Lygus bugs—Lygus species
Lygus bugs (plant bugs, family Miridae) suck and feed on buds, fruit, and young shoots of various plants. At least 19 Lygus species occur in California. The pest species are the pale legume bug (Lygus elisus), the tarnished plant bug (L. lineolaris), and the western tarnished plant bug (L. hesperus). Western tarnished plant bug is the most common pest species.
Identification
Symptoms of lygus bug presence as described below under Damage are generally what is first noticed. Other true bugs (Heteroptera) such as stink bugs can cause similar or the same damage. This feeding injury does not become apparent until after tissue has grown, by which time the bugs are commonly no longer present. It may not be possible to determine the cause of plant injury unless the bugs were earlier observed feeding on the plant(s).
Adult lygus bugs are 1/5 to 1/4 inch long. They are about one-half as wide and have a flattened upper side. Lygus species have a distinctive contrastingly colored triangle (scutellum) in the middle of the back where the wings attach. Individuals that overwintered are more dark, generally dark brown to reddish in comparison to individuals that matured from eggs laid during the current growing season.
Pale legume bug, L. elisus, adults have
- a body that is pale green or yellowish green with black or dark brown
- wings that are translucent grayish, which can cause this species to appear gray depending on the extent to which the body is visible through the wings
- cunei (cuneus), triangular-shaped areas near the end of the forewings, which blend with the coloration of surrounding body parts, unlike tarnished plant bug that has contrastingly colored cunei
Tarnished plant bug, L. lineolaris, adults
- are mostly reddish brown with black, yellowish, and whitish
- have numerous black, reddish, and yellowish markings on the frons (between the eyes) and extensive black markings on the pronotum, unlike pale legume bug and western tarnished plant bug
- have cunei that are pale or greenish with black tips that contrast with the rest of the body's coloration. This differs from the other two pest Lygus species where the coloration of cunei matches that of the surrounding body parts
Western tarnished plant bug, L. hesperus, adults
- are mostly yellowish to greenish brown with black and sometimes orange or red, but when the bug is at rest the abdomen can appear gray because it is viewed through the gray wings covering it
- have cunei that blend with the coloration of surrounding body parts, unlike tarnished plant bug that has contrastingly colored cunei
Eggs of lygus bugs are creamy white to translucent, oblong to slightly curved, elongated, and flattened on one end. They are about 1/25 inch (1 mm) long and easily overlooked because they are laid in plant tissue with just the flat end projecting.
First instars (nymphs) are whitish. Second through fourth instars are pale green and wingless. Fifth (last) instars have distinct wing pads and develop some coloration of the forthcoming adult, such as brownish. The last instar is about 1/6 inch long. Only an expert can identify the species of Lygus nymphs.
Lookalikes. Second through fifth instars (nymphs) resemble green or yellowish aphids. However these lygus bug instars have
- red-tipped antennae that are generally held forward
- five black spots on top
- more motility; they are more active than aphids
Aphids that feed openly on plants are distinguished by
- antennae generally held backwards over the body
- two rear-facing tubes (cornicles) apparent on top of the abdomen
Adults of lygus bugs resemble those of various other plant bugs (family Miridae) and bigeyed bugs (Geocoridae), including:
- Bigeyed bugs, Geocoris species and other genera, are 1/8 to 1/4 inch long and beneficial predators that can be discriminated from lygus bugs by this illustration.
- Buckeye bug, Neurocolpus longirostris, is about 1/3 inch long, brownish to straw-colored, and slightly hunched back. The base of antennae widen, brushlike or comblike.
- Calocoris bug, Closterotomus (=Calocoris) norvegicus, which is 1/4 to 1/3 inch long with a yellowish green head, thorax, and scutellum and a brown or green abdomen.
- Mullein plant bug, Campylomma verbasci, is grayish to greenish brown and about 1/10 inch long with blackish antenna tips, cunei, and leg spines.
- Proba bug, Proba californica, is 1/5 inch long and has a scutellum that is not contrastingly colored or prominent.
- Psallus plant bug, Pygovepres (=Psallus) vaccinicola, is 1/8 inch long and pale orange to reddish with whitish coloration. The cunei are bicolored with a darker orange or more reddish tip.
Life cycle
Lygus bugs overwinter as adults in plant debris on the ground, in protected places of woody hosts, and in uncultivated areas outside of gardens and landscapes. In late winter as temperatures rise, the adult females begin laying eggs on a wide range of plants, especially mustards. As herbaceous plants begin to dry up in uncultivated and unirrigated areas, the adult lygus bugs migrate to irrigated plants where they mate, feed, and lay eggs. Lygus bugs can have 6 to 10 overlapping generations per year.
Damage
It is believed that the adult stage is chiefly responsible for damaging fruits and vegetables. Feeding damage begins in the spring when adults lay eggs and suck and feed on shoot tips. Later these shoot tips droop, wilt, and die. This can result in growth from lateral buds that appears bushy and distorted.
When lygus bugs feed on fruit and vegetable buds, these commonly drop which reduces the potential yield amount. When lygus bugs feed on young fruits and vegetables, as these grow, they become at least slightly discolored and distorted around the feeding sites. The flesh underneath becomes discolored and pithy and fails to develop its mature color and flavor. When feeding on nearly ripe fruit and vegetables, the site of feeding becomes a small, dead area where a small cavity develops.
Lygus bug damage is sporadic and does not occur every year. In general the bugs' abundance is highest after winters of higher rainfall. This causes more lush growth of unmanaged vegetation such as mustards and other weeds that support a higher abundance and survival of the bugs during the winter and spring.
Solutions
Lygus bugs are difficult to manage. When damage on plants can be recognized, the bugs themselves are commonly no longer present. Whether their feeding damage will become abundant or present at all is generally not predictable unless the bugs are observed feeding on those plants.
Control broadleaved weeds that grow during the winter because many of these host lygus bugs that move to gardens and landscapes during later generations. Weed hosts include knotweed, lambsquarters, London rocket, mustards, redroot pigweed, shepherd’s-purse, and wild radish.
Where lygus bug is believed to have been the cause of damage to vegetables during previous growing seasons, the bugs can be excluded with fine-mesh cloth or screening installed on hoops or otherwise held above plants so the bugs cannot feed and oviposit through the covering. No insecticides are recommended for control of lygus bugs in gardens and landscapes.
Adapted from Pest Management Guidelines: Strawberry and Pests of the Garden and Small Farm: A Grower's Guide to Using Less Pesticide, University of California Statewide Integrated Pest Management Program (UC IPM). |
Lygus bug feeding when this strawberry was very small resulted in distorted growth.
Lygus bug feeding when these pears were young resulted in dead, crescent-shaped lesions.
Adult pale legume bug.
Adult tarnished plant bug.
Adult western tarnished plant bug.
First instar (lower left), third instar (top), and fifth instar of western tarnished plant bug.
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