But by far the most dangerous enemies of insect collections are the larvæ of some half dozen or more species of Dermestidæ belonging to the genera Anthrenus, Attagenus, Trogoderma, and Dermestes. Of these Anthrenus varius is the more common pest, in museums, especially in the North and East. In the South and West Trogoderma tarsale and T. ornatum (?) replace Anthrenus. The European species Anthrenus musæorum, is, on the authority of Hagen, rare in this country, and probably occurs chiefly in collections of imported insects. It is the common injurious species of Europe. Anthrenus scrophulariæ (see [Fig. 67]) occurs also in collections, Dr. Hagen stating that he has found it nearly as common as A. varius, and certainly more dangerous. In my own experience it is rarely found in insect collections. Two species of Attagenus (A. pellio and A. megatoma) have also been found in collections. A. megatoma has been found by Dr. Hagen to do not a little damage to insect collections in Cambridge, as well as to equal if not exceed the Carpet Beetle in its disastrous attacks upon carpets and household furniture. The other species, A. pellio, is rarely found in this country, but is much more common and obnoxious in Europe than A. megatoma. Dermestes lardarius is sometimes found in collections, and is attracted by the presence of animal matter such as skins, etc. The two particularly destructive pests, as pointed out, are Anthrenus varius and Trogoderma tarsale. These species, together with most of the others, have no definite breeding period, but, in the uniform temperature of the laboratory or museum, breed all the year round and present no definite broods. It is the experience at the Museum that the boxes on the lower tier of shelves are very much more subject to attack than those on the upper tiers, from which it would seem that the parent beetle deposits her eggs outside the boxes on the floor of the cases and that the young larvæ work their way into the smallest crevices. The danger of infection by these pests is greater in warm climates like that of Washington than in regions further north, as the warm season begins earlier, lasts longer, and furnishes better conditions for breeding and multiplication.
[Remedies.]—The following remedies and preventives will prove efficient in checking or preventing the work of these pests.
Fig. 122.—A naphthaline
cone.
[Naphthaline.]—Where tight boxes are employed little fear of the work of these destructive agents need arise, especially if the boxes are kept supplied with repellent naphthaline cones. These are hard cones of naphthaline, mounted on pins for convenient placing in the boxes (see [Fig. 122]), and may be obtained of dealers in entomological supplies. Naphthaline cones act as repellents to these insects and also to some extent retard the development of the larvæ in all stages and particularly of the eggs.
Mr. Schwarz states (Proc. Ent. Soc. of Washington, Vol. i, page 63) that in place of these cones a form of naphthaline may be used which is known in commerce as “white carbon,” and is put up in the form of small square rods for use in intensifying the flames of gaslight. The material is very cheap, costing only 8 cents per pound wholesale, and may be broken up into small pieces, wrapped in paper, and pinned. The use of naphthaline cones is not advisable in boxes containing delicate specimens, as it leaves a deposit which dulls the colors and encourages greasing. The deliquescence of the naphthaline cones produces a blackish, oily residuum which will soil the lining of the box, and it is always advisable either to pin a piece of blotting paper beneath the cone or to wrap this in paper.
Constant watchfulness is necessary to see that the eggs which have been deposited and checked in development by the application of this insecticide do not ultimately hatch and start a new generation in the insect box.
[Bisulphide of Carbon.]—If the collection is found to be infested with insect pests, it may be renovated by pouring a little bisulphide of carbon into the boxes and closing them at once. This substance evaporates rapidly and will destroy all insect life, and does not injure specimens or pins nor stain the boxes. If infested specimens are received, these should be inclosed in a tight box and treated with bisulphide of carbon before being added to the general collection, and it is always well for those who are receiving pinned specimens by exchange or otherwise to keep a quarantine box of this kind on hand.
[Mercury Pellets.]—The use of mercury pellets is recommended to free boxes from Mites, Psoci, etc., and also to collect any particles of dust which may gain entrance. A few small pellets of mercury, placed free in the bottom of the horizontal box will, by the movement of the box, be caused to roll to and fro and accomplish the desired end.