250 



Insect Pests. 



in 1898 many females were on the wing as late as the 16th of 

 October. 



These migrating viviparous females fly back to damson and 

 sloe, but, as stated before, in smaller numbers to other prunes. I 

 have also seen them giving rise to the next generation on hawthorn 

 hedges and cherry, but these latter never survived. This migra- 

 tion, as far as observations go, takes place chiefly on still days and 

 when the air is warm. They do not seem to fly instinctively to 

 the damson, but rather are carried there by chance. Oaks, ash and 

 all manner of trees get covered by the migrants, the majority of 

 which could never reach the prunes, and even where a large damson 

 plantation adjoined a hop garden, thousands of the aphides were 



moving in an opposite direction. The direction of their migration is, 

 it seems, dependent on currents of air — hence hundreds of thousands 

 die, for the ovigerous females do not seem to be able to live on other 

 trees than prunes. 



These migrants, a few hours after they have become located on 

 their proper plant, produce a few lice, which grow into oviparous 

 wingless females. It seems that these winged return-migrants 

 produce very few lice, usually only four are produced by each winged 

 female, but a few give rise to five or six. The embryos can easily be 

 seen in the parent's body. 



About this time winged males also make their appearance. 

 These males are smaller than the winged females. They come 



