The mouthparts and sensilla of the adult tomato leafminer moth, Tuta absoluta (Meyrick, 1917) (Lepidoptera: Gelechiidae)

Morphological and genetic differences in legs of a polygamous beetle between sexes, Glenea cantor (Coleopter: Cerambycidae: Lamiinae)

The legs of insects play an important role in their daily behaviour, especially reproduction. Entomologists have performed much research on the role of the leg in different behaviours of beetles, an important group in the insect family, but relatively little has been done to study the ultrastructure and transcriptome of their legs. Hence, we systematically studied the ultrastructure and gene expression of the leg of G. cantor, a polygynous beetle, and compared its male and female diversity. In this study, we found the fore-leg, mid-leg and hind-leg of the female were significantly longer than those of the male. From the perspective of intuitive structural differences, we also compared the ultrastructures of the adhesion structure (tarsal) of males and females. The tarsal functional structure of the adult leg mainly includes sensilla and an adhesion structure. The sensilla on the tarsal joint mainly include sensilla chaetica (SCh II, SCh III) and sensilla trichodea (ST II). The adhesion structure includes disc-shaped bristles (di), lanceolate bristles (la), serrated bristles (se), spatula-shaped bristles (spl) and mushroom-shaped bristles (mus). Although there was no significant difference in sensillum distribution or type between males and females, there were significant differences in the distribution and species of adhesion structures between the fore-leg, mid-leg, and hind-leg of the same sex and between males and females. Therefore, different adhesion structures play different roles in various behaviours of beetles. On the other hand, the transcriptome results of male and female legs were screened for a subset of olfaction- and mechanics-related genes. We discovered that the male leg showed upregulation of 1 odorant binding protein (OBP), 2 Olfactory receptors (ORs) and 2 Chemosensory proteins (CSPs). Meanwhile, the female leg showed upregulation of 3 OBPs, 1 OR, 1 Gustatory receptor (GR) and 3 Mechanosensitive proteins (MSPs). An in-depth examination of the ultrastructure and molecular composition of the legs can elucidate its function in the reproductive behavior of G. cantor. Moremore, this investigation will serve as a cornerstone for subsequent research into the underlying behavioral mechanisms.

The ultrastructure of nymphal dermal pores and the genitalia of adult male of Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

The cotton mealybug, Phenacoccus solenopsis, has established itself as an invasive insect pest worldwide. It causes structural and physiological damage to various crops and can cause substantial financial losses in their production. The successful reproduction of this pest under a wide range of conditions is a key to its success. Despite this, the morphology of its genitalia, genital sensilla, and wax-producing dermal pores has received little attention, with little descriptions of their ultrastructure. By investigating those features with SEM, the present study revealed considerable new insights into the identification of the nymphal and adult stages of P. solenopsis. In addition, the description of the ultrastructural genital morphology of the immature stages of P. solenopsis has revealed characteristics that facilitate their discrimination. Trilocular pores were observed on both sides of the body, while the quinquelocular pores were distributed only on the ventral surface in both the first and second nymphal instars. The adult male is characterized by two pairs of waxy caudal filaments surrounded by clusters of 55 to 60 stellate pores, and each pregenital segment bears a pair of stellate pores composed of 4 or 5 peripheral loculi. Sensilla trichodea and numerous microtrichia are present on the pregenital segments. The penile sheath bears three subtypes of sensilla basiconica and also campaniformia, whereas the style bears three subtypes of sensilla campaniformia. The findings of this study could assist in the identification of the adult and nymphal stages of P. solenopsis, and also provide insights into the structures found on the genitalia of the adult male that possibly have an important role in mating events and copulatory behavior. Furthermore, these findings were able to contribute to better understanding the functional morphology of P. solenopsis.

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.

Fine Structure of the Mouthparts of Three Tomicus Beetles Co-Infecting Pinus yunnanensis in Southwestern China with Some Functional Comments

Tomicus yunnanensis, T. brevipilosus, and T. minor are the most economically significant pests of Pinus yunnanensis in Southwestern China. Chemical and physical factors play critical roles in diverse biological activities. Here, we describe the fine structure of the adult mouthparts of these three Tomicus species using scanning and transmission electron microscopy. We identified three types of mandibular shapes, which determine their biomechanical properties, their ability to process food, and their preferred foraging locations on tree trunks. Eleven types of sensilla were discernible, including sensilla basiconica (Sb.1-2), sensilla twig basiconica (Stb.1-3), sensilla coeloconica (Sco), sensilla chaetica (Sch.1-2), sensilla trichoidea (Str.1-2), and sensilla digitiformia (Sdi). Each basiconic sensillum occurs on the palpal tips and is innervated by 2-6 dendrites. Sb.1 are gustatory receptors, Sb.2 are olfactory receptors, and the three other sensilla have dual taste and mechanical functions. Sco, Sch, and Str are mechanoreceptors. Sdi are mechanical vibration receptions, given that they are innervated by one dendrite with numerous dendritic branches into the nonporous cuticle. No significant differences among the sexes or species were identified; however, intraspecific variability in the number of Stb.3 and Sdi sensilla was evident. These results will aid future studies of Tomicus beetle behaviors.

