The germarium of panoistic ovarioles of Bacillus rossius (Insecta Phasmatodea): Structure and function during imaginal life

Summary

In adult females of Bacillus rossius (Insecta Phasmatodea) the germarium, localized at the ovariole tip just below the terminal filament and above the vitellarium, progressively reduces in size and eventually disappears at the end of the ovulatory period. The observations with light and electron microscopes show that in the end-chamber most germ cells are arrested in a post-pachytenic diffuse stage, which just precedes diplotenic oocyte growth. These observations also indicate that the reduction in size of the germarium of ovulating females should probably be ascribed to a progressive and extensive activation of the resting germ cells. The average number of ovulated eggs per ovariole (6.7±0.9) is consistent with this view. However, occasional findings of lepto-zygotenic germ cells in some preovulatory ovarioles of adult females do not completely rule out the persistence of scarce undifferentiated germ elements (oogonia) in the larval germarium at the onset of adult life. Furthermore, the reduction of the germarium in ovulating females and its subsequent disappearance in post-ovulating ones also includes the somatic cells, which are always present among the germ cells in previous stages. Since each early growing oocyte becomes surrounded by a thin monolayer of follicle cells, the diminution of end-chamber somatic cells supports the view that they actually represent prefollicular cells, which are progressively utilized from the onset of imaginal life onwards.     

Pharynx, esophagus, and associated structures in the booklouse, Liposcelis divinatorius

Abstract. Ultrastructural features of the pharynx, esophagus, and associated intrinsic visceral muscular and nervous structures of the booklouse, Liposcelis divinatorius , were studied to determine whether the anatomical arrangements of these structures differed from the general pattern found in insects. The results are compared with previous light microscope studies of this tiny insect. Variations from the usual arrangement reported for intrinsic visceral muscles associated with the pharynx in insects are described. Intrinsic visceral muscles include a narrow band of circularly disposed fibers and both extra-circular and intra-circular longitudinally disposed fibers. This represents a departure from the slightly developed inner longitudinal and more prominent outer circular fibers seen in most insects. The outer surface of some circular muscle cells has apparently unique pouches packed with mitochondria, which contain many cristae. Numerous bacteroids appear in the esophageal epithelial cells and in the sub-esophageal ganglion. Nerve processes associated with the foregut contain neurotubules, synaptic vesicles, and electron-dense granules.     

Saprolegnia strains isolated from river insects and amphipods are broad spectrum pathogens

Saprolegnia species are destructive pathogens to many aquatic organisms and are found in most parts of the world. Reports based on phylogenetic analysis suggest that Saprolegnia strains isolated from aquatic animals such as crustaceans and frogs are close to Saprolegnia strains isolated from infected fish or fish eggs and vice versa. However, it has often been assumed that host specificity occurs for each individual isolate or strain. Here we demonstrate that Saprolegnia spp. can have multiple hosts and are thus capable of infecting different aquatic organisms. Saprolegnia delica, Saprolegnia hypogyna, and 2 strains of Saprolegnia diclina were isolated from aquatic insects and amphipods while S. delica, Saprolegnia ferax, Pythium pachycaule, and a Pythium sp. were isolated from the water of a medium to fast flowing river. The ITS region of the rRNA gene was sequenced for all isolates. In challenge experiments, all four isolates from insects were found to be highly pathogenic to eggs of Atlantic salmon (Salmo salar) and embryos of the African clawed frog (Xenopus laevis). We found that Saprolegnia spp. isolated from salmon eggs were also able to successfully establish infection in nymphs of stonefly (Perla bipunctata) and embryos of X. laevis). These results suggest that Saprolegnia spp. are capable of infecting multiple hosts, which may give them an advantage during seasonal variation in their natural environments.     

