INSECT PESTS OF OHIO SHADE AND FOREST TREES 309 



entire leaf structure dries up and dies. Entire defoliation may 

 result. Indeed, it is no infrequent thing in Cincinnati for basswood 

 to lose two crops of foliage in a year because of the work of these 

 mites. The rusty, unhealthy appearance of tree foliage, particu- 

 larly during late summer, usually is due to the work of these mites. 

 During dry seasons, the injury as a rule is much more severe than 

 at other times. 



Food plants. The spider mites are almost omnivorous, and to 

 give the complete list of food plants would mean naming almost 

 every common plant in the State. However, some are much more 

 severely injured than others, and of the trees, the linden or bass- 

 wood may be given as the most susceptible to attack. However, 

 the oaks and some other species are attacked with almost equal 

 severity. 



Distribution. The spider mites abound throughout the State, 

 but may be said to be more injurious in the southwestern than in 

 other sections. In the southern and western states this pest is 

 unusually prevalent, though it undoubtedly occurs in every state of 

 the Union. It is also a well-known pest in Europe and in other 

 parts of the world. 



Natural enemies. Ewing (47) gives a list of fourteen natural 

 predators, including other mites, lady beetles, Syrphid larvae and 

 lace- wings. 



Control. No very satisfactory control methods are known for 

 this species when attacking shade trees. In the spring of 1916 the 

 writer tested the value of miscible oil, 1 part to 15 parts of water, 

 applied during the dormant season with the view of destroying the 

 over-wintering eggs. The application was made to a European lin- 

 den located in Eden Park, Cincinnati, Ohio, which had lost two sets 

 of foliage the season previous because of the mite injury. The tree 

 was well supplied with over- wintering eggs at the time of applica- 

 tion. The summer following the treatment, the tree retained its 

 foliage during the entire season although the mite was prevalent 

 in 1916. Some injury was noted on the sprayed tree which might 

 be attributed to but partial control or to reinfestation from neigh- 

 boring untreated trees. 



With valuable trees, the spraying with oil would be practicable, 

 but under average park conditions it is questionable whether the 

 expense involved would be justifiable. 



Frequently drenching the infested trees with water is practiced 

 by some with fair success. Where such facilities are available this 

 method undoubtedly has more practical merit than any other. The 

 object in the drenching is to dislodge and destroy the mites. 



