30 



MONTANA EXPERIMENT STATION BULLETIN 333 



unsprayed for two seasons yielded 40 per cent wormy cherries 

 in the 1935 season. Maggots were found in sweet cherries in 

 several locations near sour cherry trees. In one sour cherry 

 orchard where control measures have been in force for four 

 seasons the infestation remains at a fraction of 1 per cent and 



Figure 4. — Sweet cherry buds in different stages of 

 development. The correct time for applying the 

 spray for the black cherry aphid is shown in the 

 twig to the right. 



no worms occur in sweet varieties. It is not desirable to eradi- 

 cate sour cherry trees, the preferred hosts, but rather use them 

 as a trap crop and thus keep the fly population down. The flies 

 also propagate in wild pin cherries, the original host. 



Observations over the past four seasons indicate that in 

 odd years a much larger number of fruit flies emerge than 



