SHADE TREE INSECTS 69 



Description. The adult, a sawfly, is a small, black, fly-like insect about 1/8 

 inch long with a wingspread of about }/i inch. These sawflies may be seen hover- 

 ing above young birch trees or crawling over the leaves all summer. 



The oval-shaped eggs are ver\- minute, being 1/50 inch in length. Their pres- 

 ence in a leaf may be detected by the minute raised areas in the upper and lower 

 leaf surfaces. When a leaf is held up to the light the eggs can be plainly seen. 



The larvae are typical leaf miners. They are slightly flattened and in the 

 young stages are translucent white in color. When fully mature they are yellowish 

 white. Near the head are the three pairs of true legs which are small but distinct. 

 The newly hatched larvae are less than 1/25 inch long and when full grown almost 

 J4 inch long. 



The cocoons in which the larvae pupate in the ground are small earthen cells. 

 The pupae inside are white, almost 1/6 inch long, and show the presence of all the 

 adult appendages. 



Life History. The first tiny sawflies begin to appear about the middle of May, 

 and lay their eggs in the young developing birch leaves, often when the leaves 

 are J^ to ^ inch long and before they completely unfold. Eggs are not deposited 

 in the older mature leaves in which the tissues have hardened. Because of this 

 selection only the newly developing leaves at the tips of the branches are selected 

 for egg laying as the season advances. The eggs are laid separately throughout 

 the central area of the leaf. They soon hatch and each young larva begins to 

 excavate a mine in the leaf tissues. The mines are separate when small; but, as 

 the larvae increase, the mines coalesce and form a large, hollowed-out, brown area 

 in the leaf. Although the period of development varies widely, usually the 

 larvae mature in about 10 to 15 days. They then emerge from the leaf, drop to 

 the ground, burrow beneath the surface and form a cocoon of particles of soil, 

 transform to pupae, and emerge as adults about 2 or 3 weeks later. There are 

 perhaps 3 generations a year, but due to the variation in the time of development 

 the various generations overlap, especially toward the end of the season. Fast- 

 growing birch sprouts which put out an abundance of new foliage all season, may 

 be expected to be attacked constantly during the growing season. On well- 

 grown trees, howe\'er, on which the foliage hardens in midsummer, the infestation 

 will decrease sharply after that time. From early August on, an increasing 

 proportion of the larvae which enter the soil remain there over winter as prepupae 

 and transform to pupae and adults the next spring. 



Control. Recent experiments indicate that the eggs can be killed by a contact 

 spray of 40 percent nicotine sulfate at the rate of 1 pint to 100 gallons of water. 

 For the first generation of eggs, 2 applications spaced about a week apart should 

 be applied. The first should be put on in late May. For eggs of the second 

 generation, 3 applications spaced about a week apart are necessary, the first to 

 be applied about the first week in July. Both surfaces of the leaves should be 

 well sprayed. 



Friend, R. B. Jour. Econ. Ent. 24(1) :171-177. 1931. 

 Friend, R. B. Conn. Agr. Exp. Sta. Bui. 348. 1933. 



Birch Leaf-JMining Sawfly 



Phyllotoma nemorata Fallen 



About 1905 this insect was first found in America in Nova Scotia. At first 

 it was thought to be a newly discovered native species but later it was found to 

 be of European origin. It aroused little concern until 1927 when a very heavy 



