410 



NATURAL HISTORY OF ARTHROPODS. 



FIG. 513. Cecidomyia destructor, Hessian 

 fly; a, larva; b, pupa; c, pupse on wheat 

 straw. 



spring, when pupae are produced from the last brood which undergo their transforma- 

 tion into the sexual forms, and from which a new series of eggs, agamic broods of 

 larva?, and pupa? in their turns result. 



Several species of this family are very destructive to some of our useful plants. 

 The most important of these is < 'ecidomyia destructor, commonly called the Hessian 



fly, from the belief, probably erroneous, that they 

 were first introduced into this country in straw 

 with the Hessian troops at the time of the Revolu- 

 tion. The fly is very small, but little more than the 

 eighth of an inch in length, of a prevailing opaque 

 1 thick color, with the abdomen below chiefly, and 

 above with transverse and longitudinal lines, blood 

 red. They seem very insignificant, yet in many 

 years their devastation in fields of growing grain 

 can only be reckoned by the thousands, if not by 

 millions, of dollars. There are two broods, in 

 spring and autumn. The female deposits her eggs, 

 one or two at a time, on the upper sides of the leaves, to the number of from eighty 

 to one hundred. These eggs are very minute, not more than the fiftieth of an inch 

 long ; in from four to eight days, if the weather is not too cold, they hatch. The very 

 small, yellowish red larva? then crawl downward on the leaves till they insert them- 

 selves in the sheath between the leaf and the stalk. Here they remain quiescent, grow- 

 ing by means of absorption, or imbibition of the juices of the plant, till they reach the 

 size of a small grain of rice. When a number, as it usually happens, become thus 

 imbedded in the growing stalk, they not only cut off the flow of sap to the grain above, 

 and thus cause the kernels to be illy filled out, but they weaken the strength of the 

 plant, so that rains and storms cause them to be beaten down and so perish. The 

 larva? that are hatched in April, in a few weeks, or by the latter part of June, assume 

 the pupa state, called the flaxseed stage ; the larval skin becomes firmer and brown, 

 enclosing the true pupa, and in size is like a grain of rice. In August the second 

 brood appears, the female of which deposits her eggs in the young winter wheat or 

 other grain, where the larvae soon hatch and acquire the flaxseed condition in Novem- 

 ber, in which state they pass the winter. 



Small as are these flies, they are preyed upon in the early stages by hymenopterous 

 parasites, which destroy the greater portion. The most important of these is the 

 minute Chalcid, Semiotellus destructor. 



Another species, Diplosis tritici, is, in both Europe and America, destructive to 

 grain, but its habits are very different. The female, likewise a very small fly, deposits 

 her eggs, from three to ten in number, within the head or ear of wheat, or in default 

 of this, in wild species of the same genus, Triticum. In about eight days the eggs 

 hatch, and the larvae, creeping about, suck out the juices from the tender kernels. In 

 about three weeks the larva? escape, and burrowing from one to four inches deep in 

 the ground, remain for about two weeks more, when, coming near the surface, they shed 

 the larval skin and become pupa? ; here they remain till the next season. 



Still another species, which, although it has not yet received a name, has been 

 observed of late years in some places destructive to the cranberry. The writer has 

 seen in the latter part of June large meadows in which nearly every plant was 

 infested by one or more delicate silky cocoons, attached to the terminal leaflets, 



