REPORT OF THE ENTOMOLOGIST. 483 



MODE OF SPREAD AND DISTRIBUTION. 



The spread of this species will be aided by very much the same 

 agencies that affect the spread and dissemination of other species of 

 scale-insects. We have already, in 1868, in treating of the Oyster- 

 shell Bark-louse of the Apple,* and again four years later,! dis- 

 cussed the principal methods by which such spread is promoted, viz, 

 by the agency of wind and running water; by the young being carried 

 upon birds and other animals, particularly flying insects frequenting 

 the same trees; but primarily by transport upon scions and nursery 

 stock. 



In insects like the Coccidje, where the locomotive power is confined 

 for the most part to a few days in early larval life, the species would 

 be very much restricted in range, and would never pass from one coun- 

 try to another, except by some of the agencies above indicated. Our 

 observations since we first wrote upon this subject, as well as the 

 extended observations of Mr. Hubbard in Florida, and given in the 

 special report on Insects affecting the Orange, as also Mr. Coquil- 

 lett's observations on the distribution of the particular species in ques- 

 tion, all go to confirm the potency of these means of distribution. 

 Thus Mr. Hubbard found that lady-birds (Coccinellidse), and more 

 particularly gossamer spiders, are active agencies in such distribu- 

 tion. The agency of the wind, as indicated by the more rapid spread- 

 ing in the direction of prevailing winds, has often been verified. Mr. 

 Coquillett reports: "In the infested part of this city (Los Angeles) 

 is a large vineyard, and on both the north and south "^sides of it is an 

 orange orchard infested by these insects; but, while the recently 

 hatched insects occur on the vines as far out as the tenth row of 

 grape-vines on the south side of the vineyard, they are not found 

 upon the vines beyond the third row on the north side, the wind, as 

 stated above, blowing from the southwest. No adult females are to 

 be found on any part of this vineyard, and the young insects must 

 have been carried by the wind from the infested orange trees on 

 either side of the vineyard." Our own experience in California 

 showed that similar evidence of the influence of the prevailing wind 

 in promoting the spread of the species is general. 



While Mr. Hubbard's observations show that the action of the wind 

 is indirect rather than direct, by influencing the flight of winged in- 

 sects and the floating of spiders which transport the scale-insects, yet 

 we have every reason to believe that winds have a much more direct 

 influence than is generally supposed, especially in the case of severe 

 storms passing over infested districts at the right season. We laid 

 emphasis on this in our earlier writings, and Mr. Coquillett, while 

 admitting the influence of birds, insects, and water in the transporta- 

 tion of our leery a, lays greatest stress upon the direct agency of the 

 wind. Young scale-insects are not easily dislodged, but where a tree 

 is badly infested there is every reason to believe that thev instinctively 

 cirop from the terminal twigs, and their specific gravity is so slight, 

 that they may be carried long distances in strong wind"'currents. 



In regard to the influence of birds upon the spread of the Cottony 

 Cushion-scale, Mr. Coquillett observed that whenever the nest of a 

 bird IS found upon a tree recently infested with this insect, the latter 

 will be found to be most numerous in the immediate vicinity of the 



* First Report Insects of Missouri, p. 15. 



t Fifth Report Insects of Missouri, pp. 85, 86. 



