The Feeding of Chaoborus flavicans Meigen (Diptera,Chaoboridae). and its Predation on Lake Zooplankton

In a study of Chaoborus feeding in a eutrophic lake, selectivity was found to be positive with Crustacea (especially copepodit stages). and negative with Rotatoria. Daily food rations were about 20% for most of the feeding period, but higher (106%). during the month of intensive growth after hatching. Feeding intensity correlated positively with amount of food an temperature, and negatively with Chaoborus concentration. Elimination of Crustacea (in the epilimnion of the central zone of the lake). equalled about 30–40% of Crustacea production in June and September and slightly exeeded the August production (it was almost zero in the remaining months because Chaoborus larvae stayed at the bottom). This applies, however, only in the central zone – about 50% of the lake volume. Chaoborus probably influences both the density of zooplankton and the quantitative relations between zooplankton species.     

Studies on the biology of Chaoborus flavicans (Meigen) (Diptera: Chaoboridae) in a fish-free eutrophic pond,Japan

Population dynamics of Chaoborus flavicans larvae of various instars was studied from November 1986 to December 1987 in a eutrophic, fish-free pond, Japan. First and 2nd instar larvae were observed from late April to late October, indicating a reproductive period of about half a year. C. flavicans overwintered in the 4th instar larvae. In water column samples, total density of all instars was 680–23680 m^-2, and pupal density 0–2600 m^-2; larvae of the 1st, 2nd, and 3rd instars showed 5–6 density peaks in 1987, suggesting that 5–6 generations occur during a year (peaks of the 4th instar larvae were not clear, probably due to their longer development than those of younger instars). In sediment samples, no 1st and 2nd instar larvae were found, 3rd instar larvae were found occasionally but density of the 4th instar larvae was 280–18600 m^-2, and pupal density varied between 0–502 m^-2. Fouth instar larvae accumulated in sediment in the cold season and in the water column in the warm season; high temperature and low oxygen concentration were the most important factors limiting the distribution of larvae in the sediment in summer in the NIES pond. The dry weight of total C. flavicans larvae was 0.08–4.2 g m^-2 in sediment samples and 24–599 μg l^-1 (0.10–2.40 g m^-2) in water column samples. Comparisons of maximum densities in the NIES pond in different years and in waters of different trophic status show that density is generally higher in eutrophic than in oligotrophic habitats. This revised version was published online in July 2006 with corrections to the Cover Date.     

Factors contributing to coexistence of Chaoborus flavicans and C. punctipennis (Diptera,Chaoboridae) in a small meromictic lake

In Crawford Lake, a small meromictic water body in southern Ontario, Canada, the life cycles of planktonic Chaoborus flavicans and C. punctipennis were out of phase by about two months, the former pupating from mid May through mid June and the latter from July through September. C. flavicans possibly produced a second annual generation. Fourth instars of both species were strong diel migrators and occupied similar strata at most times. C. punctipennis fourth instar diet consisted almost entirely of rotifers. C. flavicans ate rotifers but fed heavily also on daphnids in May and August. C. punctipennis fourth instars showed little growth until early spring, possibly owing to a sparseness of rotifers, then grew rapidly until pupation. C. flavicans had a slow, but relatively constant growth rate at all times during the open water season, presumably because its greater mouth gape allowed it a wider range of food items.     

Vertical migration of Chaoborus flavicans in a Scottish loch

The pattern of diel vertical migration of Chaoborus flavicans larvae in a shallow Scottish loch varies according to the instar and, in third and fourth instars, according to the season. The planktonic phase of the migration is not exclusively concerned with predation, the larvae feeding at least equally actively in the benthos. Although there is no conclusive evidence as to the role of vertical migration in Chaoborus flavicans, it has some of the characteristics of an epideictic display. Upward and downward locomotion can be induced experimentally in a plankton wheel by manipulating light intensity alone. However, the responses are complex and there is a great deal of individual variation, suggesting that additional factors are involved.     

