224 SCIENCE AND FRUIT GROWING 



effect, but only retarded it. Nicotine did no damage whatever 

 to the trees, and, so far as could be ascertained, it had no effect 

 on bees and other insects, for these continued their visits to the 

 flowers immediately after the spraying, and no dead insects 

 were found near the trees or in the adjoining hives. 



(3) APHIS (Reports, VIII, 95 ; X, 42) 



Various series of experiments on treating apples and plums 

 for aphis were carried out at Woburn, the trees being sprayed 

 with paraffin emulsions, and also with tobacco decoctions of 

 various strengths. Considerable variation was observed in the 

 different series as to the efficiency of the emulsions : in one case 

 a complete mortality was obtained with all emulsions contain- 

 ing more than 0-5 per cent, of paraffin, whereas in another series 

 a i per cent, emulsion caused a mortality of only 10 per cent ; 

 in a third series a 1-5 per cent, emulsion gave entirely satisfactory 

 results with the mealy plum aphis. The results with tobacco 

 in that season were more uniform, and indicated a complete 

 mortality as being effected by a solution containing about -075 

 per cent, of nicotine ; and a weaker tobacco solution could be used, 

 if supplemented by paraffin emulsion, but calcium arsenate pro- 

 duced no enhancement of the effect. Paris green caused a 

 mortality ranging up to only 50 per cent. 



In the following season nicotine solution was further examined 

 as regards its effect on six different species of aphis Aphis pomi, 

 Chermes laricis, Beech aphis, Aphis pnmi, Hyalopteris pruni, and 

 Schizoneura lanigem. Five different strengths of nicotine were 

 used in most cases, from 0*075 to 0*005 P er cent., and the spray- 

 ings were performed on various dates from July 2 to Sep- 

 tember i. One of the most conspicuous features of the results, 

 was the great variation in the effect produced, just as in the 

 case of the sprayings with emulsions in the preceding season; 

 in some cases the whole of the aphides were killed, even by the 

 weaker solutions, whereas at another time, and with the same 

 aphides, even the strongest solutions had very little effect. 

 Such variation is not surprising, for aphides pass through various 

 stages of existence, when their susceptibility to poisons may be 

 very different, and, moreover, the effect of the spraying must 

 vary greatly with the extent to which the leaves have become 

 curled and afford a protection to the insects from the spray- 

 fluid. As an instance of the character of the results obtained, 

 (which have not yet been published), those with the Aphis pomi 



