Apical antennal sensilla in nymphs of Libellula depressa (Odonata: Libellulidae)

Abstract. In an ultrastructural study of the apical antenna of the last nymphal stages of Libellula depressa (Odonata: Libellulidae), we found long sensilla trichodea, 2 sensory pegs, and a coeloconic sensillum on the last article of the flagellum (the distal part of the antenna). The long sensilla trichodea are mechanoreceptors, almost identical to the long filiform hairs of some terrestrial insects and the first sensilla of this kind to be described in aquatic insects. Particular attention was given to the complex coeloconic sensillum, a compound sensillum innervated by 2 groups of 3 neurons wrapped in a dendritic sheath. A cuticular sleeve envelops the distal portion of the outer dendritic segment. The cuticle of the coeloconic sensillum shows wide channels and is contiguous to the underlying granular and fibrillar layer. Similar structures on the antennae of the adults of other dragonflies were identified as chemoreceptors in previous studies. We hypothesize that this larval coeloconic sensillum might likewise have a chemosensory function, responding to molecules that diffuse through the cuticle and the underlying granular and fibrillar layer, as no clear pore or pore-tubule system is visible. Alternative functions are also explored on the basis of morphological details.     

The antennal lobe of Libellula depressa (Odonata,Libellulidae)

Here we describe the antennal lobe of Libellula depressa (Odonata, Libellulidae), identified on the basis of the projections of the afferent sensory neurons stemming from the antennal flagellum sensilla. Immunohistochemical neuropil staining as well as antennal backfills revealed sensory neuron terminal arborizations covering a large portion of the antennal lobe. No clear glomerular structure was identified, thus suggesting an aglomerular antennal lobe condition as previously reported in Palaeoptera. The terminal arbors of backfilled sensory neurons do, however, form spherical knots, probably representing the connections between the few afferent neurons and the antennal lobe interneurons. The reconstruction revealed that the proximal part of the antennal nerve is divided into two branches that innervate two spatially separated areas of the antennal lobe, an anterioventral lobe and a larger posteriodorsal lobe. Our data are consistent with the hypothesis that one tract of the antennal nerve of L. depressa contains olfactory sensory neurons projecting into one of the sublobes, while the other tract contains thermo-hygroreceptive neurons projecting into the other sublobe.     

Hygroreceptors in the larva of Libellula depressa (Odonata: Libellulidae)

Ultrastructural and electrophysiological (single-cell recordings) investigations were carried out on the coeloconic sensilla borne by the apical antenna of the larvae of Libellula depressa (Odonata: Libellulidae). These sensilla appear as pegs located in pits. One of them is a compound sensillum constituted of two fused pegs in a common pit and the other two are single pegs located in separated pits close to each other. Coeloconic sensilla show position and ultrastructural details very similar to those described in insect hygroreceptors. The electrophysiological recordings on the apical antennae of the last larval instar of L. depressa clearly show the presence of moist and dry cells responding antagonistically to humidity changes. This study gives the first evidence of hygroreceptors in dragonfly larvae and represents the first electrophysiological approach to larval sensilla of aquatic insects. The presence of hygroreceptors in L. depressa larvae is in agreement with the hygropositive response shown by these insects in laboratory and field behavioural experiments.     

The larva of Libellula foliata (Kirby, 1889) (Odonata: Libellulidae)

The larva of Libellula foliata (Kirby) is described based upon mature larvae from the Biosphere Reserve of ??El Triunfo?? in the state of Chiapas. It belongs to the small group of species without dorsal protuberances, L. composita (Hagen), L. comanche Calvert and L. saturata Uhler. The following combination of characters permits the separation of L. foliata larva from the other aforementioned larvae: tergites 6?C10 uniformly colored, no lateral spines on segments 8?C9, 5?C6 palpal setae and 3 long premental setae. After this finding, only the larvae of Libellula gaigei Gloyd and L. nodisticta Hagen remain undiscovered for the Mexican species of Libellula.     

Egg envelope synthesis and chorion modification after oviposition in the dragonfly Libellula depressa (Odonata, Libellulidae).

