April, 1931] Agricultural Research in N. H., 1930 17 



Apparatus used for photographing drops of spray material in the study of con- 

 tact insecticides. 



How Contact Insecticides Work 



How contact sprays kill insects is partly explained by recent stud- 

 ies of W. C. O'Kane, W. A. Westgate, L. C. Glover, and P. R. Lowry. 



The surface activity of certain insecticides suspended or diluted in 

 the droplets of water was found to influence the power of the spray to 

 kill. Toxicity was found to depend partly on the ease with which the 

 spray enters the breathing system of the insect. 



Series of related chemical compounds, or different dilutions of one 

 compound, were found to vary in toxicity according to the surface 

 activity of the spray. Fatty acids, esters, alcohols, and phenols were 

 included in the studies. The contact performance of the different com- 

 pounds was determined from measurements of surface tension, and 

 the angle of contact formed by the droplets of the spray on the body 

 of an insect. 



The purpose of the experiments is to learn how contact insecticides 

 act — information which it is expected will play an important part 

 in the future development of better sprays. The station published a 

 report of progress during the year as Technical Bulletin 39. 



Pine Thinnings Measured 



Thinnings in white pine stands between 30 and 50 years of age can 

 easily amount to a cord per acre per annum, finds K. W. Woodward. 

 The stands are fully stocked. Most of the material removed goes into 

 fence posts and cordwood. 



In plantations now 10 to 15 years old of different species, red pine 

 seems to be making, next to white pine, the most satisfactory growth. 

 (Hatch Fund) 



Study of Wholesale-Milk Farms 



About 300 of the 414 wholesale-milk farms surveyed in Grafton and 

 Coos counties under the direction of M. Gale Eastman averaged a 

 labor income of less than $300, according to preliminary figures. The 

 farmer with the lowest labor income was statistically "in the hole" 

 $4,000, while the most fortunate farmer was $7,000 to the good. 



The average farmer used farm products in his home valued at more 



