Studies of insects associated with Lotus corniculatus L.
The major objectives of this study were to describe the insect fauna associated with L. corniculatus and to obtain information on the response of insects to cyanogenesis. The latter is of particular interest because some molluscs and small mammals have been shown to prefer to feed on plants which have acyanogenic leaves, and the density of these selective herbivores is considered to be one of the factors which influence the frequency of cyanogenic plants in populations of L. corniculatus. During 1977 and 1978 a survey of the insects feeding on L. corniculatus, and their parasites, was carried out at Eppleworth Quarry, E. Yorkshire and was supplemented by samples from a number or additional sites in England, Wales and Norway. The flowers and seed pods of L. corniculatus were found to support a diverse insect fauna, composed of eight common phytophages and over twenty species of parasites. Competition amongst the phytophages living in the pods was investigated, and the moth Cydia campositella was found to displace the other species when densities were high. At Eppleworth Quarry seed predation was estimated to result in the destruction of at least 20% of the seeds in 1977 and 8.5% in 1978. Laboratory feeding choice experiments showed that SOme grasshoppers and beetles preferentially eat acyanogenic L. corniculatus floeers. Greater damage to acyanogenic flowers in field populations could not be confirmed however. At Porthdafarch (Anglesey) it was found that in one area the leaves of the acyanogenic plants were more heavily chewed, but this was attributable mainly to differential feeding by molluses rather than insects. In the Jostedal Valley of Norway the L. corniculatus populations groving in harsh periglacial conditions were found to contain an unexpectedly high proportion of cyanogenic individuals. Possible explanations for this distribution were investigated. The impact of insect herbivory on L. corniculatus is discussed, together with an evaluation of the role of cyanogenesis in the chemical defence of this species.