Organization and Structure of the Tracheal System

A tracheal system is present in all Insecta and in other hexapods with the exception of the Protura and many Collembola. It arises during embryogenesis as a series of segmental invaginations of the integument. Up to 12 (3 thoracic and 9 abdominal) pairs of spiracles may be seen in embryos, though this number is always reduced prior to hatching, and further reduction may occur in endopterygotes during metamorphosis. Various terms are used to describe the number of pairs of functional spiracles, for example, holopneustic (10 pairs, located on the mesothorax and metathorax and 8 abdominal segments), amphipneustic (2 pairs, on the mesothorax and at the tip of the abdomen), and apneustic (no functional spiracles). The last condition is common in aquatic larvae, which are said, therefore, to have a closed tracheal system (Section 4.1).

The proportion of the body filled by the tracheal system varies widely, both among species and within the same individual throughout a stadium. In active insects whose tracheal system includes air sacs (see below) the tracheal system occupies a greater fraction of the body than in less active species. Further, in the former, the volume of the tracheal system may decrease dramatically during a stadium (e.g., in Locusta from 48% to 3%) as the air sacs become occluded by the increased hemolymph pressure that results from tissue growth. After ecdysis, when body volume has increased (Chapter 11, Section 3.2), the tracheal system expands because of the lowered hemolymph pressure.

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