CHAPTER XXII 

 INSECTS (continued) 



(i) WOOLLY APHIS (Report X, 2) 



WOOLLY APHIS or American Blight (Schizoneura lanigera) is 

 unfortunately a well-known pest, the treatment of which is 

 rendered difficult by the white, cottony threads, covering the 

 body of the insect, which prevent it from becoming wetted by 

 insecticides unless these are sprayed on to it with great force; 

 and also by the fact that the adults, besides existing on the stems 

 and branches of the trees, infest the roots, migrating spasmodic- 

 ally during the summer to the above-ground portions of the 

 trees. In winter the insect exists as a purplish brown adult in 

 the crevices of the bark or roots, or occasionally in the egg stage, 

 which eggs, in the spring, give rise to larvae, and these, when 

 mature, form the mother queens, producing viviparously the 

 woolly insect familiar in the summer. 



No systematic investigation of the treatment of trees in the 

 summer for this pest has been conducted at Woburn, though it 

 was shown that undiluted paraffin oil might be used for the 

 purpose, without any very serious damage to the trees, provided 

 the oil was neither one of the lighter nor heavier oils (p. 154) ; 

 more attention, however, was paid to .the treatment of nursery 

 stock, and such stock, especially when received from abroad, 

 should always be treated for woolly aphis before being planted. 



The treatment usually recommended is fumigation with hydro- 

 cyanic acid ; but this was found to be very unsatisfactory : out 

 of some thousands of trees which had been fumigated, 20 per 

 cent, were found to be affected by the aphis in the following June 

 and July, whilst another 43 per cent, became affected before the 

 end of September. It was in accordance with the results ob- 

 tained at "Woburn with the black currant gall mite and the 

 mussel scale (pp. 206, 216) that such fumigation, though it might 

 kill the insects, would not kill the eggs, and would, therefore, 

 be at best but an imperfect remedy. Apparently, F. V. Theobald 

 has on occasions obtained satisfactory results with hydrocyanic 



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