NOTES ON THE NATUEAL CONTROL OF OYSTER- SHELL SCALE. 187 



was doubtless feeding on the egg debris left by the predator Hemisarcoptes. Two 

 years later, in his " Insects injurious to Fruits," the same author says " a species of 

 mite, Tyroglyphus malus, Shimer, preys on the bark-louse as well as on its eggs ; and 

 this mite, so insignificant that it can scarcely be seen without the aid of a magnifying 

 glass, has probably done more to keep this orchard pest within bounds than any other 

 thing." Though the species figured seems once again to be Monieziella, the feeding 

 was undoubtedly done by Hemisarcoptes malus. H. G. Hubbard, in his " Insects 

 affecting the Orange " (1885), devoted a chapter to organisms preying upon bark-lice 

 and found that mites " exert a constant and very powerful influence in checking 

 their increase." Lignieres, working on the oyster-shell scale in France, discovered 

 two mites at work and recognised that one was a predator and the other a scavenger. 

 The predator he called Hemisarcoptes coccisugus, but this later proved identical 

 with the species already described by Shimer from North America. His account 

 of the habits of this mite (Mem. Soc. Zool. France, 1893, pp. 16-25) leaves little to 

 be desired. T. D. Jarvis, among his illuminating notes on the habits of many mites 

 (Ann. Kept. Ont. Ent. Soc, 1910) reports this species as " attacking the eggs of 

 oyster-shell scale ... at St. Catherines, Ontario." He clearly recognized the 

 usefulness of the mite, saying (I.e.) " the mites deserve a great deal of credit for their 

 very efficient service to the fruit-grower, in that they consume large numbers of scale- 

 insects all through the season. . . . Two species are found attacking the eggs of 

 the oyster-shell scale. Tyroglyphus longior (Monieziella) is very common at Guelph, 

 and Hemisarcoptes malus at St. Catherines, Ontario." In August 1912, H. E. Ewing 

 and R. L. Webster (Psyche, xix, no. 4) published an excellent account of " Mites 

 associated with the Oyster Shell Scale." As a result of making examinations of 

 oyster-shell scales from various places in the State of Iowa, these authors say " it 

 is quite evident that the Oyster Shell Scale is in many cases kept in check by mites 

 . . . the most important of which is Hemisarcoptes malus." 



In discussing the question of distribution of this mite it seems convenient to 

 commence with the single tree and to pass by easy transitions to the question of 

 continental distribution. 



Six collections of twigs were made from the six main branches of an unsprayed 

 apple tree at Fredericton, N.B., that was heavily infested with scale and moderately 

 infested with the mites. From each of the six sets of twigs a hundred scales containing 

 1916 eggs or egg remains were examined for the mites under a binocular. On every 

 twig the mite was present, the lowest egg destruction being ten per cent, and the 

 highest twenty per cent. ; in no case was a scale found packed with mites and dozens 

 were found with one or two or three mites. Thus although the mite was rather 

 scarce on the tree, it was scattered over it in very regular fashion. Such regularity 

 in distribution on a single tree seems to be the general condition and tends greatly 

 to enhance the value of the organism as a factor in the control of the scale. 

 The mite evidently passes quite readily from tree to tree, perhaps through the 

 medium of tree-visiting organisms. The result is a comparative evenness of 

 distribution through orchards and districts. At Moncton, N.B., scale-infested twigs 

 were examined from ten trees selected at random from the city and surrounding two 

 miles of country. In the case of each twig the turning of a hundred 1916 scales 

 revealed the mite. Seven collections out of ten from various parts of Mount Royal, 



