Morphological comparison of proboscis sensilla between Plusiinae and Noctuinae (Lepidoptera: Noctuidae)

Ultramorphology of the proboscis and sensilla of the Asian corn borer Ostrinia furnacalis (Lepidoptera: Crambidae)

The Asian corn borer, Ostrinia furnacalis (Guenée), is one of the most destructive lepidopteran pests affecting maize in Asia. Previous research on the feeding behavior of O. furnacalis has mostly focused on larvae, but the adult feeding preference has been unclear hitherto. In this study, we investigated the ultramorphology of the proboscis and sensilla of O. furnacalis using scanning electron microscopy and made morphological comparisons between the sexes, attempting to make predictions on the food preference and feeding behavior of the adults. The proboscis of O. furnacalis is divided into zones 1 and 2 with three types of sensilla, namely chaetica, basiconica, and styloconica. The entire proboscis and zone 2 of the females are significantly longer than those of the males. The main sexual difference in the sensilla is shown in the number of sensilla styloconica, which are eight in females but nine in males. The feeding preference of adult O. furnacalis is discussed based on the morphology of the proboscis and sensilla.

Antennal and proboscis sensilla characteristics of Paranthrene tabaniformis (Lepidoptera: Sesiidae)

The poplar clearwing moth, Paranthrene tabaniformis (Lepidoptera: Sesiidae) is a serious wood-boring pest of several trees. The ultramorphology of the antennae and proboscis sensilla of adult P. tabaniformis was examined using scanning electron microscope to determine their structures and sex-specific differences. The results showed that the antennae of both sexes are composed of three segments: scape, pedicel and flagellum. Female antennae are clavate while male antennae are pectinate. The number of flagellomeres for females was significantly greater than for males. Seven different types of sensilla were identified on antennae of both males and females: Böhm sensilla, sensilla squamiformia, sensilla trichodea (three subtypes), sensilla chaetica, sensilla coeloconica, and sensilla auricillica (two subtypes), and apical sensors. Three different types of sensilla were found on the proboscis of adult P. tabaniformis: sensilla styloconica, sensilla chaetica, and sensilla basiconica (three subtypes). The sexual dimorphism difference in the number, distributional pattern, the length and the basal width of various sensilla on the antennae and proboscis were determined. This study clarifies the types and sexual dimorphism of the antennal and proboscis sensilla of adult P. tabaniformis and provides useful theoretical foundations for studies on behavioral mechanisms and functions of sensilla of P. tabaniformis. RESEARCH HIGHLIGHTS: Various types of sensilla on the antennae and proboscis of adults Paranthrene tabaniformis were observed. The sexual dimorphism of various sensilla on the antennae and proboscis were determined.

Ultramorphological Comparison of Proboscis and Associated Sensilla of Scotogramma trifolii and Protoschinia scutosa (Lepidoptera: Noctuidae)

Simple Summary

The clover cutworm, Scotogramma trifolii Rottemberg, and the spotted clover moth, Protoschinia scutosa (Denis & Schiffermuller), are worldwide polyphagous pests, and the larvae feed mainly on the leaf backs of many agricultural crops. However, the food sources and feeding habits of the adults are still poorly known. We investigated the ultramorphology of the proboscis and associated sensilla of S. trifolii and P. scutosa using scanning electron microscopy. The results show that the proboscises of S. trifolii and P. scutosa are structurally similar, both including three sensillum types and three zones (Zone 1–3). The sensillum chaeticum is non-porous hair-like, the sensillum basiconicum is a short smooth cone with a sensory pore on the blunt tip, and each sensillum styloconicum is composed of a uniporous sensory cone inserted into a ribbed stylus. In addition, the movement and fluid uptake mechanisms of the proboscis and the possible function of sensilla are briefly discussed.

