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

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.

Antennal and palpal sensilla of three predatory Lispe species (Diptera: Muscidae): an ultrastructural investigation

Antennae and maxillary palps are the most important chemical reception organs of flies. So far, the morphology of antennae and maxillary palps of flies of most feeding habits have been well described, except for that of relatively rare aquatic predatory species. This study describes sensilla on antennae and maxillary palps of three aquatic predatory Lispe species: Lispe longicollis, L. orientalis and L. pygmaea. Types, distribution, and density of sensilla are characterised via light and scanning electron microscopy. One type of mechanoreceptors is found on antennal scape. Mechanoreceptors (two subtypes) and one single pedicellar button (in L. pygmaea) are located on antennal pedicel. Four types of sensilla are discovered on antennal postpedicel: trichoid sensilla, basiconic sensilla (three subtypes), coeloconic sensilla and clavate sensilla. A unique character of these Lispe species is that the coeloconic sensilla are distributed sparsely on antennal postpedicel. Mechanoreceptors and basiconic sensilla are observed on the surface of maxillary palps in all three species. We demonstrated clear sexual dimorphism of the maxillary palps in some of the Lispe species, unlike most other Muscidae species, are larger in males than females. This, along with their courtship dance behaviour, suggest their function as both chemical signal receiver and visual signal conveyer, which is among the few records of a chemical reception organ act as a signal conveyer in insects.

Structural megadiversity in leaf litter predators - the head anatomy of Pselaphus heisei (Pselaphinae, Staphylinidae, Coleoptera)

The head anatomy of Pselaphus heisei (Pselaphitae) is described and documented. The structural features are evaluated in comparison with findings presented in earlier studies on the subfamily, with a special focus on correlations with predacious habits and the groundplan of Pselaphinae. We found the tentorium, labrum, maxillary palps, shape of head, and a system of dorsal pits and sulci highly variable within the subfamily, reflecting multiple transformations, including many homoplasious changes. The following major characters are identified as groundplan features of Pselaphinae: falciform mandibles; small mola; semiglobular neck; ventrolateral antennal articulation; steep clypeal region; setiform labial palpomere 3; tentorium with nearly vertical main branches and lacking laminatentoria; separation of tentorial bridge from tentorial arms; fusion of dorsal tentorial arms with the head capsule; large brain placed in the posterior third of the head; and a triple cluster of well-developed cephalic glands. The last feature supports a hypothesis that multiple and independent cases of adaptations to myrmecophilous habits observed in various lineages of Pselaphinae were possible by re-programming already existing glands to produce appeasement secretions. The cephalic muscle apparatus of P. heisei is similar to what is found in other staphylinoid groups, with some exceptions, whereas it is strongly modified in the myrmecophile Claviger testaceus. We propose that the unparalleled structural megadiversity in Pselaphinae is primarily linked with life in the upper soil layers combined with specialized carnivorous habits, with small and agile or mechanically protected arthropods as prey. Within the group, various specialized life habits have evolved, including myrmecophily, termitophily, and also life in deep soil or caves, each with unique morphological adaptations.

Nouvelles espèces malgaches du genre Homilia McLachlan, 1877 (Trichoptera, Leptoceridae)

New Malagasy species of the genus Homilia McLachlan, 1877 (Trichoptera, Leptoceridae). Since the transfer of Homilia grandis Mosely, 1932, to the genus Ceraclea Stephens, 1829, no Homilia McLachlan, 1877, was currently known from Madagascar. We describe here seven new species: Homilia andratina n. sp., H. coppai n. sp., H. electra n. sp., H. elisae Gibon, n. sp., H. elodiae Gibon, n. sp., H. tacheti n. sp. et H. tiouchichineae n. sp. They are characterized by a mottled loss of sclerotization of the fourth article of the maxillary palps, so far only known and characteristic of the genus Ceraclea. These species are endemic to the island, their geographical distributions and ecological preferences are described and briefly discussed.

Studies on Raspy Crickets: A new Andean Hyperbaenini genus (Orthoptera: Gryllacrididae: Hyperbaeninae)

Mikrohyperbaenus n. gen. is the first Andean genus for the tribe Hyperbaenini, the other genera such as Hyperbaenus and Dibelona inhabit the low and humid lands of South America. The new genus is distinguished by the structure of the male terminalia and the apex of the labial and maxillary palps, which are unusually naked or without the cuticle, that covers the other body segments. Mikrohyperbaenus n. gen. is a monotypic genus, found in the surroundings of the Zapatoca municipality, Santander, Colombia, a territory inhabited in the past by the Guane indigenous people, for which the new species Mikrohyperbaenus guane n. gen. et n. sp. is dedicated to that particular Pre-columbian indigenous people.

