Appendix. 503 



Since the larva; only can wander about, and these for a comparatively 

 short distance, their distribution can only take jDlace by outside agencies 

 to any appreciable extent. The larval scale insects are no doubt blown 

 about by the wind, especially such as are of a woolly nature, but Aspidioius 

 perniciosus also is disseminated in that way. That birds and various 

 insects carry scale larvae from tree to tree and even over considerable 

 distances is a well established fact. Amongst insect distributors have 

 been noticed ants, upon which the young scale larvas have been seen. 

 They have also been seen upon the wing covers of ladybirds.* The 

 main distribution of scale insects is on nursery stock and ornamental 

 plants. No more potent means of distribution exists. In nearly all cases 

 the introduction into various States in America of this pest has been 

 traced either to imported nursery stock or to infested cuttings. Should 

 any such stock be obtained from any of the American States or other 

 parts where the San Jose scale exists they should be subjected to a com- 

 plete examination and fumigation. Fruit, especially pears from infested 

 areas, also carries the scale, and from this way we must partly guard 

 against its introduction into this country. 



A way in which we might obtain this Aspidiofus is by the scales 

 attached to the imported fruit being thrown with the skin of the pear 

 near some fruit or other tree, when the young hatching from the gravid 

 females might easily ascend and set up a colony from which numerous 

 other areas might receive the disease by various natural agencies. 



But the chance, it seems, of the disease spreading from infested fruit 

 is very slight. Professor Webster says | : " While there is a certain amount 

 of danger from this source, yet up to the present time not a single 

 instance has been recorded where infections from this source could even 

 be suspected. So far as known to me, every outbreak of this scale has 

 been traced to nursery stock." 



There is certainly some risk that these infested fruits, finding their 

 way into the country, may enable the disease to get a foothold in our 

 orchards and hothouses. But it is especially on imported plants, both 

 fruit and ornamental, that we must keep watch. 



The Probability op Its Introduction and Spread in England. 

 That the San Jose scale is sent to this country there is no doubt, a 

 very meagre and cursory examination having revealed its jjresence on 

 pears. It is, of course, very difficult to say whether the imported insects 

 if they reached our fruit trees would stand the rigours of our climate. 

 But judging from the history of other species, we know that some can 

 withstand very great differences of temperature. We cannot, in fact, rely 



* Eleventh Eeport of New York State Entomologist, p. 224, Lintner. 

 t The San Jose Scale in Ohio Bull. 21, Ohio Agri. Exp. Station, 1.S97, 

 p. 192. 



