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Monochamus saltuarius is an important wood-boring pest of forests and a vector insect for the transmission of Bursaphelenchus xylophilus in China and other East Asian regions. To gain insight into the Mo. saltuarius olfactory system, we characterized the sizes and morphological characteristics of sensilla on antennae, maxillary palps, and labial palps of adults by scanning electron microscopy. Eight types of antennal sensilla were identified on the antennae: Böhm bristles (BBs), sensilla chaetica (SChs, with subtypes SChI and SChII), sensilla trichodea (STs, with subtypes STI, STII and STIII), sensilla auricillica (SAus), sensilla basiconica (SBs, with subtypes SBI and SBII), sensilla grooved peg (SGPs), dome shaped organs (DSOs), and cuticular pores (CPs); among these, BBs, STIs, STIIs, SChIs, and SChIIs may be mechanoreceptors, and STIIIs, SAus, SBIs, SBIIs, SGPs and CPs may be chemoreceptors. Seven sensillum types were identified on maxillary palps and labial palps: BBs, STs (with subtypes STII, and STIII), SChs, sensilla placodea (SPs), sensilla coeloconica (SCos), CPs, and sensilla twig basiconica (STBs, with subtypes STBI, STBII, STBIII, and STBIV), among which BBs, STIIs, and SChs may be mechanoreceptors, and STIIIs, SPs, CPs, STBIs, STBIIs, STBIIIs, and STIVs may be chemoreceptors. DSOs on the antennae and SCos on the palps may be hydroreceptors, and/or thermoreceptors. The types and densities of sensilla increased from the base to the tip of the antennae, and sensilla with chemical-sensing functions were concentrated mostly on the flagellum. Identification of these sensillum types provides a basis for analyzing the mechanisms of host recognition and environmental perception of Mo. saltuarius .

A comparative SEM study of palp sensory surfaces in 25 caddisfly species representing seven families reveals seven types of sensilla: long trichoid, blunt chaetoid, campaniform, mushroom-like pseudoplacoid, petaloid, thick basiconic and thin basiconic sensilla. Long trichoid and chaetoid sensilla are present on all segments of both pairs of palps. First and second segments of maxillary palps bear groups of long and sclerotised chaetoid sensilla on their medial surface. Other segments of maxillary palps and all segments of labial palps have shorter and thinner chaetoid sensilla mainly on their ventromedial surfaces. Campaniform sensilla usually occur on the first segment of labial palps and second segment of maxillary palps. Mushroom-like pseudoplacoid sensilla may occupy all palp segments or only distal ones. Petaloid sensilla form sensory fields on apical segments of both pairs of palps in most studied species. Thick basiconic sensilla occur only in apical sensory complexes on tips of maxillary and labial palps. A comparison with the Lepidoptera suggests the similarity in palp sensilla and conservative evolution of the palp surface. The reconstructed ground plan for the palp sensory surfaces in Trichoptera and Amphiesmenoptera is provided.

A comparative morphological study of the structure and distribution of sensilla on the maxillary and labial palps in caddisflies of the family Hydropsychidae was performed. Morphology of palpal sensilla was studied by scanning electron microscopy in 17 species from 12 genera. The palps of the studied species have four types of sensilla: long trichoid, chaetoid, campaniform, and petaloid; at the same time, no basiconic and pseudoplacoid sensilla were found on the palps. All the studied species lack apical sensory complexes at the tips of both pairs of palps, where only long chaetoid sensilla are present. Petaloid sensilla form sensory fields on the 4th (in Arctopsychinae) or on the 3rd and 4th segments (in Diplectroninae, Hydropsychinae, Macronematinae) of the maxillary palps, but sensilla of this type are never present on the labial palps. The sensory fields include from 5–10 sensilla in Hydropsychinae to 40 sensilla in Arctopsychinae.

Larvae of the group Holometabola (beetles, wasps, flies, moths and others) differ significantly in their morphology from their corresponding adults. In most larvae, appendages and other structures protruding from the body (antennae, palps, legs, trunk processes) appear less elongate than in their corresponding adults, providing the impression that these larvae are restricted to a certain degree in developing more elongate structures. We provide here numerous counterexamples of larvae of lacewings (Neuroptera). These include different forms of elongated antennae, mandibles, maxillae, labial palps, legs, trunk processes and neck regions. Most of these examples are larvae preserved in different types of 100 million-year-old amber. The longest neck region was found in an extant specimen. All these examples demonstrate that certain branches of Neuroptera indeed had larval forms that possessed strongly elongated structures. Hence there is no principal constraint that hinders holometabolan larvae to develop such structures.

CA was supported by a Ph.D. fellowship BES-2017-081131 from the Ministerio de Economía, Industria y Competitividad (MINECO, Spain) joint financing by the European Social Fund. This study was supported by research grants AGL2016-77373-C2-2-R MINECO and PID2019-107030RB-C22 MICINN.

A potent and heat-stable tetrodotoxin (TTX) has been found to accumulate in various marine bivalve species, including Pacific oysters (Crassostrea gigas), raising a food safety concern. While several studies on geographical occurrence of TTX have been conducted, there is a lack of knowledge about the distribution of the toxin within and between bivalves. We, therefore, measured TTX in the whole flesh, mantle, gills, labial palps, digestive gland, adductor muscle and intravalvular fluid of C. gigas using liquid chromatography-tandem mass spectrometry. Weekly monitoring during summer months revealed the highest TTX concentrations in the digestive gland (up to 242 µg/kg), significantly higher than in other oyster tissues. Intra-population variability of TTX, measured in the whole flesh of each of twenty animals, reached 46% and 32% in the two separate batches, respectively. In addition, an inter-population study was conducted to compare TTX levels at four locations within the oyster production area. TTX concentrations in the whole flesh varied significantly between some of these locations, which was unexplained by the differences in weight of flesh. This is the first study examining TTX distribution in C. gigas and the first confirmation of the preferential accumulation of TTX in oyster digestive gland.

