Pests of rhododendrons in Britain with special reference to the weevil Otiorhynchus singularis (L.)

Abstract

The principal rhododendron pests of Great Britain are described; these comprise Rhododendron Whitefly, Dialeurodes chittendeni Laing; Rhododendron Bug, Stephanitis rhododendri Horvath; Rhododendron Leaf hopper, Graphocephala coccinea (Forst. ); Azalea Whitefly, Aleurodes azaleae Baker and Moles; Clay coloured Weevil, Otiorhynchus sinsularis (L); and the tortricid moth, Tortrix viridana (L.).
The first four mentioned pests have a restricted distribution mainly in the south of England and have not spread to other parts of the country during the past thirty years, but there are tears that they may become established in some of the w~er parts of the British Isles in the near future.
The last two pests appear to be more common on rhododendron than previously.
Some pests including aphids, nematodes, slugs and certain Lepideptera and Coleoptera are mentioned, as are pests found in the U.S.A. and other parts of the world. A key to damage caused by insects on rhododendrons has been produced.
A more detailed description is given of Otiorhynchus singularis, together with the results of experiments on the effects of humidity, temperature, light and food on the oviposition, feeding habits and longevity of the adult weevil.
Humidity was found to have a great effect on the life span, oviposition and eating habits, a high humidity being favourable to the weevils. A high temperature increased egg laying and the amount of food eaten, but reduced longevity. The presence or absence of food and light were not significant factors.
Comparisons of some British species of Otiorhynchinae are made, and a new simple key to the imagines is given.
A brief description is provided of the parasite Pygostolus sticticus (Fab.), a new record as a parasite on O. singularis.