SHADE TREE INSECTS 71 



infestation occurred over wide areas in Maine, causing the birch foliage to turn 

 brown as if scorched by fire. The insect has since spread into New Hampshire, 

 across into northeastern New York, and also into parts of Massachusetts. Although 

 all species of birch except black birch, Betula lenta, have been reported attacked; 

 white birch, B. papyrifera, and gray birch, B. populifolia, are evidently preferred. 

 The leaves of alder and hazelnut have also been reported mined. The larvae 

 e.Kcavate blotchy mines in the tissues of the leaves. The affected areas turn 

 brown but, unlike those mined by the birch leaf miner, Feniisa pumila, which 

 become wrinkled and contain frass, these leaves usually retain their normal form 

 and are fairly free from e.Kcrement. Severe infestation greatly reduces the rate 

 of growth in the season following the attack since it occurs when the trees are 

 storing up food for the succeeding \ear. 



Description. The adult female is from 1/8 to 3/16 inch long and 1/25 to 2/25 

 inch wide. The general body color is jet black. The wings are hyaline and 

 somewhat iridescent and the fore part of each front wing bears a dark spot. No 

 males have been reported found. 



When first deposited, the egg is about 1/50 inch long, half as wide, and oval 

 in shape. It is grayish-white in color. 



The full-grown larva is about 3-i inch long. The head is dark; the three body 

 segments behind the head, broad and flat; and the rest of the body segments 

 taper toward the rear. 



The pupa is creamy- white to yellow, changing to dark gray and black. All the 

 adult appendages are present and closely appressed to the body. 



Life History. Near Bar Harbor, Maine, the female sawflies begin to appear 

 about June 20, and may be found through part of July. In Massachusetts they 

 may appear a few weeks earlier, while in the higher and more northern parts of 

 Maine they may appear a few weeks later. The greatest emergence occurs on 

 warm, calm, sunny daA's. Soon after emerging, the female inserts her eggs through 

 a slit in the upper surface of the leaf into the inner tissues on the margin of the 

 leaf, usually on the two-thirds of the leaf margin nearest the tip. As a rule the 

 full-grown, well-formed leaves on the current year's stem growth are chosen for 

 egg laying. In a short time the leaf tissues surrounding the egg begin to darken 

 and the location of the egg can easily be seen. The egg apparently swells soon 

 after being laid and its presence can be detected by the appearance of a bulge on 

 the surface of the leaf. Twelve eggs may be laid in a single leaf. The eggs hatch 

 m about 20 days. As the larvae begin to feed, the mined areas appear as small 

 brown patches on the edges of the leaf. They are hardly noticeable at first but 

 in about a week show very plainly. As the individual mines enlarge they maj' 

 merge with one another. In feeding, the larvae shear through the veins. Most 

 of the mining is done in the outer two-thirds of the leaf blade. Feeding continues 

 into the fall. At that time, unlike the larvae of the other introduced birch leaf 

 miner, Fenusa pumila, which when full grown desert the leaf, hibernate, and then 

 undergo their transformation in a small earthen cell in the ground, the full-grown 

 larvae of Phyllotonia nenwrata form inside the leaf mine flat, usually circular cells 

 in which they pass the winter in the fallen leaves. Although larvae are said to kill 

 each other when their mines meet, it is not unusual to find 2 to 5 of these cells in a 

 single leaf. Each cell is about 4^ inch in diameter, quite tough, and coated inside 

 with a varnish-like, waterproof substance that protects the larva during the 

 winter. If an infested leaf is held up to the light, the enclosed larva in its cell 

 may be easily seen. In the latter part of June the larvae transform to pupae 

 inside these cells in the leaf and soon become adults, emerge, and fly away. Larvae 

 are said to develop somewhat more rapidly in gray birch than in white. In Maine 



