Morphology and ultrastructure of a secretory region enclosed by the venom reservoir in social wasps (Insecta, Hymenoptera)

Ontogenetic morphological changes of the venom apparatus in 4 eupelmid egg parasitoids

Parasitoid wasps, notably egg parasitoids of the family Eupelmidae (Hymenoptera: Chalcidoidea), a key natural enemy of insect pests, offer a sustainable approach to pest management in agriculture. This study investigated the venom apparatus's developmental dynamics across 4 species of eupelmid egg parasitoids: Anastatus. japonicus, Anastatus fulloi, Mesocomys trabalae and Mesocomys albitarsis. A comprehensive anatomical investigation revealed differences in the dimensions of the venom apparatus across different developmental stages in adult females. We found that the venom apparatus of these 4 studied species consists of a venom gland and a reservoir with an associated Dufour's gland. As the length of post-emergence increases, a significant enlargement in the venom apparatus is evident across all the studied parasitoid species. Notably, M. albitarsis consistently exhibites the shortest venom gland length, whereas that of A. fulloi is the longest among the observed species. At the high day age, the width of venom glands of the 2 Mesocomys species surpasses those of the Anastatus species; for the volume of the venom reservoir, there is a steady increase in all 4 species before the age of 6–7 days, with a decline on 8th day, especially for A. japonicus. This research provided new insights into the developmental trajectories of venom apparatus in eupelmid egg parasitoids and the potential impact of venom potency on their success.

Morphology and ultrastructure of the colleterial glands in Myzinum flower wasps (Tiphiidae, Hymenoptera)

The strategies used by females to ensure the survival of their offspring are one of the key elements in insect reproductive biology. Ectoparasitoid hymenopterans, such as tiphiid wasps, use their ovipositor to deliver a single egg on the host body, where the larva develops. Here we describe the colleterial glands in females of two species of Myzinum and discuss the homology with other glands among Hymenoptera. The glands appear as two large opaque round sac-like structures that are connected to the oviduct. Histological sections revealed a compound gland, with a single layer of class-1 epithelial cells surrounded by a layer of class-3 gland cells, which is uncommon in Hymenoptera. Ultrastructure points to active protein synthesis, consistent with the role of colleterial glands. Despite the consensus that colleterial glands in Hymenoptera evolved with two distinct forms, the venom gland and Dufour's gland, the three glands were present in both Myzinum species. The few studies regarding the structure, function, and homology among the female accessory glands in Hymenoptera do not allow to make conclusive statements about the evolution of these glands. Therefore, the finding in Myzinum is probably the reflection of a lack of information, rather than an exception within Aculeata.

General morphology and ultrastructure of the female reproductive apparatus of Trichomalopsis shirakii crawford (Hymenoptera, Pteromalidae)

The morphology and ultrastructure of the female reproductive system were examined for a larval-pupal parasitoid Trichomalopsis shirakii Crawford of Oulema oryzae Kuwayama using light and electron microscopes. The reproductive system includes two ovaries, two pairs of accessory glands, an unbranched venom gland, a large venom reservoir and a Dufour gland. Each ovariole contains follicles and oocytes at different stages of maturation. A fibrous layer covers the surface of mature egg. The accessory glands are made up of a layer of secretory cells surrounded by muscle fibers. In these secretory cells, numerous mitochondria, electron-dense secretory granules and vesicles filled with dense granular particles are present. These granular particles appear as virus-like particles (VLPs). The venom gland consists of a single layer of secretory cells which are organelle rich with abundant rough endoplasmic reticulum, mitochondria and vesicular organelles, a layer of duct cells and an inner intima. The reservoir consists of a muscular sheath, epidermal cells with few organelles and an intima layer. The Dufour gland has a relatively large lumen surrounded by a single layer of columnar epithelial cells which are characterized by clusters of smooth endoplasmic reticulum and lipid droplets. Aside from the venom, the fibrous layer coating the egg and the granular particles which may be VLPs have been discovered in our study. They may serve as one of the parasitoid-associated factors in their host-parasitoid relationship and play a role in host immune suppression. Microsc. Res. Tech. 79:625-636, 2016. © 2016 Wiley Periodicals, Inc.

