Albert G. Orr

Global diversity of dragonflies (Odonata) in freshwater

Larvae of almost all of the 5,680 species of the insect order Odonata (dragonflies and damselflies) are dependent on freshwater habitats. Both larvae and adults are predators. The order is relatively well studied, and the actual number of species may be close to 7,000. Many species have small distributional ranges, and are habitat specialists, including inhabitants of alpine mountain bogs, seepage areas in tropical rain forests, and waterfalls. They are often successfully used as indicators for environmental health and conservation management. The highest diversity is found in flowing waters in rain forests of the tropics, the Oriental and Neotropical regions being the most speciose. This paper discusses diversity, summarises the biogeography of dragonflies in the different biogeographical regions and gives the total number of species and genera per family per biogeographical region. Examples are given of areas of particular diversity, in terms of areas of endemism, presence of ancient lineages or remarkable recent radiations but no well-based review of areas with high endemism of dragonflies is available so far. The conservation status of dragonflies is briefly discussed. Species confined to small remnants of forest in the tropics are most under threat of extinction by human activities.

Remarks on the taxonomy of Megapodagrionidae with emphasis on the larval gills (Odonata)

Abstract A list of genera presently included in Megapodagrionidae and Pseudolestidae is provided, together with information on species for which the larva has been described. Based on the shape of the gills, the genera for which the larva is known can be arranged into four groups: (1) species with inflated sack-like gills with a terminal filament; (2) species with flat vertical gills; (3) species in which the outer gills in life form a tube folded around the median gill; (4) species with flat horizontal gills. The possible monophyly of these groups is discussed. It is noted that horizontal gills are not found in any other family of Zygoptera. Within the Megapodagrionidae the genera with horizontal gills are, with the exception of Dimeragrion, the only ones lacking setae on the shaft of the genital ligula. On the basis of these two characters it is suggested that this group is monophyletic.

Subtle design changes control the difference in colour reflection from the dorsal and ventral wing-membrane surfaces of the damselfly Matronoides cyaneipennis

The hind wings of males of the damselfly Matronoides cyaneipennis exhibit iridescence that is blue dorsally and green ventrally. These structures are used semiotically in agonistic and courtship display. Transmission electron microscopy reveals these colours are due to two near-identical 5-layer distributed Bragg reflectors, one placed either side of the wing membrane. Interestingly the thicknesses of corresponding layers in each distributed Bragg reflector are very similar for all but the second layer from each outer surface. This one key difference creates the significant disparity between the reflected spectra from the distributed Bragg reflectors and the observed colours of either side of the wing. Modelling indicates that modifications to the thickness of this layer alone create a greater change in the peak reflected wavelength than is observed for similar modifications to the thickness of any other layer. This results in an optimised and highly effective pair of semiotic reflector systems, based on extremely comparable design parameters, with relatively low material and biomechanical costs.

Critical species of Odonata in Malaysia, Indonesia, Singapore and Brunei

Abstract Malaysia, Brunei and the Indonesian archipelago comprise a total land area of ca 1.84 million km2 including ca 13,000 islands, lying entirely within the tropics. The region is bisected by Wallaces line and supports a rich Oriental fauna to the west (Sundaland) and mainly Australian elements to the east. Taxonomic studies throughout the region were greatly advanced in the first part of the last century by M.A. Lieftinck especially, but many areas remain totally unexplored. Present knowledge suggests ca 700 species occur in the region of which ca 500 are endemic. Many species are known from limited material, often a single specimen or a type series from a poorly defined locality. It is certain that many are highly stenotopic and sometimes occur naturally at low abundance. The most critical habitats are mixed-dipterocarp terra firma forests and fresh-water swamp forests, both of which exhibit high α and β diversity and harbour a majority of stenotopic species. However all potentially critical species must presently be classified as data deficient. On present knowledge it is not possible to recommend specific action against any species or habitat. No red listings are appropriate. There is an acute need for baseline data, especially from Central Borneo. Wholesale, unregulated habitat destruction for short-term profit poses the gravest threat to the region. Formerly well-studied areas such as Java are in urgent need of reassessment.

The Australian monsoon tropics as a barrier for exchange of dragonflies (Insecta: Odonata) between New Guinea and Australia

Recent studies show a remarkable scarcity of faunal exchange events between Australia and New Guinea in the Pleistocene despite the presence of a broad land connection for long periods. This is attributed to unfavourable conditions in the connecting area associated with the long established northern Australian Monsoon Climate. This would be expected to have impacted strongly on freshwater faunas with the following results: (1) limited overlap in species, (2) most higher taxonomic groups present in both areas sharing no species or even genera and (3) shared species dominated by lentic species with high dispersal capacity. Testing these predictions for dragonflies showed the turnover in the family, genus and species composition between Australia and New Guinea to be higher than anywhere in the world with only 50% of families and subfamilies, 33% of the genera and 8% of the species being shared. Only one of the 53 shared species favors lotic waters compared with 64% of the 652 combined Australian–New Guinean species. These results agree with our predictions and indicate that the dragonfly fauna of Australia and New Guinea have effectively been separated during the Pleistocene probably due to the prolonged unfavourable climatic conditions in the intervening areas.

