712 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



Farasitcs. — Artificial means of driving off this pest have not yet been 

 ooutrivccl. It has been suggested to kindle fires, throw on damp straw, 

 and let the wind carr^' the smoke over the field. 



But the external enemies of this aphis are ready to help us. The 

 lady-bugs, coccinella, as larvae and beetles, the golden-eyed llies,c/tr?/.so7>fl, 

 as larvie, have been seen the past season in great numbers in wheat- 

 fields, busily engaged in devouring the plant-lice. 



These minute insects have also their internal parasites, little ichneu- 

 mons of the genus AjMdius. We have to go again to Dr. Fitch's arti- 

 cle for information respecting their habits : 



" On many of the wheat-heads, may at present (August 6) be noticed 

 frotn one to a half dozen or more of these lice, which are very large, 

 l)lump, and swollen, of the color of brown paper, standing in a posture 

 so perfectly natural you suppose they are alive. Touch tliem with the 

 point of a pin, you find they are dead. Pick off a ])art of their brittle 

 skin ; you see there is inside a white maggot doubled together like a 

 ball. Put one or two of these wheat-heads in a vial, closing its mouth 

 M'itli a wad of cotton. In a week's time, or less, you find running 

 lively about in the vial some little black flies, like small ants. These 

 you see have come out from the dead lice, through a circular opening 

 which has been cut in their backs. Drive one or two of these flies into 

 another vial, and introduce to them a wheat-head having some fresh lice. 

 See how the fly runs about them, examining them with its antenme. 

 Having found one adapted to its wants, watch how dexterously it 

 curves its body forward under its breast, bringing the tip before its face, 

 as if to take accurate aim with its sting. There, the aphis gives a shrug, 

 the fly has pricked it with its sting, an egg has been lodged under its 

 skin, from which will grow a maggot like that first seen inside the dead, 

 swollen aphis. And thus the little fly runs busily around among the 

 lice on the wheat-heads, stinging one after another, till it exhausts its 

 stock of eggs, a hundred jirobably, or more, thus insuring the death of 

 that number of these lice. And of its progeny, fifty it may be supposed, 

 will be females, by which five thousand more will be destroyed. We 

 thus see what efficient agents these parasites are in subduing the insects 

 on which they prey. I find three different species of them now at work 

 in our fields destroying this grain-aphis." 



The Wheat-Head Army-Wohm, Albilinea Huebuer.— Injuring ILe heads of wheat, 

 rye, and barley, beginuing at the base, sometimes the center of the ear, sometimes 

 hollowing out the soft grains, leaving nothing but the shell and the chaff; a caterpil- 

 lar resembling the northern army-worm, but striped with sulphur-yellow and light 

 and dark brown. 



Though this is a common and wide-spread insect, rangingfrom Maine to 

 Kansas and southward, it was not known to be injurious to crojis until 

 1872, when it was found, according to Eiley, seriously injuring oats in 

 Pennsylvania, In 1874 and 1875 it was reported to injure wheat and tim- 

 othy heads in Maryland and Pennsylvania. It was described as " hollow- 

 ing out the soft grains and leaving nothing but the shell and the chaff'," 

 and "in some rye-fields the heads are almost void of grains and the ground 

 literally covered with chaff', and that late-sowed rye would not be worth 

 the harvesting were it not for the straw." It was more widely destruc- 

 tive in the Eastern States in 1875 than in 1871. June 11, 187C, Mr, J, AV. 

 Eobson, of Dickinson County, Kansas, wrote Mr. Ililey that for ten days 

 past it had been noticed in the wheat. " The caterpillars begin their 

 depredations at the base of the ear, and sometimes near the center of the 

 ear. In one field that I examined to-day the caterpillars were abundant. 



