134 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETV. 



Besides differing in structure, the species of the two genera can 

 be differentiated on the two hosts as follows : — 



Chermes, s. str. 



Spruce — (i) The Fundatrices 

 feed at the base of fairly 

 strong buds; (2) the galls 

 rarely terminate the shoots, 

 and only the needles on 

 one side of the shoot are 

 galled (Plate II. Fig. i). 



Larch — (3) The Colonici feed 

 on the bark of the trunk 

 and branches of the larch, 

 and they secrete much 

 "wool" (Plate II. Fig. 3). 



Cnaphalodes. 



(i) Fundatrices feed on 

 shaded, hence weak, 

 buds. 



(2) The galls usually termin- 



ate the shoots, and all the 

 needles of the bud are 

 galled (Plate II. Fig. 2). 



(3) The Colonici feed at the 



base of the dwarf shoots 

 of older larch, and on 

 trunks of very young 

 trees. They secrete very 

 little "wool" (Plate II. 

 Fig. 4)- 



The following is an account of the life-histories of the species 

 of the two genera as shown by my researches : — 



Genus Chermes, s. str. (Borner). 

 Chermes abietis (Kalt.). 



The life-cycle of this species consists of two generations — 

 Fundatrix and Gallicola non-migrans— and is passed on spruce 

 only. It takes only one year to complete. 



(i) Fundatrix Generatio/i. — The Fundatrices hatch during 

 August and September from eggs laid by the Gallicolae non- 

 migrantes. They are yellow in colour. After wandering over 

 the branches of spruce, they settle down in a crevice at the 

 base of a fairly strong bud, generally on the under side. 

 After they insert their suctorial mouth apparatus, they secrete 

 short, curly "wool," which gives them a grey appearance. 

 Thus they pass the winter. These first-stage larvae wake up 

 in March, and commence to feed. They moult three times 

 during April, and become adult at the beginning of May. The 

 adult females lay 40-60 yellow eggs under the protection of 

 copious "wool.'' The feeding of the Fundatrices causes the 

 needles on the lower side of the open bud to remain stunted, 



