Alcaloides pirrolizidinicos utilizados por insetos na defesa quimica contra predadores vertebrados e invertebrados

AUTOR(ES)
DATA DE PUBLICAÇÃO

2000

RESUMO

Pyrrolizidine Alkaloids (PAs) are secondary plant compounds with a unique role in the interaction between plants, herbivorous insects, and their natural enemies relationships. The chemical defense due to PAs in Arctiidae moths and butterflies of sub-families Danainae and Ithomiinae (Nymphalidae) has been investigated with regards to vertebrate and invertebrate predators. One of the most used model for PAs bioassay is the spider Nephi/a c/avipes L. (Aranae, Tetragnathidae) which rejects adult Ithomiinae and Danainae, releasing then unharmed from the web. This work tested the role of PAs chemical structure (macrocyclics and monoesters, free base and N-oxide, necine base, necic acids and a insect-PA) and concentration in anti-predator activity. Domestic chicks Gallus gallus and spiders Nephila c/avipes were used as models in assays with palatable prey treated with PAs. The macrocyclic PAs integerrimine:senecionine N-oxide were more effective against spiders than its free base. For the monoester senecioilretronecine, no differential response from the spider was found between free base and N-oxide. Callimorphine, an exclusive insect-PA, was more effective against Nephi/a c/avipes predation than its necine base retronecine, supporting the hypothesis that insect-PAs are produced to optimize the insect chemical defense. For ali PAs tested there was a clear correlation between dosage and predator negative response in Nephi/a c/avipes; higher concentrations generated higher prey release. In the vertebrate predator bioassays no differences were found between free base and N-oxide macrocyclics and monoesters PAs. As with the spider, the retronecine was not effective against predation. The tested PAs dosages did not trigger an effective negative response by the chicks. Domestic chicks were less sensitive to lower PAs dosages than Nephi/a c/avipes. In an another set of experiments, recently emerged adults of Mechanitis po/ymnia (lthomiinae) were fed PAs and tested at various time intervals afier ingestion with the spider predation. Freshly emerged Mechanitis po/ymnia those fed senecioilretronecine and integerrimine:senecionine were more released by Nephi/a c/avipes than those fed retronecine. The different responses from vertebrate and invertebrate predators tested in this work, in relation to different PAs structures, demonstrates the importance of PAs mixture to obtain an effective chemical defense against different potential predators. And the prey protection rises in accordance with the PA concentration in theirs tissues Resumo Abstract

ASSUNTO(S)

pirrolizidinas alcaloides

ACESSO AO ARTIGO

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