Investigating the subspecific designation of the brown stink gug, Euschistus servus (Say) (Hemiptera: Heteroptera: Pentatomidae), using a combined landmark- based geometric morphometrics approach

Euschistus servus (Say, 1831) (Heteroptera: Pentatomidae) is distributed throughout North America and is currently subdivided into two subspecies E. s. servus, found in the southern U.S., and E. s. euschistoides (Vollenhoven, 1868) in the northern U.S. An intergrade population inhabits the central U.S. from Maryland to Kansas. This study sought to reevaluate the established subspecific designations and determine whether E. servus subspecies and intergrade populations express distinct suites of taxonomically important morphological characteristics throughout the U.S., or if the characteristics exhibit clinal variation. We quantified landmark-based geometric morphometric data in conjunction with traditional morphometrics (i.e., relative lengths of the juga and tylus) from specimens collected along a wide geographic area and used a principal component analysis to determine if there is a significant difference within the subspecies’ morphology. Principal component analysis assessing shape between morphogroups failed to produce clusters commensurate to the E. s. servus and E. s. euschistoides forms. Analysis of the shape, connexivum, and antennal color characters suggested that there is linear relationship between the taxonomic characters and latitude as the predictor and explanatory variable which may be indicative of clinal variation. This data leads us to dispute the existing subspecific designation of the E. servus species complex. We believe E. servus should be recognized as polymorphic as opposed to polytypic.