CASTE ALLOMETRIES IN THE SOLDIER-PRODUCING APHID PSEUDOREGMA-ALEXANDERI (HORMAPHIDIDAE, APHIDOIDEA)

Colonies of the aphid Pseudoregma alexanderi produce morphologically-s pecialized first-instar larvae, termed soldiers, that defend the colon y from predators. The environmental cues and physiological mechanisms governing soldier production are currently unknown. Here we present a morphometric study of soldiers and normal first-instar larvae of P. al exanderi. Several morphological features (fore-leg length and width, h ind-leg length, and horn length) plotted against body length display r elationship that are similar to a sigmoidal curve. We found further su pport for an earlier finding that soldiers fall into two size categori es, majors and miners, although both types of soldiers appear to follo w the same allometry. The patterns of allometry in the soldier-produci ng aphids are very different from those found in other social insects and do not easily fit into the traditional categorization of allometri es. We present two simple alternative models of soldier development as a framework for guiding future studies of the mechanisms of soldier p roduction.