Libellula depressa (Odonata, Libellulidae) is an exophytic dragonfly ovidepositing eggs in clutches on the surface of floating plants and algae. The present work investigates, at ultrastructural level, the gradual differentiation of the egg envelopes and the chorionic changes after egg deposition in water. The ovary of the mature female of L. depressa is composed of numerous strings of panoistic ovarioles, where the eggshell formation takes place gradually throughout the activity of the follicle cells. The present data show that the egg envelopes are constituted of a very thick electrondense vitelline envelope, a thin endochorion and an extremely thick exochorion composed of a fibrillar matrix resting on a thin electrondense layer. After deposition in water, L. depressa eggs, initially white and almost transparent, gradually become brown spots in a semitransparent jelly coat, rich of incorporated debris. The jelly coat enveloping the eggs of L. depressa derives exclusively from the exochorion, constituted of a fibrillar matrix, which swell at contact with water. The jelly-like coat performs an adhesive function and presumably a protective role during egg segmentation and ensuing larval hatching.     

Potential distribution of the critically endangered dragonfly Libellula angelina (Odonata: Libellulidae) under shared socio-economic pathways

Libellula angelina is an endangered dragonfly species that is native to East Asia. Recently, their population has become severely reduced through habitat loss. To protect L. angelina populations, we need to understand which factors determine their distribution and how their potential habitats will change in the future. In this study, the habitat preference of L. angelina was identified through field surveys, and the potential distribution of L. angelina and the impact of integrated climate–land cover changes were simulated using the MaxEnt model. Furthermore, the wetland loss scenario was applied to areas where the current trend in wetland loss will continue in the future. The field survey identified that L. angelina prefers small inland wetlands: permanent freshwater, ponds; permanent rivers, ponds; irrigated land; and estuarine waters. From the MaxEnt results, altitude was the variable with the greatest contribution and distance from wetlands was the most unique variable. MaxEnt described the geographic pattern of occurrences under the current climate well, with few areas requiring any further survey. In the future projection, the potential habitat area was increased by up to 48.8% and 30.6% in the 2050s and 2080s, respectively. However, potential habitat loss was expected if wetlands continue to decline as they have done in the last 20 years. The wetland loss scenario resulted in potential habitat losses of 1.9%–2.3% and 4.5%–6.1% in the 2050s and 2080s, respectively. Therefore, to protect L. angelina populations we must minimize the loss of current populations, secure wetlands and strengthen the connectivity between wetlands.     

Postcopulatory Behavior in Libellula pulchella Drury (Odonata: Libellulidae) and Female Tactics for Avoiding Male Interference with Oviposition

Postcopulatory behavior was studied in Libellula pulchella, a North American dragonfly in which ovipositing females face frequent harassment by unpaired males seeking matings. Although males performed noncontact guarding of their mates after copulation, females received minimal protection since their guarders tended to leave on extended chases of other males when harassment was intense. Ovipositions by unguarded females were even more likely to be terminated by harassment and were disrupted sooner. Female tactics to minimize interference included rapid escape flights, repeated return visits to the water within short time periods, perching when severerly harassed, and proceeding with mating when clasped. Female use of multiple oviposition sites is discussed in the context of guarding effectiveness and mate recognition by males.     

Foraging behavior ofPachydiplax longipennis (Odonata: Libellulidae)

Food intake, prey availability, and prey capture behavior at feeding areas were quantified in the dragonflyPachydiplax longipennis by observing focal individuals on artificial perches, where they exhibited marked short-term site fidelity. Prey capture success was high and relatively constant, but the frequency and duration of feeding flights depended on the time of day and season (at least in part because of associated variation in temperature and other physical factors), study site, sex, density of other dragonflies, and prey density. Individuals rapidly responded temporally and spatially to changes in prey availability, particularly to localized prey concentrations.     

