Lehr's fields of campaniform sensilla in beetles (Coleoptera): Functional morphology. II. Wing reduction and the sensory field Leonid Frantsevich a, * , Stanislav Gorb b , Vladimir Radchenko c , Dmytro Gladun c , Alexey Polilov d , Lyubov Cherney e , Vassily Browdy f , Maxim Kovalev g a Department of Ethology and Social Biology of Insects, Schmalhausen-Institute of Zoology, B. Chmielnicki Street 15, 01601 Kiev, Ukraine b Department of Functional Morphology and Biomechanics, Christian-Albrechts-University of Kiel, Am Botanischen Garten 1-9, D-24098 Kiel, Germany c Institute for Evolutionary Ecology, Acad. Lebedev Street 37, 03143 Kiev, Ukraine d Department of Entomology, Biological Faculty, Lomonosov Moscow State University,1-12 Leninskie Gory,119991 Moscow, Russia e Department of Scientific Fundamental Collection, Schmalhausen-Institute of Zoology, B. Chmielnicki Street 15, 01601 Kiev, Ukraine f Department of Zoology, Dragomanov Pedagogical University, Pirogov Street 9, 01601 Kiev, Ukraine g Department of Zoology, Institute of Biology, National Shevchenko-University, Volodymirska Street, 64, 01601 Kiev, Ukraine article info Article history: Received 14 February 2014 Received in revised form 22 October 2014 Accepted 24 October 2014 Available online 1 November 2014 Keywords: Insect flight Coleoptera Campaniform sensilla Wing reduction Elytra abstract Loss of the flight ability and wing reduction has been reported for many taxa of Coleoptera. If elytra are closed, their roots are clenched between the tergum and the pleuron, forces applied to the elytra can not be transmitted to the field of campaniform sensilla situated on the root. That is why it is plausible to assume that the field becomes redundant in non-flying beetles. We examined the relationships between the hind wing reduction and characters of this mechanosensory field in beetles of six families. We measured the size of the elytron, that of the hind wing and counted the number of sensilla in the sensory field. Mesopterous non-flying beetles retain one half to one third of sensilla present in macropterous species of the same body size. Further reduction of the sensory field in brachypterous species is obvious, but sensilla are still present in insects with strongly reduced wings, as long as their elytra are separable and mesothoracic axillaries are present. Complete loss of sensilla coincides with the existence of a permanent sutural lock. However, some beetles with permanently locked elytra and absence of axillaries still retain few campaniform sensilla. A very special case of an extreme wing modification in feather-wing beetles is considered. No sensilla were revealed either on the root of the elytron or on the basal segment of such fringed wings in flying ptiliid species. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction The present paper is the second of three articles on the structure and size of the field of campaniform sensilla (CFS) situated on the root of the elytron in the elytron-to-body articulation. The field of CFS has been initially described by Lehr (1914), this is why we designate this sensory field as Lehr's field. Our first paper treated the morphology of the root and composition of Lehr's field, as well as allometric relationships between the size of the elytron and the number of sensilla within this field in flying beetles (Frantsevich et al., 2014). The present paper considers the correlation between the grade of hind wing reduction in non-flying beetles and the reduction in number of sensilla within the field. Loss of flight ability and wing reduction was often reported among Coleoptera. Elytra in non-flying beetles are permanently closed. The root is tightly clenched between the tergum and pleu- ron and thus obtains only a negligible portion of forces acting on the elytra. In such a situation, the non-signaling Lehr's sensory field becomes redundant. Functionality of Lehr's field in non-flying beetles may be potentially preserved only in such a rare case, when the elytra still are able to separate, open and close themselves actively, not for the function of flight but rather for righting. What has happened with Lehr's field in the evolution of non-flying bee- tles, which gradually lost their flight ability? One can hypothesize different degrees of the reduction of the field depending on the degree of wing reduction. The early stage of loss of the flight ability appears as underde- velopment of direct wing muscles during metamorphosis or degeneration of those muscles in the second half of the imaginal life. The wings themselves and the external appearance of the * Corresponding author: E-mail address: leopup@izan.kiev.ua (L. Frantsevich). Contents lists available at ScienceDirect Arthropod Structure & Development journal homepage: www.elsevier.com/locate/asd http://dx.doi.org/10.1016/j.asd.2014.10.003 1467-8039/© 2014 Elsevier Ltd. All rights reserved. Arthropod Structure & Development 44 (2015) 1e9