Morphology and distribution of antennal sensilla in a parasitoid fly, Gymnosoma rotundatum (Diptera: Tachinidae)

Scanning electron microscopy study of the antennal sensilla of cob borer, Stenachroia elongella (Lepidoptera: Pyralidae)

Stenachroia elongella is an important pest of maize in Meghalaya, India. To understand the roles of sensory organs in the biological behaviors of this insect, we determined the structure and distribution of sensilla found on the antenna of both male and female S. elongella by scanning electron microscope. The antenna of both sexes is a filiform type, and the overall length of the female antenna is significantly longer than the male antenna. In both sexes, seven types and two subtypes of antennal sensilla are identified; sensilla trichodea, sensilla chaetica, sensilla styloconica, sensilla coeloconica, sensilla auricillica (I, II), sensilla squamiformia and Böhm sensilla. No sexual dimorphism on the specific occurrence of sensilla is observed. Probable functions are discussed based on their external morphology. These results would be helpful for further studies on TEM investigations, electrophysiological recordings, and behavioral studies. RESEARCH HIGHLIGHTS: Seven types and two subtypes of antennal sensilla were observed in both male and female Stenachroia elongella. Morphology and distribution of the antennal sensilla were discussed. Sexual dimorphism was observed on the overall length of the antenna where the female antenna is longer than the male antenna. No sexual dimorphism was observed on specific occurrences of antennal sensilla.

Antennal and maxillary palp morphology, and sensillar equipment, of the spruce bark beetle predators, Medetera signaticornis and Medetera infumata (Diptera: Dolichopodidae)

Many long-legged Medetera flies are natural enemies of bark beetle pests, which they detect using olfactory cues, likely through olfactory sensilla on the antennae and maxillary palps. Morphological characterisation of olfactory sensilla among insects can provide a basis for future taxonomic, phylogenetic or electrophysiological studies. Scanning electron microscopy was used to describe the morphology of olfactory organs and sensillar equipment of Medetera signaticornis and M. infumata. Three different olfactory sensillum types were found in both fly species, sensilla trichodea, s. basiconica and grooved pegs. Based on size and wall structure, s. trichodea and s. basiconica were categorised into different subtypes. Sharp-tipped curved s. trichodea, and small, large and thin s. basiconica were found on the antennal postpedicel of M. signaticornis adults, while grooved s. basiconica were found in M. infumata. The density of sharp-tipped long s. trichodea was significantly higher in males compared to females, and in M. signaticornis compared to M. infumata. Long-grooved s. basiconica were found grouped in a small pit on the maxillary palps of both species. Comparison of our results with the limited available ecological data suggests that differences in numbers of specific sensillum types may reflect adaptations related to olfactory-driven behaviours such as host seeking.

Abundance and distribution of antennal sensilla on males and females of three sympatric species of alpine grasshopper (Orthoptera: Acrididae: Catantopinae) in Aotearoa New Zealand

Brachaspis nivalis, Sigaus australis and Paprides nitidus are grasshopper species endemic to Aotearoa, New Zealand where they are sympatric in several regions of South Island. On mountains of Kā Tiritiri o te Moana (Southern Alps), B. nivalis is more abundant on scree/rock habitat, whereas S. australis and P. nitidus are prevalent in alpine tussock and herbfields. It is expected, therefore, that these species have different sensory needs that are likely to be apparent in the type, abundance, and distribution of chemo-sensilla on their antennae. It is also likely that natural selection has resulted in sexual differences in sensilla. To test these hypotheses, abundance and distribution of the chemo-sensilla on the dorsal and ventral surfaces of their antennae were characterized in adult males and females of the three species. Five types of chemo-sensilla were identified on the distal portion of their antenna: chaetica, basiconica, trichoidea, coeloconica, and cavity. All species had significantly more chemo-sensilla on the ventral than the dorsal surface of antennae and a similar distribution pattern of chemo-sensilla. Despite having relatively short antenna, B. nivalis had the largest number of olfactory sensilla, but the fewest chaetica of the three species studied. A plausible explanation is that B. nivalis is abundant on  less vegetated habitats compared to the other species, and therefore may rely more on olfaction (distance) than gustatory (contact) reception for finding food. No significant differences were observed between the sexes of B. nivalis and P. nitidus, however, S. australis males had significantly more basiconica sensilla than females.

Comparative morphology of antennal ultrastructure in Tachinidae parasitoid flies (Diptera): The phylogenetic importance of antennal sensilla

Tachinidae are one of the most diverse clades of Diptera. All tachinids are parasitoids of insects and other arthropods, and thus are considered an important source of biological pest control. Antennae are the most important olfactory organs of Tachinidae playing key roles in their lives, especially in locating hosts, and details of antennal ultrastructure could provide useful features for phylogenetic studies and understanding their adaptive evolution. Despite the ecological and evolutionary importance of antennae, the current knowledge of antennal ultrastructure is scarce for Tachinidae. Our study examined antennal sensilla of thirteen species belonging to thirteen genera within eleven tribes of all the four subfamilies (Phasiinae, Dexiinae, Tachininae, and Exoristinae): Beskia aelops Walker, Trichodura sp., Voria ruralis (Fallén), Zelia sp., Cylindromyia carinata Townsend, Phasia xenos Townsend, Neomintho sp., Genea australis (Townsend), Copecrypta sp., Hystricia sp., Belvosia sp., Leschenaultia sp., and Winthemia pinguis (Fabricius). Types, length and distribution of antennal sensilla were investigated via scanning electron microscopy (SEM). Our comparative analysis summarized 29 variable characters and we evaluated their phylogenetic signal for subfamilial, tribal and generic/specific levels, showing that antennal ultrastructure could be a reliable source of characters for phylogenetic analysis. Our findings demonstrate the remarkable diversity of the antennal ultrastructure of Tachinidae.

