40 Annals Entomological Society of America [Vol. X, 



Development of the Larva. — No striking external changes 

 accompany the development of the larva. It increases in length 

 and becomes somewhat more robust in proportion to the 

 length. The yellowish tint in the color of the body becomes a 

 little more apparent, the general body-surface smoother, and 

 the intersegmental grooves less broad and deep, although they 

 continue to be distinct. The larval period has not been accu- 

 rately determined and no statement can be made at this time 

 as to the rate of development. 



The Relation to the Petiole. — Needham ('08), in describing 

 the relation of the immature stages of //. confluens to the food- 

 plant, designated the ultimate effect on the petiole as a gall. 

 This same form of designation was followed by the writer ('14) 

 in his first paper on this insect. However, subsequent work led 

 to the investigation of the problem of whether the action of the 

 larva on the petiole results in the production of a true gall or 

 whether the superficial appearance of the infested petiole is 

 merely a case of gall resemblance. Attention was called in the 

 writer's earlier paper ('14, p. 137) to the observation that not all 

 infested portions of the petioles showed swellings and often the 

 diameter was not increased at all. 



Specimens of the so-called galls were secured in all stages of 

 development and sections of the same were made with the view 

 of determining whether the growing larva produced any change 

 in the character of the plant tissue in its immediate vicinity. 

 An examination of these sections and a careful comparison with 

 similar sections of the normal petiole showed that no change in 

 the surrounding tissue occurs, that the relation of the larva to 

 the petiole is merely one of simple interior excavation of the 

 latter by the former and that the increase in diameter which 

 sometimes appears is due to foreign accumulations within. The 

 only change which was detected in the tissues was a brownish 

 discoloration of the cells which bound the cavity made by the 

 larva. Since the term gall is properly restricted to an abnor- 

 mality in plants in which the causative factor leads to the 

 development of tissues that differ from the normal ones, it 

 becomes evident that the immature stage of //. confluens does 

 not produce a true gall and that the occasional ovoid swelling of 

 the petiole is not the result of an excrescence. 



