Labial Sensory Organs of Two Leptoglossus Species (Hemiptera: Coreidae): Their Morphology and Supposed Function

SIMPLE SUMMARY: Several Leptoglossus Guérin-Méneville, 1831 species are important plant pests. Leptoglossus occidentalis (western conifer seed bug), a native of western North America, has become a highly successful worldwide invader that feeds on conifer cones and can be a significant pest in conifer seed orchards. Leptoglossus zonatus, or the large-legged bug, occurs throughout much of the Western Hemisphere and is an important pest to a wide range of crops in the southern United States. Mouthparts are necessary appendages specialised in detecting food sources and feeding. The types and quantities of various sensory organs are closely related to the feeding habits of insects. The labial sensilla occurring in the two aforementioned species were examined using field emission scanning electron microscopy, and their structural details were described for the first time. The elongated and slender, four-segmented labia have the same structure in both species. Nine types of aporous sensilla, whose function is probably mechanoreception, and three uniporous sensilla, most likely responsible for chemoreception (gustatory receptors), were found. This study increases the available detailed morphological and behavioural data for Hemiptera and contribute to improve our understanding of these pests’ feeding behaviour and sensory mechanisms. ABSTRACT: A detailed description of the labial sensory organs of Leptoglossus occidentalis Heidemann, 1910 and L. zonatus (Dallas, 1852) (Hemiptera: Heteroptera: Coreidae) is presented. The detailed morphology, location, and distribution of different sensilla types on mouthparts were investigated and shown in micrographs taken with a scanning electron microscope. Nine types of aporous sensilla, and three uniporous sensilla were found. The possible functions of these sensilla as well as similarities and differences between the mouthparts of Leptoglossus and those of other terrestrial Heteroptera are discussed. The tip of the labium constitutes a functional “touch and taste area”, combining the chemosensitivity of uniporous sensilla P1–P3 and the mechanoreceptivity of A8 and A9 hair-like sensilla. A set of two cone-like chemosensilla types (9 + 2) was found on each lateral lobe of the labial tip. Literature analysis showed that such a set of cone-like sensory organs on the labial tip may be common in terrestrial Heteroptera. This observation confirms that the number and arrangement of sensilla is conservative and can be important in diagnosing taxa at various levels and in phylogenetic studies based on morphology.