Polarization vision in water insects and insects living on a moist substrate

Summary Light polarized by reflection was tested in the field for its attractiveness to flying insects. Attracted insects include bugs: some living in water (Corixidae, Notonectidae, Pleidae), others living on its surface (Gerridae) or near it (Saldidae). Beetles were also attracted: some are aquatic (Hydrophilinae, Dytiscidae, Haliplidae, Hydraenidae), others inhabit moist substrates (Sphaeridiinae). Also included are Chironomidae among other nematocerans. Non-polarized reflected light failed to attract any of these insects even at intensities far higher.Three response groups emerge. One is attracted whenever the degree of polarization is high in the UV-range, irrespectively of the degree of polarization in other wavelength ranges, and irrespectively of colour or brightness of the background beneath the polarizing, reflecting surface. The polarization vision of these insects operates in the UV-range. Another group was attracted only by the reflecting surface over a dark background, where the reflected light was highly polarized at all wave-lengths visible to insects. The third group ranges in between.Some Helophorus species behave in spring like members of the first group; in fall, like members of the second group.The distribution of the above response groups within various taxa is provided. Sensory mechanisms and eco-physiological implications are discussed.Abbreviations B matt black surface - b; y; w; a black, yellow white material and aluminum foil, reflection characteristics as described in the text; - G glass - G/b; G/y; G/w; G/a glass panes on different materials - Gb, y, w; Gb, y, Gb types of animals differing in behavior     

Spectral regions in which aquatic insects see reflected polarized light

For diverse water insects (species of Hydrophilidae, Hadraenidae, Dytiscidae, Haliplidae and aquatic Heteroptera), the attractiveness of an artificial water surface was found to vary when the polarization of the reflected light, the property by which these insects identify water, was abolished in different regions of the spectrum. The sensitivity maxima of their reflection-polarization visual systems (max(POL)) thus determined were in various spectral regions, between < 360 nm (UV) and ca. 550 nm (yellow-green). Species with max(POL) at the short-wavelength end of the spectrum would be able to identify bodies of water by polarization regardless of whether the subsurface reflection was bright or dark; nevertheless, this group includes forms that avoid water with a bright subsurface because of the intensity of the reflected light. Species with max(POL) in the long-wavelength region fail to use certain bodies of water with a bright subsurface as habitats because the light they reflect at the longer wavelengths is insufficiently polarized. That the POL system of a species has a large max could affect habitat choice; on the other hand, it could also be that systems operating in the long-wavelength region were produced in the course of adaptation to the light conditions in or above the habitat.Abbreviations max(POL) spectral sensitivity maximum for polarization vision     

The proventriculus of the carpenter bee, Xylocopa virginica virginica (L.), with special reference to bacteria-containing luminal tunnels

Abstract. Four tunnels off the lumen of the proventriculus of the carpenter bee, Xylocopa virginica virginica , have been discovered. Light and electron micrographs revealed the presence in the tunnels of gram-positive, rod-shaped bacteria, some of which showed division stages. The occurrence of the bacteria exclusively in the tunnels—not in the lumen of the proventriculus—makes speculation as to their function difficult. The function of the tunnels is also obscure, as no glands were seen emptying into them. The bacteria may be symbionts that release enzymes into the tunnels, which are subsequently transported to the midgut to aid digestion. They could also be parasites. This is the first report of such bacterial-containing tunnels in insects.     

Oxygen consumption of the aquatic leaf beetles Macroplea mutica and Macroplea appendiculata is low and not influenced by salinity

Leaf beetles of the genus Macroplea live permanently under water. Species‐specific preferences for either freshwater or brackish water are available in the literature. To detect potential physiological differences, the oxygen consumption of Macroplea mutica and Macroplea appendiculata from habitats with differing salinities is measured at two different salinities (0 and 10). The specific oxygen consumption does not depend on oxygen saturation of the water (values in the approximate range of 25–100% occur during the experiments). There is no difference between species or sampling locations. Similarly, the salinity during the measurements does not affect the oxygen consumption of the beetles, either when compared as salinity per se (0 versus 10), or when classified as home salinity or atypical salinity. Comparisons with other chrysomelid beetles and aquatic insects (using available published data) reveal that the two Macroplea species have relatively low metabolic rates. This finding is discussed in the light of activity patterns and morphology, especially the reduction of flight muscles, which comprise a highly metabolically active tissue.     

