Evolutionary processes insect development

In termite soldiers the heads and bodies are so thoroughly modified into chemical and physical weapons that the soldiers can neither feed themselves nor reproduce. They are unique in exhibiting a diverse group of multipurpose allomones. Soldiers of the advanced genera have lost their mandibles through evolutionary processes, but have developed an ability to biosynthesize diterpenes which is unique in insects 528, 531). 

Since insects are unable to biosynthesize the steroid nucleus, they require dietary sterols for structural and physiological (hormonal) purposes. Cholesterol will satisfy this dietary need in most cases, but since phytophagous insects ingest little or no cholesterol from dietary materials, they must convert dietary C28 and Q9 phytosterols to cholesterol or other sterols. Through evolutionary development, certain insects have acquired the ability to metabolize dietary sterols in unique ways and to produce and utilize a variety of ecdysteroids (molting hormones) for hormonal control of development and reproduction. Thus, insects are able to flourish in virtually every conceivable ecological niche. Certain comparative studies that illustrate these evolutionary processes will be discussed in this chapter. 

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