%\t €mdm\ miitoniolo0bt. 



VOL. XXVII. LONDON, DECEMBER, 1895. No. 12. 



THE PLUM-TWIG GAL],-MITE. 



P/iytoptus phl(£Ocoptes, Nalepa. 



BY M. V. SLIN(;ERL,\ND, CORNELL UNIVERSITY, ITHACA, N. Y. 



\\\ January, 1895, ^ received from a fruit grower at Industry, Pa., 

 several plum-tvi^igs which were badly infested with what was to me a new 

 pest. Two of these twigs are shown, natural size, on the accompanying 

 plate. It will be seen that a ring of small, sub-spherical excrescences 

 encircles the base of each bud and also the bases of two short shoots. 

 The correspondent wrote that he had 400 trees badly infested, and a 

 majority of the plum trees in his neighborhood were affected. The 

 Damsons seem especially subject to attack, but all varieties suffer more 

 or less. 



The excrescences were then of a dark brown colour, with a slight 

 reddish tinge. Usually a slit-like opening could be distinguished on the 

 surface. Upon carefully cutting through one of the excrescences, I was 

 surprised to find a cavity in the interior that was packed nearly full of 

 very minute whitish creatures, which proved to be four-legged mites or 

 Phytoptids. Thus, these excrescences were the galls formed by the 

 •mites, and in which they were then hibernating. There were hundreds 

 of the mites in each gall and all of them in a dormant condition. Thus, 

 each twig was harbouring thousands of the little creatures. The fleshy 

 portion of the galls, between the cavity and the outer skin, is of a dark 

 magenta colour. The galls vary in size, some of the larger ones 

 containing two or three cavities. 



But little is known of the life-history of this curious gall-mite. The 

 correspondent writes that the mites also live in the galls during the 

 growing season. They probably leave the galls in which they hibernate 

 and form new galls in the summer. On several twigs I found a ring of 

 old, dry, deserted galls below a ring of inhabited galls. 



Having ascertained the nature of the pest, I ransacked the literature 

 for records of similar attacks by gall-mites. In Insect Life, Vol. 1., p, 

 343, is recorded some correspondence which Dr. Riley had in January, 



