Introduction

Fundamental to insect society organization are behavioral and morphological differentiation of individuals into distinct castes. A hierarchy of caste differentiation is widespread among eusocial hymenopterans. All individuals are separable by sex, with striking differences between male and female behavior. Sex determination in hymenoptera generally follows Dzierzon's rule; unfertilized eggs are hemizygous at sex-determining loci and become male whereas diploid eggs are usually heterozygous at these loci, thereby developing into females. Interactions among nestmates are critical determinants of the proximate mechanisms of caste differentiation. Research motivated by evolutionary reasoning leads to further exploration of within-colony mechanisms of developmental control. The most spectacular examples of caste specificity and its ergonomic payoffs are those ant species with polymorphic worker castes, such as leafcutter ants. Differentiation of workers is dependent on larval nutrition; also, endocrine influences on worker development, notably juvenile hormone, have been implicated.