The arthropod fauna of fields of ware potatoes in eastern Scotland was
assessed to determine the species composition and relative abundance of
the natural enemies of aphids on potato. Aphids and aphid-specific predators
and parasitoids were surveyed by visual searches of foliage; epigeal arthropods
were assessed by pitfall trapping.
Aphid-specific natural enemies were generally uncommon but may have
been underestimated. Approximately 11,000 animals were caught in pitfall
traps and most were of the ground beetle genus Pterostichus (Coleoptera :
Carabidae). Gut dissections showed that 14.4 and 30.5 per cent of Pterostichus
melanarius and Pterostichus madidus respectively, contained aphid remnants.
In the laboratory, demeton-S-methyl applied directly to these beetles had
little apparent effect but 19.1 per cent died after consumption of treated
aphids. Field experiments indicated that demeton-S-methyl influenced the
trap catch of Pterostichus spp by altering their predatory activity. Caution
should thus be exercised when interpreting such data.
It is suggested that certain species of Carabidae may be important in the
control of aphids on potato. Their potential is discussed and suggestions
given for further research.