Defense Mechanisms of Arthropods. X. a Pheromone Promoting Aggregation in an Aposematic Distasteful Insect.

A striking feature of many aposematic insects is their habit of mainraining dense and often conspicuous aggregations (Cott, 1957). Rather than spacing themselves more or less evenly throughout what is seemingly a uniformly favorable habitat, they occur in distinct, sporadically distributed clusters.. Many meloid and coccinellid beetles, as well as a variety of pentato.mid, coreid, and lygaeid Hemiptera, among others, are well known for this habit. These insects possess chemical defense mechanisms that protect them against predators, and their tendency to advertise themselves to visually oriented predators such as birds by pooling their aposematic resources in a collective display, appears to have obvious adaptive value. Moreover, by restricting themselves to a few relatively widely-spaced sites, the insects are exposed to but a fraction of the total number of predators in the area. This is likely to be of particular importance with respect to predators such as birds, which are known in many cases to have well-delimited foraging territories, and each of which may be expected to inflict a toll upon the insect population during the training period when the bird is learning to discriminate against the insect. Clearly, the fewer the foraging territories occupied, the greater will be the number of insects spared. Hitherto no studies have been made on the mechanism by which such aggregations are established and maintained. The purpose of