Morphometric parameters of the midgut cells of Aedes aegypti L. (Insecta,Diptera) under various conditions

Summary Previous morphometric or biochemical investigations have yielded different data on the distribution of free and membrane-bound ribosomes in midgut cells of Aedes aegypti. In the present paper ribosomal distribution has been morphometrically analysed to determine whether different mosquito strains, different food and different narcosis used in these previous studies, and/or methodological errors, could account for the different results.Most of the cellular parameters in the stomach epithelium of female A. aegypti, strain Rockefeller, and their changes during blood digestion, are comparable to those measured for another Aedes strain (Segemaganga, Hecker and Rudin 1979), and are generally similar to those of Anopheles stephensi (Hecker 1978). Proteolytic activity against casein is similar for both Aedes strains with a maximum activity being registered around 30 h after a blood meal. During digestion of human serum there is no increase in the ratio of membranebound to free ribosomes, and no significant increase in the surface area of the rough endoplasmic reticulum or of the number of bound or free ribosomes. Proteolytic activity is distinctly lower than during blood digestion. Immobilization of mosquitoes prior to dissection by ether narcosis or by shaking in a test tube has no significant influence on cellular parameters in females fed on sugar solution and investigated 3days after emergence.It is concluded that the differences in ribosomal parameters previously obtained by morphometrical (Hecker and Rudin 1979) and biochemical (Gander et al. 1980) methods, can only partly be explained by the selection of different food for the mosquitoes, and must also have been caused by methodological inadequacies.

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Zusammenfassung Frühere morphometrische und biochemische Untersuchungen erbrachten teilweise unterschiedliche Resultate betreffend Verteilung freier und membrangebundener Ribosomen in Mitteldarmzellen von Aedes aegypti. In der vorliegenden Arbeit wurde morphometrisch untersucht, ob diese Unterschiede bedingt waren durch die Verwendung verschiedener Mückenstämme, unterschiedlichen Futters und verschiedener Narkosemethoden durch die beiden Arbeitsgruppen, oder ob methodische Einflüsse dafür verantwortlich waren.Die meisten Zellparameter im Magenepithel von A. aegypti, Stamm Rockefeller, wie auch ihre Änderungen während der Verdauung eines Blutmahls, entsprachen den für einen andern Aedes-Stamm (Segemaganga, Hecker und Rudin 1979) gemessenen Werten und stimmten im allgemeinen mit denjenigen für Anopheles stephensi (Hecker 1978) überein. Die proteolytische Aktivität gegen Casein war bei beiden Stämmen gleich mit einem Aktivitäts-Maximum um 30h nach Blutmahl. Bei der Verdauung von menschlichem Serum konnte keine Zunahme des Verhältnisses von membrangebundenen zu freien Ribosomen, keine signifikante Oberflächenvergrößerung des rauhen endoplasmatischen Retikulums und keine signifikante Erhöhung der Zahl gebundener und freier Ribosomen gemessen werden. Die Proteaseaktivität war deutlich schwächer als während der Verdauung von Blut. Betäubung der Mücken vor der Sektion mit Aether oder durch Schütteln in Reagenzgläsern ergab im Vergleich keinen signifikanten Einfluß auf die Zellparameter von Zuckerwasser-gefütterten Weibchen, die drei Tage nach dem Schlüpfen untersucht wurden.Unterschiede in den Ribosomenparametern, die mit morphometrischen Methoden (Hecker und Rudin 1979) einerseits und biochemischen (Gander et al. 1980) andererseits untersucht wurden, konnten nur teilweise durch die Wahl unterschiedlichen Futters für die Mücken durch die beiden Arbeitsgruppen erklärt werden. Es müssen zusätzlich methodische Einflüsse für diese Unterschiede verantwortlich sein.

