Scale insect (Hemiptera: Coccomorpha) morphology is transformed under trophobiosis

Authors: SODANO, JAMES - Towson University; OUFIERO, CHRISTOPHER - Towson University; Schneider, Scott; LAPOLLA, JOHN - Towson University

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2023
Publication Date: 12/2/2023
Citation: Sodano, J., Oufiero, C.E., Schneider, S.A., Lapolla, J.S. 2023. Scale insect (Hemiptera: Coccomorpha) morphology is transformed under trophobiosis. Annals of the Entomological Society of America. 117(1):49-63. https://doi.org/10.1093/aesa/saad033.
DOI: https://doi.org/10.1093/aesa/saad033

Interpretive Summary: Root mealybugs are a critically understudied group of potentially economically important scale insects. Recent phylogenetic studies have highlighted artificiality in the generic classification of root mealybugs, likely reflecting convergent morphological evolution among other causes. One potential source of convergence involves close ecological association with ants. This study quantifies characteristics of morphological evolution among mealybugs and root mealybugs that correspond with obligatory ant association, pointing out certain traits that either have or could confound root mealybug classification. This work helps establish a foundation upon which a natural classification of root mealybugs can be built. The study also discusses the evolution and traits of domestication in a non-human (ant) agricultural system. The results are important to evolutionary biologists, scientists studying mutualisms, scale insect systematists, and regulatory agencies.

Technical Abstract: Ants have great potential to exert influence over the morphological evolution of their obligate mutualist partners. Obligately myrmecophilic mealybugs are noted for their unusual morphology, and while this is often attributed to their relationship with ants, a quantitative assessment of this link is lacking. We address this need by evaluating morphological change among mealybugs as a function of ant association. This study considers the associates of two independent ant clades—Acropyga ants associated with root mealybugs from the families Xenococcidae and Rhizoecidae and herdsmen ants from the Dolichoderus cuspidatus species-group associated with mealybugs from the tribe Allomyrmococcini (Pseudococcidae)—and compares them to free-living or potentially myrmecophilic species sampled from among the mealybugs and root mealybugs. We use a combination of geometric morphometric and linear datasets to evaluate characteristics of body shape, body size, leg metrics, and ostiole development. Obligate myrmecophily significantly influences both body shape and size; myrmecophilous mealybugs are smaller than their free-living counterparts and are either pyriform or rotund in shape rather than oval. Ant-associates from Rhizoecidae also have significantly reduced anterior pairs of ostioles compared to free-living species. Ostioles are involved in defense against natural enemies and mutualist ants typically protect their partners, supplanting the need for structures like ostioles among myrmecophilous species. We discuss the influence ants have on the evolution of their associates in the context of domestication and offer avenues for future exploration.