Eighteenth Report 



State Entomologist of Minnesota 



To the Governor 



Bv A. G. RUGGLES 



SUBJECT INDEX 



Page 

 General report on the activities of the State Entomologist, including insect 

 conditions, a Financial Statement, and a List of Nurserymen. By 

 A. G. Ruggles 3 



Observations on Mites Infesting Flour and Mill Feed. By R. N. Chapman 20 



Factors Influencing the Subcortical Temperatures of Logs. By S. A. 



Graham 26 



Studies of the Flight of Nocturnal Lepidoptera. By William C. Cook .... 43 



The Principles of Film-Forming Sprays. By William Moore 57 



Contribution to the Knowledge of the Group Aphidina, Family Aphididae 



(Homoptera). By O. W. Oestlund 63 



Monograph of the North American Species of Deraeocoris ( Heteroptera, 



Miridae) 77 



Agricultural Experiment Station 



University Farm, St. Paul, Minn. 



December 1, 1920 



