Lepidoptera Facts The Management Of Butterfly And Moth Pupa
The disappointments connected with the rearing of Lepidoptera are by no means at an end when all have passed successfully into the pupal condition, and the number of perfect insects obtained will often fall far short of the number of pupa in your boxes; but we must now see what can be done to minimise the death rate of the captives.
One or more suitable boxes must be prepared for the reception of the pupa, and the following suggestion will answer all purposes:
Get a wooden box, quite rough and unplaned inside, large enough to accommodate your pupa with ease, and not less than eight inches deep. Make several holes in the bottom, or else knock the bottom completely out, and nail in its place a sheet of perforated zinc. Also make a lid consisting of gauze attached to a light wood frame.
Place a layer of clean gravel, about an inch deep, in the bottom, and over this a few inches of sifted soil or cocoa-nut fibre.
Now take all the pupa that are ‘earthed’ in your cages, and arrange them on the prepared bed; also add to them the pupa you may have dug out during your various excursions. Cover all with a layer of the material selected for the bed, and then add a layer of moss.
Next come the pupa that are suspended by silky fibres, or are inclosed in cocoons. These should be fixed with pins around the sides of the box, running the pins either through the tuft of silk at the ‘tail,’ or the outer layer of the cocoon, or through the portion of the dried food plant to which they are attached.
Here your pupa will remain till they emerge, and the box may be kept in any airy place where it is not likely to be forgotten, for it is essential that the perfect insects should be removed as soon as possible after quitting their cases. It does not matter much whether the pupa be kept in or out of doors, providing they are sheltered from rain and very severe frosts; but of course, if the former, the imagines will emerge a little earlier, even if the room in which your specimens are stored has no fire.
Even when protected in boxes such as that described the pupa are subject to enemies and dangers. The soil and moss employed may contain slugs, mites, or other creatures which prey on insects, and the amount of moisture present in these materials and in the atmosphere may prove too little for some species or too much for others.
The remedy for the former evil is a simple one. Bake the soil or fibre well before fitting up the box, and boil and afterwards dry the moss. You may then be sure that all life previously contained is quite destroyed.
But the degree of humidity is a point not so easily settled, and so variable are the experiences and opinions of different entomologists that it is difficult to advise a beginner on the subject. The fact that some strongly advise a perennial dampness, while others recommend no attempt at the application of water, would seem to show that there are probably important points to be urged on both sides.
Nothing can be better than a very careful observation of pupa in their natural conditions. When engaged in pupa digging you will observe that the larger number are to be found on the east and north sides of trees where the soil is protected from the heaviest rains; on the other hand a good many are certainly found in very moist and sometimes even in wet situations.
Particular notice should be taken of such experiences, making every allowance for the exceptions that prove the rule, and then let the natural conditions be maintained in your nurseries at home. To carry this out two pupa boxes should be kept, one for those species that seem to require dry situations, and the other for the species that apparently do best with moist surroundings.
But when it is desired to maintain the pupa in a moist condition, great care must be taken not to allow any accumulation of stagnant water. The box we have described, with its bottom of perforated zinc, is well adapted for this purpose. Let it stand on a couple of strips of wood, so that any excess of moisture may readily drain through. The perforated bottom will also allow of a free circulation of air, thus securing the ventilation that is desirable in all boxes, whether wet or dry.
If you have any insects that have pupated within moist stems, they should be kept in a moist condition till they emerge. The simplest way of doing this is to support the stems in a layer of wetted but well-drained silver sand.
Forcing may be resorted to when it is required to obtain the imagines for early setting in order to get them in the cabinet before the busy season begins. The method is simple. Place the pupa box on a shelf in a room where a fire is kept every day. By this means you may get all your specimens out within a few weeks, even when you start the forcing at the beginning or middle of the winter. If, however, you require the imagines for breeding, you must be careful that the eggs are not laid long before the buds of the necessary food plants are due.
When you are expecting the appearance of perfect insects, the pupa boxes should be examined every day. A morning visit to your pupa (for most insects emerge in the morning) may reward you with the sight of a newly emerged imago, clinging to the rough surface of the box, thus affording you an opportunity of observing the wonderful expansion of the wings. But the greeting is not always of such a pleasant character, for your disappointed eyes will sometimes be cast on a host of horrid ichneumons that have just quitted a shell from which you were expecting a prize of some specially valued species.