Phylogeny of the dragonfly genus Sympetrum (Odonata: Libellulidae)

The libellulid dragonfly genus Sympetrum has been recognized since 1833, but lacks any morphological synapomorphies to unite the taxon. Previous researchers have disagreed over which species belong in Sympetrum, bringing the monophyly of the genus into question. We use DNA sequence data from 6 genetic loci (16S, tRNA-valine, 12S, elongation factor 1 alpha, cytochrome oxidase subunit I, and the second internal transcribed spacer region) and 25 morphological characters (mainly genitalic) to test the monophyly of Sympetrum with Bayesian inference and maximum likelihood analyses. Under Bayesian inference, all Sympetrum species included in this study form a clade, which also contains the Hawaiian monotypic genus Nesogonia, often considered a close relative of Sympetrum. Phylogenetic analyses also reveal at least six strongly supported clades (treated as species groups) within Sympetrum, but relationships between these species groups remain unresolved or unsupported. Although the relationships between Sympetrum species groups remain unresolved, several species groups include taxa from multiple biogeographic regions/continents, and the species group sister to the rest of Sympetrum contains migratory species from the New World and Africa. This pattern suggests a complex biogeographic history in Sympetrum shaped by vicariance and dispersal. Preliminary estimates of the divergence dates of Sympetrum species groups outline a rapid radiation of the groups approximately 32-38 million years ago, possibly influenced by cooling and drying climates of the late Eocene and early Oligocene.     

Phylogenetic relationship among Libellula, Ladona and Plathemis (Odonata: Libellulidae) based on DNA sequence of mitochondrial 16S rRNA gene

Abstract. The type genus for the dragonfly family Libellulidae is Libellula. At present, Libellula s.l. includes twenty-nine species, whose distribution is largely Nearctic. Whether two other libellulid taxa, Ladona and Plathemis, should be considered synonyms of Libellula, subgenera of Libellula, or separate genera, has been a subject of intermittent debate for over a century. Earlier proposals concerning Ladona and Plathemis were based on a limited number of morphological characters and lacked rigorous phylogenetic analyses. Therefore, we used the DNA sequence of a portion of the mitochondrial 16S rRNA gene and parsimony, maximum likelihood and neighbour-joining analyses to explore whether Ladona and Plathemis are monophyletic lineages distinct from Libellula. We obtained ≈ 415 bp of DNA sequence from twenty-three taxa including thirteen species of Libellula s.s., all three recognized species of Ladona, the two species of Plathemis and representatives of four other libellulid genera. Tetragoneuria williamsoni (Odonata: Corduliidae) was included as the outgroup. Parsimony analysis suggested that Ladona and Plathemis are monophyletic lineages distinct from Libellula s.s. with a sister group relationship between Libellula and Ladona. The monophyly of Ladona, Plathemis and Libellula was supported in > 90% of bootstrap replications and in trees five to ten steps longer than the most parsimonious trees. Relationships inferred from maximum likelihood and neighbour-joining analyses also supported the monophyly of Ladona and Plathemis. The four other libellulid genera included in the study formed a monophyletic clade distinct from Libellula, Ladona and Plathemis. Based on our analysis, we propose that Ladona and Plathemis be considered either genera or subgenera within Libellulidae.     

The structure and function of the genitalia in the Libellulidae (Odonata)

An outline of the morphology of the secondary genitalia of libellulid dragonflies is given together with a more detailed treatment of the components of the fourth (distal) segment of the penis. The variations of penis structure in 70 species, representing ten of the 11 subfamilies, are surveyed and catalogued. There is remarkable diversity in the presence and form of penis structures, particularly those associated with the medial process, namely the flagelium, cornua and inner lobes. A comparable survey of females shows that they can be provisionally divided into ten types according to the number and size of their sperm-storage organs. Comparisons of penis structures with the sperm-storage organs of females suggests that in species whose females store large amounts of sperm, usually doing so in one or a pair of organs, males possess highly extensible, lobate and bristly penes, commonly equipped with cornua. By contrast, in those species in which the females store small volumes of sperm, usually doing so in three organs, the penes bear either flagella equipped with proximally directed spines or with large terminal barbs, or they have narrow, spiny inner-lobes which resemble flagella. Some functional interpretations are proposed in the light of sperm competition. The variability of genital structure can be interpreted adaptively and does not closely reflect phylogenetic relationships. Functionally convergent structures have evolved a number of times from different origins.     