Abstract

The proboscis is an important feeding organ for the glossatan moths, mainly adapted to the flower and non-flower visiting habits. The clover cutworm, Scotogramma trifolii Rottemberg, and the spotted clover moth, Protoschinia scutosa (Denis & Schiffermuller), are serious polyphagous pests, attacking numerous vegetables and crops, resulting in huge economic losses. However, the feeding behavior and mechanisms of the adult stage remain unsatisfactorily explored. In this study, the proboscis morphology of S. trifolii and P. scutosa are described in detail using scanning electron microscopy, with the aim of investigating the morphological differences and feeding behavior of these two species. The proboscises of S. trifolii and P. scutosa are similar in morphology and structure and are divided into three zones (Zone 1–3) based on the morphological changes of the dorsal legulae. Three sensillum types are located on the proboscises of both species, sensilla chaetica, sensilla basiconica, and sensilla styloconica. Significant differences were observed in the length of the proboscis and each zone between these two species, as well as in sensilla size and number. Based on the morphology of the proboscis and associated sensilla, S. trifolii and P. scutosa are potential flower visitors, which was also reinforced by the pollen observed at the proboscis tip. These results will strengthen our understanding of the structure of the proboscis related to the feeding behavior of Noctuidae.

Sensilla of the antenna and proboscis of Athetis lepigone (Möschler) (Lepidoptera: Noctuidae)

Sensory structures on the antennae and mouthparts of insects are associated with various activities, such as host location, feeding, attracting a mate, and identifying a suitable oviposition site. Athetis lepigone (Möschler) is an important polyphagous Eurasian pest with more than 30 species of host plants. The larvae target bud leaves, prop roots, and tender stems of many agricultural crops, but the feeding habits of the adults remain poorly known. Aiming to understand the feeding behavior of the species, we investigated the fine morphology of its antennae and proboscis using scanning electron microscopy. The antennae of both sexes are filiform, and bear eight types of sensilla: Böhm's bristles, sensilla squamiformia, trichodea, chaetica, basiconica, coeloconica, styloconica, and auricillica. Sensilla trichodea are the most abundant among these sensillum types. The proboscis consists of two elongated, interlocked maxillary galeae that enclose the food canal by dorsal and ventral legulae. The external galeal surface is covered with numerous triangular microtrichia on Zone 1 and abundant blunt microbumps on Zone 2. The surface of the food canal bears closely connected and smooth semicircular ridges, gradually tapering toward the proboscis tip. Three types of sensilla are noticeable on the proboscis: sensilla trichodea, basiconica, and styloconica. We briefly discuss the putative functional significance of the antennal and proboscis sensilla and, based on the specific structural modifications of the proboscis, predict a flower-visiting habit for A. lepigone.

Measuring proboscis length in Lepidoptera: a review

Mouthpart morphologies relate to diet range. Differences among or within species may result in resource partitioning and speciation. In plant-pollinator interactions, mouthpart length has an important role in foraging efficiency, resource partitioning and pollination, hence measuring nectarivorous insect mouthparts’ morphological variation is important. Most adult lepidopterans feed on nectars and participate in pollination. Although a vast range of studies applied morphometric measurements on lepidopteran proboscis (tongue) length, general recommendations on methodologies are scarce. We review available proboscis length measurement methodologies for Lepidoptera. Focusing on how proboscides have been measured, how accurate the measurements were, and how were these constrained by sampling effort, we searched for research articles investigating lepidopteran proboscis length and extracted variables on the aims of measurements, preparation and measurement methodology, and descriptive statistics. Different methods were used both for preparation and measurements. Many of the 135 reviewed papers did not provide descriptions of the procedures applied. Research aims were different among studies. Forty-four percent of the studies measured dead specimens, 13% measured living specimens, and 43% were unclear. Fifteen percent of the studies used callipers, 9% rulers, 1% millimetre scales, 4% ocular micrometers, 3% drawings and 14% photographs; 55% were non-informative. We emphasise the importance to provide detailed descriptions on the methods applied. Providing guidelines for future sampling and measurements, we encourage fellow researchers planning measurements to take into account the effect of specimen preparation techniques on the results, define landmarks, consider resolution, accuracy, precision, choose an appropriate sample size and report details on methodology.

