136 



LEAF-MINING INSECTS 



or small and ovoid formed of frass and silk as are those of 

 L. caryaealbella and L. aeriferella, or merely an oval ring 

 with an outline of frass like that of L. basi&trigella, or an 

 oval, flattened transparent cell like that of L. lucetiella. 



In species of the group of Lithocolletis proper the mine is 

 often^narrow and somewhat winding at first but it soon 



Fig. 43. Lithocolletis hamadryadella. (From Comstock.) a, mine; 

 b, young larva; c, full grown flat form larva; d, head of same, enlarged; e, 

 antenna of same; /, round form larva from above; g, same from below; A, 

 head of same enlarged; i, antenna of same; k, maxilla and palpus of same; 

 I, labum, labial palpi and spinnerets of same; m, pupa; p, cocoon; q, moth. 



spreads into a blotch which often involves the part of the 

 leaf which contained the earlier winding portion. 



When the larvae assume the cylindrical form in the fourth 

 instar they cease to separate the cuticle and from that time 

 on the outline of the mine does not change. The newly- 

 developed spinneret is usually employed almost at once in 

 spinning silk in sheets or bands under the separated epi- 

 dermis, and it is the shrinking of this silk in drying which 



