l^fjotjotientiron ^ocietp ^otesi, 
INSECT ENEMIES OF RHODODENDRONS. 
Contributed by The Rt. Hon. Sir Herbert Maxwell, Bart. 
Flitherto one of the cardinal merits of the genus Rhododendron has been 
reckoned its comparative immunity from insect enemies ; but during the summer 
of 1917 I have noted two or three remarkable exceptions to previous experience. 
The classification of some of the Microlepidoptera is stiU unsettled, owing to 
the extreme difficulty of dealing with many hundred species of minute moths ; 
but one is painfully familiar with the ravages of the larvae of a species of the 
Torticidae, whereby the oaks in the southern counties of England are so often 
stripped of their foliage in early summer. Such was the case in 1917, many 
woodlands in Sussex and Bucks being sadly disfigured by this pest. Nothing 
new in that ; but the serious matter I have to report is that in two places, in 
Mr. Gerald Loder’s beautiful park at Wakehurst Place in Sussex, and in Mr. 
Yorke’s picturesque wild garden near Iver Heath in Bucks, the moths, having 
polished off the oaks, proceeded to attack the young growths on Indian Rhodo¬ 
dendrons. I ought to add that, not having seen the caterpillars at their evil 
work, only the results of their voracity, I cannot affirm positively that they were 
the offspring of the oak Tortrix ; but the fact that the Rhododendrons which 
suffered were growing among defoliated oaks suggested that the damage was 
wrought by a common agency. It will be well if a strict watch be kept in future, 
so that the actual assailant of these Rhododendrons may be identified. Whatever 
it is proved to, be the oak Tortrix or some other enemy, it can probably be con¬ 
quered by spraying, which of course is impracticable upon forest trees. 
In the north and west our oaks seldom suffer from the ravages of Tortrix. 
Only once, about twenty years ago, have I seen the oak woods on Loch Lomond 
side laid bare in June. The prevailing oak there and in the west generally is the 
sessile-flowered species or varietj'^ (Ouercus sessiliflora), whereas in the districts 
in which Tortrix usually swarms it is the pedunculate oak (Q. pedunculata). 
The Hon. Gerald Lascelles, late Deputy Surveyor of the New Forest, has borne 
striking testimony to the immunity of the former species from attack by the 
moth—the few sessile oaks which had been planted in the Forest standing green 
and luxuriant after thousands of indigenous pedunculate oaks had been stripped. 
Nevertheless, a new enemy made its appearance in 1917, at Castle Kennedy, 
Wigtownshire. The Hon. Hew Dalr 5 miple, M.P., tells me that bushes of Rhodo¬ 
dendron NivEUM, 15 to 18 feet high, were infested by numbers of a large caterpillar 
which had stripped most of the foliage before they were detected. He had them 
picked off and destroyed, most unfortunately without taking any measures to 
identify the species. He could only tell me that they were three or four inches 
long, of a prevailing green colour, with stripes on the sides. He did not notice 
whether they had the curved horn on the eleventh segment of the body—the 
invariable badge of the clan Spinx ; but I strongly suspect they were larvae of the 
convolvulus hawk-moth (Sphinx convolvuli), which appeared in extraordinary 
numbers in all parts of Great Britain in the summer of 1917. If that be so. 
Rhododendron lovers need be under no apprehension, for this fine insect only 
abounds at rare intervals in these islands. HERBERT MAXWELL. 
November, 1917. 
169 
