The combined effects of temperature and food consumption on body weight,egg production and developmental time in Chaoborus crystallinus De Geer (Diptera: Chaoboridae)

Summary Chaoborus crystallinus fourth-instar larvae were reared individually at 14°, 17° and 20° C under different food conditions. Daphnia magna of 1.25 mm average length served as prey. The following were measured: amount of prey ingested, larval weight gain, duration of fourth instar, body weight of the adults, and egg number per female. At a given temperature, the body weight, egg-number and developmental rate increased with food consumption. At a given food consumption, higher temperatures caused a decrease in body weight and egg number, and an increase in developmental rate. Gross production efficiencies for fourth-instar larvae were highest at temperatures around 17° C. The results clearly indicate that from an energetic point of view higher temperatures are disadvantageous. In C. crystallinus vertical migration is evidently a way of lowering the temperature to which the animals are exposed and hence optimizing food conversion into biomass and offspring production, especially if prey densities are below the saturation level.     

Persisting stemma neuropils in Chaoborus crystallinus (Diptera: Chaoboridae): Development and evolution of a bipartite visual system

Stemmata or “larval” eyes are of crucial importance for the understanding of the evolution and ontogeny of the hexapod's main visual organs, the compound eyes. Using classical neuroanatomical techniques, I showed that the persisting stemmata of Chaoborus imagos are connected to persisting stemma neuropils neighboring the first and second order neuropils of the compound eyes, and therefore also the imago possesses a stemma lamina and medulla closely associated with the architecture and the developmental pattern of those of the compound eyes. The findings are compared with other arthropods, e.g. accessory lateral eyes in Amandibulata and Myriapoda, suggesting some ancestral rather than derived character states. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Development of the sensory system in larvae and pupae of Chaoborus crystallinus (DeGeer, 1776; Diptera, Chaoboridae): sensory cells, nerves and ganglia of the tail region

Using various microscopical techniques, we have studied changes in the sensory equipment and architecture of the peripheral nervous system (PNS) around the first metamorphic molt from larva to pupa in the phantom midge Chaoborus. The transparent larvae and pupae of this dipteran with ancestral features allow us to investigate sensilla and their central projections from whole-mount preparations of complete groups of segments. Each sensillum on the posterior larval and pupal segments was identified using its external shape and position, and the morphology of the abdominal ganglia and segmental nerves was investigated. In addition, retrograde fills with the carbocyanine dye DiI were used to trace the axonal paths of most of the extero- and proprioreceptors. These findings were combined to produce maps of the sensory elements of larval and pupal abdomens that were analyzed at three levels: seriality (homonomy), ontogenetic changes of individual sensilla, and homology of the PNS between different species. Comparison of different segments shows for both stages that primarily there is a homonomous basic design of the PNS, but segment-specific modifications are evident in segments 8-10. Comparison of corresponding larval and pupal segments shows that many sensilla retain their internal structure and axonal projections. However, their external cuticular parts are changed in relation to the different life habits of larvae and pupae. Furthermore, some sensilla are completely reduced during the pupal molt, especially those of the tenth segment which appears as a distinct larval structure (caenogenesis). Comparison between species indicates that despite the varying types of sensilla their basic segmental arrangement and their axonal trajectories are conserved.     

Larva-adult relationships in an ancestral dipteran: A re-examination of sensillar pathways across the antenna and leg anlagen of Chaoborus crystallinus (DeGeer, 1776; Chaoboridae)

 In one of his classical studies on insect metamorphosis, Weismann compared the imaginal anlagen of the ancestral phantom midge, Chaoborus, with those of advanced brachycerans. We have expanded his findings on the relationships between larval and imaginal organs using electron microscopy and cobalt backfilling of the antenna and leg anlagen and the axonal trajectories of corresponding larval sensilla. We show that both primordia are confluent with the larval antennae and ”leg” sensilla (an ancestral Keilin organ), respectively. These fully developed larval organs represent the distal tips of the imaginal anlagen rather than separate cell clusters. The axons of the larval antenna and leg sensilla project across the corresponding anlagen to their target neuromeres within the central nervous system (CNS). Within the discs, nerves composed of these larval axons, developing afferent fibres and efferences ascending from the CNS are found. Both the structure of the primordia and the axonal trajectories thus relate the situation found in advanced brachycerans with that seen in more ancestral insects. In addition, the larval antennae, legs, wings and even the eyes possess very similar afferent pioneer trajectories supporting the idea that the described pattern is generally used in the ontogeny of sensory systems. Received: 30 June 1998 / Accepted: 27 September 1998     

Functional morphology of the mandibles of the larvae of Episyrphus balteatus (De Geer, 1776) (Diptera : Syrphidae)

