National Geographic : 1989 Sep
Almost all aphids are females that reproduce by par - thenogenesis-without sex. This results in offspring genetically identical to their mothers. Aphids lack the larval and pupal stages of many insects, and for most of the year they also skip the egg stage. Thus live birth is a common sight in an aphid colony. Emerging from her mother, a Pseudoregmasoldier reaches down with her legs to pull her self free (top). Moments later the mother seems to cradle her off spring (middle), but in fact she provides no parental care. Her next birth may be either a nor mal aphid or another soldier; how an offspring's caste is determined is not known. In fact, the non-soldier embryos inside her body already contain her developing grandchildren. This is one reason why aphids reproduce so rapidly. Different types of soldiers are found on primary and secondary host plants. The primary host soldiers of Ceratoglyphina bambusae lack horns-they bite their enemies rather than pierce them. These soldiers develop from nymphs who have molted once. Pseudoregmatypify most secondary host soldiers, armed at birth with pronounced horns and massive forelegs. Scientists believe that the behavior of the Taiwanese aphid Astegopteryx bambucifo liae provides clues to the evolu tion of soldiers. This species-a relative of samurai aphids lacks a distinct soldier caste. However, all of these aphids possess some warrior character istics, such as diminutive horns that are too small to be lethal. Fighting over a feeding site, a hungry Astegopteryx aphid uses her horns to butt another drink ing plant sap. The aggressor is shoved back by her colony mate, who swings at her with her body (right). Ceratovacunalanigerarepre sents a more advanced stage in samurai aphid evolution. This species also lacks soldiers, yet any newborn can use its horns to crush a predator's eggs. By developing specialized soldiers, samurai aphids have taken on a far more dangerous function: killing large and aggressive predators. Still, even samurai aphids sometimes use their horns for their original function-contests over food. Biting soldiers have evolved along a different pathway. In subtropical and tropical areas many species-including samurai aphids -have colonies that last for more than a season. For example, Pseudoregma aphids are found on bamboo year-round. Yet Japanese biolo gists Seiki Yamane and Tsukasa Sunose have discovered the per centage of soldiers in a colony varies; it is nearly 20 percent in late autumn, when soldiers can protect the growing brood of winged migrants.