|1Insect ecologist, Lake States Forest Experiment Station, Forest Service, U.S. Department of Agriculture. The author is assigned to the Station's field office in East Lansing, which is maintained in cooperation with Michigan State University.|
The introduced pine, sawfly (Diprion similis (Hartig)) in North America was first discovered in 1914 in a nursery in New Haven, Conn. This insect might have been introduced in the cocoon stage on nursery stock or packing material from Holland. Since its arrival, it has advanced steadily westward, reaching Pennsylvania before 1920 and Ontario by 1931. The present range in North America is along the Atlantic seaboard from Maine to Virginia, across the, Central and Lake States, through parts of southern Ontario and Quebec, and westward to Minnesota. In its homeland in the Eastern Hemisphere, this sawfly occurs throughout most of Eastern and Northern Europe and part of Russia.
Hosts and Injury Favored hosts of all sizes are susceptible to attack by Diprion similis Both natural and planted pines are attacked. In general, the five-needle pines are preferred, but several species of two-needle pines are fed upon. Common hosts are white pine (Pinus strobus L.), Scotch pine (P. sylvestris L.), jack pine (P. banksiana Lamb.), and red pine (P. resinosa Ait.). Eggs are laid and larvae feed on several other less common species of pine also.
Hosts and Injury
Favored hosts of all sizes are susceptible to attack by Diprion similis. Both natural and planted pines are attacked. In general, the five-needle pines are preferred, but several species of two-needle pines are fed upon. Common hosts are white pine (Pinus strobus L.), Scotch pine (P. sylvestris L.), jack pine (P. banksiana Lamb.), and red pine (P. resinosa Ait.). Eggs are laid and larvae feed on several other less common species of pine also.
Austrian pine (Pinus nigra Arnold) appears to be fairly resistant to injury by the young larvae. The older larvae, however, will feed readily on its foliage.
White pine is preferred by the female sawfly for egg laying, but egg survival is not as high on white pine as on other common pines. However, the greater number of eggs laid on white pine and a very high survival of young larvae contribute toward making it the most injured species.
Injury to trees is caused by the loss of needles. Young larvae consume only the outer, tender parts of the needles, so that the first evidence of damage is the straw like remains of these needles. Older larvae consume the entire needle and nibble the bark. First-generation larvae feed exclusively on the old foliage because they emerge and feed in the spring before the new needles are fully developed. Later generations feed indiscriminately on old or new needles.
Where the insect population is high enough, the host may be denuded in one season. Late season defoliation, when buds are already formed, is sufficient to kill most conifers; and branch killing is common. Despite occasional high populations locally, only a small amount of mortality has occurred to date. Trees under heavy larval attack, however, lose considerable height growth.
The egg, when freshly laid, is pale whitish blue, translucent, and shiny. Just prior to hatching it becomes bluish green to dark green. It is nearly oval with blunt rounded ends. A few days after it is laid, it swells slightly, becoming about 1.5 mm. long by 0.5 mm. wide.
The newly emerged larva has a dull gray body with black legs. When fully grown, it is about 25 mm. (I inch) long with a shiny black head (fig. 1 A, B). The body is marked on top along the entire length by a dark brown or black double stripe. Lateral to this is a wide irregular yellow stripe broken into oval yellow patches by numerous, narrow, transverse lines. The background color of the body is dark brown or black, but is nearly inconspicuous because of the numerous yellow and white spots on each segment. The, underside of the larva is pale yellow or white.
Figure 1. Larvae of the introduced pine sawfly: A, Lateral view: B, dorsal view (X 4)
|The cocoon is cylindrical with hemispherical ends (fig. 2). It is
finely textured, somewhat glossy, and brown. The average size is 9 mm. long by
5 mm. wide.
The adult is fly-like in general appearance but has four shiny transparent wings. The average length of the female is 8 mm., that of the male 7 mm. Both sexes have black heads and thoraxes; the abdomen of the female is yellow and black, that of the male black to brown. The male can be easily distinguished from the female by his broad feathery antennae.
|Life History and Habits
The first eggs of the season are laid from early to mid-May or later depending on locality. Each female may contain more than 100 eggs, but the average is about 70. The eggs are deposited serially in slits cut in the edge of old needles, and generally about 10 eggs may be found on 1 needle.
Larvae emerge from the eggs in 10 to 14 days. At first the larvae feed gregariously, but as they become older they disperse and become solitary feeders
Figure 2. Cocoons of the introduced pine sawfly (X 6).
|Cocoon spinning begins in early July, and pupation occurs shortly
after. The peak of pupation takes place in late July. Cocoons are most
frequently spun on the host among the needles, at the bases of the small
branches, or on the trunk in bark crevices. Occasionally, they are found on
non-host trees, shrubs, or grasses.
