THE REARING OF INSECTS.
[General Directions.]—The importance, even to the mere collector, of rearing insects to obtain specimens for the cabinet has been referred to from time to time in these pages. The philosophic study of entomology, however, requires much more than the mere collecting of specimens, and one of the most profitable and, at the same time, most fascinating phases of the study relates to the life-history and habits. In no branch of natural history are biologic studies more easily carried on, or the biologic facts more remarkable or interesting. The systematist by such study will be saved from the narrow and hair-splitting tendencies which study of slight difference of characters tends to, while to the economic entomologist it is most essential.
In the rearing of insects success will be attained in proportion to the extent to which the conditions of nature in the matters of temperature, moisture, food-supply, and conditions for pupation, are observed.
“In the hands of the careful breeder an insect may be secured against its numerous natural enemies and against vicissitudes of climate, and will, consequently, be more apt to mature than in a state of nature. The breeding of aquatic insects requires aquaria, and is always attended with the difficulty of furnishing a proper supply of food. The transformations of many others, both aquatic and terrestrial, can be studied only by close and careful outdoor observation. But the great majority of insect larvæ may be reared to the perfect state indoors, where their maneuverings may be constantly and conveniently watched. For the feeding of small species, glass jars and wide-mouthed bottles will be found useful. The mouths should be covered with gauze or old linen, fastened either by thread or rubber, and a few inches of moist earth at the bottom will furnish a retreat for those which enter it to transform and keep the atmosphere in a moist and fit condition.
[The Breeding Cage or Vivarium.]—“For larger insects I use a breeding cage or vivarium which answers the purpose admirably. It is represented in figure 123, and comprises three distinct parts: First, the bottom board a, consisting of a square piece of inch thick walnut with a rectangular zinc pan ff, 4 inches deep, fastened to it above, and with two cross pieces gg below, to prevent cracking or warping, facilitate lifting, and allow the air to pass underneath the cage. Second, a box b with three glass sides and a glass door in front, to fit over the zinc pan. Third, a cap c, which fits closely on to the box, and has a top of fine wire gauze. To the center of the zinc pan is soldered a zinc tube d just large enough to contain an ordinary quinine bottle. The zinc pan is filled with clean sifted earth or sand e, and the quinine bottle is for the reception of the food plant. The cage admits of abundant light and air, and also of the easy removal of excrement or frass which falls to the ground; while the insects in transforming enter the ground or attach themselves to the sides or the cap, according to their habits. The most convenient dimensions I find to be 12 inches square and 18 inches high: the cap and the door fit closely by means of rabbets, and the former has a depth of about 4 inches to admit of the largest cocoon being spun in it without touching the box on which it rests. The zinc pan might be made 6 or 8 inches deep, and the lower half filled with sand, so as to keep the whole moist for a greater length of time.”
Fig. 123.—Insect breeding-cage or vivarium.
The sand or earth in the zinc pan at the bottom of the breeding cage should be kept constantly moistened, and in the case of hibernating pupæ the constant adding of water to the top of the earth or sand causes it to become very hard and compact. To overcome this objection it was suggested in the Entomologists' Monthly Magazine for June, 1876, page 17, that the base should be made with an inner perforated side, the water to be applied between it and the outer side, and I have for some years employed a similar double-sided base, which answers the purpose admirably (See Figure 124). It is substantially the same as that made for the Department by Prof. J. H. Comstock in 1879. It consists of a zinc tray a, of two or three inches greater diameter than the breeding cage, which surrounds the zinc pan proper containing the earth, and the tube d for the reception of the food-plant. The lower portion of the inner pan b is of perforated zinc. Zinc supports, c c, are constructed about halfway between the bottom and the top of this pan, on which the breeding cage rests. In moistening the earth in the cage, water is poured into the tray, which enters the soil slowly, through the perforations in the zinc pan. I have found this modification of very decided advantage and use it altogether in the work of the Division, and heartily recommend it.
The base of the vivarium or breeding cage should never be made of tin, but always of zinc. If made of tin, it will soon rust out. Galvanized iron may be used in place of the zinc, and will doubtless prove equally satisfactory.