THE BIOLOGY OF LEPTOBYRSA RHODODENDRI HORVATH (HEMIPTERA, TINGITIDAE), THE RHODODENDRON LACEBUG: FEEDING HABITS AND THE HISTOLOGY OF THE FEEDING LESIONS PRODUCED IN RHODODENDRON LEAVES

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Abstract
SUMMARY: Brief mention is made of the plants attacked by Leptobyrsa rhododendri Horv. and of the problem of immunity and susceptibility of rhododendrons to attack by the bug. The methods and habits of feeding of L. rhododendri on rhododendrons are described. The principal feeding method consists in probing the leaf with the stylets and results in the production of a characteristic, whitish mottling on the upper leaf surface (lesion I). A less common feeding method, in which no probing occurs, often produces a brown spot (lesion II). The character and histology of lesions I and II are described. Lesion I consists mainly of empty palisade cells with an occasional cell showing a similar reaction to saliva as cells in lesion II. Lesion II is composed mostly of unbroken cells which show a browning of the cell contents and the cell walls: apart from the change in colour, the cells in lesion II have, in sections, a normal appearance for at least 3 days after the production of the lesion. No stylet sheath is present in lesion I or lesion II. Toxic action of the saliva appears to play only a small part in the production of extensive damage, most of which results from the emptying of palisade cells (lesion I). L. rhododendri is a mesophyll feeder and the object of the stylets is the palisade tissue of the leaf. Vascular bundles are only accidentally pierced and never become plugged as the result of salivary action. Microchemical tests on the brown substance in lesion II are described. Lesions very similar to lesion II can be made by scratching the surface of a rhododendron leaf with a needle. The production and spread of the brown area around a scratch is much slower than from the puncture made by a bug. The brown material in lesion II is probably produced by the oxidation of chromogens. The lesions produced by L. rhododendri are discussed and compared with hemipterous lesions described by other workers.