926 



AN INTRODUCTION TO ENTOMOLOGY 



Fig. 1 163. — The large empty 

 oak-apple. 



The large empty oak-apple, Amphiholips indnis. — There are two 

 oak-apples which are ver>^ similar in structure, and which may be 



termed the empty oak-apples. In these 

 the space between the central larval cell 

 and the outer shell contains only a few, 

 very slender, silky filaments, which hold 

 the larval cell in place (Fig. 11 63). The 

 larger of these two galls, measures from 

 25 to 35 mm. in diameter, and is found 

 on the leaves of the scarlet oak and red 

 oak. Externally this gall resembles that 

 of the preceding species but is easily dis- 

 tinguished by its internal structure. The 

 adult gall-flies emerge in June and early 

 in July; they are male and female; an 

 agamic form of this species is not known. 

 The smaller empty oak-apple, Diplo- 

 lepis centncola. — -This gall is found on the 

 lower side of leaves of the post-oak and measures from 1 5 to 20 mm. 

 in diameter. It is sometimes tinged with pink and covered with a 

 white bloom. The adult gall-flies emerge in October and are all 

 females. A sexual generation of this species is not known. 



The oak-bullet- 

 gall, Disholcdspis 

 globulus. — One of 

 the most common 

 galls on white oak, 

 chestnut oak, and 

 scrub chestnut oak 

 is a bullet-shaped 

 gall which is at- 

 tached to the small 

 twigs of these trees. 

 This gall measures 

 from 8 to 16 mm. 

 in diameter and oc- 

 curs singly or in 

 clusters of two, 

 three, or more. In- 

 ternally it is of a 

 compact, rather 

 hard, corky texture, 

 and contains a free, 

 oval, larval cell, re- 

 sembling an Qgg. 

 The adult gall-flies emerge during October and November; these are 

 all females; a sexual generation of this species has not been identified. 



The giant oak-gall, Andricus califdrnicus. — This is the most com- 

 mon oak-gall of the Pacific Coast. It is ver>^ abundant on the twigs 



Fig. 1 164. — The mossy rose-gall. 



