Lygus lineolaris, was first identified in British Columbia as a serious pest in bareroot and container nurseries in 1983. Damage can now be found at many nurseries and on most species across the province. Feeding by the adults and nymphs initially causes distortion of seedling terminal shoots, which later become multiple-leadered. This insect is an important pest of many agricultural crops and has a wide range of native hosts.
To date, the major host of the Lygus bug in British Columbia appears to be 1+0 bareroot (Figure 95) and container pine, although significant damage has also occurred on larch, Douglas-fir, and both 1+0 and 2+0 spruce. Lygus bugs feed on rapidly growing tissue such as growing tips, buds, and flowers. Both adults and nymphs feed by sucking plant juices, while simultaneously introducing a toxic saliva into the plant. General symptoms begin to appear within a few weeks and an elongate scar often shows down one side of the stem.
Feeding usually results in the loss of apical dominance and the development of weak multiple leaders. In pine, a distinctive terminal distortion results. Needles (Figure 96) are thicker and shorter, and twisted with the entire seedling tip curled over. Mature foliage may develop. The bud, if present, grows at an angle. In spruce, attack results in a checking or shepherd's crook forming at the stem tip, which subsequently often develops into two leaders. Damage in both bareroot and container nurseries has an edge distribution. In pine, damage often occurs in patches of two to five seedlings; in spruce it appears as a single attack.
Lygus bug adults (Figure 98), 7 mm long and half as wide, are broad, flattened, and oval-shaped with a small projecting head. They range in color from yellowish-green to reddish-brown and are covered with small, irregular splotches of white, yellow, reddish-brown, and black. Adults overwinter in the crowns of plants and in debris, and remain active under mild conditions. They become active very early in the spring, feeding on newly developing buds and shoots. Soon after, emerging adults mate and insert single eggs full length into many different plants. Eggs are elongate, slightly curved, and the outer end of each is cut off squarely, with a lid that is usually flush with the stem. Nymphs, which emerge in about 10 days, are 1 mm long, yellowish-green, and similar in appearance to aphids, although they move around more rapidly. Nymphs grow quickly, molting five times. Older nymphs are marked with rounded black dots: four on the thorax and one on the base of the abdomen.
The life cycle is completed in 3 or 4 weeks. There are two or three generations per year in British Columbia. By late summer, Lygus bugs occur everywhere in profusion, but because of their protective coloration and hiding habits they are rarely noticed.
It may be necessary to control these insects, which are very active throughout the growing season and readily invade nurseries from mid-May to late September. Stock is most susceptible during the 1st year of growth, from the time true or secondary needles have developed until budset. A preventive program of insecticidal foliar sprays applied during the 1st week of June, July, and August has reduced seedling damage in areas where the insect has been a chronic pest. Because the Lygus bug has a wide range of native hosts, keeping the nursery and surrounding area free of weeds and other possible alternative hosts will help reduce migrating populations.
Schowalter, T.D. 1987. Abundance and distribution of Lygus hesperus (Heteroptera: Miridae) in two conifer nurseries in western Oregon. Environ. Entomol. 16: 687-690.
Schowalter, T.D., D.L. Overhulser, A. Kanaskie, J.D. Stein, and J. Sexton. 1986. Lygus hesperus as an agent of apical bud abortion in Douglas-fir nurseries in western Oregon. New Forests 1: 5-15.
Shrimpton, G. 1985. Four insect pests of conifer nurseries in British Columbia. In Western Forest Nursery Council - Intermountain Nurseryman's Assoc., U.S. Dep. Agric. For. Serv., Gen. Tech. Rep. INT-185: 119-121.
|
Principal, locally grown hosts |
Host age and season when damage appears |
|
Nursery type and location |
|
|
|
|---|---|---|---|---|---|---|
|
Bareroot |
Container |
|||||
|
Age |
Season |
Coastal |
Interior |
Coastal |
Interior |
|
| All species, larch, Douglas-fir, spruce, especially pines |
1+0 |
Spring through summer |
Yes |
Yes |
Yes |
Yes |
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Figure 95. Lygus bug damage on bareroot pine
Figure 96. Bareroot pine with symptoms of Lygus bug feeding. Note stunted needles and twisted terminal.
Figure 97. Life history of Lygus bug (two or three generation per year).