Reproduction

Two male stick-insects fighting over a female. (After Sivinski 1978.)

Most insects are sexual and thus mature males and females must be present at the same time and place for reproduction to take place. As insects are generally short-lived, their life history, behavior, and reproductive condition must be synchronized. This requires finely tuned and complex physiological responses to the external environment. Furthermore, reproduction also depends on monitoring of internal physiological stimuli, and the neuroendocrine system plays a key regulatory role. Mating and egg production in many flies is known to be controlled by a series of hormonal and behavioral changes, yet there is much still to learn about the control and regulation of insect reproduction, particularly if compared with our knowledge of vertebrate reproduction.

These complex regulatory systems are highly successful. For example, look at the rapidity with which pest insect outbreaks occur. A combination of short generation time, high fecundity, and population synchronization to environmental cues allows many insect populations to react extremely rapidly under appropriate environmental conditions, such as a crop monoculture, or release from a controlling predator. In these situations, temporary or obligatory loss of males (parthenogenesis) has proved to be another effective means by which some insects rapidly exploit temporarily (or seasonally) abundant resources.

This chapter examines the different mechanisms associated with courtship and mating, avoidance of interspecies mating, ensuring paternity, and determination of sex of offspring. Then we examine the elimination of sex and show some extreme cases in which the adult stage has been dispensed with altogether. These observations relate to theories concerning sexual selection, including those linked to why insects have such remarkable diversity of genitalic structures. The concluding summary of the physiological control of reproduction emphasizes the extreme complexity and sophistication of mating and oviposition in insects.

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