308 OHIO EXPERIMENT STATION: BULLETIN 332 



Control. — In the experience of the writer, the sulphur sprays 

 in dormant strength appHcation have failed completely to control 

 this species. Good success has been had, however, from the use of 

 miscible oils used at the rate of 1 gallon to 12 1/2 and also 15 gallons 

 of water. These materials even when applied during adverse wea- 

 ther conditions, viz. : when the thermometer stood at 31° F. were, so 

 far as could be ascertained, 100 percent efficient. Because of these 

 favorable results miscible oil is recommended as the best control 

 measure. The application should be made in the spring before the 

 buds break. 



Kerosene emulsion and whale-oil soap sometimes are recom- 

 mended as summer applications when the young appear, but because 

 of the uncertainty of the time of this period and because of the 

 difficulty involved in spraying when the plants are in foliage, the 

 dormant miscible oil application is much to be preferred. 



THE COMMON RED SPIDER OR SPIDER MITE 



(Tetranychus sp.) 



Description. — The effects of the work of this mite are more 

 noticeable than the creature causing the trouble. Indeed it is only 

 the most critical observer who ever sees the mite proper, since it 

 is much smaller than a pin head. The unaided eye may detect 

 tiny moving objects but a lens is required to differentiate details. 

 When viewed with a lens, the spider mites are found to be eight- 

 legged creatures, actively running about over a network of webs 

 which they spin upon the surface of the host. They may be red, 

 green or brown in color and usually have two well-defined spots on 

 the back. 



The eggs are minute and almost spherical in shape. When first 

 deposited they have a faint pearly color, but later become reddish. 

 (See Plate LVII.) 



Life history and habits. — Under outdoor conditions the winter 

 is passed in Ohio in the e^g stage, the young appearing after the 

 foliage IS well developed in the spring. There are several genera- 

 tions annually, and each female is capable of producing a large num- 

 ber of eggs. In greenhouses and conservatories development is 

 continuous the year around. Badly-mfested plants invariably are 

 found to be covered with a network of very fine webs which the 

 mites use for concealment and also to enable them to run about 

 quickly from one place to another. 



Nature of work. — The mites feed by piercing the leaf tissues 

 from the underside and sucking out the juices. During the process, 

 some of the chlorophyll is removed and the leaf may take on a 

 mottled appearance. If the mites are sufficiently numerous the 



