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earlier, but from numerous examinations made during October the majority of the eggs had not hatched even as late as October 28. Early in November, 1915, the eggs began hatching in great numbers, and this continued until the latter part of the month.
The larva When hatched, the young larva (fig. 116) is whitish in color and greatly resembles a miniature June-beetle grub except that the posterior end is the smaller and the larva is legless. It lies curled up in the egg cavity and begins at once to feed on the soft plant tissues. It is 1.5 millimeters in length, and 0.6 millimeter thick at its widest part. FIG. 116. YOUNG LARVA, It is regularly transversely wrinkled, but the skin
JUST HATCHED is nearly smooth except for scattering fine hairs. The head and the mouth parts are light brown except the mandibles, which are dark brown with black tips. The larva is cylindrical in shape, gradually tapering toward the posterior extremity.
The larva feeds on the tender tissues of the plant and soon reaches the soft cambium layer. Externally the beginning of feeding can be easily recognized by the blackish, wet frass that fills the outer part of the egg cavity. Feeding continues until cold weather, the early-hatching larvæ attaining a considerable growth.
In the spring feeding begins as soon as the weather has become sufficiently warm, usually the first week in April. Moist frass, black to brownish in color, is forced out of the burrow as the larva feeds ravenously. The direction of the larval channels is nearly always around the trunk or the branch, and the larvæ feed at first exclusively in the bark and the cam
bium layer. As a result the tree is frequently FIG. 117. CHANNELS MADE BY girdled, especially if several larvæ are at work LARVÆ IN A YOUNG CARO
near the same place (fig. 117). The larval LINA POPLAR TREE
channels vary greatly in shape; some are cylindrical and girdle the tree, others are flat, irregularly shaped chambers, while the majority zigzag in various directions through the cambium layer.
As the larvæ grow, the channels become larger and the amount of frass is greatly increased. In order to make room for the developing larva
the frass is forced outside the channel, by small openings cut through the outer bark. This is well shown in figure 118.
The larvæ become nearly full-grown before they leave the cambium layer. They then burrow at an angle upward into the hard wood of the tree. The beginning of this burrow is easily recognized, as the character and quantity of the frass suddenly changes. It becomes white and much larger in quantity, and consists of small particles of the wood cut off by the mandibles of the larva (fig. 119). In New York the formation of the pupal channel begins about June 1. By the middle of June the majority of the larvæ have begun their pupal burrows. At this
time, as one looks FIG. 118.
down the rows of BY poplars in the
nursery the white, sawdust-like frass can be seen distinctly on the infested trees and on the ground beneath them.
In the formation of the pupal chamber the larva bores upward and into the heart of the small nursery trees. This burrow varies from slightly over an inch to several inches in length. From three to four weeks are required FIG. 119. CHARACTER OF THE for its completion. When ready for pupation
GINS TO BORE INTO HEARTthe burrow is solidly packed with frass, the WOOD pupal chamber being formed at the upper end (figs. 120 and 121). The larva then places itself head downward in preparation for pupation,
FRASS FORCED OUT THROUGH SMALL OPENINGS MADE IN THE BARK YOUNG LARVÆ
WHEN LARVA BE
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
way of identification is by its habits.
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. Pupa 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 FIG. 120.
cells for two or three weeks
before emerging. A general
TWO-YEAR - OLD
CAROLINA POPLAR 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
PUPA IN SITU
notum. The tip of the abdomen is armed with a pair of strong, incurving, brown, chitinized hooks.
THE MATURE LARVA
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.
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 FIG. 122.
throughout the summer. According tɔ 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
to the fairly exposed condition of the young larvæ in their burrows. It 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