Detoxification of pyrrolizidine alkaloids by the harvestman <Emphasis Type="Italic">Mitopus morio</Emphasis> (Phalangidae) a predator of alkaloid defended leaf beetles |
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Authors: | Email author" target="_blank">Thomas?HartmannEmail author H?kan?H?ggstr?m Claudine?Theuring Rainer?Lindigkeit Martine?Rahier |
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Institution: | (1) Institut für Pharmazeutische Biologie, Technische Universität Braunschweig, 38106 Braunschweig, Germany;(2) Écologie Animale, Université de Neuchâtel, rue Emile Argand 11, 2007 Neuchâtel, Switzerland |
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Abstract: | Summary. The harvestman Mitopus morio (Phalangidae) is
a generalist predator. It is known to prey on larvae of the
chrysomelid leaf beetle Oreina cacaliae defended by plant
acquired pyrrolizidine alkaloids (PAs). Tracer feeding
experiments were performed to determine how harvestmen
tolerate protoxic PAs. Minced meat containing either
14C]senecionine or 14C]senecionine N-oxide was fed to
M. morio and subsequently feces and bodies were analyzed.
Labeled alkaloid N-oxide remained stable and was eliminated
almost unaltered with the feces; only 10% was recovered
as tertiary PA. In contrast, approximately 80% of
labeled tertiary alkaloid (senecionine) ingested with the diet
was N-oxidized and eliminated; the remaining 20% consisted
of unchanged senecionine and a polar metabolite
of unknown structure. Harvestmen process their diet by
excreting digestive juice, indicated by bleaching of the meat
color. Analysis of the processed diet revealed some N-oxidation
of 14C]senecionine, suggesting the gut as the site of Noxidation.
Analysis of the bodies of harvestmen 80 hours
after the tracer feeding pulse revealed only trace amounts of
the polar metabolite. Neither senecionine nor its N-oxide
could be detected in the body extracts. The results are discussed
in relation to the strategies of PA adapted insects to
avoid accumulation of tertiary PAs in living tissues. |
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Keywords: | Alkaloid sequestration Detoxification Chemical defense Mitopus morio Oreina leaf beetles Predation Pyrrolizidine alkaloids |
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