Piperidine alkaloids are predominant in ant venom glands of S. invicta and S. saevissima. These ants are broadly sympatric in Southeastern Brazil, and potentially diagnostic compounds could assist in ant identification. We determined the absolute configuration of 2,6-dialkyl-piperidines of S. invicta and S. saevissima workers and used these data to group Southeastern Brazil species. The monitoring of venom samples by chiral gas chromatography coupled to a flame ionization detector (GC-FID) revealed that S. saevissima produces the four stereoisomers of 2-methyl-6-undecyl-piperidines, 2-methyl-6-tridecyl-piperidines and 2-methyl-6-tridecenyl-piperidines, while S. invicta venom consisted primarily of a single enantiomer cis and trans from each piperidine alkaloid. Our findings showed that the absolute configuration of piperidine alkaloids of fire ant venom may be a potential chemical tool to distinguish S. invicta and S. saevissima sympatric species in Southeastern Brazil.

Pyrrolizidine alkaloids (PAs) are defensive compounds present in several plant families. However, some specialist herbivore insects have overcome these toxic compounds and sequester PAs converted to N-oxide as a defense against predators and a precursor of male sexual pheromones. In this context, we investigated PA sequestration by the specialist pericopine moth Scearctia figulina (Erebidae: Arctiinae), which feeds on leaves of Heliotropium transalpinum (Boraginaceae) as larvae. Additionally, we examined the role of PAs against different predators. The PAs sequestered from the host plant were metabolized by larvae and transferred to adults via two main pathways: (i) rinderine and its acetyl derivative (7S,3'R) were epimerized to intermedine (7R,3'R) and lycopsamine (7R,3'S), and (ii) insect PAs were biosynthesized from necine bases obtained from plant-acquired PAs, with necic acids of insect origin. Both metabolic products may be related to the biosynthesis of 7R male pheromone and to chemical defense. Larvae and adults were chemically protected against the spiders Nephila clavipes and Lycosa erythrognatha and the chick Gallus gallus, and this defense may be associated to PAs.

Defesas químicas em lepidópteros contra predadores têm sido observadas desde o século XIX. O caso clássico de proteção química contra predadores é o da borboleta monarca, Danaus plexippus, cuja larva seqüestra cardenolidas de sua planta hospedeira Asclepias curassavica e transfere-as para os adultos tornando-os impalatáveis para pássaros. Entretanto diversas outras substâncias podem estar envolvidas na proteção química de lepidópteros neotropicais (glicosídeos iridóides, glicosídeos cianogênicos, glicosinolatos, alcalóides pirrolizidínicos e tropânicos, ácidos aristolóquicos, inibidores de glicosidase, pirazinas). Esses compostos podem ser seqüestrados da planta hospedeira larval, obtidos de fontes vegetais visitadas por adultos ou biossintetizados de novo. Os lepidópteros conhecidos como impalatáveis para predadores vertebrados e/ou invertebrados são as borboletas Troidini (Papilionidae), Pierinae (Pieridae), Eurytelinae, Melitaeinae, Danainae, Ithomiinae, Heliconiinae e Acraeinae (Nymphalidae) e mariposas Arctiidae. Entretanto informações sobre as substâncias que são responsáveis pela impalatabilidade e como elas são adquiridas nem sempre são obtidas. Esse artigo de revisão aborda principalmente observações de campo e laboratório sobre a rejeição de borboletas e mariposas neotropicais por predadores, correlações entre impalatabilidade e substâncias químicas encontradas nos insetos e bioensaios que demonstrem a atividade dessas substâncias contra predadores. Perspectivas são sugeridas para esses tópicos.

Chemical defense against predation in butterflies and moths has been studied since nineteenth century. A classical example is that of the larvae of the monarch butterfly Danaus plexippus, which feed on leaves of Asclepias curassavica (Asclepiadaceae), sequestering cardenolides. The adults are protected against predation by birds. Several other substances may be involved in chemical defense, such as iridoid glycosides, cyanogenic glycosides, glucosinolates, pyrrolizidine and tropane alkaloids, aristolochic acids, glycosidase inhibitors and pyrazines. The acquisition of these substances by lepidopterans can be due to sequestration from larval or adult host plants or de novo biosynthesis. Many Lepidoptera are known to be unpalatable, including the butterflies Troidini (Papilionidae), Pierinae (Pieridae), Eurytelinae, Melitaeinae, Danainae, Ithomiinae, Heliconiinae and Acraeinae (Nymphalidae), and Arctiidae moths, but knowledge of the chemical substances responsible for property is often scarce. This review discusses mainly three topics: field and laboratory observations on rejection of butterflies and moths by predators, correlation between unpalatability and chemicals found in these insects, and bioassays that test the activity of these chemicals against predators. Perspectives and future directions are suggested for this subject.