THE WALNUT SPANWORM. 



(Boarmia plumigeraria Hulst.) 



By D. W. Coquillett. 



In former times it was quite generally believed that the walnut tree 

 was singularly free from the attacks of leaf-eatiDg insects. So pro- 

 nounced was this belief that even economic entomologists of note 

 recommended making a strong decoction of its leaves and spraying this 

 upon other trees and plants for the purpose of protecting them from 

 the attacks of leaf-eating insects. While this supposed immunity from 

 insect attack may hold true in regard to our native species, this is not 

 the case with the imported English walnut, as events in a certain local- 

 ity in California have abundantly proven during the last few years. 

 This tree is quite extensively grown in the southern part of the State, 

 and in proportion to the care bestowed upon it from a cultural point of 

 view yields a larger revenue than any other nut or fruit tree grown in 

 that region. 



During the early summer of the year 1890 there appeared in very 

 large numbers a spanworm not heretofore known to be injurious, and 

 attacked the leaves of English walnut trees in Santa Barbara County, 

 Cal. Nearly every tree in a grove of 20 acres was attacked by them, 

 but they were most numerous near the center of the grove, which 

 would seem to indicate that they had been present in former years, but 

 not in sufficient numbers to attract attention. The trees measured 

 about 30 feet in height, and the branches expanded about 40 feet; and 

 quite a large number of them had been almost defoliated by the span- 

 worms. The owner of the grove had himself planted and cared for it, 

 but had never previously observed any spanworms upon it, and, in view 

 of the fact that the female moths are wingless, it is quite impossible 

 to account for the sudden appearance of the worms in such unusual 

 numbers. 



The eggs from which these spanworms hatch are of a dark grayish- 

 drab color, with a strong brassy tinge; they are flattened oval, as if 

 compressed between the thumb and finger; the surface is quite rough, 

 and bears numerous minute transverse ridges; at each end are many 

 rather shallow punctures, and the egg measures about five-sixths of a 

 millimeter in length. They are attached to the smaller twigs by one of 

 their flattened sides in loose, irregular patches, and are not arranged 

 in any given order. Sometimes as many as 200 eggs are deposited in a 

 single patch or cluster. 



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