Detoxification of pyrrolizidine alkaloids by the harvestman Mitopus morio (Phalangidae) a predator of alkaloid defended leaf beetles

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 [ 14 C]senecionine or [ 14 C]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 [14 C]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.

Chemical defence of the warningly coloured caterpillars of Methona themisto (Lepidoptera: Nymphalidae: Ithomiinae)

“…Tropane alkaloids are effective against monkeys but not spiders . Hartmann et al (2003) verified that the harvestman Mitopus morio (Phalangidae), a generalist predator, which eats the larvae of the pyrrolizidine alkaloidcontaining Oreina cacaliae (Coleoptera: Chrysomelidae), is able to detoxify these compounds. Why are some compounds active against some predators and inactive against others, as reported here for Methona themisto caterpillars?…”

Effects of pyrrolizidine alkaloids through different trophic levels

“…The ants are common visitors of extrafloral nectaries of Crotalaria pallida, a host plant of U. ornatrix (Ferro et al 2006). Hartmann et al (2003) verified that the harvestman Mitopus morio (Opiliones: Phalangidae), feeding on a diet treated with PAs, was able to N-oxidize and excrete the PAs. The harvestman is the main predator of the PA-containing leaf beetle larvae O. cacaliae in their natural environment.…”

“…Some predators and parasitoids can overcome the PAs and are able to feed on PA specialist phytophagous insects. Predators may be able to feed and to detoxify PAs as has been studied by Glendinning et al Phytochem Rev (2011) 10:83-98 93 (1990 for vertebrates, and Hartmann et al (2003) for a harvestman predator. These authors showed that some predators might present similar behavioural or physiological mechanisms that enable them to overcome toxic compounds.…”

Eating chemically defended prey: alkaloid metabolism in an invasive ladybird predator of other ladybirds (Coleoptera: Coccinellidae)

“…However, there are relatively few well-studied examples of predator physiological adaptation to such prey (e.g. Geffeney et al, 2002;Hartmann et al, 2003). This stands in contrast to the large body of work on the adaptations of herbivores to plant chemical defences (Brattsten, 1992;Li et al, 2007).…”