Nervous And Chemical Integration

4.1.2. Caste-Regulating Pheromones

As noted in the previous section, in social insects very few members of a colony ever mature sexually, their reproductive development being inhibited by pheromones so that these individuals (forming the worker caste) can perform other activities for the benefit of the colony as a whole. In addition to the worker caste, there exists in termites and ants a soldier caste. The number of soldiers present is proportional to the size of the colony, a feature suggesting that soldiers regulate the numbers in their ranks by production of a soldier-inhibiting pheromone. However, the situation is made more complicated by a positive influence on soldier production (presumably pheromonal) on the part of the reproductives.

The regulation of caste differentiation in social insects is a morphogenetic phenomenon, just as are the changes from larva to larva, larva to pupa, and pupa to adult. Such changes depend on the activity of the corpora allata (level of juvenile hormone in the hemolymph) for their manifestation. It is not surprising, therefore, that the pheromones regulating caste differentiation (including the development of reproductives) exert their effect, ultimately, via the corpora allata (Chapter 21, Section 7). In lower termites, for example, soldier formation can be induced in experimental colonies by administration of juvenile hormone (through feeding, topical application, or as vapor). Thus, the soldier-inhibiting pheromone may act by inhibiting the corpora allata or by competing with juvenile hormone at its site of action (Luscher, 1972).

4.1.3. Aggregation Pheromones

Aggregation pheromones are produced by either one or both sexes and serve to attract other individuals for feeding, mating, and/or protection. They occur in Collembola, Diptera, Hemiptera, Orthoptera, and Dictyoptera, but are especially well known in Coleoptera, particularly the bark and ambrosia beetles (Scolytinae). Larvae of the crane fly Tipula simplex

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