Ultrastructure of the proboscis sensilla of ten species of butterflies (Insecta: Lepidoptera)

The ultrastructure of the sensilla on the proboscis of ten species of butterflies, Iphiclides podalirius, Parara guttata, Colias fieldii, Celastrina oreas, Sasakia charonda, Tirumala limniace, Acraea issoria, Stichophthalma neumogeni, Callerebia suroia, and Libythea celtis, among five families were investigated using scanning electron microscopy. They were compared to reveal the morphological differences in the proboscis sensilla among these butterflies. Four distinct types of sensilla were found on the proboscis among these species. The types of proboscis sensilla of I. podalirius and T. limniace were sensilla chaetica, sensilla coeloconica, and sensilla basiconica. The types in the other eight species were sensilla chaetica, sensilla styloconica, and sensilla basiconica. The number of sensilla styloconica on the proboscis of non-flower-visiting species was greater than that of flower-visiting species.

Morphological comparison of proboscides and associated sensilla of Helicoverpa armigera and Mythimna separate (Lepidoptera: Noctuidae)

Proboscides are important feeding devices for most adult Lepidoptera and exhibit significant morphological modifications and types of sensilla associated with feeding habits. In this study the architectures of the proboscides and sensilla were compared between the cotton bollworm Helicoverpa armigera (Hübner) and the armyworm Mythimna separate (Walker) using scanning electron microscopy. The proboscides of both species consist of two elongated maxillary galeae joined by dorsal and ventral legulae, forming a food canal. The dorsal legulae in H. armigera disappear a short distance from the proboscis apex, whereas those in M. separate exist up to the apex. Three types of sensilla are present on the proboscides of both species: sensilla chaetica, basiconica, and styloconica. The morphological differences of the sensilla mainly concern the sensilla styloconica, whose styli have six to seven smooth-edged ridges in H. armigera but six serrate-edged ridges in M. separate. No significant sexual dimorphism was found in the proboscides and sensilla of both species except for the length of the zone without the dorsal legulae in H. armigera. The morphological similarities and differences of the proboscides and sensilla between the two species are briefly discussed.

Chemoreception of Mouthparts: Sensilla Morphology and Discovery of Chemosensory Genes in Proboscis and Labial Palps of Adult Helicoverpa armigera (Lepidoptera: Noctuidae)

Siphoning mouthparts, consisting of proboscis and labial palps, are the exclusive feeding organs and important chemosensory organs in most adult Lepidoptera. In this study, the general morphology of the mouthpart organs and precision architecture of the proboscis was described in adult Helicoverpa armigera. Three major sensilla types with nine subtypes including three novel subtypes were identified. The novel sensilla styloconica subtype 2 was the only one having a multiporous structure, which may play olfactory roles. For further understanding of the chemosensory functions of mouthpart organs, we conducted transcriptome analysis on labial palps and proboscises. A total of 84 chemosensory genes belonging to six different families including 4 odorant receptors (ORs), 6 ionotropic receptors (IRs), 7 gustatory receptors (GRs), 39 odorant binding proteins (OBPs), 26 chemosensory proteins (CSPs), and 2 sensory neuron membrane proteins (SNMPs) were identified. Furthermore, eight OBPs and six CSPs were identified as the novel genes. The expression level of candidate chemosensory genes in the proboscis and labial palps was evaluated by the differentially expressed gene (DEG) analysis, and the expression of candidate chemosensory receptor genes in different tissues was further investigated by quantitative real-time PCR (qRT-PCR). All the candidate receptors were detected by DEG analysis and qRT-PCR, but only a small part of the OR or IR genes was specifically or partially expressed in proboscis or labial palps, such as HarmOR58 and HarmIR75p.1, however, most of the GRs were abundantly expressed in proboscis or labial palps. The reported CO2 receptors such as HarmGR1, GR2, and GR3 were mainly expressed in labial palps. HarmGR5, GR6, and GR8, belonging to the "sugar receptor" clade, were mainly expressed in proboscis or antenna and were therefore suggested to perceive saccharide. The results suggest that the mouthparts are mutually cooperative but functionally concentrated system. These works contribute to the understanding of chemical signal recognition in mouthpart organs and provide the foundation for further functional studies.