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Tinea granella. |
WHEAT MOTH. There are two kinds of moths which do serious injury to grain crops, not only in America, but also in Europe, where they both originated; one is the tinea granella, frequently called corn moth, and the other the butalis or gelechia cerealella, which has received the name of Angoumois grain moth, from the district in France where its ravages first proved extensive. The first is a minute insect, closely allied to the common clothes moth, belonging to the same family tineadæ, The caterpillar which does the injury attacks stored grain and not the growing wheat; it is a small, soft, pale buff, cylindrical worm, with a dark head and dark spot behind the head and is scarcely half an inch in length when fully grown; these caterpillars pass from one grain to another, gnawing large holes in them, and spinning little threads of silk wherever they go, so that grain much infested by them will frequently be entirely entangled in webs. It spins a cocoon made of grains of wood mingled with silk, much of the size and shape of the wheat grains, and emerges as a moth in the succeeding summer, having very much the appearance of the clothes moth, except in its markings; the wings are very long and narrow, and heavily fringed, spreading but little more than half an inch; the upper wings are pale buff mottled with dark brown, and the under wings uniform pale brownish. The Angoumois grain moth belongs to the family yponomentadæ, and is even smaller than the preceding; yet so abundantly does it propagate itself that in France whole provinces have been threatened with famine by the almost total destruction of their crops of barley and wheat. The upper wings are pale cinnamon brown, having the lustre of satin; under wings of a leaden color, and very broadly fringed. About 76 eggs are laid by a single insect, spread about in groups upon three or four different grains; in a few days the caterpillars are hatched, and the work of destruction begins; each seeks a grain of wheat, into which it burrows, closing up the minute entrance; a single grain affords just sufficient nutriment to last the caterpillar during its life; at maturity it is only about a third of an inch long, very smooth and quite white, with its head only a little brown; it partitions off at one side of its abode the loose particles of rejected material by a thin web, and then eats a hole through the shell, leaving only so thin a pellicle as the escaping moth may break through, after which it changes within the grain to a smooth chrysalis, blunt at either end. There are two broods at least of the moth, one appearing in the autumn, and laying eggs to produce the caterpillars which live in the hearts of the grain during the winter, the other appearing as moths in the late spring, whose progeny require but a short time for their maturity. The best mode of checking their ravages appears to be by kiln-drying the grain which has been attacked.