228 OHIO EXPERIMENT STATION: BULLETIN 332 



Nature of work. — The prime injury caused by the walnut 

 datana is the destruction of the leaves. Since the larvae feed in 

 clusters, it is natural that they should destroy all the leaves on a 

 limb, or a part of the tree before moving, and this actually is what 

 occurs. Sometimes but one or two limbs will be defoliated, some- 

 times half of the tree, but in case of a severe attack the entire tree 

 may be defoliated, as is illustrated in Plate XXX. Two or three 

 annual defoliations are sufficient to kill the tree. Isolated trees, 

 or trees in small clumps are more susceptible to injury than groves 

 of the preferred host, or when such are located in woodlands. It, 

 therefore, quite frequently occurs that a prized lawn tree or a land- 

 mark may fall prey to this species and be destroyed. 



When the insect infests lawn trees, the caterpillars are very 

 obnoxious during the wandering period just before pupation when 

 they may invade porches or houses, drop on passersby, and in gen- 

 eral render the lawn quite Useless for recreation because of their 

 repulsive appearance and the danger that their crushed bodies and 

 droppings will soil clothing. 



Food plants. — Their favorite food is the foliage of the black 

 walnut, and under Ohio conditions where this is available other 

 trees rarely are harmed. However, the butternut, or white walnut, 

 sometimes is injured in this State to a considerable extent and in 

 the southern states the insect is recognized as a destructive pest 

 of the pecan, both cultivated and wild. A few other trees have been 

 listed as host plants. These are hickory, beech, oak, willow, honey 

 locust, thorn and apple. 



Distribution. — This insect has been taken in Maine and is a 

 pest in Florida, and in all hkelihood it occurs throughout the eastern 

 United States. Westward it has been taken as far as Kansas. 

 Thus its range is obviously quite extended. Of this area, the pest 

 is most harmful in the south and central part. 



As stated previously, isolated trees or trees in small clumps are 

 attacked with greater severity than those distributed through wood- 

 lands or those growing in groves of pure stands. 



Natural enemies. — Four parasites attacking the eggs are re- 

 ported from Florida. These are Trlchogramma minutum Riley, 

 Baryscapus sp., Telenomus sphingis Ashm and Ooencyrtus sp. In 

 the opinion of H. M. Russell, these egg parasites are sometimes of 

 sufficient significance to affect seriously the numbers of the host. 

 In 1907, when the walnut datana was particularly abundant 

 in the fall, but the following spring, when egg parasitism was 

 prevalent, the numbers of the first brood were greatly decreased. 



