Alkaloids in insects

The major volatile component of the scent organ in male moths of 

Males of the flea beetle Gabonia gabriela feed on withered Heliotropium plants. This may provide a source of pyrrolizidine alkaloids but the significance of this observation is not yet clear.  

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The toxic effects of alkaloids in insects (Table I) can be caused by their interference with diverse cellular and intracellular targets. Since most mechanisms have not yet been elucidated for insects, this issue is discussed below in the section on vertebrate toxicity (see Table IV). With some caution we can extrapolate to insect toxicity. 

Levinson, H. Z., The defensive role of alkaloids in insects and plants, Experientia, 32, 408-411 (1976). 

Biological Activity of Tropane Alkaloids Distribution of Tropane Alkaloids Piperidine Alkaloids Alkaloids from Piper Species Piperine Alkaloids Involving Condensation with Acetate/Malonate Sedum Alkaloids Lobelia Alkaloids Lycopodium Alkaloids Piperidine Alkaloids in Insects Polyketide-Derived Alkaloids Coniine... 

Biological Activity of Indolizidine Alkaloids Indolizidine Alkaloids in Insects Elaeocarpaceae Alkaloids... 

Pyrrolidine alkaloid transformations in insect organisms 98EJ013. 

Hartmann T, Ober D (2000) Biosynthesis and Metabolism of Pyrrolizidine Alkaloids in Plants and Specialized Insect Herbivores. 209. 207-243 Haseley SR, Kamerling JP, Vliegenthart JFG (2002) Unravelling Carbohydrate Interactions with Biosensors Using Surface Plasmon Resonance (SPR) Detection. 218 93-114... 

In this discussion, we have restricted ourselves to the consideration of only a few examples of arthropod chemistry. From these alone, it is evident that insects synthesize defensive compounds by using all of the major biosynthetic pathways, producing acetogenins, simple aromatics and quinones, isoprenoids, and alkaloids. In addition, some of the millipedes, coccinellid beetles, and spiders we have studied utilize biosynthetic pathways that have yet to be characterized. 

When disturbed or molested, these insects release small droplets of hemo-lymph from the tibio-femoral joints of their legs, and it is now well established that the deterrency exhibited by many species of coccinellids towards potential predators results from the presence of repellent and bitter alkaloids in that fluid [ 12,13]. In ladybirds, this unpalatability is associated with a bright aposematic coloration and a characteristic smell due to 3-alkyl-2-methoxypyrazines [14, 15]. The beetles use these molecules not only to reinforce the visual alerting signal on an olfactory level, but also as aggregation pheromones [16]. 

Frogs of the genus Dendrobates are ant specialists. Of the more than 20 structural classes of lipophilic alkaloids found in the frogs, six occur in myrmicine ants. However, many dendrobatid alkaloids such as the batrachotoxins, histri-onicotoxins, and pumiliotoxins, have not yet been found in insects and other leaf-litter prey such as beetles and millipedes (Daly et al., 2000). The snake Lio-phis epinephelus feeds on Dendrobates and may further bioaccumulate alkaloids. 

Figure 3. Structures of Some Plant Alkaloids Used in Insect Control...

There exists evidence that some insects store dietary alkaloids derived from natural sources. Figure 98 presents insect species that are known to accumulate pyrrolizidine alkaloids during different developmental stages. The larvae and adults of these insects can metabolize pyrrolizidine alkaloids in current physiological activities. These alkaloids are not toxic for these organisms. Moreover, there is observed trace accumulation of a portion of these compounds in the liver. There is no definitive purpose for these traces. Generally, the opinion presented in 1888 by Stahl in Germany that the accumulation of alkaloids is for defensive purposes has been most often cited in the research literature. 

A diagram of the accumulation of pyrrolizidine alkaloids in some insect species during various developmental stages. 

Hartmann, T. and Ober, D. (2000). Biosynthesis and metabolism of pyrrolizidine alkaloids in plants and specialized insect herbivores. Topics in Current Chemistry 209 207-243. 

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