The mature larva (fig. 122) is a thick, legless grub, resembling that of the June beetle. It measures from 12 to 13 millimeters in length, with

a maximum width of 4 millimeters. It is
white or yellowish white in color, with a
reddish brown head. The heavily chitinized
mouth parts are black. There are no out-
standing markings that distinguish this grub
from many other wood-
boring larvæ, and the
surest way of identifica-
tion is by its habits.

The pupa

Pupation begins in the last few days of June and continues throughout July. The pupal period varies from ten to eighteen days, depending largely on weather conditions. Pup formed early in July require only ten days, while those of late July require as long as eighteen days, to transform into adults. From two to three days are required for the adult to become fully colored and hardened. Those maturing early in the season usually remain in the pupal cells for two or three weeks before emerging. A general

emergence of the adults occurs during the latter part of July. The beetle, when ready to leave, simply cuts its way out through the frass that had been packed in the burrow by the larva before pupation.

The pupa (fig. 123) measures 9 millimeters in length. It varies from almost white to yellowish in color, the brown spiracles showing distinctly. Scattered over the dorsal surface are many small spines. Some of them stand out prominently on the pro

The tip of the abdomen is armed with a pair of strong, incurving, brown, chitinized hooks.

Observations of European workers

The life history of the insect as outlined in the preceding paragraphs differs very markedly from that given by European workers, all of whom record the beetles as hibernating and state that mating and oviposition takes place during the spring months.

FIG. 122. THE MATURE LARVA

The latest worker, Scheidter (1913), states that the beetles emerge from hibernation about the first of May, and that in a short time mating takes place and egg laying continues throughout the summer.

According to his observations, these eggs do not hatch until the following spring, so that each year both eggs and beetles of different generations hibernate. He concludes that with this insect there is a complete generation every two years: beetles emerging in 1910 hibernated, and laid eggs in 1911; these eggs hibernated, and hatched in the spring of 1912, the beetles reaching maturity in late July and August; these beetles in their turn mated and oviposited in the following spring.

Munro (1914) finds that in northern Scotland there is a complete generation every year, the beetles hibernating and ovipositing during the spring months.

Caesar (1916) finds that in Ontario considerable numbers of the beetles appear in the early spring months, but he does not know whether these have hibernated as beetles or as larvæ or pupa. He also failed to determine whether they lay eggs during the spring months.

It would thus seem that the life history and habits of this insect are complex and vary greatly.

CONTROL MEASURES

When the writer began work on the poplar and willow borer, no efficient control measures had been devised. The general recommendations had been the cutting-out and destruction of infested trees. Schoene (1907 a)

states that the use of arsenicals during July and August will kill the majority of the beetles and reduce infestation in nurseries. In practice it has been found that paris green and lead arsenate, even when used in large quantities, have no effect in reducing the annual loss. At the time when the writer began to look into this problem, in 1913, several large nurseries in New York State had about decided to stop raising carolina poplars, although there was a steady demand for this stock.

Early observations led the writer to the conclusion that the insect could be destroyed by some contact spray applied to the trunks of the trees in autumn, after the leaves had fallen, or in spring before the young larvæ had begun actively feeding. This seemed very reasonable, owing

It

to the fairly exposed condition of the young larvæ in their burrows. seemed that some oil emulsions would penetrate the outer bark or be absorbed through the very small quantity of frass at the entrance to the burrows, and would destroy the insects. Consequently, varying strengths of miscible oils and kerosene emulsion, applied both in the fall and in the spring, were experimented with. In order to secure a strong penetrating fluid, it was felt that carbolineum avenarius should be given a thorough trial. Very little is known about the constituents of this preparation, and furthermore very little is known of its effects on actively growing or on dormant trees.

Experiments in 1913-14

In the fall of 1913, seventy-six badly infested two-year-old poplar trees were planted near the insectary at Cornell University (fig. 124). On Decem

ber 1, 1913, a part of this block was treated with scalecide at varying strengths, and a few trees were treated with carbolineum and its emulsion.' as indicated in table 1. This experiment was closely watched the following spring, but no injury to the trees could be noted except that the carbolineum-treated trees did not seem so vigorous as the others. However, they grew, and in 1916 they were large, healthy trees. Examination and careful count of the burrows in all the trees was made on June 17, 1914. The infestation is shown in table 1:

In the spring of 1914 a series of experiments was undertaken in a large nursery. Stock three years old was chosen, as it was the most readily available at the time. Badly infested trees were selected at one side of a large block which had been recently dug. Directly across the roadway was a block of young poplars. On March 31, scalecide at varying strengths, carbolineum, and carbolineum emulsion were applied to the trunks from the ground up to the young growth. The day was fair, but rain began to fall before the various treatments were completed. However, the rainfall was slight, so that it should have had no effect on the insecticidal qualities of the preparations.

The treated trees were examined carefully on May 14, 1914. The various treatments had no effect on the growth of the trees, every tree growing vigorously and there being no difference, as far as could be detected, between the checks and the trees under experimentation. In the checks the larvæ were actively at work and their abundance was

The carbolineum emulsion was prepared by dissolving I pound of sodium carbonate in 1 quart hot water, adding 1 quart of carbolineum, and stirring the mixture vigorously.

of

indicated by the amount of sawdust exuding from the numerous burrows. All the trees treated with different strengths of scalecide showed just as high a percentage of infestation as did the checks. This preparation had no appreciable effect. In the trees treated with carbolineum, either pure or as an emulsion, not a trace of infestation could be found. After a search of several hours, one shriveled and blackened larva was discovered in its burrow. It was not desirable, however, to injure the trees too much by cutting into all suspicious egg punctures.

The trees were again carefully examined on June 18, when the previous observations were confirmed. The checks and the trees treated with scalecide were nearly all badly infested, many trees having from eight to ten borers present, while a few, both of the treated trees and the checks, were apparently free from infestation. The trees treated with carbolineum and its emulsion were growing even more vigorously than were the untreated trees, and not a trace of the work of the borer in any one of the twelve treated trees could be discovered. These preparations colored the trunks of the trees deep brown, but other than that no injury could be seen.

Experiments in 1914-15

In view of the possibility that such perfect control might be due to other causes than the effect of the treatment, a larger series of experiments was planned for the fall of 1914 and the spring of 1915. The miscible oils were discarded, and kerosene emulsion, which had been recommended for the control of the locust borer (Cyllene robinia), was given a trial. In a block of over ten thousand trees, ready for digging in the fall of 1915, rows were selected at the end showing the greatest amount of the feeding work of the beetles. On December 4, 1914, groups of twenty trees each were treated respectively with pure kerosene emulsion, carbolineum emulsion, and carbolineum. Rows for checks were left between the treated rows. The material was applied directly to the trunks, up to the younger growth. On April 9, 1915, twenty-five trees were treated with pure kerosene emulsion, fifty with carbolineum emulsion, and twentyeight with pure carbolineum. Just previous to these treatments the trees in the whole block had been pruned carefully. The material was carefully brushed over the trunks, covering all the cut surfaces of the recently removed branches.

The trees were examined on June 28. The block as a whole showed severe infestation, sawdust being present at the base of a great many trees, and this could be seen for a long distance down the nursery row. In the rows treated with carbolineum or its emulsion no sawdust, could be seen and the trees were growing vigorously, the trunks showing a deep