2 Control of the Greenhonm White Fly 



autumn owe their origin mainly to the adults which are continually 

 passing out of the greenhouses and, to a less extent, to those which have 

 been fostered in cold frames over the winter. At the same time it is 

 highly probable that the insect can survive mild winters out of doors 

 in the south of England and it can certainly do so in the Channel Islands 

 where it is a more serious pest than in the Lea Valley. In the winter of 

 1919-20, when the insect was being bred for the purposes of this study, 

 the adults could be found around the experimental house throughout, 

 especially on Althaea rosea and Aquilegia. The first emergence of the 



Fie;. 1. Adult A. vapor ari or vw ( x 100). 



adults of the insects breeding outside was observed on July 1. Through 

 the summer and autumn they were excessively numerous in the garden 

 and became a serious pest on runner beans. At the beginning of December 

 the greenhouses and cold frames were free from the pest but the adults 

 were still to be found on Digitalis and Althaea where a batch of recently 

 laid eggs was seen. Unfortunately the leaf which held these perished. 

 In early December there was a week of snow with 23 degrees of frost on 

 one occasion. Two adults were seen alive after this. The latter half of 

 the month was cold and wet and no more of the insects were found in 