Morphology, distribution and function of the sensilla associated with mouthparts of female mosquito, Culex pipiens (Diptera: Culicidae) were studied by using the scanning electron microscope. The female mosquito mouthpart is a piercing and sucking type and carrying many sensory organs which plays major role in host seeking, and oviposition behaviour of mosquitoes. Six types of mouthpart sensilla have been identified and described, Sensilla trichoidea, chaetica, basiconica, Capitate peg, campaniformia and squamiformia. Females mosquito were irradiated as pupae with 20, 40 and 80 Gy of gamma radiation to investigate their effect on mouthparts sensilla. Dose of 20 Gy had slight effect on the different types of the sensilla as compared with the control. Features of malformation observed in the maxillary palp segments at this radiation dose include falling of some scales (sensilla squamiformia) at certain parts of the 1st segment leaving vacuoles. At 40 Gy, the maxillary palp segments were liquefied in some areas leaving undistinguished shape. At the highest dose 80 Gy, the tip of labial palps had many tears and showed were most affected, especially, at the trichoid, basiconic and chateica sensilla. All these malformations may lead the mosquitoes to not reaching the host, impeding their ability to transmit diseases or killing the mosquitoes, and this is the main objective of this study.

Tomicus pilifer is a major pest that threatens Pinus koraiensis forests in the northeast region of China. In this study, we employed scanning electron microscopy (SEM) to observe the sensilla on the antennae, mouthparts, and legs of both male and female T. pilifer adults, analyzing the differences in sensillum types, external morphology, and quantities between sexes. The results revealed six types of sensilla on the antennae of both males and females, including sensilla trichoidea, sensilla zigzag, sensilla coeloconica, sensilla chaetica, Böhm bristles, and sensilla basiconica. Among these, sensilla basiconica was the most abundant, with four subtypes identified, and sensilla basiconica III was observed only on the male antennae, indicating sexual dimorphism in sensillum types. The mouthparts exhibited the greatest diversity in sensilla, with seven types identified: sensilla basiconica, sensilla twig basiconica, sensilla coeloconica, sensilla trichoidea, sensilla chaetica, sensilla zigzag, and sensilla digitiformia. Of these, sensilla basiconica and sensilla twig basiconica, responsible for olfactory or gustatory functions, were concentrated at the distal ends of the maxillary palps and labial palps. On the legs, sensilla trichoidea, sensilla zigzag, and sensilla chaetica were distributed on all segments. The findings of this study provide a scientific basis for further research into the olfactory and feeding behaviors, as well as electrophysiological studies, of T. pilifer.

Bristletails (Microcoryphia) represent a relatively understudied group of class Insecta. These wingless hexapods, which retain numerous plesiomorphic structures, remain less well understood compared to most other insect lineages. Through detailed morphological examination of specimens collected from southern China, we describe six new species (Pedetontus (Verhoeffilis) elegans sp. n. from Zhejiang; P. (V.) hezhouensis sp. n., P. (V.) jinxiuensis sp. n., and P. (V.) nanningensis sp. n. from Guangxi; and P. (V.) shenzhenensis sp. n. and P. (V.) xanthospilus sp. n. from Guangdong) of subgenus Verhoeffilis Paclt, 1972. This subgenus is distinguished from other members of the Petrobiinae by several diagnostic features: paired ocelli shoe-shaped (fusiform-shaped) and submedian; two pairs of retractile vesicles on abdominal segments II–V; parameres restricted to coxite IX; penis opening small and apical; male genitalia not exceeding coxite IX; and ovipositor of primary type. The new species can be distinguished from known species and each other by the morphology of the compound eyes, maxilla, labial palps, legs, and genitalia; here, we provide detailed illustrations, tables, and descriptions. Furthermore, we sequence the COX1 gene to construct a phylogenetic tree of Microcoryphia. This contribution increases the total number of reported Pedetontus species in China to seventeen.

Megabruchidius dorsalis (Fåhraeus, 1839) (Coleoptera: Bruchinae) is an important pest that damages the seeds of Gleditsia L. (Fabaceae: Caesalpinioideae). This beetle searches for host plants with its sensory system. To further explore the mechanisms of host location and to understand the ultrastructure of M. dorsalis, we examined the morphology and distribution of its sensilla on the antennae and mouthparts of male and female adults, using scanning electron microscopy (SEM). Both male and female antennae are serrated and can be divided into scape, pedicel, and flagellum. There were seven types and eight subtypes of antennal sensilla, including Bőhm bristles (BB), two subtypes of sensilla trichoid (ST1, ST2), two subtypes of sensilla chaetica (SC1, SC2), four subtypes of sensilla basiconic (SB1, SB2, SB3, SB4), sensilla cavity (SCa), sensilla auricillica (SA), and sensilla gemmiformium (SG). Five types of maxillary and labial palp sensilla in the mouthparts were observed: sensilla chaetica (SC), sensilla trichoidea (ST), sensilla styloconica (SSt), sensilla coeloconica (SCo), and sensilla digitiform (SD). No sexual dimorphism in sensilla type was observed, but there were variations between males and females in the numbers and distribution along the antennae. There were more SA in males than in females, while the number of ST sensilla in the maxillary palps were lower in males than in females. ST1 were most abundant in both sexes. We discussed potential function related to structure via comparisons with previous investigations of bruchids and other insects. Our results provide a theoretical basis for further studies on sensory physiological function, using semiochemicals as effective biological controls of M. dorsalis.