156 



FOREST ENTOMOLOGY. 



Teras terminalis (Fabr.) 



The gall of this species (fig. 154) is the well-known oak-apple or 

 King Charles apple, which is worn by country boys in the south of 

 England on the 29th May. When first the oak-apple appears, it is 

 of a very beautiful scarlet colour. On making a longitudinal or 

 transverse section, we find that the interior of the gall is many- 

 chambered, and the outside soft, spongy, and rich in tannin. 



The gall matures in June, and the flies emerge in J uly. This being 



the case, and considering that the 

 gall is abundant and common, it 

 is very easily reared. 



With regard to the fly, I have 

 made from microscopical observa- 

 tions the following notes : 



Length of body 2 mm. ; breadth 

 or expanse of wings 5 mm. ; wings 

 slightly pubescent, with short 

 hairs; head and thorax brownish ; 

 abdomen considerably narrower 

 than thorax, blackish, shining, 

 egg - shaped, and pointed ; eyes 

 black and shining; three ter- 

 minal joints of antennae more 

 slender than the other joints. 

 The males are paler than the females, and always winged, but the 

 females have often rudimentary wings. 



The alternate generation between Biorhiza aptera and Teras ter- 

 minah'shas been demonstrated by Adler and corroborated by Beyerinck, 

 and yet notwithstanding this there are apparent natural difficulties to 

 fully realise the same correctly. First of all, we have the agamic 

 generation Biorhiza aptera living on the roots and always apterous. 

 But the next generation is often found on the tops of comparatively 

 tall trees, and the question arises, How do the apterous flies in a 

 natural state reach the topmost boughs to deposit their eggs'? 



We have seen that apterous insects are often born amongst oak- 

 apple flies. This might be considered advantageous in assisting the 

 insect to deposit its eggs on the roots. The apterous flies on the oak- 

 apple are the exception, but the apterous flies from the root galls, so 



Fig. 154. Gall of Teras terminalis (oak-apple). 



