Testing for morphometric differentiation between pecan- and water hickory-associated populations of the yellow pecan aphid, Monelliopsis pecanis (Hemiptera: Aphididae)

Host-associated differentiation (HAD) is a form of ecologically mediated speciation by which two or more parasite populations (e.g., insect herbivores) from the same species become genetically distinct due to their associations with different host species (e.g., host-plants). HAD has been proposed as a potential explanation for the vast species diversity observed throughout parasitic insect lineages. However, it is unclear which components of parasite-host interactions best explain the occurrence of HAD. One such explanation involves host-plant species generating or maintaining divergent selection pressures on insect morphology. To test the relationship between morphological differentiation and HAD, several morphological traits were compared between pecan- and water-hickory associated populations of the yellow pecan aphid, Monelliopsis pecanis (Hemiptera: Aphididae). Both geometric morphometric and meristic characteristics were integrated into a robust statistical framework to assess which of the measured traits best explained morphological variation between host-associated populations of yellow pecan aphids.