Western tarnished plant bug,
Tarnished plant bug, Lygus lineolaris
Pale legume bug, Lygus elisus
There are three predominant species of lygus in Texas cotton: the western tarnished plant bug, the tarnished plant bug, and the pale legume bug. The western tarnished plant bug is the most common species in the western half of Texas, and the tarnished plant bug domi- nates in the eastern half of the state. These species are similar in appear- ance, biology, and the damage they cause. In this publication, we will call them lygus and discuss them as a single pest.
Lygus bugs feed on cotton terminals, squares, flowers, and small bolls. Adults are ¼ inch long, have a conspicuous dark-colored triangle in the center of the back, have wings, and vary from pale green to yellowish brown with reddish brown to black markings (Fig. 52). Nymphs (imma- tures) are uniformly pale green with red-tipped antennae; late instars have four conspicuous black spots on the thorax and one large black
spot near the base of the abdomen (Fig. 53). The nymph’s wings are not developed, but they can move rapidly and are difficult to detect in cotton foliage. It is easy to mistake small nymphs with aphids, cotton fleahop- pers, and leafhopper nymphs, but their broader shape, quick movements, larger size, and the specific characteristics discussed above help differen- tiate them.
Lygus bugs prefer legumes to cotton and usually occur in large numbers in alfalfa, potato fields, or on wild hosts such clovers, dock, mustard, pigweed, Russian thistle, vetches, and wild sunflower. Lygus bugs are attracted to succulent growth (Fig. 54). In cotton, their feeding causes:
- Deformed bolls
- Dirty bloom (damaged anthers in blooms) and puckered areas in petals
- Shedding of squares and small bolls
- Stunted growth
- Small black spots or small, dark, sunken lesions on the outer surface of the developing bolls that can penetrate the boll carpel wall and damage developing seeds or lint
Scouting and Decision Making
The abundance of lygus bugs in relation to the fruiting condition of the cotton plants determines the need for control measures. Inspect fields for lygus bugs at 4- to 5-day intervals throughout the fruiting period.
Before peak bloom, using a sweep net is the most accurate way to sample for lygus. After peak bloom, a drop cloth is best. How to use beat bucket, drop cloth, and sweep net sampling are discussed in the scouting section of this guide on pages 5 and 6. Research in Arizona and California indicates that the western tarnished plant bug may be more difficult to control with insecticides and may require using higher labeled rates of suggested insecticides.