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The maximum length of the third instar is 8 days and the minimum 2 days, while the average period for two years at Fredonia and North East, Pa., is 3.7 days.
TOTAL FEEDING PERIOD OF LARVA.
The data bearing on this point consists of records by Herrick * and Matheson on nine larvse, those of Cushman2 and Isley on two hundred twenty-seven larva), and our observations on one hundred forty-four larvse. These are tabulated in Table XIII.
Table XIII.— Total Feeding Period Of Larva Of The Cherry Leaf-beetle.
From these figures it would appear that from twelve to thirteen days constitute the average period of the larvse during a normal year in the Lake Erie valley. The Ithaca records indicate that on the Alleghany plateau of western New York the average length of life of the larva may be several days longer.
When the larvae have completed their growth they burrow into the leaf mold or, if not present, into the soil, which they penetrate a very short distance, usually about one centimeter, where they form a small spherical cell. Sometimes the larva forms scarcely any cell but transforms underneath rubbish. Moisture appears to be the chief factor in determining the depth of these cells. In such situations the larvse pupate and the pupae later transform to adults. The larvse do not transform immediately on their entrance
^oc. cit. p. 947.
2Loc. cit. pp. 12 and 14-17.
in the ground but require a number of days before undergoing a change in form. Cushman1 and Isley found that the period was from five to eight days, depending on the temperature, and they also found the pupal stage varied from seven to eleven days. By means of Comstock root cages efforts were made to obtain pupae, where they could be under constant observation, but our efforts resulted in failures. The only data obtained that bears upon the duration of the pupal period were the number of days that the insects were actually in the ground. In our cages there was considerable mortality, and of one hundred forty-four larvae that entered the ground only fifty beetles finally emerged. The data bearing on the extent of the period occupied by the insect in the ground are summarized in Table XIV.
Table XIV.— Period Of Existence Of Insect In The Ground During Pupation.
As will be observed, there is quite a little variation in the figures given by the different observers. This is believed to be due to variations in climate but may be partially due to differences in methods of rearing the insects. As will be explained later, weather conditions during 1915 and 1916 were somewhat abnormal, the two years differing greatly in the Lake Erie valley. The climate of Ithaca during 1915 differed markedly from that of the Lake Erie region.
PERIOD FROM HATCHING TO EMERGENCE OF ADULT.
The total period of development of the cherry leaf-beetle from the larval stage to adult was found by all observers to vary considerably, and in our studies there was a difference of twenty days
^oc. cit. p. 12.
between the minimum and maximum periods. As shown in Table XV the records indicate that about one month is required for the average individual to reach the adult stage after hatching from the egg. If to these figures there are added thirteen days for the egg stage, the period for the complete development of the insect ranges from forty to forty-seven days for the Grape Belt along the shores of Lake Erie and about forty-eight days on the higher lands to the south.
Table XV.— Total Developmental Period Of The Cherry Leaf-beetle.
CLIMATE VARIATION DURING 1915 AND 1916.
The climatic conditions during the developmental period of the cherry leaf-beetle during 1916 are shown in Figs. 18 and 19.
In order that the results of the studies by various workers may be fairly compared the meteorological conditions that prevailed in the different localities where the insect was studied should be noted (Table XVI). In regard to 1915 we have used the weather reports of Westfield, N. Y.,1 which is only fourteen miles from North East, Pa.; and the location of the cooperative observer is about the same distance from Lake Erie and at only a slightly greater elevation than the laboratory where Cushman and Isley conducted their studies. We have also used the Westfield records to secure the departure from normal for 1916 since the Fredonia records do not cover a long enough period for such a calculation. As the Westfield observer is only fourteen miles distant and only slightly higher than the Vineyard Laboratory no great error is introduced. The amount
1 Wilson, W. M. Climatological Data, New York Section. U. S. Dept. Agr., Weather Bureau. June to September 1915; and June to August 1916.
of cloudiness during both years except at Ithaca * and all other records for 1916 were obtained from the report of our laboratory at Fredonia.
Table XVI.— Climatic Conditions During 1915 And 1916 At Westfield, Ithaca And Fredonia, N. Y.
* From the records of the observer at Volusia (5 miles from Westfield but 500 feet higher) since the data are not given in the Westfield records.
SUMMARY OF THE SEASONAL HISTORY.
With respect to western New York the insect emerges from the pupal cell as an adult during August and the early part of September. In 1916 the adults emerged from July 31 to September 2, but during 1915 adults emerged as late as September 18. Little feeding is done at this season and during the latter part of September the beetles seek sheltered locations in which to pass the winter. They burrow for a short distance into the soil and form their hibernating cells, where they remain for nearly eight months. Emergence from hibernation takes place during the latter part of May of a normal year. After the beetles abandon their winter quarters they feed voraciously for a time on the bird cherry and then begin to disperse. This movement of the beetles is usually to other bird cherry trees. However,
12 Furnished thru the kindness of Prof. W. M. Wilson.