Residual Activity of Selected Insecticides on Green and Brown Stink Bug Adults
Stink bugs are key pests in soybean production systems across the southern United States. The predominant species of stink bug that infest soybeans are the green stink bug, the southern green stink bug, and the brown stink bug. Stink bug populations typically increase in August and reach peak levels in late September and October. They feed by piercing plant tissues with their piercing mouthparts, often directly on the fruiting forms. Both adults and immatures can damage soybeans, but adults and fifth-instar nymphs cause most of the damage.
Studies of southern green stink bugs in soybeans have shown that feeding causes yield and quality loss, decreases pod fill and seed weight, delays crop maturity, reduces seed oil content, increases seed protein levels, and reduces germination of harvested seed (McPherson, Newsom, and Farthing, 1979). Feeding punctures form minute discolored spots on the developing seed, and heavily damaged seeds may be shriveled or distorted (Miner, 1966). Stink bug damage may reduce the value of soybean seed, and, if severe enough, it may result in the crop having little to no value (Todd, 1976). In Mississippi, the action threshold for southern green, green, and brown stink bugs is nine per 25 sweeps or one per row foot.
Materials and Methods
During 2011, both green and brown stink bugs were collected from unsprayed soybean fields in Sunflower County. Stink bugs were kept in plastic boxes with mesh lids in an insect-rearing room at 27°C and 60 percent RH for up to 4 days until used in the assay. The boxes contained shredded paper to increase surface area in the box, and soybean pods were added as sources of food and moisture.
The insecticides and rates used were based on those suggested by the Mississippi State University Extension Service (Catchot, 2010). Thiamethoxam, which is not labeled in soybeans, was included in order to evaluate each of the components of Endigo ZC®, which is labeled in soybeans. The following insecticide treatments were tested:
- Untreated control
- Bifenthrin (Brigade® 2EC, FMC Corporation, Philadelphia, PA) at 0.1 lb a.i./A
- Lambda-cyhalothrin (Karate Z® 2.08CS, Syngenta Corporation, Wilmington, DE) at 0.03 lb a.i./A
- Acephate (Orthene® 90S, AMVAC Chemical Corporation, Axis, AL) at 0.75 lb a.i./A
- Thiamethoxam (Centric® 40WG, Syngenta Corporation, Wilmington, DE) at 0.05 lb a.i./A
- Thiamethoxam + lambda-cyhalothrin (Endigo ZC®, Syngenta Corporation, Wilmington, DE) at 4.5 oz form/A
- Methyl parathion (Methyl® 4EC, Cheminova, Durham, NC) at 1.0 lb a.i./A
- Acephate + bifenthrin (Orthene® 90S + Brigade® 2EC) at 0.75 lb a.i./A 0.1 lb a.i./A
The treatments were applied using a Mudmaster® (Bowman Manufacturing, Newport, AR) sprayer with TX6 hollow cone tips applying 93.5 L/ha. Plots were four rows wide by 23 meters long with four border rows between plots. Treatments took place August 16, 2011. At 1 hour and at 1, 3, 5, 7, and 10 days after application, 10 leaves were collected from each plot. Leaves were collected from the second node down from the terminal bud. One leaf and one adult stink bug were placed in a petri dish with a 10-centimeter diameter. Mortality was determined after 24 and 48 hours of exposure. Stink bugs were considered dead if no coordinated movement was observed within 5 seconds of being prodded. A treatment was no longer tested after it failed to increase mortality compared to the untreated control. Insecticide treatment data were corrected for natural mortality using Abbott’s formula (Abbott, 1925). Corrected data were analyzed as a completely randomized design in SAS using Proc GLM at a 0.05 level of significance.
