354 REPORT OF THE COMMISSIONER OF AGRICULTURE. 



for their nests or lairs almost always proved infested with scale, if infested trees 

 were found in the neighborhood. This I was at first inclined to attribute solely to the 

 protection from enemies and parasites afforded by the web and presence of the spider. 

 No doubt, where the source of infection is near at hand, this may give a sufficient ex- 

 planation of the observed facts. Lately, however. I have been examining with great 

 care a lot of one and two year old trees which I set out myself last March. The 

 stock from which these trees were taken was to my certain knowledge almost, abso- 

 lutely Free from scale-insect. At the time of setting, the weather was excessively dry 

 and unfavorable; in consequence of which the trees, 600 in number, were badly 

 checked, and to a great extent lost their tops and nearly all their leaves, so that the 

 present growth is all new, produced during the past summer. Notwithstanding, I 

 find, to my surprise, scale-insects begiuning to appear on a large proportion of the 

 plants. Upon some of them the insects have beguu to spread over the branches, and 

 the exact spot where the trouble began is no longer ascertainable. In a strikingly 

 large number of instances I find two or more leaves bound together with silk and 

 occupied by a spider, and the inner surfaces of these leaves completely coated with 

 scale-insect, when not a trace of the insect can be found elsewhere upon the tree. 

 Furthermore, this lot of trees occupies a position west and north of the remainder of 

 the grove, in the path of the prevailing [S. E.] winds. The adjoining rows of older 

 trees, on the southeast, are many of them quite badly infested with, for the most 

 part, chaff-scale (Parlaloria perqandii), there being usually a relatively small number 

 of long-scale (Myiilaspis ijlorerii) mixed with the other spech s. As is often the case, 

 the proportions of this mixture of species remains quite constant throughout the in- 

 fested part of the grove. Now, I find in the newly-infested young grove these two 

 scales mixed in about the same proportions, so that no doubt exists in my mind as to 

 the source of their infection. As to the manner in which it has been accomplished, I 

 submit that if, as many persons think, the young lice are transported bodily by the 

 winds, we would have had a very different distribution from that which exists upon the 

 older trees. The larger and heavier young of the chaff-scale would have been car- 

 ried to a less distance and in smaller numbers than the long scale. (There have been 

 no unusual storms or very high winds during the past summer.) Again, in a chance 

 distribution by the wind I can see no reason for any evident connection with spider- 

 web shelters "such as I have mentioned. Individual scale-larvae do not, as far as I 

 have observed, wander far in search of such protection, and do not need it until the 

 colony becomes sufficiently numerous to attract enemies and parasites. The part 

 played by winds is evidently a secondary one, inasmuch as nearly all the web-inhab- 

 iting spiders make use of the wind to carry themselves and their bridges of web from 

 tree to tree, and the spiders transport as passengers upon their bodies the migrating 

 larva? of the scale insect. 



The agency of winds is, as just stated, a secondary one of great im- 

 portance in transporting spiders, and is of primary value in the carry- 

 ing; of infested leaves and twigs to greater or less distances. That the 

 young lice are blown bodily from one tree to another by heavy winds, 

 as formerly supposed, has been disproven by the experiments of Mr. 

 Hubbard, who has shown that they will cling tenaciously to a twig or 

 leaf under a heavy blast from a bellows or from the mouth. 



NATURAL ENEMIES. 



The Cottony Maple Scale is subject to the attacks of very much the 

 same natural enemies as other scale-insects. A number of predaceous 

 beetles feed upon the eggs and young larvae. We have observed the 

 common lady-bird, Chiloconis bivulnerus, engaged in this work, and also 

 the Cocci nel lids Hyperaspis signata and R. hiyeminata. In addition to 

 these Putnam mentions Anatis lo-punctata, "the larva of a species of 

 Chrysopa," and "the larvae of two species of Reduviidce." 



The interesting lepidopterous insect Dakruma coccidivora Comstock, 

 was originally bred from this bark-louse. Its larvae construct tubular 

 passages of silk and wax from one Pulviuaria to another on a thickly 

 infested branch, and eat both the eggs and the waxy filaments which 

 surround them. This insect and its curious habit were described at length 

 by Professor Comstock in the annual report of this Department for 1879, 

 pp. 241-243. It has been found preying upon Pulviuaria only in the 

 vicinity of Washington, but in Florida destroys both a large Lecanium 



