222 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 4 



Natural Enemies 



The natural enemies of the cabbage aphis are numerous and in 

 most seasons effective in holding this pest in check. The season of 

 1910 was especially favorable for these natural enemies and although 

 the aphis promised in the early part of the season to become abundant, 

 it was eventually controlled in most of the cabbage growing areas of 

 New York State by its enemies. 



The larvse of several species of Syrphus flies have been observed to 

 feed upon the aphides. These flies were especially abundant this year 

 in a badly infested patch at Groton, N. Y. It was interesting to 

 observe the flies depositing their long, oval, white eggs among the 

 aphides. We have reared two species, Sphcerophoria cylindrica, and 

 Allograpta obliqua. In addition, Syrphus americana and Syrphus 

 ribesii were seen to oviposit among the aphides. 



The two lady-birds, Adalia hipundata and Hippodamia convergens 

 were exceedingly abundant this year and did tremendously effective 

 work in destroying the aphides. 



Xystus brassicce and Aphidius piceus are the two most effective 

 parasites. There were literally thousands upon thousands of aphides 

 parasitized this season by these two insects, especially by the latter. 

 Hundreds of Aphidius were bred from aphides brought from the field 

 in the latter part of August. It seems to me that these two parasites 

 and the two species of lady-birds already named, especially Aphidius 

 piceus and Hippodamia convergens, are the most efficient natural 

 means of control. 



Other insects issuing from the boxes containing leaves of cabbage 

 were Asaphes rufipes and Pachy neuron micans. Just how far these 

 are true parasites or hyperparasites or both is not known to us. 



Methods of Control 



Clean Cultivation. — In consideration of the egg-laying habits and 

 consequent production of stem-mothers on cabbage stumps in the 

 spring of the year it must be admitted, it seems to me, that the dis- 

 posal of all leaves and stumps is very desirable. They could be easily 

 pulled, laid in the bottoms of the furrows and plowed under in the fall 

 or winter. Simply plowing a field without pulling the stumps does 

 not bury them, as was shown in a trial field during the spring of 1910. 



The destruction of weeds, serving as food plants, in the vicinity of 

 the fields should also be practiced. 



Seed-Beds and Plants. — Inquiries are often received regarding 

 the infestation of plants in the seed-beds and means of freeing the 



