BR. J. ENT. NAT. HIST., 7: 1994 



Dr Simon Leather spoke on insects on bird cherry (Prunus padus I..). The bird 

 cherry is a native British tree mainly found growing naturally in northern Britain. 

 It has 28 species of insect associated with it, including three added by the speaker 

 during the course of his studies. This compares with 1 53 species associated with Prunus 

 spinosa L., 67 species with Prunus domestica L. and 40 species with Prunus avium 

 (L.) L. It would appear that P. padus and P. avium are under-represented in terms 

 of associated insects in Britain. 



Dr Leather gave some details of the leaf beetle Phytodecta pallida (I..). This 

 polyphagous chrysomelid beetle is one of the species that Dr Leather added to the 

 bird cherry's insect list. At his main study site at Roslin Glen near Edinburgh, adults 

 emerge in March and lay eggs in April. Larvae are present from April to June and 

 pupate in July. Adults emerge in July but later return to the soil where they overwinter. 

 The adults and larvae eat holes in the leaves. 



The main part of the talk concerned the bird cherry aphid, Rhopalosiphum padi ( L. ), 

 the bird cherry small ermine moth, Yponomeuta evonymella (L.) and their inter- 

 relationships. The former overwinters on bird cherry as eggs which are often placed in 

 bud axils. They hatch at bud-burst and give rise to several generations of wingless female 

 aphids that cause a downward rolling of the leaf margins. In early summer winged 

 females develop and migrate to cereals and other grasses. In late summer and autumn 

 there is a return migration of winged males and females. In mild areas the aphid can 

 persist on grasses all the year round. Numbers of the aphid on bird cherry vary from year 

 to year. The date of arrival of aphids on the tree at the end of summer varies from 

 August to September with the majority arriving in October. The overwintering mortality 

 of eggs is about 70-80% regardless of numbers laid. Eggs placed in the favoured position 

 between the buds and stem are more likely to survive than those placed in more exposed 

 positions. Counts of eggs during the winter are being used as a means of warning farmers 

 of potentially bad bird cherry aphid years when cereal crop spraying will be necessary. 

 Heavy infestations on bird cherry in the spring can cause the shoot tips to die back 

 and more than ten aphids per leaf can cause no fruits on the tree. This damage also 

 changes the physiology of the plant with the shoots developing with buds more closely 

 adpressed to the stems which have shorter internodes between the buds. Such shoots 

 provide better egg-laying sites for the aphid later in the year. Roadside trees were 

 noted as being more heavily infested than those in woods, and they also had a lower 

 winter egg mortality, possibly as a result of fewer predators being on roadside trees. 



The small ermine moth lays batches of 50-100 eggs on young shoots in August. 

 These hatch and overwinter as first instar larvae under the protective shield formed 

 by the egg mass. The caterpillars become active in the spring and begin webbing the 

 foliage. By mid-summer they may have caused severe defoliation and covered the 

 tree in spectacular swathes of white silk. Woodland trees are generally more heavily 

 infested than exposed trees, possibly because the weak-flying adults need shelter. 

 Counting the number of overwintering egg shields gives a good correlation with the 

 degree of summer defoliation. 



A negative correlation was noted between numbers of bird cherry aphid eggs and the 

 egg shields of the moth. In experiments with trees artificially defoliated to varying (k 

 it was found that fewer aphid eggs were laid on the more severely defoliated shoots. This 

 effect on 2-year-old trees was still apparent up to 5 years later. When small ermine moths 

 naturally invaded the experimental plot, the heavily defoliated plants were targeted 

 as egg laying sites. The shoots on these plants have more widely spaced buds which 

 are less closely adpressed, which creates more space for the moths to lay. This research 

 shows that the aphid and moth are in competition for egg laying sites and both insects 

 are capable of altering the host plant's growth pattern to their own advantage. 



