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19 Reproduction 1. Introduction As was discussed in Chapter 2 (Section 4.1), an important factor in the success of the Insecta is their high reproductive capacity, the ability of a single female to give rise to many offspring, a relatively large proportion of which may reach sexual maturity under f favorable conditions. | III Reproduction and Development 19 Reproduction 1. Introduction As was discussed in Chapter 2 Section 4.1 an important factor in the success of the Insecta is their high reproductive capacity the ability of a single female to give rise to many offspring a relatively large proportion of which may reach sexual maturity under favorable conditions. As reproduction is almost always sexual in insects there arise within insect populations large numbers of genetic combinations as well as mutations which can be tested out in the prevailing environmental conditions. As these conditions change with time insects are able to adapt readily through natural selection to a new situation. Over the short term their high reproductive capacity enables insects to exploit temporarily favorable conditions for example availability of suitable food plants. The latter requires that both the timing of mating egg production and hatching and the location of a suitable egg-laying site must be carefully assessed by an insect. Like other terrestrial animals insects have had to solve two major problems in connection with their reproductive biology namely the bringing together of sperm and egg in the absence of surrounding water and the provision of a suitable watery environment in which an embryo can develop. The solution to these problems has been the evolution of internal fertilization and an egg surrounded by a waterproof cover chorion respectively. The latter has itself created two secondary problems. First because of the generally impermeable nature of the chorion structural modifications have had to evolve to ensure that adequate gaseous exchange can occur during embryonic development. Second the chorion is formed while an egg is still within the ovarian follicle that is prior to fertilization which has necessitated the development of special pores micropyles to permit entry of sperm. 2. Structure and Function of the Reproductive System The external structure of male and female reproductive