Insights into the Antennal Characteristics and Olfactory Strategy of the Endangered Rhino Stomach Bot Fly Gyrostigma rhinocerontis (Diptera: Oestridae)

Gyrostigma rhinocerontis (Diptera: Oestridae) is a rare obligate intestinal parasite of both white and black rhinoceroses, which can induce severe myiasis, cause secondary infection, and lead to enormous economic and scientific loss. Antennae are the main sensory organs of G. rhinocerontis, which may have evolved a series of specialized adaptive structures to facilitate the exploitation of their hosts. Here, we thoroughly examine the antennae of G. rhinocerontis via light and scanning electron microscopy. Only microtrichia and chaetic sensilla were observed on the scape and pedicel, and the latter is enlarged, half-enveloping the postpedicel. Four types of sensilla (trichoid sensilla, basiconic sensilla, coeloconic sensilla, and clavate sensilla) and sensory pits are detected on the postpedicel. A set of coeloconic sensilla and a chaetic sensillum are located on the arista. Distribution, type, size, and ultrastructure of antennal sensilla are presented. The antennae of G. rhinocerontis are the largest among Oestridae species, with the most sensilla and the most sensory pits. These antennal characteristics could be correlated to their adaptation for more sensitive and accurate olfactory organs, used to locate their rare and endangered hosts. Accordingly, this morphological evidence supports that the host is an important driving factor in the diversity of antennal morphology in the bot flies.

Ultrastructure of Antennal Sensory Organs in Nine Flesh Flies (Diptera: Sarcophagidae): New Insight into the Definition of Family Sarcophagidae

Simple Summary

The antennal sensilla of species in all three subfamilies of Sarcophagidae are studied for the first time via scanning electron microscopy. The morphology, density, and distribution of each type are described for each species. A total of eight types of antennal sensilla (chaetic sensilla, setiferous plaques, pedicellar buttons, trichoid sensilla, basiconic sensilla, coeloconic sensilla, clavate sensilla, bottle-shaped sensilla) and sensory pits are found in both sexes. The existence of bottle-shaped sensilla in the sensory pits in all three subfamilies of the sarcophagid species suggests a potential synapomorphy of sarcophagids and a new morphological diagnosis character of the family Sarcophagidae.

Abstract

The antennae are the main olfactory organ of flies, playing key roles in their survival and the success of all life stages. Antennal ultrastructural morphology has been well described in the representative species of most calyptrate families, yet only a few studies have focused on Sarcophagidae species, those with ecological and medical relevance. Antennal morphology and the types, shapes, distribution, and density of the antennal sensilla of nine Sarcophagidae species are studied in detail with scanning electron microscopy, including Miltogramminae: Metopia campestris (Fallén) and Mesomelena mesomelaena (Loew), Paramacronychiinae: Agria mihalyii (Rohdendorf & Verves), Wohlfahrtia bella (Macquart), and W. magnifica (Schiner); Sarcophaginae: Sarcophaga (Parasarcophaga) albiceps Meigen, S. (Bercaea) africa (Wiedemann), S. (Boettcherisca) peregrina (Robineau-Desvoidy), and S. (Liosarcophaga) portschinskyi (Rohdendorf), covering all three subfamilies of this family. The morphology of the three segments of the antennae has been described. The scape has only one type of chaetic sensilla, while three subtypes of chaetic sensilla were detected on the pedicel. The postpedicel has four types of sensilla: trichoid sensilla, coeloconic sensilla, clavate sensilla, and three subtypes of basiconic sensilla. Bottle-shaped sensilla were observed in sensory pits on the postpedicel in all nine species. These sensilla have not been discovered in other calyptrate species, suggesting that they are a potential sarcophagid synapomorphy.

Ultrastructure of the Sensilla on the Antennae and Mouthparts of Bean Weevils, Megabruchidius dorsalis (Coleoptera: Bruchinae)

Simple Summary

In this paper, we used scanning electron microscopy (SEM) to describe the morphological types, number of sensilla, and their distributions on the antennae and mouthparts of both sexes of the bean weevil, Megabruchidius dorsalis (Coleoptera: Bruchinae). The results showed twelve subtypes on antennal sensilla and five types of sensilla on maxillary and labial palps. No sexual dimorphism in sensilla type was observed, but there were variations between male and female in the numbers and distribution along with the antennae. In addition, we discussed potential function related to structure, through comparisons with previous studies of bruchids and other insects. This information will support further studies of semiochemicals as effective biological controls of this pest.

Abstract

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.