Stink bugs never got much respect when the boll weevil and tobacco budworm were kings of the pest complex in the Mid-South and Southeast. But with those two pests either eradicated or in diminished roles, they’re getting their due.
“The stink bug complex is an excellent example of a pest group that has shifted in importance and continues to draw attention,” said Jeremy Greene, Extension entomologist, Southeast Research and Extension Center in Monticello, speaking at the Cotton Incorporated Crop Management Seminar, Tunica, Miss. In light of this shift, “economic thresholds for stink bugs need to be updated, and producers educated on biology and control,” said Greene.
In addition, “Many important stink bug species have developed tolerance to commonly used insecticides. The availability of alternative chemistries is important to the future management of stink bugs.”
Twenty years ago, the stink bug was more a novelty than a nuisance. In 1984, no losses to stink bugs were reported in the southern Cotton Belt. Ten years later, a less than one tenth of one percent yield reduction was reported. In 2003, losses had climbed to three-fourths of a percent. That made stink bugs the third most significant pest in cotton production in 2003.
In 2003, stink bugs were the third most damaging pest in Arkansas, Louisiana, Mississippi and North Carolina and the second most damaging pest in South Carolina, Tennessee and Alabama. Stink bugs were the No. 1 pest for Florida and Georgia in 2003. In Georgia, stink bug losses climbed to 1.6 percent in 1999, declined for three straight years, then rose to 2.7 percent in 2003. Florida reported a 3.1 percent loss to stink bug in 2003.
Severe infestations of stink bugs can develop in areas where either Bt cotton or boll weevil eradication has reduced insecticide use. According to Greene, “losses can exceed hundreds of pounds per acre in addition to price reductions due to inferior lint quality.”
The current treatment threshold for stink bugs in the Southeast is one stink bug per six row feet and/or 20 percent internal injury to medium-sized bolls, noted Greene. “In the Mid-South, where plant bugs are also a major part of the boll-feeding bug complex, treatment is required more often (10 percent to 20 percent damage). These thresholds continue to need refinement and validation to aid cotton producers.”
In laboratory research conducted by Greene, methyl parathion and Bidrin, standard organophosphates used for control of bug pests, provided superior control of field-collected fifth instars and adults of the green stink bug, the southern green stink bug and the brown stink bug. Pyrethroid insecticides alone provided variable results due to considerable tolerance by the brown stink bug, Greene said.
Boll feeders Primary damage from stink bugs in cotton occurs to developing bolls, according to Georgia Extension entomologist Phillip Roberts. “Stink bugs have piercing sucking mouth parts and feed primarily on fruiting structures and meristematic tissues.”
When stink bugs feed, “a digestive enzyme is injected into plant tissue and dissolved plant tissues are extracted,” Roberts said. “Damage to cotton includes physical damage to the seed and developing lint and the potential for pathogens to enter feeding sites or be introduced during feeding into developing bolls.”
External symptoms of stink bug feeding on developing bolls include small sunken purplish-black lesions on the outer surface of the boll. Roberts noted that external symptoms of feeding are not a reliable indicator of feeding or damage, and that other insects can leave similar lesions on bolls.
Internal symptoms of feeding include callous growths or warts on the inner surface of the boll wall. These are a more reliable indicator of feeding, according to Roberts. These callous growths or warts will form within 48 hours of feeding.
Stained lint, noticeable a few days after feeding, is also an indication of stink bug feeding.
In some cases, only localized discoloration of an individual lock may occur, according to Roberts. Hard lock or failure of locks to fluff may also be indicative of stink bug damage. In more serious cases, one or more locks, or the entire boll may rot and not be harvestable.
A two-year study conducted by Roberts and Greene indicated a 22 percent loss in lint per bolls, when bolls with external damage were compared to bolls without external damage. In addition, damage to small bolls -- under 10 days old -- can cause abscission.
A study by Roberts and Greene also suggests that stink bugs can influence fiber quality. For example, micronaire can be affected by the number of bug damaged locks in bolls. Bolls with no damaged locks averaged a mike of 4.5, while mike of bolls with 4-5 damaged locks averaged 3.5. Fiber length also declined as the number of damaged locks increased.
Roberts advises growers to begin sampling for stink bugs when bolls can be found. Stink bugs can be found on wild hosts from February through November, in wheat from April to June, corn from May to August, cotton from July to October, soybeans from July to November and peanuts from July to September. Stink bugs have a relatively long life cycle, requiring 35-40 days to complete development from egg to adult.