February, '10] COOLEY : oyster shell scale 63 



In all of these tests a small power sprayer owned by the ^lontana 

 State Board of Horticulture was used. A representative of the board, 

 under the pay of the board, did the actual spraying, under ray di- 

 rection. The board also furnished practically all the material and 

 supplies used in these experiments. It gives me pleasure to express 

 my appreciation of the assistance and courtesy extended by the 

 Board of Horticulture, through Mr. M. L. Dean, state horticultural 

 inspector. 



In conducting the work twelve trips to the Bitter Root valley were 

 made, as follows : March 25-28, April 17-19, April 24r-25, May 6-8, 

 May 18-21, May 31-June 1, June 10, June 14-17, June 21-23, July 

 12-16, August 26-27, October 4^7. 



Even under ideal conditions in orchards selected for such tests, 

 it would be impossible to make entirely reliable statements concern- 

 ing the comparative benefits following different treatments. We 

 found that certain of the oily insecticides, applied before hatching of 

 the eggs, caused a part of the scales to drop off, but it was impossi- 

 ble to determine what proportion had dropped. It would have been 

 of some value if we had given the various trees a rating designed to 

 indicate the comparative degree of infestation before the trc/atment, 

 although on trees of which we made microscopical examinations and 

 counts such a rating would have been of but little value, for the ex- 

 aminations were made on smaU twigs, which naturally would not con- 

 form closely to a tree rating. In examining the scales on the twigs 

 we found a Zeiss binocular microscope of great service. Besides using 

 it as a dissecting microscope we took off the lenses, with the mount- 

 ings, and used the detached part in the hand, as with a field binocular. 



The apparently conflicting results following the use of lime-sulfur 

 solutions for this insect while the trees are dormant are striking. 

 It is possible that differing weather conditions may explain the killing 

 at one time and failure to kill at another. It is well understood that 

 the sulfur compounds deposited upon the trees by the spray are acted 

 upon chemically by the carbon dioxide of the air, resulting in the 

 liberation of the gaseous sulfureted hydrogen and leaving on the 

 tree pulverulent deposits of finely divided free sulfur and calcium 

 carbonate. It has been shown on a previous page that this insect is. 

 killed by the winter application of lime-sulfur solutions only after the 

 eggs hatch. It seems clear that the actual agent in the killing of the 

 young, tender lice is the free sulfur resulting from the decomposition 

 of the sulfur compounds. This decomposition has all taken place long 

 before the hatching of the eggs. Therefore it seems possible that con- 



