360 



THE AMERICAN 



THE CHALCILEOUS PARASITE OP THE APPLE-TREE 

 BARK-LOUSE. 



(Chalets \_Aphelinui\ mytilaspidis , n. sp.*) 



BY DR. WM. LE BARON, GENEVA, ILLS. 



[Fig. 220.; 



Color— Yellow, (a) Fly; (6) antenna;; (<■) larv.i. 



It is the general opinion of nurserymen and 

 orcliardists that tlie Oyster-shell Bark-louse of 

 the apple tree has, for a number of years past, 

 been gradually disappearing, so that it no longer 

 occuijies the rank which it has heretofore so pre- 

 eminently held, of a first-class noxious insect. 



The causes which have been instrumental in 

 bringing about this result, and which are still 

 operating to its completion, are matters of much 

 interest. The agencies to which it has been 

 usually attributed are the four following: In- 

 sectivorous birds ; predaceous insects, especially 

 the Coccinell.-E, or Lady-bugs, and their larvas ; 

 the larva; of the parasitic Chalcis-flies ; and the 

 Mites or Acari. 



It has been generally supposed that the smaller 

 insectivoi'ous birds, such as the wrens and 

 warblers, devour many of the eggs of the Bark- 

 louse ; but these eggs are so minute, and so com- 



• This insect belongs to the genus Aphelinut of Dalman, 

 and comes into Mr. Walker's fourth section, which contains 

 the similar European species, Aphelinusjlavus. The follow- 

 ing description gives the principal characters, both generic 

 and specific . 



Generic Description .— q Head a little wider than thorax ; 

 antenna; 6-jointea, first joint elongate, the other five forming 

 a fusiform club of which the first and fourth joints are equal, 

 second and third very short, fillh longest; mandibles three- 

 toothed; palpi very short; eyes hirsute; three ocelli. Fro- 

 thorax somewhat rounded anteriorly, not strongly quadrate. 

 Abdomen sessile; ovipositor originating from the middle of 

 the venter, lying in a groove, its point extending a very 

 little beyond the tip of the abdomen ; from each side of the 

 penultimate segment projects a fine hair, which furcates : 



i origin and extends but little beyond the tip, forming 

 minute peculiar appendage the oflice of which it is di"" 

 to conjecture. Surface of the wings beset with bristly points 



litficult 



and fringed around the greater part of their margin, the 

 fringe or cilia on the hind wings verv long; sub-costal vein 

 consolidated with the costa, except its basal third, and ex- 

 tending half the length of the wing, and then deflected so as 

 to torm a very short stigmatic branch or stiunp . Legs simple, 

 all the tibia; spurred at their extremities, spurs on middle 

 legs longest, spurs on anterior tibia; a little incurved; tarsi 

 flve-joiuted. 



Specific Description — jlpftcZtnM mytilaspidis, n. sp. 

 —Length one twenty-fifth of an inch, some individuals (if 

 the same species) do not exceed one tlilrtieth Pale lemon 

 yellow; mandibles reddish-brown; ocelli coral red; oviposi- 

 tor reddish; a vacancy in the punctuation of the anterior 

 wings, forming a narniw space or pathway across the basal 

 half, wxteniling inwards obliquely backwards from the stig- 

 ma; cilia on the posterior margin of the hind wings longer 

 than half the width of tlie wing. In the smaUer individuals 

 the fringe on both wings is proportionally longer, that on 

 the hind wings being fhlly as long as the width of the wing. 

 These may possibly be a distinct speciea. 



pletely concealed under the bark-like scales, that 

 even the sharp eyes of a bird could scarcely de- 

 tect them, unless it were endowed with a special 

 instinct for the purpose, and I know of no record 

 of any actual observations which confirm this 

 supposition. I am therefore inclined to the 

 opinion that birds have done little or nothing in 

 the way of exteiininating the Bark-louse. 



The CoccinellsB devour a very small proportion 

 of these insects, whilst they are in their incipi- 

 ent and active state ; but this lasts only three or 

 four days, and therefore but very few of them 

 can be thus destroyed. These predaceous insects, 

 and especially their larviE, also destroy a few of 

 the Bark-lice, in their subsequent stages, by 

 gnawing ragged holes through the scales, and 

 thus getting access to the insect beneath. Mr. 

 Walsh conjectured that these rough holes were 

 made by Acari, but I have repeatedly seen the 

 larva of the Two-spotted Coccinella in the act of 

 gnawing just such holes in the scales of the Bark- 

 louse of the pine tree, and devouring its contents, 

 and it is therefore probable that they are the 

 authors of the similar holes on the apple tree. 

 But the smaU number of scales eaten into shows 

 that but few bark-lice are destroyed in tliis way. 



The destructive work of the Acari is supposed 

 to be indicated by the brownish, discolored rem- 

 nants of the eggs from which the contents seem 

 to have been extracted, easily distinguished from 

 the pure white shells from whicli the insects have 

 been hatched. Both Mr. "Walsh and Dr. Shimer, 

 who were the first to notice these mites, attribute 

 much efficacy to their depredations, but that they 

 are the sole authors of this work is rendered 

 somewhat doubtful by the fact, that in some lo- 

 calities, at least, where the scales containing 

 these discolored eggs are not uncommon, the 

 Acari are comparatively rare. Of eighty-one 

 scales just examined (Sept. 26), containing tliese 

 shriveled and discolored eggs, in only four were 

 Acari seen. It is possible, however, that they 

 may have left them after having extracted their 

 contents. 



But, besides the ragged holes above mentioned 

 as the work of the Coccinellse, a much larger num- 

 ber of scales are found through which has been 

 bored perfectly smooth and round, or slightly 

 oval, holes, which we know from analogy must 

 have given exit to some parasitic fly. These 

 holes have been particularly mentioned by seve- 

 ral of our entomological writers, and must have 

 been seen by all who have made a special study 

 of the Apple-tree Bark-louse. 



So long ago as the year 1855, Dr. Fitch in his 

 first report upon the noxious insects of New York, 

 gave a history of this Bark-louse, so far as it was 



