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Free keywords:
Cionus hortulanus; aucubin; catalpol; sequestration; verbascum; Scrophularia; plant-insect interactions; Coleoptera; Curculionidae
Abstract:
Weevils of the genus Cionus (Curculionidae,
Mecininae) sequester the iridoid glycosides (IGs) aucubin
and catalpol from their host plants Scrophularia or Verbascum
(Scrophulariaceae). Cionus hortulanus is the only member of
the genus that feeds on both plant genera. We previously
showed that sequestration patterns in C. hortulanus depend
on the local host. To investigate whether IG patterns are driven
by their availability in the hosts or genetic differences between
populations, we collected C. hortulanus from S. nodosa in the
field and reared them either on S. nodosa or on V. nigrum. The
differences in IG concentrations were specific for the host
plant upon which the weevils developed. Similar to monophagous
species of the Cionini, individuals from S. nodosa had
more aucubin than catalpol and mirrored the concentrations of
their host plants. Specimens from V. nigrum, on the other
hand, had higher concentrations of aucubin and of catalpol
than their host. On V. nigrum, the ratio of catalpol to aucubin
differed significantly between plant and beetle samples due to
much higher catalpol concentrations in the weevils. Our data
thus contradict genetically fixed differences between populations
living on either plant but rather document the host plants’
influence on the beetles’ metabolism.
