Lygus Bugs

Lygus spp. are plant bugs (family Miridae) that pierce and suck buds and shoot terminals with their needlelike mouthparts. Lygus develop through three life stages as with all true bugs (Heteroptera). After eggs hatch, nymphs develop through five increasingly larger instars before becoming adults. Adult plant bugs characteristically have a flattened upper side with a conspicuous triangular or heart-shaped area (scutellum) between the base of the wings.

At least 19 species of Lygus occur in California. Pale legume bug and especially western tarnished plant are common pests. Adults at rest are 1/5 to 5/16 inch long and about half as wide. Coloration varies and generally is darker for individuals overwintering as adults. Use A Field Key to the Most Common Lygus Species Found in Agronomic Crops of the Central San Joaquin Valley of California (PDF) to identify the crop-feeding Lygus to species.

Western tarnished plant bug adults are mostly yellowish to greenish brown with black and sometimes orange or red. Adults have more than two dark blotches or spots on the upper surface of the thorax immediately behind the head (pronotum).

Pale legume bug adults may or may not have two dark spots on the pronotum. Their body is mostly pale green or yellowish green with black or dark brown. At rest the adult's body can appear grayish viewed through the translucent wings

Lygus eggs are 1/25 inch (1 mm) and oblong, slightly curved, and flattened on one end. They are laid singly in soft plant tissue of hosts that include numerous ornamentals, tree fruit and nuts, vegetable crops, and various broadleaved weeds and grasses. For example in gerbera eggs are laid below the inflorescence embedded in the involucre, the whorl (rosette) of bracts that surround the flower head. Eggs hatch about 1 week after being laid.

Nymphs resemble small, wingless adults. Wing pads (developing wings) become increasingly apparent and large in older instars. Pale legume bug nymphs are pale green to yellowish. Nymphs of western tarnished plant bug are mostly green, orangish, or yellow. First instars are especially pale-colored to whitish. Five small, black spots become increasingly apparent on the upper surface of older instars of L. elisus, L. hesperus, and certain other plant bugs.

Lygus bug nymphs may be mistaken for aphids because of their green or yellowish color and similar size and shape. However, aphids that feed openly on plants generally have two rear-pointing tubes (cornicles) on top of the abdomen and the antennae are generally held backwards over the body. Lygus bug nymphs lack cornicles, generally point their antennae forward, and move more rapidly than aphids.

Lygus bug adults and nymphs can be confused with numerous other true bugs including some beneficial types, and several bug species commonly can occur on the same plants. See Insects Confused With Lygus for side-by-side comparisons of common look-alikes, which include:

• bigeyed bugs, Geocoris spp. and others
• black grass bugs, Irbisia spp.
• buckeye bug, Neurocolpus longirostris
• calocoris bug, Closterotomus (=Calocoris) norvegicus
• false chinch bug, Nysius raphanus
• psallus plant bug, Psallus vaccinicola
• tomato bugs, Tupiocoris (=Cyrtopeltis) spp.

In greenhouses heated during winter and with supplemental lighting and suitable host plants, Lygus can reproduce and feed throughout the year. Outdoors during winter Lygus spp. occur as inactive adults under bark, in crop debris, and in natural and weedy vegetation. Adults become active in late winter or early spring when they resume feeding and other activities. Adults are most abundant May through August; populations commonly migrate into irrigated crops from drying, unmanaged vegetation. Outdoors in California, depending upon species, host plants and location, pest Lygus spp. have up to seven generations per year.

Low numbers of Lygus bugs can cause economic damage from feeding on shoot tips and developing buds, especially flower buds. Where Lygus bugs fed, as tissue grows flower buds and blossoms discolor, distort, become spotted, or fail to mature. Damage to the plant results from a combination of the bugs' puncture-feeding wounds and toxic saliva. Dark feces may be deposited on blossoms and leaves.

In gerbera for example, damage results in fewer flowers overall and flowers that do mature exhibit petal spotting and reduced petal size, which renders the plants unmarketable. Practices such as the application of broad-spectrum, persistent insecticides to control Lygus bugs can disrupt integrated pest management for other major pests in the crop.

Lygus feed and reproduce on more than 300 plant species. Common cultivated hosts include alfalfa, black-eyed peas, canola, celery, cotton, eggplant, gerbera, potato, strawberry, tomato, and tree fruit and nuts. Wild hosts include California burclover, California poppy, chickweed, common groundsel, curly dock, filaree, lambsquarters, little mallow (cheeseweed), lupines, pigweed, milk thistle, mullein, mustards, pineapple weed, redmaids, shepherd's purse, stinkweed, wild mustard, and wild radish.