Results and Discussion
Figures 1–6 display the residual toxicity data for green and brown stink bugs, respectively. Against brown stink bugs, acephate and acephate + bifenthrin caused significantly higher mortality 2 days after application (t = 11.18; df = 1; P < 0.0001) (Figure 3) and 3 days after application (t = 8.67; df = 1; P < 0.0001) (Figure 4). The treatments containing acephate provided the highest efficacy against brown stink bugs from 2 days on and were the only treatments that provided more than 40 percent control 2 days after application. These were twice as effective as all the other treatments 2 days after application (Figure 3). At 5 days after application, the acephate and the acephate + bifenthrin treatments were still providing 83 percent and 92 percent mortality of brown stink bugs, respectively (Figure 6). After 5 days, brown stink bug mortality in the acephate treatment was not significantly different from mortality at 1 hour after application (t = 1.14; df = 1; P = 0.2856). Thiamethoxam caused the least mortality on brown stink bugs of all the insecticides tested. One hour after application, it only resulted in 28 percent mortality.
Overall, efficacy of the insecticides declined over time, with the exception of acephate against brown stink bugs. Three days after application, treatments containing a pyrethroid insecticide, namely acephate + bifenthrin, lambda-cyhalothrin + thiamethoxam, and lambda-cyhalothrin, resulted in greater mortality of green stink bugs than the other insecticides. After 3 days, none of the treatments resulted in more than 50 percent mortality of green stink bugs. Brown stink bugs tended to be more susceptible to acephate than green stink bugs. Green stink bugs tended to be more susceptible to the pyrethroids and thiamethoxam than the brown stink bugs. The lack of residual activity for methyl parathion has been previously documented (Way and Wallace, 1990). Way and Wallace (1990) also showed that acephate provided 40 percent control of rice stink bugs 9 days after application. Based on our observed high level of control 5 days after application, control of brown stink bugs with acephate may be this long, as well.
In conclusion, all of the insecticides tested resulted in very little mortality of green stink bugs after 4 days. Acephate provided residual control of brown stink bugs through 5 days and may have had longer residual control. This was longer than any of the other insecticides tested. In years when stink bug numbers are very high and frequent migration into soybean fields occurs, it will be necessary for producers to make multiple applications due to lack of residual efficacy with currently labeled products.
Abbott, W. S. 1925. A method of computing the effectiveness of an insecticide. Journal of Economic Entomology, 18: 265–267.
Catchot, A. L., Jr. 2010. Insect control guide for agronomic crops 2018. Mississippi State University Extension Service Publication 2471. http://extension.msstate.edu/publications/publications/insect-control-guide-for-agronomic-crops
McPherson, R. M., L. D. Newsom, & B. F. Farthing. 1979. Evaluation of four stink bug species from three genera affecting soybean yield and quality in Louisiana. Journal of Economic Entomology, 72: 188–194.
Miner, F. D. 1966. Biology and control of stink bugs on soybeans. Arkansas Agricultural Experiment Station Bulletin 708: 3–40, Fayetteville, AR.
Todd, J. W. 1976. Effects of stink bug feeding on soybeans and seed quality. Proceedings: World Soybeans Research Conference. I. R. Shibles, Ed. Westview Press, Boulder, CO. 611–618.
Way, M. O. & R. G. Wallace. 1990. Residual activity of selected insecticides for control of rice stink bug (Hemiptera: Pentatomidae). Journal of Economic Entomology, 83: 591-595.
Publication 2728 (POD-03-18)
By Angus Catchot, PhD, Extension Professor, Biochemistry, Molecular Biology, Entomology, and Plant Pathology; Fred Musser, PhD, Professor, Biochemistry, Molecular Biology, Entomology, and Plant Pathology; Donald Cook, PhD, Assistant Research Professor, Delta Research and Extension Center; Jeffrey Gore, PhD, Associate Extension/Research Professor, Delta Research and Extension Center; Wes McPherson, former graduate student, Biochemistry, Molecular Biology, Entomology, and Plant Pathology; and Clint Allen, PhD, Research Entomologist, USDA Research Unit, Stoneville, MS.