PROCEEDINGS, 1917. 69 



EMPOASCA UNICOLOR GILL. AS AN APPLE PEST. 



By W. H. Brittain and L. G. Saunders. 



DURING THE SEASONS of 1915 and 1916 a small yellowish-white rather flat- 

 tened leaf-hopper was found in abundance upon apple foliage. Its life history 

 habits and injuries were studied and its identity as Empoa rosae Linn, was es- 

 tablished. This proved to be the most common leaf-hopper infesting the apple in Nova 

 Scotia, but while observations on this insect were being made another leaf-hopper, 

 greener in color and rather more active as to habit, was also noted from time to time 

 among the nymphs of Empoa rosae. Sometimes, indeed, the individuals of the second 

 species predominated and sometimes they appeared to be the only ones present. From 

 the close resemblance of the nymphs to those of the Empoasca mali LeB., it was thought 

 that these insects belonged to that species and no further attention was paid to them. 



In the spring of 1917 it was decided to make a detailed study of the life history of 

 the insect and accordingly an orchard where it had been noticed in abundance the pre- 

 ceding year, was closely watched for the emerging nymphs. A number of individuals 

 were secured immediately upon hatching and reared to the adult stage. Upon exam- 

 ining these adults, it was found that they were not specimens of Empasca mali, but 

 agreed very well with Gillette's description of Empoasca unicolor (Pro. U. S. Nat.Mus. 

 Vol. XX. No. 1138, ; 731) Prof. Gillette writes as follows regarding the specimens from 

 which his description was prepared: "Described from a large number of specimens from 

 Salineville, Ohio, sent, by Cornell University, a small number of specimens from Michi- 

 gan Agricultural College taken by Professor Davis, July 12, on apple trees and a good 

 number taken by myself from Cratagus coccinea in Horsetooth Gulch, near Fort Col- 

 lins, August 16. I have arso seen specimens from the U. S. Natural Museum, labelled 

 D. C, 6-9, on grape." 



Parrot (Journ. Ec. Ent. II, ; 79, 1909) records the insect as infesting apples. Os- 

 born (Me. Agr. Exp. Sta. Bull. 238,; 152, 1915) who, however, places an interrogation 

 mark after his determination of the species writes: "This species is interesting as one 

 of the rather rare cases where a leaf-hopper has adapted itself to feeding on coniferous 

 trees. The specimens taken so far were all secured from arborvitae or from other coni- 

 fers where the food plant was noted." Since this is the only record of this insect having 

 been taken from conifers it is possible, considering the uncertainty of the determina- 

 tion, that Prof. Osborn was dealing with another species. 



INJURIES. 



The injuries produced by Empoasca unicolor on apple foliage are similar to those 

 produced by its relative, Empoa rosae. These first become evident as whitish or yel- 

 lowish white spots upon the leaf, which, in severe cases, run together forming large 

 blotches and giving the leaf a decidedly mottled appearance. In still more severe cases, 

 almost the entire leaf may be involved, the uninjured areas showing as small islands of 

 green tissue among the surrounding white. We have never seen any sign of curling 

 such as follows the attacks of the other apple leaf-hoppers, nor have we observed at- 

 tacks of sufficient severity to cause any noticeable stunting of the growth. It is dif- 

 ficult to measure or accurately estimate the damage which such insects as leaf hoppers 

 actually cause. It would be necessary to secure the crop returns from treated and un- 

 treated plots over a period of years and this has never been attempted. It is possible 

 that orchard leaf-hoppers cause more harm than is generally supposed, but from our 

 observations it does not seem likely that this species will ever be regarded as a serious 

 pest of the apple. 



