The Bionomics ofLampronia Rubiella(Bjerkander), The Raspberry Moth, in Scotland

Abstract

The raspberry moth causes serious damage to cultivated raspberries during certain years, particularly in the Scottish fruit-growing areas where it is a major pest. In the south of England it is less abundant, although in recent years there have been indications that it may become more widespread and plentiful there (Massee, 1939, 1942, 1946).The female moth lays eggs during June and July in the fleshy tissue at the base of the corolla and androecium. The larva, on hatching from the egg, feeds for a short time on the surface tissue of the developing fruitlet, but within a few days it penetrates into the fruit to feed on the fleshy receptacle. During this period it casts its skin once. From the fruit the second instar larva migrates in search of a place in which to hibernate. Hibernacula appear to be situated mostly in the soil close to the roots of the raspberry plants. Prior to hibernation taking place, the larva moults for the second time, so that it passes the winter as a third instar larva.With the approach of spring, at the time when the raspberry buds are bursting, the larva leaves its hibernaculum and crawls up a cane until it finds a suitable bud into which it eats a tunnel through the closely packed leaflets. Sometimes a larva, after having consumed the contents of its first bud, leaves it and attacks a second bud which, by this time, may have developed into a young lateral two to three inches long. The larva, which infests a single bud during its spring life, pupates in that bud, but that which infests more than one bud pupates on tie-wires, leaves, canes, supporting posts or similar places. During its spring life the larva passes through another two instars (the fourth and fifth) before pupating.The full-grown larva prepares for pupation by spinning a white silk cocoon in some suitable place. This takes approximately five days to complete. Within the cocoon the larva pupates and the pupa remains for a period of three weeks.Adult moths appear in June and are abundant during the second half of the month. Egg- laying then commences and a new generation of the species begins.The summer larvae, which hatch during July from eggs laid in the flowers by the female moths, do little damage to the fruit because they are very small and their feeding is largely confined to the receptacle tissue.The most serious damage is perpetrated by the larvae which emerge from hibernation in early spring and bore into the developing buds and laterals. Although their primary buds are killed by the caterpillars these are usually replaced by secondary buds; if these in their turn are largely destroyed by migrating caterpillars the plant’s recovery is prevented because there are no further replacements to overcome the second wave of attack.