     

Ultrastructure of the chromatophore system on the tracheal bladders of the phantom larva of Chaoborus crystallinus (Insecta,Diptera)

The chromatophore system on the tracheal bladders of the phantom larva of Chaoborus crystallinus has been investigated by light and electron microscopy. The pigment cells are attached to a restricted region of the outer surface of the bladders and have the capacity to change both their shape and position on the bladder in response to changes in background illumination. The whole pigment system is tightly spanned by an extracellular membrane, which is in contact with two small muscles inserting at the anterior inner wall of the bladders.Nachdem das Manuskript eingereicht worden war, ist Walter Weber verstorben. An seiner Stelle hat Herr Dr. Lehmann (Köln) zur Fertigstellung der Druckfassung der Arbeit beigetragen     

Feeding and breeding aspects of Stomoxys calcitrans (Diptera: Muscidae) under laboratory conditions

Bionomic aspects of Stomoxys calcitrans (Linnaeus, 1758) (Diptera: Muscidae) were studied under laboratory conditions. For this reason, laboratory-rearing techniques were optimized at the National Veterinary School of Toulouse. The colony was maintained at 25 ± 2 °C, 50 ± 10% RH under a 12-hour light cycle and observed daily. The size of each adult cage is 30 x 30 x 30 cm and designed to house about 500-1,000 flies. The average cycle from egg to adult was 19.2 ± 1.7 days. The mean longevity of imagos was 9.3 ± 5.8 days and not significantly different between sexes. Stable flies were split into two groups; the first was fed with blood, honey and water, and the second was fed only with honey and water. The mean weight of a blood meal was 11.1 ± 3.8 mg with no significant differences between males and females. The mean longevity of non-blood fed flies was found to be significantly higher (10.4 ± 3.9 days) than those fed with blood. The maximum lifespan was shorter for non-blood fed males (17 days) and females (18 days) than for those fed with blood (females: 24 days, males: 23 days). Under these laboratory conditions, S. calcitrans rearing was successfully established. In the end, the number of expected generations of S. calcitrans and the net reproduction rate were estimated to be 11.8 generations/year and 16.2 living females per female respectively.     

Sperm ultrastructure in Chironomoidea (Insecta, Diptera)

The fine structure of spermatozoa from several species of chironomids, of Culicoides sp. (Ceratopogonidae) and of Odagmia pontina (Simulidae) was studied. A synapomorphic feature, consisting of nine kidney-shaped structures forming the centriole adjunct, was found in the chironomid species. All members of Chironomoidea share a mono-layered acrosome and a flagellar axoneme, provided with accessory tubules with 15 protofilaments in their tubular wall. The axoneme has a 9+9+2 pattern, but in an unidentified species of chironomid, a 9+9+0 model was observed where the central complex and the spokes are missing. Sperm motility is, however, maintained in all the examined species. The spermatozoa of this taxon have the tendency to complete maturation during their progression along the deferent ducts. Thus, in the proximal region of these ducts, they often show remnants of the spermatid cytoplasm.     

Campaniform sensilla of Calliphora vicina (Insecta,Diptera)

Summary A classification scheme of campaniform sensilla using morphological criteria was developed. All variations of the two most important outer structural elements, the cuticular cap and the cuticular collar, were taken into consideration: (a) the external shape of the cuticular cap; (b) the position of the cuticular cap in relation to the remaining cuticle; (c) the position of the cuticular collar in relation to the cuticular cap. This resulted in a classification of campaniform sensilla into 24 types. This typology was applied to the campaniform sensilla of Calliphora, which show considerable variations in their outer structures. According to SEM (scanning electron microscope) pictures and TEM (transmission electron microscope) sections we found only 9 out of 24 different types of campaniform sensilla in the fly.     

Armored cuticular membranes in Brachycera (Insecta,Diptera)