Ultrastructural features of gametogenesis during the life cycle in Branchiura sowerbyi Beddard (Oligochaeta,Tubificidae)

An ultrastructural analysis of the gametogenetic phases in Branchiura sowerbyi, a tubificid oligochaete, has been accomplished. These phases mostly conform to the usual pattern for the family, however, some interesting peculiarities are pointed out. The regression of sexual apparatus after reproductive period and its regeneration up to a new period of sexual maturity, has been followed throughout the year.     

水生昆虫肠道微生物研究进展

水生昆虫在水生生态系统中具有重要的生态功能,扮演着有机物降解、水质净化和营养循环等角色,对维持水体健康至关重要。水生昆虫肠道微生物在与宿主长期的共进化过程中,形成了极为多样的菌群结构和丰富的生物学功能。变形菌门Proteobacteria和厚壁菌门Firmicutes是大多数水生昆虫肠道微生物中的优势菌,但受宿主分类学差异、栖息地转变、生活环境参数改变、食性和免疫的影响,不同水生昆虫的肠道微生物组成呈现多样性。肠道微生物参与调节水生昆虫生长发育、消化代谢、免疫防御和解毒等功能。通过宿主交配和取食,水生昆虫肠道微生物在宿主种间和种内传播。本文简要回顾了水生昆虫肠道微生物的组成及对其主要的影响因素,总结了其与宿主间的关系及传播方式,并对未来研究方向进行了展望。本研究可为挖掘具有特殊功能的微生物资源和探索昆虫水生适应的肠道微生物学机制提供参考。     

Seasonal patterns of stream macroinvertebrate communities in response to anthropogenic stressors in monsoonal Taiwan

Freshwater ecosystems are affected by a variety of anthropogenic stressors. Temporal variability of biotic communities in these ecosystems makes it difficult to accurately assess the impacts of specific stressors, which has seldom been considered in understudied regions of Asia. We studied the seasonal effects of anthropogenic stressors on stream macroinvertebrates based on sampling every three months over two years at five stream sites in central Taiwan. Several macroinvertebrate metrics (taxon richness, Shannon diversity index, and relative abundance of Trichoptera) were lower during the wet season than the dry season. The presence of dams caused changes in the structure of macroinvertebrate communities, decreased the seasonal variability in relative abundances of Trichoptera, as well as resulted in lower dissolved inorganic nitrogen concentrations and larger substrate size. The presence of urban areas had less or no influence on environmental factors and structural changes. However, significantly lower total abundance, taxon richness, and relative abundance of Trichoptera occurred in the presence of either dams and/or urban areas. One key management implication from the present study is that bioassessment utilizing macroinvertebrates should be facilitated by awareness of the potential role of temporal factors on the effects of anthropogenic stressors, especially in monsoonal Asia.     

The mechanoreceptors on the endophytic ovipositor of the dragonfly Aeshna cyanea (Odonata,Aeshnidae)

This study investigates the mechanoreceptors located on the cutting valvulae of the ovipositor of the dragonfly Aeshna cyanea (Aeshnidae), using both SEM and TEM, with the aim of providing an overview of the sensory equipment of an odonatan endophytic ovipositor. Four kinds of sensilla have been described. Notwithstanding their different external and internal morphology, they show features typical of mechanoreceptors. Three of them are evident along the external surface of the two cutting valvulae in the form of sub-spherical pegs, pit organs type 1 (holes) and pit organs type 2 (depressions), these last are similar to amphinematic scolopidia, while the fourth type is represented by subintegumental mononematic scolopidia having no direct relationship with the cuticle. In spite of their structural differences, the morphology of the described mechanoreceptors is consistent with performing a main role in allowing the perception of compression/stretching of the thick cuticle of the valvulae and their bending due to the pressure acting on the distal end of the ovipositor during substrate penetration. Such an organization is coherent with the need of endophytic Odonata to be able to evaluate the stiffness of the plant where to lay eggs.