Hlx

650 occur in the pupa. In primitive endopterygotes most organs grow progressively during larval life, and metamorphosis consists mainly of the development of the flight mechanism. In most endopterygotes considerable differentiation of adult tissues occurs during metamorphosis, often from imaginal discs, groups of cells that remain embryonic through larval life, probably because of the hormonal milieu in juvenile instars.

Several types of endopterygote larvae may be distinguished: oligopod (including scarabaeiform and campodeiform larvae), which are most primitive; polypod (eruciform); and apodous (including eucephalous, hemicephalous, and acephalous larvae).

Pupae may be decticous (having functional mandibles) and exarate (appendages not sealed against the body), or adecticous and exarate or obtect (appendages sealed against the body). For protection, a pupa may be enclosed within a cocoon or cell, or may be heavily sclerotized and/or camouflaged, or in cyclorrhaph Diptera remain inside the cuticle of the last larval instar (the puparium).

Adult emergence (eclosion) is achieved by swallowing air to increase the body volume and thus split the pupal cuticle. When an insect pupates in a cocoon, etc., it may chew or tear its way out, either as a pharate adult or after eclosion, using mandibles, spines, or cocoon cutters. The cocoon of some species is equipped with an escape hatch.

Hormones regulate development. A molt cycle is initiated with the release of protho-racicotropic hormone from the brain, which stimulates release of ecdysone from the molt glands. The nature of a molt is determined by the concentration of JH at a critical period in the stadium. When the JH concentration is above a threshold value, a larval-larval molt follows; at below-threshold concentrations the molt is larval-pupal or pupal-adult.

Polymorphism is the existence of several distinct forms of the same stage of a species. It may have a genetic basis (as in transient and balanced polymorphism) or be induced by changing external conditions (polyphenism), whose effects are manifest via the endocrine system, specifically the concentration of JH at critical periods. Examples of polyphenism are caste differentiation in social insects, seasonal polymorphism in aphids, and the phases of locusts.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

Get My Free Ebook


Post a comment