Aposematic insects

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]. 

Many aposematic lepidopteran insects are associated with poisonous plants and sequester the toxins from their host instead of, or in some cases in addition to, biosynthesizing their own defensive compounds. 

Sequestration of toxic alkaloids also has another benefit for the insects that feed on these forbidden fruits. In a very real sense these herbivores are conspicuously marked with colorful patterns that designate them as toxic animals. They are described as aposematic or warningly colored organisms, in much the... 

Solenopsis ants produce piperidine alkaloids which resemble the plant alkaloid coniine. These alkaloids are strong deterrents and inhibit several cellular processes, such as electron transport chains (Table IV) 28,494). Many insects indicate the content of toxic natural products by warning colors (aposematism) or by the production of malodorous pyrazines 4,17,231,494). 

Because the butterfly carries warning coloration (aposematic labeling) that the bird learns to recognize quickly, only a fraction, about 50% of the insects, need to have the toxic compounds within their bodies for all of the insects to be protected (Brower, 1969). Both the plants and the insects differ in cardenolide content. Monarch butterflies do not accumulate each of the compounds in the plant equally well. Some cardenolides are absorbed intact, others are biochemically modified, and yet others are excreted. 

The larvae of the bug, Caenocoris nerii, feed on ripening seed pods of Nerium oleander plants and also accumulate cardenolides such as oleandrin (28). At night, when aposematic colors are less useful, these insects abandon the conspicuous pods and shelter in twos or threes on the underside of leaves of the plant (Rothschild, 1973). 

Eisner, T. and Kafatos, F. C. (1962) Defense mechanisms of arthropods. X. A pheromone promoting aggregation in an aposematic distasteful insect. Psyche, 69, 53-61. 

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