ENTOMOLOGIST AND BOTANIST. 



361 



then known, and mentions the frequent occur- 

 rence of these round holes in the scales at that 

 time. He also discovered under some of the 

 scales a little oval, footless maggot, which he 

 conjectured might be the larva of some Hjnien- 

 opterous parasite, which, in its exit, made the 

 holes in question. 



In 1867, Mr. Walsh, in his histoi-y of the Bark- 

 louse, in his first annual report upon the noxious 

 insects of Illinois, refers to Dr. Fitch's statement, 

 and adds that he had often noticed the round 

 holes in the scales, wliich he also attributes to 

 the exit of a parasitic insect belonging to the 

 Chalcis or Proctotrupos family. But he says he 

 had never met with the lai-va described by Dr. 

 Fitch. 



In the course of a series of obsei-vations upon 

 the Apple-tree Bark-louse, during the past sea- 

 son it has been my good fortune to trace the 

 history of this interesting little insect, which, if 

 it has ever been seen before, has not been identi- 

 fied, and whose very existence has been only a 

 matter of inference from the visible marks of its 

 beneficent operations. 



In the early part of the season, whilst examin- 

 ing the lice upon an apple tree, I noticed two or 

 three little yellow Chalcides running along the 

 infested twigs, which I conjectured might be the 

 parasites of the Bark-louse, but had no proof 

 that tills was the case. But about the first of 

 August, upon raising one of the scales, I hap- 

 pened to uncover one of these insects in the last 

 stage of its transformation. Its wings were not 

 yet unfolded, but it ran so rapidly that I had 

 some difiiculty in keeping it within the field of 

 the lens. As soon as it paused long enough to 

 be examined, it was easily recognized as a Chalcis 

 by its general aspect, and especially by the pe- 

 culiar vibratile motion of its short geniculate 

 antennas. 



Having once become familiar with its appeai*- 

 ance, I have had no difficulty in capturing, in 

 the latter part of August and September, all the 

 specimens I desired on the infested trees. I have 

 repeatedly watched the female Chalcis in the act 

 of inserting her ovipositor through the scale of 

 the Bark-louse, for the purpose of depositing her 

 egg in the cell beneath. She always places her- 

 self transversely with respect to the scale. Some- 

 times she mounts upon it, and then her tiny body 

 is seen to be considerably less in length than the 

 width of the scale. Usually she backs up upon 

 it only so fiir as to bring the tip of her abdomen 

 about opposite the middle of the scale. Then 

 bringing her ovipositor down perpendicular to 

 her body, she forces it through the scale by a 

 series of boring or short plunging motions. 



Having accomplished this she remains stationary 

 for many minutes, whilst by some invisible in- 

 testine motion the egg is carried down the 

 ovipositor and deposited beneath the scales. So 

 absorbed is she in this delicate operation, upon 

 the successful accomplishment of which not only 

 her own hopes, but those of the horticulturist, so 

 largely depend, that nothing can deter her from 

 it. In one instance, having drawn down a 

 branch of an apple tree, I discovered a Chalcis 

 in the act of depositing. Whilst holding the 

 branch in one hand, and viewing the insect 

 through a lens held in the other, the branch 

 slipped through my fingers and flew back with 

 violence to its place. Drawing it down again, 

 the twig I had hold of broke, and it flew back a 

 second time. I supposed that that observation 

 had, of course, been brought to an abrupt ter- 

 mination. But, upon drawing down the limb 

 the third time, there stood my little Chalcis as 

 immovable as a statue at her post. She may be 

 touched with the finger whilst thus engaged, or 

 even crushed, as I have often inadvertently done 

 in my attempts to capture her, but nothing short 

 of this actual violence can move her from her 

 position. With such wonderful perseverance 

 and devotion do these living atoms of creation 

 perform their allotted part in the complicated 

 economy of nature. 



The egg thus deposited hatches into the Uttle 

 footless larva previously mentioned. This larva 

 is so admirably described by Dr. Fitch, in a 

 single sentence, that I can not do better than 

 copy his description: "Under these scales I have 

 repeatedly met with a small maggot, three-him- 

 dredths of an inch long, or frequently much 

 smaller, of a broad oval form, rounded at one 

 end and tapering to an acute point at the other, 

 soft, of a honey-yellow color, slightly translucent 

 and shining, with an opaque brownish, cloud in 

 the middle, produced by alimentary matter in 

 the viscera, and divided into segments by faintly 

 impressed transverse lines." (See Fig. 220, c.) 



The only motion of which this small grub is 

 capable is a slight extension and contraction of 

 its body, particularly at the two extremities, by 

 which its form is correspondingly modified. 



T here ^ is usually but one larva under each 

 scale, and I have never seen more than two. In 

 the earlier part of the season it is seen adhering 

 to the body of the Bark-louse, but later it is found 

 in the midst of the eggs or their remains. 



Whether there is more than one brood of tliis 

 parasitic fly in a year, I have not yet been able 

 to determine. At the time I am now writing — 

 the last of September— we find numerous in- 

 stances of the round holes, which must have 



