|Purple-spotted lily aphids, Macrosiphum lilii. Click to enlarge.|
The nymph is exactly like its mom except for size. It's a clone! Throughout the summer, aphids in this genus reproduce without sex by a process called parthenogenesis. Offspring develop from unfertilized eggs that do not undergo meiosis.
This method of reproduction is one of the reasons that an infestation of aphids can grow so quickly -- no need to date and mate. If an infested plant gets too crowded, winged females may be born and fly to another host plant. Near the end of the year, after many parthenogenetic generations, males and sexually reproducing females are born. They mate and lay eggs. The eggs lie dormant over the winter to hatch in spring and start it all over again.
An odd thing about aphids that reproduce like this is the possibility of telescoping generations: a female may be carrying an unborn daughter that is parthenogenetically pregnant with its own daughter. Like those nested Russian dolls. Cool!