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Spruce sawflies are various sawfly species found in North America that attack spruce. There are multiple species of sawflies, including, European spruce sawfly, yellow-headed spruce sawfly, green-headed spruce sawfly, little spruce sawfly, and spruce webspinning sawfly. Each kind of sawfly attack particular parts of the spruce during different times of the year. These insects first begin feasting, or attacking, spruce as () and continue until they are fully grown. ==Yellow-headed spruce sawfly== The yellow-headed spruce sawfly (''Pikonema alaskensis'' Rohwer) is widely known in the northern United States and Canada as a destructive pest of spruce (Shenefelt and Benjamin 1955).〔Shenefelt, R.D.; Benjamin, D.M. 1955. Insects of Wisconsin forests. Univ. Wisconsin, Coll. Agric., Exten. Serv. – Experiment Sta. and Wisc. Conserv. Dep., Madison WI. 110 p.〕 It attacks white, black, Norway, and Colorado blue spruces. The larvae at first prefer new foliage, but after becoming about half-grown, old needles are included in their diet too. Young plantations become susceptible a few growing seasons after establishment. The insect overwinters underground as a larva in a dark-brown papery cocoon encrusted with soil (Rose and Lindquist 1985).〔Rose, A.H.; Lindquist, O.H. 1985. Insects of eastern spruces, fir and, hemlock, revised edition. Gov’t Can., Can. For. Serv., Ottawa, For. Tech. Rep. 23. 159 p. (cited in Coates et al. 1994, cited orig ed 1977)〕 In the spring, the cocoon changes into a pupa, from which the adult emerges, mainly in May or June at about the time the spruce bud scales are sloughed off. The spring-emerging females lay their eggs in shallow slits at the base of expanding needles, generally 1 per needle. Hatching takes place in 6 to 14 days, and the larvae feed in groups on the new needles until only short, brown stubs are left, after which the larvae move back on the twig to feed on the older needles until they are full-grown—usually in late July or early August. Larvae drop to the ground and spin overwintering cocoons. A single generation occurs per season. Larvae are about 20 mm long when fully grown, and have chestnut-brown to reddish-brown heads. The body is yellowish-green above, lighter beneath, with a double row of broad, brown to olive-green stripes along the back, with another green stripe on each side. A small spot occurs near the legs on all but the rearmost section of the body. In spite of the large numbers of parasites that attack this sawfly, planted spruce can be heavily damaged. Any insecticide would maximize larval mortality when applied about 10 days after bud caps have been shed, but when only few trees are infested, the larvae can be picked off by hand. Other than in young plantations, this sawfly generally causes little or no mortality of trees in spite of its widespread presence. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Spruce sawflies」の詳細全文を読む スポンサード リンク
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