October, '16] quayl^: scale dispersiox 487 



Hewit, Hine, Howard, Hodge, Hindle, Zetek, and Parker, however, 

 has given us positive data as to the dispersal of the house-fly, Musca 

 domestica} Parker has given us evidence for the greatest range of 

 dispersion, namely, 3,500 yards, but this distance, as he infers, does 

 not represent the possible extreme spread, because his captures were 

 not beyond the distance indicated. ' 



Burgess- and Collins^ have determined that the gipsy moth larvae 

 may be carried by the wind for a distance of thirteen and one-half 

 miles. Hunger, Stabler,"* and Weldon have shown that the almond 

 mite, Bryobia pratense, may be carried by the wind a distance of 650 

 feet and to an elevation of 50 feet. This definite information concern- 

 ing the agency of the wind in spreading insects has a very important 

 bearing on any control measures that may be employed. The ques- 

 tion, of course, is not so pertinent for insects that are controlled by an 

 arsenical spray because the protective poison is present on the plant, 

 and it makes little difference whether the insect comes from an ad- 

 joining tree or from a neighboring orchard. 



In the citrus sections of California, where more regulation and en- 

 forcement of insect control are probably practiced than in any other 

 part of the world, the matter of neighboring groves serving as a source 

 for reinfesting treated ones is a question of considerable importance. 

 Our previous work^ has shown that there is little possibility of a young 

 scale insect making its way from one tree to another by its own powers 

 of locomotion. It has also been shown that insects and birds, as well 

 as man in his usual cultural operations, may be factors in spreading 

 the scales, and these agencies may account for the origin of an infesta- 

 tion at a considerable distance. But more important, we believe, than 

 all of the above agencies in distributing scale insects, is the wind. 

 While many of ovir horticultural officers have appreciated the impor- 

 tance of the spread of the scales from adjoining groves, the question 

 has been doubted by some entomologists. It was for the purpose of 

 securing, if possible, some definite data that experiments were under- 

 taken along this line. 



1 See Jour. Econ. Ent., vol. 9, no. 3, p. 353, 1916, for these references. 



- Burgess, A. F. The Dispersion of the Gipsy Moth. Bui. 119, Bur. Ent". U. S. 

 D. A., 1913. 



' Collins, C. W. Dispersion of Gipsy Moth Larva- bj- the Wind. Bui. 273, Bur. 

 Ent. U. S. D. A., 1915. 



^ Stabler, H. P. Red Spiders Spread by the Wind. The Monthly Bulletin, Cal. 

 State Com. Hort. II: 12, p. 777, 1913. 



'^Quayle, H. J. The Red Scale. Cal. Exp. Sta. Bui., p. 129-131, 1911. The 

 Black Scale. Cal. Exp. Sta. BuL, p. 160-16.5, 1911. The Purple Scale. Cal. Exp. 

 Sta. BuL, p. 330-332, 1912. Locomotion of Certain Young Scale Insects. Jour. 

 Econ. Ent., vol. 4, no. 3, p. 301, 1911. 