Formica species (Hymenoptera, Formicidae, Formicinae) in late Eocene Rovno amber

A new species, Formica ribbeckei Radchenko & Perkovsky, sp. nov., is described based on four workers from late Eocene Rovno amber (Ukraine). It most resembles F. flori Mayr, 1868 but differs from the latter mainly by the 5-segmented maxillary palps with the preapical segment subequal in length to the apical one, and by the shorter first funicular segment. Fossil F. luteola Presl, 1822, F. trigona Presl, 1822, F. macrognatha Presl, 1822 and F. quadrata Holl, 1829 are considered incertae sedis in Formicidae. Thus, ten valid Formica Linnaeus, 1758 species (including F. ribbeckei) are known now from late Eocene European ambers. The diversity of Formica in the early and middle Eocene deposits of Eurasia and North America is considered. It is assumed that the genus Formica most likely arose in the early Eocene.

Revision of the long-proboscid scorpionflies, Lichnomesopsyche Ren, Labandeira, and Shih, 2010

The Mesozoic mecopteran family Mesopsychidae has attracted extensive attention by their long proboscis that is presumably associated with pollination of early gymnosperms. Three previously reported species of Lichnomesopsyche Ren, Labandeira, and Shih, 2010 from the Middle−Upper Jurassic Haifanggou Formation at Daohugou (Inner Mongolia, northeastern China) display distinct resemblances in wing venation, so that their classification, based on currently described characters, remains elusive. Herein, we describe and figure exquisitely preserved male genital structures of L. gloriae Ren, Labandeira, and Shih, 2010, L. daohugouensis Ren, Labandeira, and Shih, 2010, and L. prochorista Lin et al., 2016, which can be used for defining and recognizing the three species. Our discovery indicates that the male genitalia are the major critical structures for species-level classification of the peculiar genus Lichnomesopsyche. Details of the maxillary palps and legs of L. gloriae and L. daohugouensis are also described.

Ultrastructure of the Olfactory Sensilla across the Antennae and Maxillary Palps of Bactrocera dorsalis (Diptera: Tephritidae)

The sensilla on the antennae and maxillary palps are the most important olfactory organs, via which the insect can perceive the semiochemicals to adjust their host seeking and oviposition behaviors. The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is a major agricultural quarantine pest infesting more than 250 different fruits and vegetables. However, the sensilla involved in olfaction have not been well documented even though a variety of control practices based on chemical communication have already been developed. In this study, the ultrastructure of the sensilla, especially the olfactory sensilla on the antennae and maxillary palps of both males and females, were investigated with field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Three types of olfactory sensillum types including trichodea, basiconica, and coeloconica, and two non-olfactory sensilla including both chaetica and microtrichia, were observed. Each of these three types of olfactory sensilla on the antennae of B. dorsalis were further classified into two subtypes according to the morphology and number of receptor cells. For the first time, the pores on the sensilla trichodea and basiconica cuticular wall were observed in this species, suggesting they are involved in semiochemical perception. This study provides new information on B. dorsalis olfaction, which can be connected to other molecular, genetic, and behavioral research to construct an integral olfactory system model for this species.

Prolonged activation of carbon dioxide-sensitive neurons in mosquitoes

Many insects can detect carbon dioxide (CO 2 ) plumes using a conserved receptor made up of members of the gustatory receptor (Gr) family Gr1, Gr2 and Gr3. Mosquitoes are attracted to host animals for blood meals using plumes of CO 2 in the exhaled breath using the receptor expressed in the A neuron of the capitate peg sensilla type on the maxillary palps. The receptor is known to also detect several other classes of odorants, including ones emitted from human skin. Here, we discover that a common skin odorant, butyric acid, can cause a phasic activation followed by an unusually prolonged tonic activity after the stimulus is over in the CO 2 neurons of mosquitoes. The effect is conserved in both Aedes aegypti and Anopheles gambiae mosquitoes. This raises a question about its role in a mosquito's preference for the skin odour of different individuals. Butyric acid belongs to a small number of odorants known to cause the prolonged activation of the CO 2 receptor. A chemical informatic analysis identifies a specific set of physico-chemical features that can be used in a machine learning predictive model for the prolonged activators. Interestingly, this set is different from physico-chemical features selected for activators or inhibitors, indicating that each has a distinct structural basis. The structural understanding opens up an opportunity to find novel ligands to manipulate the CO 2 receptor and mosquito behaviour.