Factors determining the distribution of the green spruce aphid, Elatobium abietinum, on young and mature needles of spruce

1. The green spruce aphid Elatobium abietinum , was less active and more likely to feed when on mature rather than young needles of Sitka spruce.
2. Compared with survival on mature needles, survival of aphids on young needles was significantly reduced, especially on newly flushed needles, but became less so as the needles matured. The survival of aphids kept close to, but not in contact with, young needles was similarly reduced.
3. On young needles stripped of epicuticular wax, aphids were less active and fed and survived for longer than aphids on untreated young needles. In contrast, the supply of additional amino acids to shoots bearing young needles did not significantly improve the survival of aphids on these needles.
4. In a choice test, aphids were able to discriminate between epicuticular wax from young and mature needles. The reciprocal transfer of wax between young and mature needles reversed the aphids' marked preference for mature needles.
5. These results indicate that the aphid is deterred from settling and feeding on young needles by a volatile substance present in the epicuticular wax.