710 REPORT UNITED STATES GEOLOGICAL SURVEY. 



Sometimes the larva descends to the ground and molts there. Harris 

 states that ' it is shorter, somewhat flattened, and more obtuse than 

 before, and is of a deeper yellow color, with an oblong greenish spot in 

 the middle of the body. In this state, which is intermediate between 

 the larva and pupa states, which has, by Dr. Fitch, been termed the 

 "embryo-pupa" and by us "semi pupa," the insect spins a minute 

 silken cocoon, which, according to Dr. Fitch, is smaller than a mustard 

 seed, and remains in the ground through the winter, situated at the 

 depth of an inch beneath the surface. In the next June they are trans- 

 formed to pupa?, with the limbs free. When about to assume the adult 

 state, the pupa works its way to the surface in June and July.' " 



Description. — The eggs of the wbeat-midge are long, oval-cylindrical, and tinged, 

 with pale red. When the larva is at rest it is oval, tlattened on the under side, deep 

 yellow, and 0.08 inch long. The female fly is nearly one-tenth of an inch long, bright 

 orange or lemon-yellow, and tarnished or slightly smoky on the back forward of the 

 wings, the latter dear, with a small cross-vein near their base; the antenna' are about 

 as long as the body, and composed of twelve oblong joints, which are narrower in 

 their middles and separated by short pedicels. In the males the autennic are remark- 

 ably long, slender, and delicate, and consist of twenty-four globular joints; it is 

 smaller, but in other respects agrees with the female. — (Fitch.) 



Parasites. — Dr. Fitch has shown that when the midges increase or di- 

 minish in numbers its parasites increase or diminish in the same ratio, 

 "the same as the Hessian fly, once so frightfully destructive to our wheat- 

 crops here in America, has become subdued by its parasites, whereby it is 

 seldom noticed now or known to be present in our country, although it 

 can be found almost every .year in our wheat-fields, showing it is still 

 with us, everywhere ready to again increase and become destructive 

 were it not constantly repressed and kept down by its parasitic foes." 

 Mr. Curtis is quoted as saying that in Europe " these parasites so effect- 

 ually execute their mission, that it has often happened a year or two 

 after the midges were in excess not a specimen could be found." Its 

 destructiveness in this country is due to the fact that we have no native 

 parasites to keep it within proper limits, and Dr. Fitch urges that the 

 parasites be imported from Europe. 



Grain -Aphis, Jj^^^^^ are«a' Fabricius. — Multitudes of dark plant-lice, clustering on 

 the heads of wheat in August, blackening the fields of grain, and, by sucking the ker- 

 nels, causing them to shrink in size and diminish in weight. 



We will suppose a number of eggs to hatch out their wingless females ; 

 with an occasional winged individual there are as yet no males in exist- 

 ence, and yet these virgin aphides, or i^lant-lice, every few days produce 

 hundreds of young alive; each of w^hich in turn come to maturity and 

 produce their young alive. Hence, by the end of summer we have mill- 

 ions of lice overrunning our wheat- fields, the very youngest as well as, 

 the oldest as if for their lives sucking in the sap from the car of the 

 grain. For by a marvelous adaptation to their mode of life, what in 

 beetles are jaws for biting are here lengthened out and joined together 

 to form a tube, with a sucking-stomach at the base. This tube the louse 

 forces into the root of the ear, and thus anchored by their jaws, whole 

 groups cluster head downward on the heads of grain, and by their 

 numbers color a whole field. But the supply of li(}uid food is greater 

 than the aphides can manage, hence two tubes open out from the hind 

 part of the abdomen, from which exudes a sweet sticky fluid called 

 "honey-dew." Ants come to eat it as it falls on the leaves, or lap it 

 from the honey-tubes of the aphis, and as the supytly lessens, they gently 

 strike the ai)his with their anteume to make them yield more. 



At the approach of cold weather, when the whole race of aphides 



