181 

 NATURAL ENEMIES. 



The nut-infesting snout beetles are preyed upon by several 

 kinds of insects and larger animals, but these natural enemies 

 are not sufficient to keep them within the bounds of inoffensive- 

 ness. 



The habits of these snout beetles are such that it seems im- 

 pobable that we will ever be able to carry on a very successful 

 warfare against them, and, since we can do so little in the way 

 of holding them in check, it is interesting to know what nature 

 is doing to retard their multiplication. 



One of the most important of their enemies is a medium- 

 sized, four-winged fly, a bracon parasite, known technically as 

 Urosigalphus armatus Ashm. This parasite is a foe of the nut 

 weevils and issues from the ground along with the beetles in the 

 summer. It seems especially fond of the larger chestnut weevil 

 and while the beetles of this species are laying their first eggs in 

 the young chestnut burs the parasites fairly swarm among the 

 branches. On August 28th, 1906, from a low-hanging chestnut 

 branch that bore about seventy-five burs, I collected, in thirty 

 minutes, 24 of the weevils and 26 of the parasites. Since that 

 time they have been seen in equal abundance on numerous occa- 

 sions. 



This parasite has a long, external ovipositor, almost equal 

 in length to the beak of the weevil. After the weevil has pierced 

 the nut and inserted its egg, the parasite finds the same orifice, 

 thrusts in its ovipositor and deposits an egg. The grub that 

 hatches from the egg of the parasite feeds internally on the 

 "chestnut worm," and although it opens hostilities soon after 

 the weevil is hatched, it appears to cause its victim no serious 

 inconvenience until the* following year at just the time the 

 weevil larva would pupate. Then the parasites kills and almost 

 entirely devours the weevil. In the cell which the chestnut worm 

 prepared for its own transformation quarters the parasite con- 

 structs a cocoon, four-tenths of an inch in length, within which 

 it changes to the winged stage. Having reached maturity, it soon 



