28 N. H. AGRI. EXPERIMENT STATION [Bulletin 247 



The figures in Table "\TI, derived from plots at the Yale Forestry 

 School in Swanze}-, N. H., show the correlation between density and in- 

 festation. These trees were from 8 to 12 feet high. 



These trees had been left open to sunlight for three years. Up to the 

 time of these observations no advantage had been gained by mixing the 

 red pine and white pine. It is true that the percentage of total .trees at- 

 tacked in this stand was much smaller, but as the red pines were practi- 

 cally immune anyway no advantage to the white pine was obtained. 



Peirson (1922) and Graham (1926) concluded that planting white pine 

 at the rate of 1200 or more to the acre will reasonably control the weevil. 

 The writers believe that planting 1500 or preferably 1800 trees to the 

 acre will be advantageous. 



The trees should be allowed to remain dense until they are from 25 to 

 30 feet high. Careful thinning as the stand grows will make it possible 

 to produce good trees showing little unmerchantable timber. 



Biological Control 



The part nature plays in reducing the number of weevils is of vital 

 importance. If the high biotic potential of the weevil were not checked 

 their numbers would far exceed the population actually present. Be- 

 cause of various natural checks the number of weevils present year by 

 year is fairly constant; that is, the factors of control are strong enough 

 to prevent marked outbreaks of this insect. 



Since the white pine weevil is an indigenous insect it is improbable 

 that these natural checks can be artificially increased to any marked ex- 

 tent. The rearing and liberating of parasites and predators, as practised 

 against introduced insects, is probabl}- out of the question. 



In addition to insect predators birds play some part in control. In 

 this study the white-breasted nuthatch, Sitta caroUnensis, was the only 

 bird observed feeding on the larvae in a white pine leader. There are, 

 no doubt, more species that attack the weevil, for evidences of their feed- 

 ing are common. 



The insect parasites and predators that have been reported attacking 

 the weevil in its several stages comprise a considerable list of species. 

 The list of species mentioned in this paper includes only the more impor- 

 tant ones found in New Hampshire. In addition to these, there are 

 numerous insects and other Arthropods that are found inhabiting the wee- 

 viled leaders. Their co-existence with the weevil is of little importance. 

 Taylor (1928) has listed 90 species of Arthropods taken from weeviled 

 leaders, in connection with his study of parasites and predators. 



Material collected in the course of this study was submitted to Dr. R. 

 L. Taylor, then at the Bussey Institution, Harvard Uni\-ersity, and par- 

 asites and predators found were reported by him. Also records were 

 available from material sent to him from Concord by Mr. W. F. Hale, 

 assistant state forester. The list of species found, together with those 

 secured by collection and breeding, follows: 



