ABSTRACT
Gametic reproduction either involves genetic mixing, as in normal sexual reproduction and automictic parthenogenesis as in apomictic parthenogenesis. The high incidence among insects may be because they are relatively immobile compared with larger organisms and therefore less able to seek refuge from adverse climatological and biological conditions. Reasons generally cited for the abandonment of sex are that periodic shortages of males in small local populations would favor females that are parthenogenetic; parthenogens are better able to conserve particular genotypes and so more easily exploit extreme environments. Most aphids show cyclical parthenogenesis in which there is several generations of parthenogenetic reproduction between each bout of sexual reproduction. Indeed, parthenogenesis was first experimentally confirmed by C. Bonnet, working on aphids in the 18th century, and virgin birth was observed in aphids by Leeuwenhoek in the 17th century. Their role in determining sex ratios and, more important for this review, their possible role in the evolution of parthenogenesis, should not be neglected.
