OYSTER-SHELL BABK-LOTJSE. 39 



of the second brood, sometimes with the epgs oi the Bark-louse 

 upon which they have subsfsted all consumed, and sometimes with 

 a few remaining ; and in this state they undoubtedly pass the win- 

 ter. This second brood must appear in tbe winged form early 

 enough next summer to deposit the eggs from which the iirst 

 brood of next year will proceed. 



The drawing made for the American Entomologist having been 

 inaccurate, and the engraving' imperfect, Mr. Riley kindly con- 

 sented, at my request, to have a new engraving prepared, and the 

 figure here given is a copy of the improved engraving. 



From this general destruction of the Bark-louse, it would seem 

 that its virtual if not total extermination must be near at hand. 

 Yet it would be imprudent to permit ourselves to come to this 

 conviction with too much haste or certainty, since it is a truth 

 with which we have become painfully familiar, that noxious in- 

 sects have their periods both of increase and decrease, and that 

 some species, of which the Chinch-bug is a notorious example, 

 have returned with renewed life and profusion after years of ap- 

 parent extermination. One of the ways in which this is brought 

 about, I conceive to be this : the numbers of a certain species hav- 

 ing become greatly reduced by the operation of its natural ene- 

 mies, parasitic and others, these, in their turn, being deprived of 

 their appropriate nutriment, also become reduced in like propor- 

 tion. The remnant of the former species, being, we may pre- 

 sume, naturally prolific, take a new lease of life and rapidly mul- 

 tiply again in all their former profusion. Judging from known 

 facts and experiences, it is reasonable to suppose that such ebb and 

 flow in the prevalence of particular species, are ever taking place 

 in the multitudinous world of insects. Such reflections have for- 

 cibly occurred to my mind, as I have watched the parasitic Chal- 

 cis-fly of the Bark-louse, coursing busily over the branches, amidst 

 the dry and empty scales, in search of some suitable pabulum in 

 which to deposit the germs of her future progeny. Another ci - 

 cumstance which gives rise to some apprehension is, that these in- 

 sects, within the last few years, have been found farther south 

 than it has been heretofore supposed that they could subsist. I 

 have received, this year, infested twigs from Mr. A. C. Hammond, 

 of Warsaw, as far south as the northern border of Missouri. And 

 I was informed at the horticultural meeting at Mr. Flagg's, near 

 Alton, on the sixth of October, that the Oyster-shell Bark-louse 



