Tarnished Plant Bug
Plant bugs are a large, diverse family of insects that typically feed on plant parts with high rates of cell division, including buds and flowers. They feed by sucking sap from plants. They are believed to inject a toxic substance (possibly digestive enzymes) into the plant when feeding to break down plant tissues. Due to their feeding preference on buds, flowers, young developing fruit, or plant terminals, these bugs can cause economically important damage at relatively low densities. The time of feeding strongly influences the plant's response. There are typically one of five symptoms:
- abortion of young fruit or buds
- deformation of fruit
- necrosis near the site of feeding
- damage to seeds or
- reduced or deformed vegetative growth including tip die-back (when an apical bud or very young stem is the feeding site).
On a plant like cauliflower, a bronzing on the head results from feeding on many individual flower buds.
The tarnished plant bug is an important example of this group that can be a pest of vegetables and small fruit. Adults are bronze to dark brown fragile-looking insects, about 1/4inch long, with white marks or lines behind the head and sometimes along the front wing. They are about 1/4 inch long, and oval in shape. The back half of the front wing is membranous and held at a downward angle. The hind wing is membranous, and not visible unless the insect is flying, or you pull back the front wing.
Plant bugs have piercing-sucking mouthparts. The beak is three- or four-segmented, arises on the front of the head, and is held below the body and between the legs when not in use. Antennae are usually long and four- or five-segmented. Compound eyes are normally large. Nymphs (the immature stage) are typically green, although younger nymphs can be yellowish. Black spots are visible on the back of older nymphs. Nymphs do not have wings.
LIFE HISTORY AND HABITS
The tarnished plant bug is somewhat unique among plant bugs, in that it has an exceptionally wide host range. It has been recorded from 385 plants, including 130 economically important species. Examples include asparagus, celery, strawberries, cauliflower and broccoli, potatoes, beans, alfalfa (especially when it begins to flower), peaches, carrot, nursery stock and many species used as cut flowers. Its natural habitat is among species that are early colonizers, such as meadows and weedy patches that are let go to flower. The tarnished plant bug will typically begin to colonize these weeds when the plants begin to flower, populations will build while flowers are abundant, and populations will decline as the plant senesce. Examples of good hosts for tarnished plant bug are aster-like flowers, from daisy fleabane in the spring to ragweed, goldenrod, and horsetail later in the year. Other common flowers inhabited by tarnished plant bug include curly dock, cutleaf evening primrose, wild carrot, vetch, and clover. It is common to find populations much higher in those areas than in the crops themselves. Use a sweep net to detect the tarnished plant bug in these flowering weeds. A sweep net is also useful in the crops where the crop is not damaged by the sweeping. Otherwise, direct examination of the crop, including opening up plants to look in crevasses, etc., is necessary. White sticky traps will also catch tarnished plant bug adults.
The tarnished plant bug overwinters as an adult. It is active as soon as the weather is warm. Eggs are laid inside of plant tissue, in buds, soft, young stem tissue, or leaf viens. Eggs hatch in about 5 to 7 days. There are five nymphal instars. Development occurs as long as temperatures exceed about 50oF (10.5oC). Development slows or stops when temperatures exceed 94oF (34oC). As with all bugs, the life cycle involves just eggs, nymphs, and adults (there is no pupal stage, and no complex metamorphosis, thus the nymphs and adults tend to feed on the same material). It takes the tarnished plant bug as long 40 days (at 53oF, or 12oC), and as short as 12.5 days (at 93oF, or 34oC), to progress through the five nymphal instars. New adults begin to lay eggs in about 4 to 8 days, and will lay about 1 to 3 eggs per day and about 30 to 120 eggs per female over her lifespan. The sex ratio of new adults is 1:1, but the sex ratio in a new patch of flowering weeds often includes more females at first, and then shifts towards a 1:1 sex ratio.
Weed management influences tarnished plant bug management. Preventing weeds from forming young buds and flowers will keep populations lower in the weedy areas. Once weeds flower and the tarnish plant bugs colonize them, the bugs will tend to remain in the weeds unless the weeds start to senesce, dry, or are mowed. There are biocontrols that are being investigated to help reduce populations in these weedy areas, or along roadsides. Once the adults move into a crop, the type of management depends on the crop growth stage. When plants are vegetative, low densities can be tolerated. As plant begin to set buds, chemical controls may be needed. However, chemicals will have no effect on the egg stage inside of the plant tissue.
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