How to Manage Pests
UC Pest Management Guidelines
Lygus Bug (Western Tarnished Plant Bug)
Scientific Name: Lygus hesperus
(Reviewed 4/17, updated 4/17)
In this Guideline:
DESCRIPTION OF THE PEST
Western tarnished plant bug is commonly referred to as lygus bug. Adults are small (about 0.25 inch), variably colored yellowish to green to bronze true bugs with a distinctive triangular marking on the back and wings 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.
Eggs are laid in plant tissue. Immature lygus bugs are light green and resemble adults in shape but lack wings. First and second instar nymphs can be confused with aphids when casually observed, but lack cornicles and move much faster. Second and third instars have a dark spot on the abdomen. Four additional spots can be seen on the thoracic segments of fourth and fifth instars. In general, later instars can be recognized by their developing wing pads.
Lygus feeds by piercing cell membranes. This activity affects the subsequent cell division in the area of feeding resulting in sunken, callused lesions that could become necrotic with time. Egg laying injury is also associated with lesions. Adults lay eggs in the midrib areas of the leaf. The injury initially appears as holes or pits on the midrib and later expands into lesions.
Various species of natural enemies attack different life stages of the lygus bug. Egg parasitoid, Anaphes iole, nymphal parasitoid, Peristenus relictus, and predatory arthropods that include bigeyed bugs (Geocoris spp.), damsel bugs (Nabis spp.), minute pirate bugs (Orius tristicolor), and several species of spiders provide partial control of the western tarnished plant bug. Entomopathogenic fungi, Beauveria bassiana, Isaria fumosorosea, and Metarhizium brunneum can also be used to control adults and nymphs.
Manage weeds around the fields to suppress western tarnished plant bug numbers. Protect populations of natural enemies.
Organically Acceptable Methods
Use biological and cultural controls on organically certified crop. Entomopathogenic fungi, Beauvaria bassiana (e.g. BotaniGard, Mycotrol ESO) or Isaria fumosorosea (PFR-97), are available for all growth stages. Use azadirachtin (e.g. AzaGuard) for control of nymphs.
Monitoring and Treatment Decisions
Lygus bugs frequently move into crop fields in spring when weeds and native vegetation dry down. Consequently, large numbers of bugs can move into celery fields in a short period of time. Determining the level of lygus bug infestation is difficult because the insects are cryptic (hiding) and their activity cycle during any day varies greatly. Lygus bugs become inactive and secretive during temperature extremes and windy conditions.
Because of the severity of the damage to lettuce, the threshold, while not specifically established, is very low. Sweep nets and detection of adults flying out of the crop when walking through the field, are the only ways to check for the presence of lygus bug. Sticky traps are not useful for monitoring this pest.
UC IPM Pest Management Guidelines:
Insects and Other Arthropods
E. T. Natwick, UC Cooperative Extension, Imperial County
Acknowledgment for contributions to Insects and Mites:N. C. Toscano, Entomology, UC Riverside