Resistance against Pissodes strobi (Coleoptera : Curculionidae) in severedleaders and in a water-soluble bark extract of Picea sitchensis (Pinaceae): evidence for a post-ingestive mode of action
Ts. Sahota et al., Resistance against Pissodes strobi (Coleoptera : Curculionidae) in severedleaders and in a water-soluble bark extract of Picea sitchensis (Pinaceae): evidence for a post-ingestive mode of action, CAN ENTOMOL, 133(3), 2001, pp. 315-323
The levels of ovarian growth and transcription of the vitellogenin gene wer
e compared in Pissodes strobi Peck (Coleoptera: Curculionidae) feeding on s
evered leaders from susceptible and resistant Picea sirchensis (Bong) Carr
(Pinaceae) and in weevils given a dose of an aqueous extract from the bark
of such leaders. A force-feeding method was developed to deliver the extrac
ts into the alimentary canal of the weevils. Weevils given one dose of the
aqueous extract from resistant leaders, followed by feeding on sections of
laterals from susceptible trees, exhibited a 60% inhibition of oocyte growt
h relative to insects given the extract from susceptible leaders. In simila
r experiments, transcription of the vitellogenin gene of the weevils was in
hibited by about 48%. Transcription of the vitellogenin gene was reduced by
about 60% in weevils feeding on the severed leaders from the resistant clo
ne relative to those feeding on severed leaders from susceptible trees. Res
ults indicate that these effects of resistance do not require an intact tre
e. Experiments using extracts show that the observed effects result from a
post-ingestive effect of the extract.