This study describes and quantifies the ultrastructural design of some cuticular protuberances in the Diptera-Brachycera that appear to have a specialized mechanical function. The microsculpture of membranes in the transitional areas of prothorax-neck, neck-head, head-mouthparts, and in the articulations thorax-coxa and coxa-trochanter was investigated in eight species from six families (Tabanidae, Stratiomyidae, Calliphoridae, Syrphidae, Muscidae and Drosophilidae) by means of scanning electron microscopy. The membrane armatures are single or grouped microtrichia, often located on microplates in the flexible membrane. The different membranes were compared using the following details: microtrichia length, microplate length and width, the shortest distance between microplates, and the number of microtrichia per microplate. Five different types of microstructure were observed: (1) single short papilla-like microtrichia directly arising from the flexible membrane, (2) single elongated microtrichia directly arising from the flexible membrane, (3) single microtrichia located on small areas of the inflexible cuticle, here called microplates, (4) microtrichia groups located on the microplates, and (5) microplates without microtrichia in the flexible membrane. The study reveals the differences in the surface ultrastructure of membranes between different parts of body and between different taxa of flies. The prothorax-neck transition is less specialized in membrane armature as compared with the head-neck articulation, and especially with that of the head-proboscis. The head-proboscis transition has the most complex membrane armature of those species studied. The membrane of the basal joints of the legs has larger plates and a higher number of microtrichia per plate than that of the more distal joints. The complexity of the membrane armature depends on the dimensions of the animal: the smallest species have short ungrouped microtrichia or micropapillae, whereas large species have the highest degree of grouping, the longest microtrichia, and the largest microplates. Three main mechanical functions served by the different armored membranes are suggested, based on the specific characteristics of the microsculptural design: (1) fixation of the folds, (2) prevention of folding, and (3) determination of direction of folding. J. Morphol. 234:213–222, 1997. © 1997 Wiley-Liss, Inc.     

Ecological studies on Chaoborus (Diptera, Chaoboridae) in Lake George, Uganda

(1) Chaoborus anomalus and Chaoborus ceratopogones were found together throughout the year in Lake George, Uganda, the larvae forming 65-85% by number of the macro-benthos of the central lake area. (2) First and second instar larvae were wholly planktonic and third and fourth instar larvae mainly benthic during the day, migrating into the water column at night. A proportion of the third and fourth instar larvae were found in the water column during the day in the centre of the lake where light attenuation was greatest. C. anomalus showed a greater tendency to be benthic than C. ceratopogones. (3) Planktonic larvae were distributed in dense patches thought to be cohorts resulting from oviposition by swarms of adult females. The maximum density of planktonic larvae recorded was 31.7 × 10²/m² column. Third and fourth instar larvae were more evenly distributed in the benthos of the central lake area, the maximum density recorded was 79.9×10²/m². (4) First and second instar larvae occurred mainly in the inshore regions, very few were found in the centre of the lake. Oviposition is likely to take place inshore. The patches of planktonic larvae were not stationary. Dispersal of larvae away from the shore may be active or may result from complex oscillations of the water mass produced by storms. In C. ceratopogones the floating egg batches could he carried away from the north shore by currents produced by inflows and prevailing winds. (5) Adults of C. ceratopogones were more numerous during the rainy seasons than during the dry seasons. A similar, though less marked seasonality was found in the occurrence of C. anomalus adults. The biomass of benthic larvae of C. ceratopo-gones was estimated at 387.0 mg C/m² in the dry season, June 1970, and 130 0 mg C/m² in the rainy season, October 1970. That of C. anomalus was constant at 241.7 and 254.3 mg C/m² in June and October, 1970 respectively. (6) No difference was found in the horizontal distribution of the larvae, or in the size and weight attained by the various stages. (7) Interspecific differences were found in the mean number of eggs per adult female (309, C. anomalus and 224, C. ceratopogones); in the nature ofthe egg batches; n i the morphology of the larval mouthparts and pharyngeal sphincters, as well as i n the vertical distribution of the larvae and seasonal occurrence of the adults. On the basis of these differences the co-existing species are thought not to be competing for the same resources.     

Linking lakes? The population genetic structure of Chaoborus flavicans

Larvae of Chaoborus flavicans (Diptera: Chaoboridae) are commonin various lakes and are important members of plankton communities.To assess gene flow between lakes, we sampled several populationsthroughout Europe. To explicitly test whether gene flow is higherwithin regions than between regions, we examined four regionseach containing several populations. For a detailed analysisof regional gene flow, 12 populations within a region in NorthGermany were analysed. Allozymes and mitochondrial restrictionfragment length polymorphism (RFLP) were used to estimate therelative amounts of gene flow. Results indicate that most ofthe dispersal in C. flavicans takes place between lakes withinregions. Therefore, the population genetic structure of C. flavicanssets this species apart from other planktonic organisms, whichare mainly passive dispersers and display low gene flow betweenlakes within regions. Consequently, these data are the firstevidence that C. flavicans may form an important link betweenlakes within regions. Local adaptation within lakes may be decreasedbecause of these processes, and the role of C. flavicans asa biomonitor of local lake conditions needs to be carefullyreinvestigated.     