Aphidophagous syrphid (Diptera : Syrphidae) larvae have no structures for seizing and killing such as prehensile legs and strongly sclerotized external mouthparts enabling them to capture and feed on their prey. Nevertheless they are considered to be efficient predators. In order to understand this paradox in Episyrphus balteatus, 2 complementary approaches were followed. These consisted of, first, a careful analysis of the morphology of mouthparts of the larvae, and second, an investigation of their feeding behaviour. The mouthparts were found to be composed of 2 groups of dental sclerites, corresponding to the 2 inner elements of the cephalopharyngeal skeleton. The exterior elements or triangular sclerites are absent in the first-instar larvae. These elements appeared close to the mouth in the second and the third-instar larvae, were oriented in the opposite direction to the other elements, and were positioned laterally. This structure probably serves to anchor the anterior part of the predator within the prey, thus preventing it from escaping. During the feeding activity, the seizing process occurred immediately after the recognition. The lifting-up behaviour of the first-instar larvae is probably due to the absence of the triangular sclerites. The suction was marked by an active movement of the cephalopharyngeal skeleton and a peristaltic movement of the abdomen. The feeding time was inversely proportional to the larval development.     

New observation in France of a nuisance due to Simulium (Boophthora) erythrocephalum (De Geer, 1776) (Diptera, Simuliidae)

Some nuisance due to Simuliidae appeared near the French border with Spain (Pyrénées-Orientales) during the summer 1998. Larvae and pupae were collected in the lower parts of the rivers Têt, Tech and Agly. The identification demonstrated the occurrence of Simulium erythrocephalum. If the nuisance would become durable, a control campaign should be initiated.     

Food selectivity and diel vertical distribution of Chaoborus edulis (Diptera, Chaoboridae) in Lake Malawi

1. Diel diet and vertical distribution patterns of the larval instars of Chaoborus edulis were studied in deep water near the central part of Lake Malawi, Africa.
2. First instar larvae contained very little food in their crops and probably depended on reserves from the egg. Second, third and fourth instars fed on zooplankton and were size-selective in their feeding. The mean size of prey eaten by the three instars was significantly different from each other, with larger instars feeding on larger prey. Smallest available prey was selected against and the upper size of prey was probably constrained by larval gape. Nauplii were not found in any of several thousand larvae examined. Phytoplankton did not form a significant part of the diet.
3. There was a progressive and related increase in diel periodicity in feeding and vertical migrations of successive instar stages. Fourth instars migrated particularly large distances. Such migrations removed them from their zooplankton food supply but avoided predators. A refuge from predators is probably found in or near the permanent zero oxygen boundary, at depths greater than 200 m.     

The estimation of crop evacuation rates in Chaoborus larvae (Diptera: Chaoboridae) using natural prey

SUMMARY. 1. Crop evacuation rates were estimated for the first time in Chaoborus larvae, using natural prey.
2. Fourth instar C. americanus Matheson digested copepods (Diaptomus leptopus S.A. Forbes) 48.7% faster than daphnids (Daphnia rosea Leydig) of similar size; meal size did not significantly affect the instantaneous rate of digestion (IRD) within each prey type. Prey specific IRD has not been reported before for zooplankton.
3. Prey specific differences in IRD require the use of natural prey when digestion experiments are to be used to estimate natural rates of food consumption of animals.     

Zooplankton populations and the diets of three Chaoborus species (Diptera, Chaoboridae) in a tropical lake

SUMMARY. 1. Zooplankton populations in a small, natural, tropical lake are dominated by a few, small-sized taxa including the copepod Thermo- cyclops consimilis , the cladoceran Moina micrura and several rotifer species.
2. Moina micrura and adults of Thermocyclops consimilis undergo diel vertical migrations within the water column. Population densities of T. consimilis show marked intra-annual variations which may to some extent be related to variations in rainfall and to lunar periodicities In predator abundance.
3. The diets of Chaoborus lavae include other Chaoborus , Cladocera, Copepoda. Rotifera and the dinoflagellate Peridinium. The diets of late instars of the largest species, edulis , were dominated by Crustacea, while those of the two smaller species. C, ceratopogones and C. anomalus , were dominated by Rotifera and the dinoflagellate alga Peridinium , as were the diets of early instars of all species. Algae have not been previously reported to be a large component of the diet of Chaoborus populations in nature.
4. Some of the dietary differences among Chaoborus instars and species are related to the size of each prey species in relation to the mouth gape of each instar. However, there are also important differences in electivity among instars of different species of the same size.     

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.     

The Chaoborus (Diptera: Chaoboridae) component of the invertebrate drift of the Mwenda river,Lake Kariba,Central Africa

Chaoborus larvae were collected from the riverine drift of the Mwenda River during the 1972/3 rainy season. Large numbers of larvae were found in the early stages of flow following the 1972 dry season, fewer were found ten days later.Larvae which reached the lake in this way appeared to show no ill effects. Possible mortality arising prior to reaching the sampling point was doubtful since no dead larvae or parts were found in the material collected.     