Wrinkles enhance the diffuse reflection from the dragonfly Rhyothemis resplendens.

The dorsal surfaces of the hindwings of the dragonfly Rhyothemis resplendens (Odonata: Libellulidae) reflect a deep blue from the multilayer structure in its wing membrane. The layers within this structure are not flat, but distinctly ‘wrinkled’, with a thickness of several hundred nanometres and interwrinkle crest distances of 5 µm and greater. A comparison between the backscattered light from R. resplendens and a similar, but un-‘wrinkled’ multilayer in the damselfly Matronoides cyaneipennis (Odonata: Calopterygidae) shows that the angle over which incident light is backscattered is increased by the wrinkling in the R. resplendens structure. Whereas the reflection from the flat multilayer of M. cyaneipennis is effectively specular, the reflection from the wrinkled R. resplendens multilayer spans 1.47 steradians (equivalent to ±40° for all azimuthal angles). This property enhances the visibility of the static wing over a broader angle range than is normally associated with a smooth multilayer, thereby markedly increasing its conspicuousness.

The larva of Podolestes orientalis from West Malaysia, with notes on its habitat and biology (Odonata: Megapodagrionidae)

Abstract The larva of the south-east Asian megapodagrionid, Podolestes orientalis, is described and figured. Specimens were collected from shallow forest pools lined with large dead leaves in secondary lowland forest. Final and earlier stadium larvae were found concentrated around the edges of pools in very shallow water. Larvae sometimes perched in exposed situations, just below the water surface, with abdomen upturned and caudal lamellae splayed outward to expose the broad respiratory surfaces. This represents the first account of the immature stages for this south-east Asian genus. The caudal lamellae are very broad and flattened, inserted horizontally, suggesting a close relationship between the genus Podolestes and Australian region megapodagrionids.

Two new species of Chalybeothemis from Malaysia, with a redefinition of the genus (Odonata: Libellulidae)

Abstract Chalybeothemis chini sp. nov. from Pahang, Peninsular Malaysia, and C. pruinosa sp. nov. from Sarawak, Malaysian Borneo, are described from the male sex. The new species necessitate some redefinition of the previously monotypic genus, which is provided. The quiescent penis of Chalybeothemis is illustrated for the first time. Differences between C. chini, C. fluviatilis and C. pruinosa are discussed and tabulated. C. fluviatilis is reported from Sarawak for the first time. Relationships of Chalybeothemis within the Libellulidae are discussed.

A description of the larva of Heliaeschna uninervulata Martin (Odonata: Aeshnidae) from Singapore, with notes on its relationships

The larva of Heliaeschna uninervulata is described and figured for the first time. Its characters mostly fall within the limits of variation of Gynacantha spp. Comparison of the larval characters of H. filostyla, the only other member of the genus for which the larva is known, suggests that it is not congeneric with H. uninervulata.

Reproductive behaviour of Libellago semiopaca on a Bornean rainforest stream (Odonata: Chlorocyphidae)

Abstract The reproductive behaviour of Libellago semiopaca was studied on a swift-flowing shallow forest stream in Brunei. Females oviposited just below the water-line, commonly in groups, only on large, firm-textured, semi-submerged logs, usually guarded by males. Both sexes were very sedentary. Suitable sites, with good illumination and deep deposits of fine gravel and leaf mulch in dead water immediately behind the log were scarce. When stream levels were high, no oviposition sites were available. When possible, females generally oviposited every day, arriving between 10:00 and 15:00 h, and usually remaining on site for at least two hours. Males arrived earlier, between 09:00 and 13:00 h, and established small territories along the log. Females apparently began reproductive activity only when all oocytes were mature, and the egg load diminished daily as eggs were laid. Most matings occurred before 12:00 h with early-arriving females. Females mated every 2-3 days, probably to replenish sperm supplies. Male density was at its highest after 11:00 h and males shared territories, spending much of their time flying in low intensity confronting contests. Removal of males from a site, just as it was becoming available by falling water levels, resulted in little use of the site by females. Pinning decoy dead females at a good oviposition site failed to attract females if males had been removed. It is suggested that the prolonged male agonistic display attracts females to the site, and possibly commits them to future matings with the territory holders.