Phylogeny of Ptychopteroidea (Insecta: Diptera)

A phylogenetic tree is proposed for the superfamily Ptychopteroidea, reconstructed taking into account both extinct and extant taxa and based mainly on characters of wing venation.     

Phylogeny of Oestridae (Insecta: Diptera)

The phylogeny of Oestridae was analysed at the generic level using 118 characters from all developmental stages and including morphology, ontogeny, physiology and behaviour. Four major clades were given subfamilial rank with the phylogenetic relationship (Cuterebrinae (Gasterophilinae (Hypodermatinae + Oestrinae))). The subdermal parasites of the African elephant, Neocuterebra squamosa Grünberg and Ruttenia loxodontis Rodhain, had their most probable affiliation subordinate to the clade of stomach parasites, although their exact position needs further investigation. Genus Ochotonia Grunin, which is known from a single third‐instar larva only, was the probable sister group of all other Hypodermatinae. Twenty‐five oestrid genera were recognised as valid and those containing more than one species were defined through lists of autapomorphies. Cuterebra Clark was proposed as a senior synonym of Alouattamyia Townsend, Andinocuterebra Guimarães, Pseudogametes Bischof and Rogenhofera Brauer. The clade of hypodermatine ungulate parasites (Hypoderma Latreille +Pallasiomyia Rubtzov +Pavlovskiata Grunin +Przhevalskiana Grunin +Strobiloestrus Brauer) remained largely unresolved, and genus Przhevalskiana emerged without defining characters.     

Effects of predation by Chaoborus flavicans on crustacean zooplankton of Lake Lenore, Washington

1. After Chaoborus flavicans became established in 1974, the species composition of zooplankton in Lake Lenore changed. Diaptomus nevadensis disappeared and densities of Diaptomus sicilis were reduced.
2. A transplant experiment showed the D. nevadensis could survive in Lake Lenore water in the absence of Chaoborus . The disappearance of D. nevadensis was probably a consequence of Chaoborus predation.
3. Although densities of Daphnia pulicaria † were similar before and after the colonization of C. flavicans , juvenile D. pulicaria began producing neck-teeth during the first summer Chaoborus was present.
4. The seasonal pattern of neck-teeth production by juvenile D. pilicaria did not correlate with density of Chaoborus but rather with a combination of water temperature and Chaoborus density, suggesting that metabolic processes are a component of induction of neck-teeth in this species.     

On Longevity of Adult Chaoborids (Diptera,Chaoboridae) under Sugar Feeding Conditions

Entomological Review - Longevity of the adult male and female Mochlonyx velutinus (Ruthe) and the adult male Chaoborus crystallinus (De Geer) that emerged under laboratory conditions was measured,...     

Density- and Size-Dependent Winter Mortality and Growth of Late Chaoborus flavicans Larvae

Winter processes such as overwinter survival and growth of individuals can have wide-ranging consequences for population dynamics and communities within and across seasons. In freshwater organisms winter processes have been mainly studied in fish despite that invertebrates also have substantial impacts on lake and pond food webs. One of the major invertebrate consumers in lake and ponds is the planktonic larvae of the dipteran insect Chaoborus spec. However, while much is known about Chaoborus feeding ecology, behaviour and structuring role in food webs, its winter ecology and how it affects its populations are poorly understood. Here size- and density-dependent winter mortality and body growth of late Chaoborus flavicans larvae were quantified over naturally occurring size and density ranges in autumn and under natural winter conditions using two field enclosure experiments. Winter mortality increased with autumn density but decreased with autumn body size while winter growth rates decreased with autumn density and body sizes. There was also a density- and size-independent background mortality component. The proportion of pupae found in spring decreased strongly and exponentially with autumn density. These results may explain the commonly observed univoltine life cycle and multi-annual density fluctuations in northern Chaoborus populations. They further demonstrate the relevance of winter processes and conditions for freshwater invertebrates and ecosystems.