Pachybrachis Chevrolat (Coleoptera: Chrysomelidae) is a very large and complex genus of small leaf beetles with >150 species in the United States. Pachybrachis nigricornis carbonarius Haldeman is an entirely (or nearly entirely) black subspecies that is relatively common in Kentucky. Abundance and distribution records for 288 specimens collected in Kentucky are presented. Adults were found feeding on two species of legumes (Fabales: Fabaceae: Papilionoideae) over 230 km apart in Kentucky: on Desmodium paniculatum L. DC in Henry County and on Lespedeza virginica (L.) Britton in Logan County. No-choice feeding trials using female beetles and six species of legumes revealed significant leaf disk consumption after 50 hrs on all plant species. Females with narrow lateral yellow markings on the elytra were significantly larger in body size than all-black females and consumed more leaf area. The yellow-margined females appear to represent a transitional form between two previously recognized subspecies, suggesting that the current subspecies taxonomy for P. nigricornis (Say) needs re-evaluation.
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Barney et al. (2009) studied this question.
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