ADELGES COOLEY1 GILLETTE (HEMIPTERA, ADELGIDAE) OF THE DOUGLAS FIR IN BRITAIN: COMPLETION OF ITS LIFE CYCLE

SUMMARY Adelges cooleyi is a pest of Sitka spruce, the primary host, and Douglas fir, the secondary host, on the latter of which it has been known in Britain since 1913. Hitherto its life cycle in Britain has been regarded as incomplete because of the non‐viability of generation I (sexuales) on Sitka spruce and consequent absence of the subsequent generation II (fundatrix vera) and generation III (gallicolae). Both of these generations have been discovered for the first time in Britain and their development followed. The investigation began with the finding of the dead galls of A. cooleyi on Sitka spruce at Glen Tress in February 1935. Subsequently, dead galls were also found at Stobs, Melrose, Dreghorn and Murthly. At Melrose they were found on a new secondary host, the white spruce, Picea alba. Later the fundatrix vera of generation I was found. The growth of the galls was followed on cut twigs in the laboratory and on growing shoots in the field; galls of the current season were found at Glen Tress, Dreghorn and Murthly. The winged gallicolae of generation II were observed migrating to Douglas fir, where they settled and oviposited. From the eggs there hatched typical hibernating first‐instar nymphs (sistentes). Generation III (colonici) was determined to be triple‐brooded, and this character has recently been noted in Adelges cooleyi in British Columbia. The population of the sistentes on Douglas fir during any one winter was found to be composed of four categories, which hav* been designated. The migration of generation IV (sexuparae) to Sitka spruce and white spruce was observed at Glen Tress and Melrose respectively. It was also verified in the laboratory. Generation V (sexuales), for some cause or causes yet unknown, was practically exterminated during development. Only a few adults were observed. The solitary egg laid by the female of this generation was not discovered. Further investigation is required concerning: The causes of mortality of the sexuales. The oviposition of the sexual female, and the sexually produced egg. The extent of the distribution and establishment of the spruce generations in Britain. The prospective status of A. cooleyi as a pest of Sitka spruce in Britain. With regard to status, it would be unsafe, at the present juncture, to speculate, especially as the investigation has been conducted for only one year. I have, therefore, refrained from discussing possibilities of damage to the spruce host until more evidence is available.The writer is indebted to Mr R. Carrick, B.Sc, Research Student in the Department of Entomology, for the photograph of the winged gallicollae reproduced in PI. XXV, fig. 4. Part of the expenses incurred in conducting the investigation were met by a grant from the Earl of Moray Endowment of the University of Edinburgh, and it is a pleasure to acknowledge this assistance.