240 



HORTICULTURE FOR SCHOOLS 



FIG. 124. Aphids or plant-lice. 



twig. When feeding first begins in the spring of the year, it 

 will be noticed that all the lice are wingless. This is also 

 true throughout the summer. Early in the fall, however, a 

 'generation develops wings and has the ability to fly from one 

 tree or one plant to another. 



For years it was not known where these winged lice went 



after flying away from the 

 apple. It was finally dis- 

 covered by Edith M. Patch, 

 entomologist of the state 

 of Maine, that the elm tree 

 serves as an intermediate 

 host for this pest. When 

 the lice developed wings, 

 they flew from the apple to 

 the elm and there pro- 

 duced viviparously sexual forms of the species, the female of 

 which was found to deposit one egg on the bark of the elm. 

 There hatched from this egg a louse which fed for a time on 

 the elm, but the succeeding generation, 

 attaining wings, migrated back to the 

 apple. All species of plant-lice do not 

 follow this peculiar custom in their 

 migration, but nevertheless it is quite 

 characteristic of the group. 



Control of all species can be accom- 

 plished by very thorough spraying with 

 nicotine sulfate (Black leaf 40) and soap, 

 using the nicotine sulfate at the strength FlQ " 125 ^d-s P ider. 

 of one part to 1000 parts of water and about three pounds 

 of whale oil soap to two hundred gallons of the diluted 

 r spray. Thoroughness in the application of the liquid is 

 exceedingly important. 



Nicotine sulfate is a poison which must come in actual 

 contact with the insect before it will kill; therefore, in the 



