4 stages), and southern green stink bugs moving into the crop most heavily when pods are filling (R7/R8 stages). Corn appears to be an important stink bug crop until early to mid-summer, although reproduction is variable in the crop, and parasitism rates there can be relatively high (in excess of 50%) which may significantly slow population development for later crops.

Situation

Insecticide use in Georgia cotton has declined dramatically since the late 1980s, with the successful elimination of the cotton boll weevil in the 1990s and the widespread deployment of Bt-transgenic cotton, beginning in 1996. In the late 1980s, growers sprayed insecticides an average of 17 to 20 times per season. By the late 1990s, growers sprayed an average of two to three times per season, making cotton one of the more environmentally-friendly crops in the state. However, in the 1990s stink bugs became increasingly serious pests of cotton and growers began to apply more insecticides to manage these pests. This increased insecticide use threatened to offset at least some of the benefits that have been derived from boll weevil eradication and the use of Bt-transgenic cotton. Stink bugs also have been clearly linked to reductions in cotton lint quality that have created serious marketing problems for Georgia producers. Estimated quality losses inflicted by stink bugs on Georgia growers range from $10-20 million per $0.01 quality deduction. Solving the stink bug problem has been compounded by difficulties associated with sampling stink bugs in the field and defining clear treatment thresholds at which insecticide applications should be made. Further, stink bugs range across the landscape, feeding and developing on a variety of cultivated and wild plants, and demanding management across the landscape. Adults are highly mobile, allowing them to move between fields and between crops and wild systems. This problem lends itself well to enhanced activity of natural enemies, which can reduce stink bug populations outside of production systems with little or no human input. Finally, the stink bug problem is compounded by the presence of a complex of stink bug species rather than a single species. The susceptibility of these species to insecticides varies significantly with species, presenting management difficulties to growers.

Response

We continued stink bug surveys and studies in 2011 that we had initiated in 2007 to evaluate the complex of natural enemies that attacks stink bugs in Georgia. Our surveys concentrated on corn, peanut, soybean and cotton fields in Atkinson, Coffee, Colquitt, and Mitchell counties. All sampled stink bugs were identified to species and life stage, and all life stages were collected as they were found in sampling at each of these locations and the bugs were returned to the laboratory where they were held and assessed for parasitism. Stink bug abundance overall was unusually low in 2011for much of the season in our experimental areas, but patterns similar to previous years were detected. Reproduction in peanuts and cotton appears to be limited. In contrast, stink bugs colonize soybeans readily, with brown stink bugs attacking young to middle aged pods (R3/R4 stages), and southern green stink bugs moving into the crop most heavily when pods are filling (R7/R8 stages). Corn appears to be an important stink bug crop until early to mid-summer, although reproduction is variable in the crop, and parasitism rates there can be relatively high (in excess of 50%) early in the season, which may significantly slow population development for later crops. No parasitism of stink bug nymphs and adults was observed in 2011, indicating a density-dependent response by parasitoids to the very low abundance of stink bug hosts. We also continued life history studies of the exotic braconid parasitoid Aridelus rufotestaceus, first discovered in Georgia in 2007. The parasitoid population is almost entirely female, with occasional non-functional males appearing, and this skewed sex ratio is effected by a Wolbachia bacterium.. No mating is required for reproduction, which is beneficial for rearing and releasing. We have found that the parasitoid begins attacking hosts immediately upon emergence as an adult, and lives on average approximately three weeks, but ost eggs are laid in the first 12 days. Females are capable of parasitizing and killing approximately 160 stink bugs each over the course of their lifetimes. Studies of stink bug egg predation in peanuts in 2011 indicated that ant predation on the eggs was greatly reduced relative to previous years. This may be due to the significant drought conditions encountered during the experiment. Egg parasitism, on the other hand, was elevated, with some more than 50% of eggs parasitized on some sample dates.

Impact

Stink bugs, as a complex of species, range across the landscape, moving through cropping system during the season. Understanding when and where they are moving, and the cues involved will help us to develop preventative and appropriate sampling practices to address their depredations. Increased reliance on natural enemies to manage stink bug populations across this diverse landscape reduces the need for grower inputs, and can help us maintain the remarkable environmental and economic benefits that reduced insecticide inputs have accrued to Georgia cotton producers and the state of Georgia in recent years. Further, natural enemies work across the landscape so that greater efficacy of the natural enemy complex against stink bugs would benefit a range of crops in addition to cotton with no additional grower inputs. Finally, the expanding range of the exotic parasitoid Aridelus rufotestaceus, which attacks stink bug nymphs, may have considerable potential to help suppress stink bug populations. Previously, there are few records of stink bug nymphs being attacked by parasitoids anywhere in the world, but we may be able to enhance the activity of this novel parasitoid to reduce stink bug populations on a regional scale. As we continue to gather data on stink bug population dynamics and natural enemy activity, it is becoming increasingly clear that some crops (e.g., cotton and peanuts) are poor reproductive hosts, relative to others (e.g., soybeans). Thus, biological control to limit population growth would be less effective in crops where stink bug reproduction is limited, and will need to focus instead on wild and cultivated host plants where reproduction is concentrated.

State Issue

Agricultural Profitability and Sustainability

Details

• Year: 2011
• Geographic Scope: State
• County: Tift
• Program Areas:
  • Agriculture & Natural Resources