Venom and Dufour's glands of the emerald cockroach wasp Ampulex compressa (Insecta, Hymenoptera, Sphecidae): structural and biochemical aspects

The digger wasp species Ampulex compressa produces its venom in two branched gland tubules. They terminate in a short common duct, which is bifurcated at its proximal end. One leg is linked with the venom reservoir, the other one extends to the ductus venatus. Each venom gland tubule possesses, over its entire length, a cuticle-lined central duct. Around this duct densely packed class 3 gland units each composed of a secretory cell and a canal cell are arranged. The position of their nuclei was demonstrated by DAPI staining. The brush border of the secretory cells surrounds the coiled end-apparatus. Venom is stored in a bladder like reservoir, which is surrounded by a thin reticulated layer of muscle fibres. The reservoir as a whole is lined with class 3 gland units. The tubiform Dufour's gland has a length of about 350 μm (∅ 125 μm) only and is surrounded by a network of pronounced striated muscle fibres. The glandular epithelium is mono-layered belonging to the class 1 type of insect epidermal glands. The gland cells are characterized by conspicuous lipid vesicles. Secretion of material via the gland cuticle into the gland lumen is apparent. Analysis of the polypeptide composition demonstrated that the free gland tubules and the venom reservoir contain numerous proteins ranging from 3.4 to 200 kDa. The polypeptide composition of the Dufour's gland is completely different and contains no lectin-binding glycoproteins, whereas a dominant component of the venom droplets is a glycoprotein of about 80 kDa. Comparison of the venom reservoir contents with the polypeptide pattern of venom droplets revealed that all of the major proteinaceous constituents are secreted. The secreted venom contains exclusively proteins present in the soluble contents of the venom gland. The most abundant compound class in the Dufour's gland consisted of n-alkanes followed by monomethyl-branched alkanes and alkadienes. Heptacosane was the most abundant n-alkane. Furthermore, a single volatile compound, 2-methylpentan-3-one, was identified in various concentrations in the lipid extract of the Dufour's gland.

The venom apparatus in stenogastrine wasps: subcellular features of the convoluted gland

In the wasp venom apparatus, the convoluted gland is the tract of the thin secretory unit, i.e. filament, contained in the muscular reservoir. Previous transmission electron microscope investigation on Stenogastrinae disclosed that the free filaments consist of distal and proximal tracts, from/to the venom reservoir, characterized by class 3 and 2 gland patterns, respectively. This study aims to extend the ultrastructural analysis to the convoluted tract, in order to provide a thorough, subcellular representation of the venom gland in these Asian wasps. Our findings showed that the convoluted gland is a continuation of the proximal tract, with secretory cells provided with a peculiar apical invagination, the extracellular cavity, collecting their products. This compartment holds a simple end-apparatus lined by large and ramified microvilli that contribute to the processing of the secretory product. A comparison between previous and present findings reveals a noticeable regionalization of the stenogastrine venom filaments and suggests that the secretory product acquires its ultimate composition in the convoluted tract.

Morphology and ultrastructure of the venom apparatus in the endoparasitic wasp Pteromalus puparum (Hymenoptera: Pteromalidae)

The venom apparatus of the endoparasitic wasp Pteromalus puparum (Hymenoptera: Pteromalidae) was studied with light and electron microscope and was subjected to the electrophoretic and immunohistochemical analyses. Typically its venom apparatus consists of an unbranched venom gland and a venom reservoir, which is associated with a Dufour gland. The venom gland is lined by a series of secretory units. Each secretory unit comprises a secretory cell and a duct cell. The secretory cell is associated with an end apparatus to collect its secretions into the gland lumen. Secretory cells in the venom gland are characterized by extensive rough endoplasmic reticulum and numerous electron-dense vesicles in the distal and middle parts. They also exhibit several secretory granules and vacuoles. The venom reservoir presents three distinct regions: an external layer, composed by numerous fine muscle fibers; an internal layer, represented by epithelial cell with large nucleus; and an intima portion, represented by thin and uniform organization. The morphological aspect of numerous well-developed organelles responsible for protein generation observed is in agreement with the electrophoretic and immunohistochemical results which reveal that the rich proteinaceous components are present in the venom gland and venom reservoir. The venom proteins are first mainly produced in the secretory unit of venom gland, then drained to the lumen through the end apparatus, and are finally collected and stored in the venom reservoir.

