242 ANNUAL REPORT OF THE Off. Doc. 



NATURAL METHODS OF HPREAD. 



It lias been beeu already described how. Ilirough nursery stock, 

 the pernicious scale was scattered throuj-hout the Atlantic and Cen- 

 tral States; but after all, this method would reach only individual 

 orchards here and there and, on the whole, only a comparatively small 

 number of trees would be infested. Tlu^ (luestion here to be an- 

 swered is, — how, when a few trees in an orchard or a vicinity are 

 affected, does the insect get to other trees or orchards. 



The natural powers of locomotion of the scale insect are alto- 

 gether inadequate to carry it from one tree to another unless the 

 branches or twigs touch or interlace. 1 have seen in young apple 

 orchards, individuals scaly for three years and no trace of spread to 

 other trees; though those originally infested were killed. In truth, 

 no scale larva will voluntarily leave the plant on which it is born. 

 If it does, it has not the strength to enable it to get from one tree to 

 another over a rough soil, even if it had the ability to move in a 

 straight line to a determined end. In fact it has not such ability and 

 the distribution is haphazard, by external agencies alone. When a 

 badly infested tree is swarming with larvae, the little creatures get 

 upon anything that is quiet long enough for them to do so. The 

 foot of a bird, or an insect of any kind, may serve as a carrier. 

 Sparrows, where they are at all abundant, are the usual agents. 

 They sometimes congregate in flocks; crowd a tree; chatter volubly 

 and then fly to another near by or a long distance off. With them 

 they carry from one tree to another, from orchard to hedge and hedge 

 to orchard, any scale larvae that may be at the time moving on any 

 of the plants visited by them. Other birds do as much in another 

 manner. A mother seeking food for her brood will visit a tree again 

 and again, hunting caterpillars, and will carry them to her young. 

 She spends much time about her nest, and near it the first trace of 

 scale on old trees can nearly always be found. 



The very lady-birds that feed on the scales serve as agents for 

 tkeir spread. The writer has seen the twice-stabbed lady-bird busily 

 feeding on infested twigs, and half a dozen or more larvae crawling 

 safely about on its wing covers. When the beetle flies, the larvae 

 travel with it. So there are many other agencies that may carry the 

 young from place to place. Even the wind may at times serve as a 

 distributor. In one case the writer showed an orckardist how he, 

 himself, w'as infesting previously clean trees. He had been cul- 