栗山天牛成虫触角感器形态与分布观察

栗山天牛Massicus raddei(Blessig)是我国东北林区栎树的主要蛀干害虫,严重危害蒙古栎和辽东栎,已给发生地造成的重大的经济损失和生态灾害。触角是天牛与外界进行信息沟通的重要器官,触角上的感器类型与分布数量直接影响天牛对外界化学刺激的识别。本文采用扫描电镜观察的方法,对栗山天牛雄、雌虫的触角分别进行了观察。结果显示,栗山天牛雌、雄性触角的感器分布略有不同,但都着生有大量的毛形感器、锥形感器和耳形感器,以及少量的板形感器、指形感器和钟形感器等。鞭节端部各节的感器数量较多,基部各节的感器数量较少,可能与各节所行使的功能有关。     

Shade Alone Reduces Adult Dragonfly (Odonata: Libellulidae) Abundance

We demonstrate that physical habitat conditions influence adult dragonfly (Odonata: Anisoptera) riparian site selection. In naturally treeless riparian areas of South Africa, invasive trees create shade and reduce native vegetation. We hypothesized that most breeding odonates select riparian areas (1) without shade, and (2) with high density and variety of understory perch structures. In two experiments at reservoir shorelines, we varied shade and perch structures. Dragonfly abundances (predominantly Trithemis species) were lower at sites with high (75%) or moderate (55%) shade cover than at sites with no shade, and lower at bare sand sites than sites containing stick perches. Perch density and variety (variety of heights and diameters) did not affect dragonfly abundance. These results indicate that shade alone directly reduces dragonfly habitat selection, isolating one aspect of habitat change that can alter insect behaviors.     

Reproductive behavior of the dragonfly,Orthetrum japonicum (Odonata: Libellulidae)

The reproductive behavior of the dragonfly,Orthetrum japonicum, is described. Behavioral processes of turnover of territorial males, simultaneous guarding of 2 females by a male, and copulation by non-territorial males are described. The males with longer hind wings won the territorial conflicts more frequently. The total duration of territorial residence of a given male was correlated with the number of his matings, but not correlated with the length of his abdomen or hind wings. The territorial site with the lower degree of vegetation cover was occupied by males more consistently. Males in more consistently occupied territorial sites did not have longer abdomen and hind wings than males in less consistently occupied sites. The territorial site where the larger number of copulations was observed was not occupied more consistently. Selection episode analysis using the method of Arnold & Wade (1984a, b) showed that direct selection on the hind wing length favored the short wing and that direct selection on the abdomen length favored the long abdomen during mating.     

拉步甲成虫触角感器的扫描电镜观察

利用扫描电子显微镜,观察了拉步甲Carabus lafossei成虫触角感器的类型、数量和分布规律。结果表明:拉步甲触角表面存在7类、12种感器类型,包括3种毛形感器(Sensilla trichodea,ST)、3种刺形感器(Sensilla chaetica,SCh)、2种锥形感器(Sensilla basiconca,SB)、Bhm氏鬃毛(Bhm bristles,BB)、腔锥形感器(Sensilla coeloconica,SCo)、腔形感器(Sensilla cavity,SCa)和钟形感器(Sensilla campaniformia,SCam),感器类型在雌、雄个体间无差异;雌、雄个体各节触角的感器数量和分布不均匀。研究结果为今后开展电生理学和行为生态学研究打下了基础。     

Wind Drift Compensation in Migrating Dragonflies Pantala (Odonata: Libellulidae)

Tailwind drift compensation serves to maximize a migrant's flight distance on a given amount of energy, and crosswind drift compensation serves to hold a course true and minimize the distance flown. With full or part compensation, airspeeds are predicted to increase with greater crosswind drift. To test whether migrating dragonflies compensated for wind drift, I measured the velocity and heading of Pantala hymenaea and P. flavescens in natural flight over a lake and the ambient wind speed and direction. P. hymenaea flew north-easterly (58°), whereas P. flavescens flew significantly more east–north easterly (74°) throughout the day. Pantala spp. demonstrated part compensation for changes in crosswind drift within individuals (mean compensation = 54%, P = 0.0000), evidence for use of a ground reference to correct for drift when flying over water. Among individuals, P. flavescens compensated for crosswind drift. P. hymenaea overcompensated and then drifted downwind on one morning and compensated for crosswind drift on the next. As predicted from optimal migration theory, airspeed (5.0 m/s for both species with no tailwind) decreased with tailwind velocity both among individuals (data for both species pooled [n = 19], P < 0.0001) and within each individual as it crossed the lake (P = 0.0016).     