Peak adult emergence occurs in early August, and egg laying commences shortly thereafter. Some sawflies do not emerge but remain in the cocoon as a prepupa in a resting stage, called diapause. These do not emerge until 1 to 3 seasons later.
Second-generation larvae emerge in 7 or 8 days and feed until sometime in September. Most of the cocoons of this generation are spun in the leaf litter beneath the host. If the weather is favorable, a few of these insects pupate and emerge as adults soon after to produce a partial third generation, which develops until the advent of cold weather. Most, however, overwinter as prepupa in the cocoons and pupate the following season. Adults emerge from April until June. Because of the length of the adult emergence period, eggs may be deposited from early May to mid-June. As this causes some overlap between the first and second generations, all stages may be found during the season.
Male sawfly adults are usually more common than females. Females that do not mate may lay fertile eggs, which develop into males.
There is considerable evidence that parasites, predators, and low winter temperatures are important in keeping Diprion similis populations at tolerable levels. Several hymenopterous and dipterous parasites have been reared from the eggs, larvae, and pupae of D. similis. The parasite Monodontomerus dentipes (Dalm.), originally introduced from Europe, is undoubtedly the most important. Nearly 90 percent parasitization has been recorded from New Jersey and 75 percent from Montreal from this parasite alone. Other parasites too my cause up to 30 percent mortality in a given stage of the insect.
Little is known about the importance of predators. Various species of insects feed on this sawfly. Larvae have been observed being consumed by different species of spiders, and adult sawflies are found occasionally in spider webs. Second-generation cocoons suffer heavy predation by rodents burrowing in the litter. Predation by birds, especially the chickadees, appears to be heavy.
Low winter temperature is an important natural control. Up to 50 percent of the larvae of the second generation are commonly killed before they reach the cocoon stage. Cocoos on the tree above snow level suffer complete mortality. Snow cover protects the cocoons in the litter or on the lower parts of the host tree.
Large-scale chemical control is rarely recommended for this sawfly. As individual trees or short hedgerows are commonly attacked, hand or power sprayers are frequently used. Malathion is effective when used at the following dosage: 2 teaspoons of malathion (50-percent emulsifiable concentrate) is added to 1 gallon of water and mixed thoroughly. Trees should be sprayed shortly after larvae emerge. Because developmental periods overlap and two generations per year emerge, control may he needed more than once.
Caution: Malathion is poisonous to man and animals. Follow the directions and heed all precautions on the container label. Handle it with care. Special caution is required when using concentrates: wear rubber gloves and avoid contact with eyes, nose, and mouth. After mixing chemicals or spraying, wash exposed body surfaces with soap an water. Change clothing if spray has been spilled on it.
Do not apply malathion where there is danger of deposit on fruits or vegetables or on plants grazed by cattle. Avoid overdosing. Do not apply near streams, ponds, and lakes.
Store chemicals in plainly labeled containers out of reach of children. Destroy used containers.
A destructive pine sawfly introduced from Europe, Diprion (Lophyrus) Simile Hartig. W. E. BRITTON. Jour. Econ. Ent. 8: 379-382. 1915.
Parasitism of the European pine sawfly, Diprion (Lophyrus) Simile Hartig, Hymenoptera, Tenthredinidae, in Pennsylvania. E A. HARTLFY. Jour. Econ. Ent. 16: 386-388. 1923.
The imported pine sawfly. W. MIDDLETON. U.S. Dept. Agr. Dept. Bul. 1182, 21 pp., illus. 1923.
Observations on the habits of an introduced pine sawfly Diprion Simile Htg. H. A. U. MONROE. Canad. Ent. 67: 137-140. 1935.
The effect of different host species on the oviposition and survival of the introduced pine sawfly. C. H. TSAO and A. C. HODSON. Jour. Econ. Ent. 49: 400-401. 1956.
Egg-laying habits of Diprion Simile Hartig. M. P. ZAPPE. Jour.Econ. Ent. 10: 188-190. 1917.
Formatted for the Internet October 1998
U.S. GOVERNMENT PRINTING OFFICE: 1966 O 794-643
|Pesticide recommendations in publications from 1975 or earlier may no longer be be valid. Some pesticide products may not be registered anymore or may not be available to the public for use. For current recommendations, consult your local forest pathologist, county agricultural agent, or state extension agent about restrictions and registered uses of particular pesticides.|