307 



in the mixture. Further experiments are required to determine the 

 conditions of killing, but at least an economic control has been obtained 

 by the dust on some plots. 



Brittain (W. H.). The Apple Sucker {Psyllia mali, Schmidberger). 



— //. Econ. Ent., Geneva, A', i'., xv, no. 1, Februar\- 1922, 

 pp. 96-101. 



Psylla mali, Schmid., is known to occur in Austria, the Caucasus, 

 Czecho-Slovakia, England, Ireland, Germany, the central and northern 

 part of old Russia, Norway, Sweden, Denmark, Holland and Nova 

 Scotia. It has also been recorded from Japan and France, but it is 

 not known to be present in injurious numbers in either of these countries. 

 From a practical standpoint the apple ma}^ be considered as the sole 

 food-plant, although this Psyllid has also been found breeding on Euro- 

 pean mountain ash {Sorbus aucuparia), and it occasionally attacks 

 pear and quince. 



Its bionomics and control in Nova Scotia are discussed. The injury 

 is done almost entirely by the nymphs. Both the leaves and the 

 blossoms are attacked, but the latter are apparently preferred. Under 

 a heavy infestation the blossoms shrivel and die, but remain hanging 

 to the tree for some time. The injury seems to be due to the withdrawal 

 of sap from the blossoms. Injury to the foliage may cause brown 

 withered leaves that remain on the trees throughout the siimmer, 

 green leaves that are shed in showers about the end of June, or yellow 

 leaves, which may begin to fall in mid- June and continue for several 

 weeks. Injury similar to the last mentioned, but greatly aggravated, 

 is also caused by spraying the injured trees with Bordeaux mixture 

 or dusting with copper lime arsenate. The work of the insects appar- 

 ently renders the foliage particular!}' susceptible to spray injury. 

 Hatching occurs on the earliest opening varieties first, the difference 

 sometimes amounting to four or five days, though the emergence does 

 not entirely correspond with the state of the development of the buds. 

 In 1921 the first individuals emerged one week later than Aphis pomi, 

 De G., and eleven days before Lygus commtmis, Knight. The nymphal 

 stage lasts from 31 to 36 days. Oviposition does not take place until 

 August or September and continues until frosts set in. The eggs are 

 mostly laid upon the smaller fruit spurs or shoots ; they may 

 occasionally be found on nursery stock. The adults feed very little 

 and do no apparent injury, but they have a tendency to spread into 

 shade or forest trees surrounding the orchard, returning to the latter 

 for oviposition. Orchards sprayed in the spring are thus often 

 reinfested by these adults. 



The natural enemies include birds, ants and other predators, but 

 none of these are of any practical significance. The fungus Eiitomo- 

 phthora sphaerosperma appears to exercise the most effective check 

 over limited areas. 



Nursery stock may be fumigated with hydrocyanic acid gas in the 

 same way as for San Jose scale [ Aspidiotns peniiciosiis, Comst.]. 

 Though exposure for only one hour destroyed all individuals in some 

 cases, others survived an exposure of nine hours to the same strength 

 of gas. Fumigation is, however, more effective in the spring than 

 in the autumn. Carbon tetrachloride even after prolonged exposures 

 failed to give satisfactory results. Dipping also proved more effective in 

 the spring than in the autumn, the best results being obtained with a 

 5 per cent, (by volume) carbolineum emulsion. Dipping as applied to 

 nursery stock has many disadvantages compared with gas treatment. 



