A Preliminary Study of Host Selection and Acceptance Behaviour in the Cabbage Aphid,Brevicoryne BrassicaeL

Abstract

The present study investigates the role of the chemical senses in host selection and acceptance behaviour of the cabbage aphid Brevicoryne brassicae L. In order to determine the composition of this behaviour we observed aphids on hosts, non hosts and intermediate plants on which the aphid incidentally occurs (Markkula, 1953): non-cruciferous plants which contain mustard oil glucosides. About fifteen different behavioural components were distinguished and scored during a period of 30 minutes after an aphid had benn put on a plant. On formal grounds we used 1 he term "proboscis contact" (p.c.) instead of "probe". Some authors (cf. Klingauf, 1971) use the duration of the first walk or the first probe as parameters in host selection behaviour. In our experiments the frequency of p.c., its mean duration and the percentage of time spent in p.c. were used. These parameters appeared to be less sensitive to pretreatments and reflected greater differences between the various plant species than the duration of the first walk or first probe. Apterous adults showed (Fig. 1) on the host Brassica oleracea a relatively low frequency of p.c. compared to aphids on the non host Vicia faba. The mean duration of p.c. and the percentage of time spent in p.c. were relatively high on host-plants. Compared with Brassica, Tro-paeolum majus was, under our experimental conditions, an equally attractive host for aphids. Similar results were found with alate insects (Fig. 2). Aphid behaviour on Reseda odorata may be described as intermediate as compared to Brassica and V icia. Aphids migrated voluntarily from densely populated Brassica to Reseda, Tropaeolum or Vicia, but they died within three days after these plants had been placed in separate cages. Although further data are needed we found no significant differences in mortality rates during the first two days between aphids on these latter three plant species and aphids placed on filter paper. Preliminary observations on locomotion of the aphids on these plants showed that aphids on Vicia soon become restless and leave the plant. On Tropaeolum and Brassica they stayed more often at the same place. Fig. 3 represents the number of aphids found on the same place of the leaf at the previous observation. In a similar experiment Reseda elicited an intermediate response between Tropaeolum and Vicia. Within three days, the number of aphids becoming restless increased and they either died or left the plant. Increasing restlessness was also observed in aphids on cut Vicia leaves kept in solutions of sinigrin (Wensler, 1962) or glucotropaeolin (both 25 mMol) or distilled water as a control. After four hours most aphids 283 T. Jermy (ed.), The Host-Plant in Relation to Insect Behaviour and Reproduction