Comparison of Two Different Morphological Methods to Study the Pronotum of Cimicidae: Bed Bugs, Bat Bugs, and Swallow Bugs

SIMPLE SUMMARY: Several members of the Cimicidae family are ectoparasites of vertebrates. Some of these are economically and medically important, e.g., the bed bugs, which are a global pest affecting humans. The development of a method to easily identify species of the Cimicidae family, despite the high morphological similarity of its members, will bring benefits such as the early detection of emerging infestations, facilitating the setup of adequate control and management measures. One of the existing methods, traditional morphometry (linear measurements and ratios of an object), is a demanding process involving the examination of many morphological features of well-preserved samples. An alternative approach that uses only one morphological feature could be an asset. Therefore, we assessed the use of a single organ, the pronotum, to classify Cimicidae via two methods: traditional and geometric morphometry (a method capturing the geometry of an object using coordinates as opposed to simple linear measurements and ratios). Both methods were effective in classifying members of the family based on the pronotum; however, better quality data were obtained with geometric morphometry. We recommend adopting the latter approach in future surveillance programs for medically important members and poultry pests of the family. ABSTRACT: An infestation of a Cimicidae (Hemiptera: Cimicidae) member, especially the bed bug, can cause economic loss and impact health. A cost-effective and user-friendly method for identifying the infesting species will help with the early detection and control of infestations. A linear morphometric method is often used, but it requires the examination of many characters and a highly preserved specimen. We conducted a comparative morphometric study of the effectiveness of Cimicidae classification using a single organ, the pronotum, through outline-based and linear morphometric methods. Bat (Stricticimex parvus), human (Cimex hemipterus), and bird (Paracimex sp.) ectoparasites were subject of the study. With both methods, the properties of size and shape were compared and used separately to classify the specimens. Classification analyses of the two methods provided similar results, but more informative variables of size and shape were obtained with the outline-based approach. Size, as analyzed with the outline-based method, could detect sexual dimorphism, and produced better reclassification. The shape variables obtained from the linear measurements were strongly influenced by size variation, much more than the ones obtained from coordinates describing the pronotum contours. Our data suggest that the outline-based approach provides better characterization variables, thus we recommend them for a wider use in other Cimicidae family members.