Matthew Baur and Jack Baldwin
Early soybean planting has become common practice in Louisiana. Early maturing soybeans – maturity groups III to V – are planted in early spring, shifting the focus of insect control efforts to an earlier part of the season. Thus, stink bugs have become increasingly significant, especially the red-banded stink bug, also known as the red-shouldered, red-striped or Cajun red-shouldered stink bug.
The geographic range of the red-banded stink bug, which was first described in 1837, extends from the southern United States to Argentina. Red-banded stink bugs have been reported as the principal stink bug pest of soybeans in Brazil since 1970. Within the United States, the range extends from New Mexico to South Carolina and Florida, and north to Georgia and Arkansas. The red-banded stink bug was reported in North Florida in 1983, and in Georgia from 1987-1991. Red-banded stink bugs were first reported in South Louisiana in 2000 and have reached significant numbers since 2002.
Red-banded stink bugs feed on cultivated and uncultivated plants including pigweed, poison ivy, catalpa, cactus, sunflower, castor bean, wheat, cotton, pokeweed, strawberry, fennel, violets, many types of clover, alfalfa, vetch and many cultivated beans, including lentil and kidney bean. In Louisiana, the insect has been found in significant numbers on soybean and black medic and in smaller numbers on dock and hairy vetch. The geographic range information and host-plant list suggests red-banded stink bugs are not new to the United States nor is their geographic range being extended. Rather, populations of this pest appear to rise and fall to local extinction because of environmental or other causes. Brazil Studies Bug
Unfortunately, few studies have been conducted on the red-banded stink bug in the United States. Studies in Brazil indicate red-banded stink bugs caused damage in 2002, and yield loss caused by red-banded stink bug adults is equivalent to or higher than yield losses associated with southern green and brown stink bugs. The researchers in Brazil caged red-banded stink bug adults on soybean plants for 15 days at four adults per 3 feet of row during pod fill. Red-banded stink bugs damaged about 19 percent of the seeds, and southern green stink bug damaged less than 4 percent of the seeds. Plots infested with either the red-banded stink bug or southern green stink bug yielded about 10 percent to 11 percent less than control plots.
In a greenhouse experiment where two adults were infested on caged plants for 15 days during the pod-filling period, the number of fully filled pods dropped by 40 percent on plants infested with the red-banded stink bug compared to a 20 percent drop on plants infested with the southern green stink bug. The economic threshold (the level of infestation at which a control decision must be taken) used in Brazil for the red-banded stink bug ranges from two adults per 3 feet of row (about half the current threshold used for the southern green stink bug in Louisiana, Texas and Georgia) to four adults per 3 feet of row (roughly equivalent to the southern green stink bug threshold).
LSU AgCenter researchers are conducting studies of the impact of red-banded stink bugs. These are field-cage studies in which stink bug adults are collected in the field and caged on plants for three weeks during the reproductive growth stages of the plants. Red-banded stink bugs were caged at four levels – zero, one, two and three bugs per 3 feet of row – where two bugs per 3 feet of row is equivalent to the current economic threshold for the red-banded stink bug and three bugs per 3 feet of row is equivalent to the threshold for southern green and brown stink bugs. Cages measured 6 feet square and covered 12 row feet of soybean plants. Substantial Yield Loss
When stink bugs were on plants at any population density for three weeks during seed set or seed fill, substantial yield losses of 18 percent to 51 percent were observed (Table 1). During pod set, only at the highest density – three bugs per 3 feet of row – was a significant yield loss of 42 percent observed. During pod set, the weight of 100 seeds increased as infestation levels increased. This may indicate that while adult red-banded stink bugs damaged developing pods and reduced the total number of pods and seeds, the plants made up for fewer pods by shunting more nutrients to the remaining seeds, thereby increasing the weight of harvested seeds.
In Brazil, all classes of insecticides – organochlorines, organophosphates, carbamates and pyrethroids – control the red-banded stink bug. In Louisiana, pyrethroids have been ineffective at current rates recommended for control of the southern green stink bug. The control measures that have been the most effective include 3/4 pound of acephate (81 percent control), 1/3 pound of acephate combined with 2 ounces of Baythroid (95 percent control) and 9 ounces of Furadan (79 percent control).
LSU AgCenter researchers were concerned that control failures might have been caused by the movement of the adult red-banded stink bugs and the distribution of red-banded stink bug nymphs in the plant canopy. They added salt at 0.5 percent to insecticide treatments because work in Brazil shows that ordinary table salt in a 0.5 percent solution applied to plants arrests the behavior of stink bugs. The addition of salt did not increase the efficacy of pyrethroid applications, suggesting that adult movement away from treated areas does not explain control failures. They also attempted to increase coverage in the plant canopy by using different spray nozzles. None of them increased the level of control, suggesting that better coverage through the canopy may not explain control failures.
Smaller than the other green stink bug species (Figure 1), red-banded stink bugs always lay their eggs in two rows (Figure 2) on the upper surfaces of leaves and pods. None of the other stink bug species lays its eggs in two rows, and this difference allows for easy identification of egg masses.
Nymphs also are easily distinguished from other green stink bug nymphs (Figure 3). Red-banded stink bugs require at least 30 days at 80 degrees F to develop from egg to adult, and the females only begin laying eggs 20 days after they have emerged as adults. Adults live up to 40 days in the laboratory.
In Louisiana, two to three distinct population peaks are evident in soybeans: the first in June, the second in July and a third, much-broader peak in August and September. Broadly overlapping generations of all life stages – eggs, nymphs and adults present simultaneously – were observed only in the third peak. The long development time, long fertility period of females and the extended adult longevity cause the overlapping of generations during the final peak of the season. In addition, the presence of all life stages simultaneously may contribute to apparent control failures. Research is continuing.(This article was published in the summer 2006 issue of Louisiana Agriculture.)