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the maximum of one pair. However, as it was impossible to keep these cages under constant observation the actual number of copulations for each pair in confinement was not secured but was doubtless greater than that given. The time of each act was not long and the beetles during copulation were easily disturbed.
AGE AT BEGINNING OF COPULATION AND DURATION OF PERIOD.
Copulation was not observed among the beetles before the hibernation period, so all beetles must have been at least nine months from the time of hatching before reaching sexual maturity. The majority were nearly ten months of age at the beginning of this period. They continued to mate for nearly two months so the age at the end of this period would average about twelve months.
So far as is known no adult of this species deposits eggs until after passing the hibernating period, and moreover this function does not appear normally until after fertilization. Since egg laying occurs during the months of June, July and August, as will be explained later, the beetles are then never less than nine months from the time of hatching. Some individuals may be thirteen months of age at the time they deposit their last eggs.
PERIOD OF OVIPOSITION AND NUMBER OF EGGS LAID BY BEETLES.
In general the oviposition period extends from the first week in June until the middle of August, the maximum number of eggs being deposited during early July. In 1915 the first eggs were found at Fredonia on June 11, but as we were unacquainted with the eggs and especially the place of oviposition it is likely that the first eggs were laid several days earlier and not found. The first eggs discovered during 1916 were found under natural conditions on June 5. This was nine days after the first beetles were observed in coitu. For more than a week after emergence the beetles did not copulate freely so it was June 7 before we secured the first cages of copulating pairs to observe egg-laying habits and the first eggs were deposited in the cages on June 10.
Four copulating pairs of beetles were caged on June 7 and another pair on June 10; and on June 14 thirty-one additional couples taken from cherry foliage during mating were placed in individual cages. The cages consisted of glass jars of different sizes in which soil and leaf mold were placed to a depth of about one inch and careful attention was given to keep the soil conditions similar to those at the bases of cherry trees.
Foliage of the bird cherry was added to serve as food and a piece of growing bird-cherry wood was placed in the soil to imitate a growing tree, particular attention being paid to have a portion of the wood enveloped with foliage. Most of the eggs were placed on this bark just beneath the surface of the soil. It was found that the size of the cage had practically no effect on the egg laying but that the proper amount of moisture was an important factor. The cages of 1915 proved that the beetles are very fastidious regarding conditions for oviposition and that they will not lay eggs unless conditions are to their liking. Owing to the time required to find the eggs and the number of cages it was necessary to examine one-half, only, of the cages each day, hence the egg record is given in two-day periods. It was feared that unless several cages were used we would fail to secure results comparable to conditions in nature since in all life-history work individual variation is a factor that must be kept in mind. From these cages oviposition records were secured which are summarized in Tables III to VI inclusive.
Table III.— Egg-laying Period And Duration Of Life Of The Cherry LeafBeetle At Fredonia, N. Y., During 1916.
Total egg-laying period for all females 66 June 5 to Aug. 9.
Longest egg-laying period for a single female 54 June 17 to Aug. 9.
Shortest egg-laying period for a single female 10 June 17 to June 26.
Average egg-laying period for a single female 28
Maximum number of days after June 8th that female lived 66 Aug. 13.
Minimum number of days after June 8th that female lived 18 June 26.
Average number of days after June 8th that female lived 42 July 20.
Maximum number of days after June 8th that male lived 109 Sept. 25.
Minimum number of days after June 8th that male lived 21 June 29.
Average number of days after June 8th that male lived 41 July 19.
As will be noted in Table III, the egg-laying period for all females in the cages extended from June 9 to August 9 or about sixty-one days, and the total egg-laying period observed at Fredonia during 1916 was sixty-six days. After June 26 the number of females was gradually reduced by death until by August 9 only one female remained. In this respect the caged insects closely followed conditions in nature, barring accidental deaths. It was our aim to secure the copulating pairs on the same date but the sluggishness of the beetles due to rains and low temperatures for over a week prevented this. However, very few eggs were laid at the bases of cherry trees before June 15 and we believe that the results in the cages are a fair index of the number of eggs laid under outside conditions.
The number of eggs laid by a female beetle varied greatly in the thirty-six cages as Table IV shows.
Table IV.— Number Of Eggs Laid By The Cherry Leaf-beetle At Fredonia,
N. Y., During 1916.
Largest number of eggs laid by a single female 294
Least number of eggs laid by a single female 10
Mean number of eggs laid by a single female 93±7
Standard deviation (eggs) 62.8±5.0
Coefficient of variability 67. 8db5.5
Number of cages of paired beetles 36
The excessive variation in the number of eggs laid by a female as shown by the standard deviation, coefficient of variability and the high probable errors, illustrates the fastidiousness of the beetles as regards environment daring egg laying. This variation occurred notwithstanding the fact that an effort was made to keep conditions the same in all the cages.
We are inclined to believe that the true mean number of eggs laid is somewhere between the average and the maximum given in the above table; for it is probable that the number of eggs secured in several of the cages is below that which the beetles would normally have deposited in nature. It would seem that in some of the cages with low records we failed to secure the proper conditions for egglaying and therefore the beetles refused to deposit the normal number of eggs. If the records of five low cages are left out of consideration the mean would show one hundred five eggs per female.
The number of eggs deposited in all the cages during each period shows marked variation. Attention is called to Table V, which contains the egg-laying record of the insects under observation.
Table V.— Number Of Eggs Deposited By All Caged Beetles For Each TwoDay Period. Fredonia, N. Y., 1916.
The average number of eggs per female during the same period is given in Table VI. The meteorological conditions occurring during the period of egg-laying are shown in Fig. 18.
Table VI.— Number Of Eggs Laid Per Female Cherry Leaf-beetle For Each Two-day Period, Fredonia, N. Y., 1916.