Isolation of polymorphic microsatellite loci in three phantom midge species of the genus Chaoborus (Diptera: Chaoboridae)

Because of its widespread distribution in lakes and ponds Chaoborus is of great interest to many freshwater ecologists. Interestingly some species are restricted to small fish‐less water bodies, whereas other species live mostly in large lakes. To eventually test the genetic and evolutionary implications of these different lifestyles we identified microsatellite loci in three species in this preliminary study: C. obscuripes, C. crystallinus and C. flavicans. Using a biotin/streptavidin capture technique of repetitive sequences in a 96 well format, we obtained microsatellite‐enriched genomic libraries for all three species and identified six polymorphic microsatellite markers for each species.     

Musculature of the male genitalia of Xylophagus cinctus (De Geer) and relationships within the superfamily Xylophagoidea (Diptera, Brachycera)

There is no general agreement on relationships within Xylophagoidea (Diptera, Brachycera). The musculature of the male genitalia of Xylophagus cinctus (De Geer) (Xylophagidae, the most primitive family of Brachycera) is described and compared with that of some other Xylophagoidea: Exeretonevridae (Exeretonevra angustifrons Hardy), Coenomyiidae (Anacanthaspis biafasciata Röder), and Rhagionidae (Rhagio montanus Becker, Chrysopilus dives Loew, and Ch. helvolus Meigen) discussed earlier (Ovtshinnikova, 1989, 1998; Palmer et al., 2000). In spite of the differences in the structure of the genital sclerites, Xylophagidae possess all the muscles found in Coenomyiidae and Rhagionidae. The musculature of the male genitalia of Xylophagus cinctus includes two muscle pairs of the aedeagus sheath (M1 and M2); three muscle pairs of the ejaculatory complex (M30, M31, and M32); one muscle pair of the gonocoxites (M33); two muscle pairs of the gonostyli (M27 and M28); one muscle pair of the proctiger (M21), one muscle pair of the cerci (M29); two pairs of the tergosternal muscles (M5 ¹ and M5 ²); and two pairs of the pregenital muscles (M18 and M19). Muscles of the family Exeretonevridae are mostly the same, except for the muscles of the cerci M29, proctiger M29, and pregenital muscles M18 and M19, that are subdivided into two parts. This fact and also a different degree of the development of muscles M32 and M5 ² clearly distinguish Exeretonevridae from closely related families. The attachment places of the muscles of the aedeagus sheath M2 and of the gonostyli M28, as well as the split character of the tergosternal muscle pair M5 ¹ makes it possible to distinguish two sister groups, Xylophagidae plus Exeretonevridae, versus Coenomyiidae plus Rhagionidae. It should be noted that the muscles of the male genitalia of Xylophagidae, Exeretonevridae, Coenomyiidae, and Rhagionidae possess similar plesiomorphic characters, and these families should be united into the superfamily Xylophagoidea. This superfamily is the most primitive superfamily of Brachycera Orthorrhapha and possesses the most stable set and arrangement of male genital muscles within the entire suborder. An improved dendrogram of the phylogenetic relationships between the known groups of Xylophagoidea is proposed on the basis of the structure of male genital muscles.     

黑带食蚜蝇Episyrphus balteatus De Geer的复眼结构及其调光机制

【目的】观察研究黑带食蚜蝇Episyrphus balteatus De Geer成虫复眼形态、小眼结构和不同光暗条件对小眼结构的影响,以明确其光视觉的结构基础和调光机制。【方法】利用组织切片法和扫描电镜等技术。【结果】1.复眼位于头部两侧,正面观呈半球形,占据除额颜外大部分头部。雄虫与雌虫单个复眼分别有约7 180个、7 230个小眼。各小眼面呈整齐排列的规则六边形。2.小眼由角膜及伪晶锥组成的屈光器、不同水平面分布的8个小网膜细胞及其特化形成的离散型视杆、屏蔽色素细胞和基膜等组成。小眼自远端至近端由主色素细胞和12个附属色素细胞围绕。3.随光暗条件的改变小眼内的附属色素细胞色素和基细胞细胞核沿小眼纵轴移动。光适应时,附属色素细胞色素颗粒沿小眼纵轴均匀分布,基细胞细胞核位于基膜上方。暗适应时,附属色素细胞色素颗粒向伪晶锥近端压缩,基细胞细胞核亦向远端移动,到达视杆中段。【结论】黑带食蚜蝇复眼精密的小眼排列形式和内部结构均显示了其强大的生理功能;屏蔽色素颗粒的移动是其复眼适应外界光环境变化的重要机制。本试验为进一步探究黑带食蚜蝇视觉结构和光调节机制,以及与其飞行行为间的关系提供了一定的理论基础。     

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.     

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