284 Journal of Agricultural Research voi. iii.no. 4 



ment Station under the direction of Prof. A. G. Ruggles, in charge of 

 the Section of Spraying and Tree Insects, Division of Entomology. 



The aim of this paper is to report new observations on the Hfe history 

 and ecologic relations of Agrilus bilineatus. The descriptions of the 

 adults, larvae, and pupae, already referred to, are so well known to ento- 

 mologists that they will not be repeated. The drawings reproduced in 

 Plate XXXVIII of the beetles, pupae, larvae, and eggs were made at the 

 Department of Animal Biology under the direction of the author. The 

 photographs reproduced in Plate XXXIX were made at University Farm 

 by the Experiment Station photographer. 



The egg-laying habits have been described in this article in some detail 

 because they have not been known to literature, and the same is true of 

 the leaf -eating habits of the adults. The same may be said of the eggs 

 and newly hatched larvae. Some of the observations of the life history 

 of the larvae have not agreed with previous descriptions, and these, 

 together with a few additional notes on habits, are included, while others, 

 together with the details of the pupal stage, will be deferred to a later 

 report. 



ECOLOGY 



The four common species of oak in the southeastern section of Minne- 

 sota, Quercus alba L., Q. macrocarpa Michx., Q. rubra L., and Q. coccinea 

 Wang, are subject to infestation with Agrilus bilineatus. It seems that 

 the members of the black-oak group are slightly more susceptible to 

 attack than those of the white-oak group, but in localities where the infes- 

 tation is severe none of the species is exempt. 



In some cases the adult borers appear to prefer trees of a certain locahty, 

 or, in other cases, certain individual trees, to others even in the immediate 

 vicinity. In general, this preference is associated with a weakened con- 

 dition of the trees, but this is by no means universal. The env-ironmental 

 conditions of certain localities, such as drought, crowded pasturage, or 

 cultivation, have made nearly all the trees subject to infestation by the 

 two-lined chestnut borer, possibly because of a general weakened condi- 

 tion. In other cases individual trees weakened by injury or disease 

 have been attacked, while in still other cases trees which show no signs 

 of weakened vitality are attacked and killed by this insect. 



It has often been found that the shoestring fungus, Armillaria mcllca 

 Vahl, has apparently been the cause of the weakened condition of the 

 trees, and the chestnut or oak borers have followed it. In fact, it has 

 sometimes appeared that A. mellea was the primary cause of the death 

 of the trees and that the Agrilus beetle was of only secondary impor- 

 tance. An example of this was found in the neighborhood of Lake Elmo, 

 Minn., where a few dead trees were found with the fimgus Armillaria, but 

 with no traces of lar\^3e of the two-lined chestnut borer. These obser- 

 vations, together with others which showed the shoestring fungus on 

 practically every tree on which the Agrilus beetles were ovipositing, made 