Functional morphology of the mouthparts of longhorn beetle adult Psacothea hilaris (Coleoptera: Cerambycidae) and sensilla comparisons between the sexes

Psacothea hilaris is an important wood boring beetle that causes significant ecological and economic damage. The mouthparts of P. hilaris contain feeding and sensory structures that play important roles in many behaviors. The study of their functional morphologies provides insight into feeding and sensory mechanisms. The fine structures of the mouthparts and the sensilla of both sexes were observed by scanning electron microscopy, with special attention to quantitative comparisons. The general structures of the mouthparts are similar in males and females. However, the maxillary and labial palps of females are more well-developed than those of males. Six types of sensilla were found in both sexes: sensilla basiconca, sensilla trichodea, sensilla chaetica, sensilla digitiformia, sensilla coeloconica, and sensilla palmata. This was the first attempt to describe the sensilla on the epipharynx and ligula of Cerambycidae. There were differences in the number of sensilla of males and females, especially on the mandibles, maxillary and labial palps. However, not all types of sensilla have a greater number in females compared to males. The results provide basic information on the gustatory sensation mechanism of Cerambycidae.

Ultrastructural and Descriptive Study on the Adult Body Surface of Heortia vitessoides (Lepidoptera: Crambidae)

Heortia vitessoides Moore, 1885 (Lepidoptera: Crambidae) is an economically important lepidopteran pest that caused severe damage to the plantation area of Aquilaria sinensis (Lour.) Gilg, 1825 (Thymelaeaceae), resulting in extensive defoliation of the trees during an epidemic. In this study, we used scanning electron microscopy (SEM) to analyze the external morphology and ultrastructure of sensilla on various body parts of H. vitessoides. Specifically, seven, four, four, and five types of sensilla were found, respectively, on the antennae, proboscis, labial palps, and legs. We described the types, distributions, and sexual dimorphism of these sensilla on antennae, and found that the number and size of sensilla differed significantly between males and females. This study provides crucial information for future investigations into the function of these sensilla in H. vitessoides.

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.

Antennal sensory structures of Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

BACKGROUND

The cotton mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae) is one of the most devastating sap-sucking pests of cultivated plants. The success of P. solenopsis is attributable to its ecological resilience and insecticide resistance, making its control extremely difficult and expensive. Thus, alternative safe approaches are needed to prevent the pest population from reaching the economic threshold. One of these novel approaches is based on the fact that chemical communication via the olfactory system drives critical behaviors required for the survival and development of the species. This knowledge can be useful for controlling insect pests using traps based on semiochemicals. The antennae of insects are an invaluable model for studying the fundamentals of odor perception. Several efforts have been made to investigate the histological and ultrastructural organization of the olfactory organs, such as the antennae and maxillary palps, in many insect species. However, studies on the antennal sensory structures of Phenacoccus species are lacking. Furthermore, although enormous progress has been made in understanding the antennal structures of many mealybug species, the olfactory sensilla in the antennae of P. solenopsis have not yet been described. In this study, we describe, for the first time, the morphology and distribution of the antennal sensilla in male and female P. solenopsis using scanning electron microscopy.

RESULTS

Our results revealed that the entire antennae length and the number of flagellar segments were different between the sexes. Eight morphological types of sensilla were identified on male antennae: trichoid sensilla, chaetic sensilla (three subtypes), basiconic sensilla (two subtypes), and campaniform sensilla (two subtypes). Six morphological types of sensilla were found on female antennae. Sensilla chaetica of subtype 2 and campaniform sensilla of subtype 1 were distributed only on male antennae, suggesting that these sensilla are involved in the recognition of female sex pheromones. The subtype 1 of sensilla chaetica was significantly more abundant on female antennae than on male ones, while subtype 3 was only located on the terminal flagellar segment of the antenna in both sexes.

CONCLUSIONS

This study provides insightful information for future electrophysiological and behavioral studies on chemical communication in insects, particularly the cotton mealybug, P. solenopsis that could help in developing new strategies for controlling this economically important insect species.

Evolutionary functional morphology of the proboscis and feeding apparatus of hawk moths (Sphingidae: Lepidoptera)

The morphology of the proboscis and associated feeding organs was studied in several nectar-feeding hawk moths, as well as a specialized honey-feeder and two supposedly nonfeeding species. The proboscis lengths ranged from a few millimeters to more than 200 mm. Despite the variation in proboscis length and feeding strategy, the principle external and internal composition of the galeae, the stipes pump, and the suction pump were similar across all species. The morphology of the smooth and slender proboscis is highly conserved among all lineages of nectar-feeding Sphingidae. Remarkably, they share a typical arrangement of the sensilla at the tip. The number and length of sensilla styloconica are independent from proboscis length. A unique proboscis morphology was found in the honey-feeding species Acherontia atropos. Here, the distinctly pointed apex displays a large subterminal opening of the food canal, and thus characterizes a novel type of piercing proboscis in Lepidoptera. In the probably nonfeeding species, the rudimentary galeae are not interlocked and the apex lacks sensilla styloconica; galeal muscles, however, are present. All studied species demonstrate an identical anatomy of the stipes, and suction pump, regardless of proboscis length and diet. Even supposedly nonfeeding Sphingidae possess all organs of the feeding apparatus, suggesting that their proboscis rudiments might still be functional. The morphometric analyses indicate significant positive correlations between galea lumen volume and stipes muscle volume as well as the volume of the food canal and the muscular volume of the suction pump. Size correlations of these functionally connected organs reflect morphological fine-tuning in the evolution of proboscis length and function.