Lygus Bug (Western Tarnished Plant Bug)

Lygus bug is also known as western tarnished plant bug. Adults are small—about 0.25 inch (6 mm), variably yellowish to green to bronze true bugs with a distinctive triangular marking on the back. The wings are composed of both membranous and hardened sections that are carried folded over the back. The mouthparts are needlelike and long in relation to the body size.

Females lay eggs in the plant tissue, typically in the midrib areas of leaves. Immature lygus bugs are light green and resemble adults in shape but lack wings. The wings gradually appear with each molt. First- and second- instar nymphs are often confused with aphids but lack cornicles and move much more quickly. Second and third instars have a dark spot on the abdomen, and fourth and fifth instars have four additional spots on their thoracic segments. In general, later instars can be recognized by their developing wing pads.

Lygus feed by piercing cell membranes, which affects the subsequent cell division in the area of feeding. The result is sunken, callused, elongated lesions, frequently just below the first node of the celery stalk. Inner petioles may show black spots, twisting, or other distortion, especially if immature lygus are present.

Support populations of natural predators and parasites of lygus by not applying broad spectrum products, such as pyrethroids, repeatedly. Natural enemies, especially parasitoid wasps such as Anaphes iole, which attack eggs, and Peristenus relictus, which attack nymphs, help control lygus bug. However, in native vegetation where numbers of lygus increase, natural enemies are not effective at preventing large numbers of adults from migrating into crops such as celery.

The most important predators of lygus bugs are bigeyed bugs, which feed on eggs and young nymphs. Lygus adults are more difficult for predators to capture than nymphs because of their quick movements.

The entomopathogenic fungus Beauveria bassiana can be used for adults and immatures; the fungus can penetrate the eggshell and kill the egg. The fungus performs better in more humid climates.

Manage weeds around the fields to suppress lygus bug numbers. Fundamental to lygus management is controlling weeds along roadways, ditches, and field borders near cole crop fields to help prevent spring buildup of lygus bugs. See table “Key times to monitor important plant hosts of lygus bug.”

Use biological and cultural controls in a certified organic crop. The entomopathogenic fungus Beauveria bassiana is available for all growth stages. Use azadirachtin for nymphs.

Lygus bugs frequently move into crop fields in spring when weeds and native vegetation dry down. It is also a pest of alfalfa, green beans, and strawberries, and can fly over to celery when alternative host crops are harvested. Consequently, large numbers of lygus can move into celery fields in a short period of time. Determining the level of lygus infestation is difficult because the insects are cryptic and their activity cycle during any day varies greatly. Lygus become inactive and secretive during temperature extremes and windy conditions.

Because of the severity of the damage to celery, the threshold, while not specifically established, is very low. Sweep nets and keeping a careful eye out for adults flying in front of you as you move through the field are economical techniques to check for lygus. Beat sheets (shaking the plants over a white sheet) can be used to monitor for nymphs that are on the plants, but adults will fly away. A more sophisticated option is modifying a handheld yard vacuum to suck up the insects in the field.  Sticky traps are not useful for monitoring these pests.

View the UC IPM video “Identification and Management of Lygus Bug.”