Two gynandromorphs of Sympetrum striolatum (Charpentier, 1840) (Odonata: Libellulidae)

Two gynandromorphs of the dragonfly Sympetrum striolatum , with different features, are described here, with special emphasis on the genitalic structures.     

Phylogeography of a facultatively migratory dragonfly, Libellula quadrimaculata (Odonata: Anisoptera)

The biogeography of a widely distributed dragonfly (Libellula quadrimaculata) was examined via a phylogenetic analysis of 416 bp of the mitochondrial cytochrome oxidase I subunit (COI). Phylogenetic analyses under parsimony and minimum evolution produced trees with similar topologies, and revealed strong support for three clades corresponding to populations in Asia, Europe and North America. However, resolution was poor within clades, and genetic distances between populations within continents was quite low (1–2%). Several populations of this species are known to engage in periodic mass migrations, and it is possible that introgression from gene flow due to the mobility of this species has obscured phylogenetic patterns within continents. I was unable to test for phylogenetic patterns coincident with historical glacial refugia given the lack of phylogenetic patterns within continents. However, given that some sequence divergence was observed between populations within continents, it is possible that phylogenetic patterns exist, and subsequent studies should make use of larger data sets, and molecular data from faster evolving genes. Despite the propensity for periodic, short distance migrations in L. quadrimaculata, gene flow appears to be limited and does not influence the phylogenetic relationships of populations between continents.     

Flexible Mate Guarding Tactics in the Dragonfly Sympelrum Internum (Odonata: Libellulidae)

Mate guarding–a behaviour prevalent in odonates–is a post copulatory association during which males prevent females from re-mating. Some species use two forms of guarding: contact mate guarding, which is energetically costly but highly effective and non-contact mate guarding, which is less costly but less effective. This study aimed to determine if male Sympetrum internum (Odonata:Libellulidae) adjust the duration of contact mate guarding according to environmental, temporal and physiological factors. There was a significant interaction between male density and season on duration of contact mate guarding. Early in the season males increased the duration of contact guarding as the density of rivals increased. Later in the season males guarded mates longer irrespective of male density. Wind and temperature did not detectabiy alter the duration of contact mate guarding, suggesting that the trade-off between current and future reproductive success was more important than were physiological costs.     

宽胫夜蛾成虫触角和下唇须感器的超微形态

触角和下唇须是昆虫头部的重要感觉器官,其上被有多种类型的感器。宽胫夜蛾Protoschinia scutosa是一种重要的农业害虫,但其触角和下唇须感器研究较少。本研究利用扫描电子显微镜观察了宽胫夜蛾的触角和下唇须感器的类型、分布和超微形态。宽胫夜蛾的雌雄触角均为丝状,雌虫触角鞭节明显短于雄虫。雌雄触角均分布有8种类型感器,分别为Bhm氏鬃毛、鳞形感器、毛形感器、刺形感器、耳形感器、锥形感器、腔锥形感器和栓锥形感器。其中,毛形感器数量最多,且雄性毛形感器的数量明显多于雌性。宽胫夜蛾的下唇须为长管状,雌雄下唇须长度无显著差异。共观察到5种类型感器,即毛形感器、钟形感器、鳞形感器、刺形感器和棒形感器。毛形感器分布在下唇须基部第1节和端部第3节的陷窝器内,钟形感器位于第1节毛形感器簇之中,鳞形感器在各节均有分布,刺形感器和棒形感器只见于第3节。并对宽胫夜蛾的触角和下唇须感器的功能进行初步的推测和讨论。为昆虫感器功能分析、分类学和行为学研究提供依据。