270 Lawson on Aphis AvencB, 



developed, and its supply of food fails, it seeks for other means of 

 subsistence. I do not see any mention of it in Fitch's " Noxious 

 Insects," but I believe that his Aphis Maidis is the same species. 

 It has been observed on the following plants :—Secale cereale, 

 Friticum sestivum, &c., Avena sativa, Dantbonia strigosa, Hor- 

 deum vulgare, H. murinum, Bromus mollis, B. secalinus, Dactyhs 

 glomerata, IIolcus lanatus, Glyceria jfluitans, Poa annua, &c., 

 Polygonum Persicaria." 



Mr. Walker calls attention to the fact that the aphis has many 

 insect and other enemies in Europe, and it Canada it also has its 

 enemies which have during the past two seasons been busily at work 

 lessening its numbers. These have been so graphicallly depicted 

 by Dr. Fitch, in the Albany Country Gentleman, that I cite his des- 

 cription : — "On many of the wheat heads may at present be noticed 

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

 plump and swollen, of the colour of brown paper, standing in a 

 posture so perfectly natural you suppose they are alive. Touch 

 them with a point of a pin, you find they are dead. Pick off a 

 part 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 with a wad of cotton. In a week's 

 time or le>s, you find running actively about in the vial, some lit- 

 tle 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 intro- 

 duce to them a wheat having some fresh lice. See how the fly 

 runs about among them examining them with its antennsB. 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 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 of 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 probably 

 or more, thus insuring the death of that number of lice. And of its 

 progeny, fifty we may suppose to be females, by which five thou- 

 sand more will be destroyed. We thus see what effectual 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. I have not space here to describe 