Comparison of the medium molecular weight venom fractions from five species of common social wasps by MALDI-TOF spectra profiling

The average spectral profiles and the exact mass weight (MW) of biomolecules present in the medium fraction (from 900 to 3000 Da) of the venom of five social wasps (three European and one North American Polistes and the European hornet Vespa crabro) were determined by matrix assisted laser desorption ionization time of flight (MALDI-TOF) MS. Data were obtained analyzing the venom of single specimens (N = 46) and elaborated with the ClinProTools 2.0 (CPT) software to search for differences among the five species examined. Interesting differences in the spectral profiles were found, allowing the discrimination of venoms belonging to the different species, and their possible use as a quality control method in venom immunotherapy (VIT) for allergic patients.

Morphology and ultrastructure of the Dufour gland in workers of social wasps (Hymenoptera, Vespidae)

The Dufour gland in workers of vespine wasps appears as an unpaired tubiform gland that opens in close proximity to the sting base. The epithelial cells that line the central reservoir are characterized by apical microvillus-like projections and deep basal invaginations. Their cytoplasm contains a well-developed Golgi apparatus, numerous mitochondria, as well as strands of smooth endoplasmic reticulum. The Dufour gland duct occurs ventrally to the venom gland duct, and bends downward near the sting base to open in the dorsal vaginal wall. In this region, the duct is dorsoventrally flattened, and shows conspicuous bundles of parallel microtubules in the epithelial cells, that transmit the pulling forces of the myofilaments of the underlying muscular supply to the cuticle. This results in an active opening mechanism regulated by muscular contraction, while passive closure probably results from the return of the cuticular intima to a rest position.

Venom gland of Pachycondyla striata worker ants (Hymenoptera: Ponerinae). Ultrastructural characterization

Morphological data concerning the venom gland of worker ants of Pachycondyla striata revealed that this gland consists of three distinct regions: an external secretory portion, composed by a secretory filament that bifurcates in order to give rise to other two filaments; an internal secretory portion, represented by the convoluted gland; and a storage portion, represented by a sac-shaped reservoir. The ultrastructural analysis showed that the reservoir is enveloped by a simple pavementous epithelium, coated internally with a cuticle. The external secretory portion is composed by cells forming a simple cubic epithelium, in which the apical portion presents numerous microvilli while the basal portion of the cells shows infoldings of the plasma membrane containing numerous mitochondria. The convoluted gland possesses cells of irregular morphology with nuclei containing condensed chromatin, suggesting inactivity. However, these cells are in fact undergoing secretory activity, which is probably added to the final secretion produced by the gland. The cytoplasm of these cells contains several elements distributed therein, such as ribosomes and polyribosomes, lipid droplets, and protein inclusions in the form of crystals, thus suggestive of protein storage, which would be used by the insect when metabolically required.

Ectal mandibular gland in Polistes dominulus (Christ) (Hymenoptera, vespidae): ultrastructural modifications over the secretory cycle

An ultrastructural study was carried out on the secretory activity of the ectal mandibular gland in the wasp Polistes dominulus (foundress and worker females as well as males). Secretory activity in foundresses proceeds slowly during hibernation and early spring, becoming prominent in late spring and then falling sharply during the summer. This sequential pattern of ultrastructural modifications follows a functional, annual cycle. However, by comparing the subcellular changes in the gland with colonial development, it appears that secretory activity fits in with the specie's social cycle rather than merely following the seasons. The highest levels of secretory activity correspond to the early, critical breeding phases, while activity slows down with an increase in colony protection, based on both primary (passive) and secondary (active) defenses, with the emergence of the workers. These correlations suggest that the ectal mandibular gland secretory product in P. dominulus is involved in chemical nest defense.

Venom gland morphology in Pepsis pallidolimbata pallidolimbata and biological use and activity of Pepsis venom

Spider wasps, i.e., the family Pompilidae, in general, and those belonging to the genus Pepsis in particular, are acknowledged to possess venoms that are algogenic to humans and thus have the parsimonious functions of causing paralysis and providing defense against predators. The morphological organization of the venom system and its complex convoluted gland closely resembles that in social members of the Vespidae. These features distinguish the venom glands of the Pompilidae from those of the sibling family Mutillidae as well as those of the family Sphecidae, which lack convoluted glands. Although the venom glands in Pepsis species are very similar in morphology to those of social vespids, the lethality of Pepsis venom to mammals is several times less than that of the social common wasps. These findings suggest that in terms of the evolution of venom activity and the associated glandular structures, there was apparently no need for social wasps to develop extra parts of the venom system for producing toxic, lethal, or powerful algogenic components. All of the glandular parts of the venom gland of social wasps were already present in pompilids (and eumenids) and, presumably, in their ancestors.