362 



THE AMERICAN 



given exit to an early brood of flies, and we also 

 find under many scales larvffi most of which are 

 nearly or quite fully grown, which must have 

 proceeded from eggs laid by the early brood. 

 Now, whether these larv» will complete their 

 transformations before winter sets in, and lay 

 their eggs for the spring brood, or whether they 

 will remain in the larva or pupa state through 

 the winter, and come out in the winged form in 

 the spring, are points which I have not yet set- 

 tled, but which can be determined in the course 

 of the next two months. 



The Chalcis fly itself is a beautiful object under 

 the microscope. Its length is a little less than 

 half a line, or about one-twenty-fifth of an inch, 

 though I have captured a few specimens consid- 

 erably smaller, being but little more than one- 

 third of a Une. I at fii'st supposed that these 

 smaller individuals were males, but all the speci- 

 mens that I have examined have proved to be 

 females. Their color is a uniform pale lemon 

 yellow. The only variation from this color is in 

 the minute mandibles, which are reddish brown. 

 There are three coral red occelli on the summit 

 of the head, and the ovipositor, which lies in a 

 groove on the underside of the abdomen, exhib- 

 its a slight reddish tint. The wings are thickly 

 beset, over nearly their whole surface, with 

 bristly points, and their margin is ornamented 

 with a long fringe. 



But a better idea of the appearance of this 

 little insect will be obtained from the magnified 

 figures which accompany this article than from 

 any verbal description. (Fig. 220, a.) 



"What proportion of the destruction of the 

 Bark-louse is due to each of the agencies above 

 enumerated could only be determined by an 

 extensive series of observations. It would pro- 

 bably be found to vary considerably in diflierent 

 sections of the country, and perhaps also at dif- 

 ferent periods. In my own locality, actual 

 observation shows that, at the present time, the 

 larvae of the Chalcis are destroying more than 

 twice as many Bark-lice as all other agencies 

 together. As an illustration of this I have, 

 whilst writing this page, taken four twigs in- 

 fested with this year's lice, from four different 

 apple-trees in two gardens remote from each 

 other, and carefully examined the scales upon 

 them, with the following result : 



Whole number of scales 330 



Round holes made by the Chalcis fly 116 



i,arvae of Chalcis, under the scales 95 



Ragged holes made by Cocclnellse 7 



Shrunken and discolored eggs 81 



Acarl found under the scales i 



Scales containing eggs not damaged 27 



If we take this observation as a test, it appears 



that less than one-twelfth of the scales contain 



sound eggs for next year's crop, and even these 

 have two fall and three spring months to pass 

 through before the time of hatching. It also 

 appears, as stated above, that more than twice 

 as many lice are destroyed by the Chalcis (put- 

 ting, of course, the second and third of the above 

 items together) than by all other causes com- 

 bined. The discolored eggs may have been 

 destroyed by Acari. 



If anything like this degree of fatality attends 

 this insect in other parts of the country, it is 

 evident that the career of the notorious Apple- 

 tree Bark-louse is rapidly approaching its ter- 

 mination. Already the smoother bark, the 

 greener foliage, and the fairer fruit, proclaim 

 to the orchardist that this deadly insect is loos- 

 ening its hold upon the apple tree ; and many, 

 no doubt, have prided themselves upon the 

 successful application of some infallible wash, 

 or patent nostrum ; but underneath all this 

 goodly show, busily intent upon the accom- 

 plishment of her own curious economy, and 

 heedless of the momentous results she is effecting 

 in human interests, works unseen our infinitesi- 

 mal friend, the Apple-tree Bark-louse parasite 

 (^Chalcis [Aphelinus] mytilaspidis) . 

 Geneva, IUs., Oct. 1st, 1870. 

 Note. — By observations, made as late as the 

 first week in November, the opinion is confirmed 

 that the Chalcis of the Bark-louse has two broods 

 in a year. By the middle of September we find 

 many of this year's scales pierced with the round 

 holes through which the first brood of Chalcides 

 has escaped ; and late in the tall we find, under 

 about an equal number of scales, the fully-grown 

 larvae of the second brood, sometimes with the 

 eggs of the Bark-louse upon which they have 

 subsisted all consumed, and sometimes with a 

 few remaining ; and in this state they undoubt- 

 edly pass the winter. This second brood must 

 appear in the winged form early enough next 

 summer to deposit the eggs from which the first 

 brood of next yeaf will proceed. 



I will take this opportunity to add that, since 

 writing the above article, 1 have examined a 

 large number of Bark-louse scales, collected from 

 ditferent localities in Kane and DuPage coun- 

 ties, with the following result: 



"Whole number of scales examined 824 



Number destroyed by Chalcides 533 



Destroyed by Acari and unknown causes . . . 234 

 Scales containing more or less eggs 57 



From which it appears that more than twice as 

 many Bark-lice have been destroyed by Chalcides 

 than by all other causes combined, and that only 

 about one scale in fifteen contains any eggs from 

 which to perpetuate the breed of Bark-lice for 

 another year. 



