294 



INSECTS INJURIOUS TO THE GRAPE. 



Fig. 305. 



an inch long and one-fourth as wide, containing a solitary 

 orange-yellow larva^ about one-eighth of an inch long. This 

 is also the larva of an undetermined species of Gecidomyiaj 

 a family the members of which may be recognized in the 

 larval^ state by a peculiar appendage known as a breast-bone 

 attached to the under side near the head. In this species it 

 is almost Y-shaped, as shown at a in the figure; the diverging 



branches terminate in two pro- 

 jecting points, which may be 

 extended at will, and which are 

 probably used by the larva in 

 abrading the soft tissues of the 

 gall so as to cause an exudation 

 of sap, on which the larva feeds. 

 The flies belonging to this genus 

 are usually of a dull-black color, 

 like that shown in Fig. 305, a, 

 which represents a female fly; the antenna of a male is seen 

 Tit b. The gall is common in July ; the larger-sized specimens 

 bear some resemblance to a bunch of filberts or hazel-nuts, 

 hence the name filbert-gall. 



No. 168. — The Grape-vine Tomato-gall. 



Vitis tomatos Riley. 



These galls form a mass of irregular, succulent swellings 

 on the stem and leaf-stalks of the grape-vine (see Fig. 306), 

 very variable in size and shape, from the single, round, cran- 

 berry-like swelling to the irregular, bulbous protuberances 

 which look much like a grouj) of diminutive tomatoes. They 

 have a yellowish-green exterior, with rosy cheeks, and some- 

 times are entirely red; the interior is soft, juicy, and acid. 

 Each gall has several cells, as shown at a in the figure, and 

 in each cell there is an orange-yellow larva, which, before the 

 gall has entirely decayed, enters the ground, where it changes 

 to a chrysalis, and finally emerges as a pale-reddish gnat, with 

 black head and antennae, and gray wings. This fly also be- 