To successfully manage lygus bugs

• Control weeds near crops by discing or mowing, especially during winter and spring.
• Effectively exclude the pests from crops using row covers and screening.
• Keep growing areas clean and promptly remove and dispose of crop and weed residue in covered containers away from production areas.
• Monitor for the presence of Lygus bug nymphs on weed hosts and for adults migrating into crops, such as with yellow sticky traps or sweep netting around borders and visual inspection of hosts beginning late winter through at least spring. Monitor landscape plantings around growing areas which may be sources of Lygus bugs and include these plants in your management.
• Time insecticide sprays to control Lygus bugs before they cause significant damage. Various insecticides effectively kill the early instars, which might be applied to unmanaged vegetation near growing areas to control migrants. Insecticides are less effective for controlling the highly mobile Lygus adults, and many products that can be used adversely affect beneficial natural enemies and may induce outbreaks of spider mites.

Biological control of Lygus bugs generally is not sufficiently effective in crops. Tolerance for damage is very low and adults constantly migrate in during the growing season. Natural enemies of Lygus bugs can still be very important in native and unmanaged vegetation where they may substantially reduce the numbers that migrate into crops.

Anaphes iole is a parasitic wasp of Lygus eggs. It occurs in coastal-grown crops and surrounding natural and unmanaged vegetation. This blackish wasp is less than 1/25 inch (1 mm) long and its larval stage feeds inside and kills eggs of Lygus bugs. Peristenus spp. are parasites of Lygus nymphs. Peristenus relictus is a 1/8 inch long blackish to dark brown wasp that occurs in some production areas. Tachinid flies such as Hyalomyiopsis (=Alophorella) aeneoventris glue their eggs on or insert them into the Lygus bug's body. Eggs hatch into maggotlike larvae that feed inside and kill the bugs. Predators that feed on Lygus bugs, mostly on the nymphs, include bigeyed bugs, damsel bugs, green lacewings, minute pirate bugs, and various spiders.

Control weeds near greenhouses and nurseries to help prevent spring buildup of Lygus bugs that migrate into irrigated crops. Since overwintering adult Lygus lay eggs in weeds that hatch about March, control weeds by March or early April before Lygus bugs become adults and able to migrate into crops when the weeds dry or are mowed. Spraying adults with insecticide or weeds with herbicide to prevent movement will be much less effective than mowing or discing under cover crops and weeds, especially legumes, before they flower and while Lygus bugs are still immatures.

Trap crops

One cultural approach is to plant early-flowering ‘trap crop' hosts (such as alfalfa) bordering cultivated areas to attract migrating Lygus bug adults away from crops; the trap crop is treated periodically while Lygus bugs are in the nymphal stage and disced or mowed before Lygus mature into the next generation of adults. This approach requires careful monitoring and well-timed management to prevent the trap crop from becoming a reservoir of these migratory pests.

Vacuuming bugs

Some growers have used suction devices (bug vacs) to control Lygus bugs for many years. Consistent vacuuming once or twice weekly can manage low to moderate numbers of Lygus bugs in crops. Research has shown that an efficient bug-vac can reduce adult numbers by 75% and nymphs by 10% to 50%, but efficiency can vary considerably. If Lygus bug numbers are high, vacuum machines alone will not reduce damage to an acceptable level. Vacuums may increase problems with powdery mildews and gray molds by spreading their spores. If vacuuming crops where these pathogens have been a problem, coordinate with the application of effective fungicides for the pathogens. Vacuums may also remove parasites and general predators important for the control of other pests.

Biological and cultural controls are organically acceptable management methods. Certain formulations of the botanical azadirachtin (Azatin), potassium salts of fatty acids (insecticidal soaps), the microbial insecticides Beauveria bassiana, and Isaria fumosorosea are organically acceptable.

Avoid introducing Lygus bugs in stock plants. Hold incoming stock in a separate (quarantine) area for 3 to 4 weeks before moving new plants to production areas. This allows time for Lygus bug eggs to hatch and nymphs, as well as other pests, to become visible for inspection. Reject infested shipments and work with suppliers to address quality issues.

Lygus bugs can cause economic damage even from one day of feeding. Monitor frequently to detect these pests as soon as possible. For example, beginning in February inspect hosts for the first appearance of nymphs and to determine the need for management.

One strategy is to closely inspect large plots of single-variety crop plantings that in previous growing seasons have been damaged by Lygus bugs. During warm spring weather especially, regularly monitoring hosts to best time control actions for nymphs is key to avoiding economic losses. Include weeds bordering crops by regularly examining them as immature flower buds develop mid-winter through spring.

To visually inspect hosts for Lygus bug adults and nymphs

1. Tap or shake young flower buds and shoot tips over a white sheet of paper (e.g., on a clip board) to dislodge bugs from plants; they will be easily visible on the collecting (paper) surface. This is best done on cool mornings. Sweep netting can be used in some crop and non-crop areas.
2. Keep records of the number of Lygus bugs per sample on each monitoring date throughout the year.
3. Note Lygus bugs' feeding preferences to determine which cultivars are most attractive or susceptible and where to focus monitoring and control efforts.

Eggs are inconspicuous and not a useful stage for monitoring. Control decisions are also not usually based upon damage symptoms because of the delay in symptom appearance, but symptoms can be an indicator of the effectiveness of past management strategies.

Apply an effective insecticide immediately when Lygus nymphs are observed on crops. When adults are observed, treat within 3 days and then again 5 days later or as needed.

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