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Valerie M. Dowding

Bio: Valerie M. Dowding is an academic researcher from University of Cambridge. The author has contributed to research in topics: Calliphora vicina. The author has an hindex of 1, co-authored 2 publications receiving 61 citations.

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TL;DR: The anatomy and function of the pharyngeal ridges, which occur in the larvae of saprophagous Cyclorrhapha but are generally absent in biontophagous forms, were investigated and found to be correlated with the constant and high nutritive value of both the solid and the liquid fractions of the food.
Abstract: The anatomy and function of the pharyngeal ridges, which occur in the larvae of saprophagous Cyclorrhapha but are generally absent in biontophagous forms, were investigatedThe ridges extend throughout the length of the ventral aspect of the pharynx and lie in an evagination of its floor They enclose channels which narrow and disappear posteriorly but are open anteriorly Each ridge consists of a longitudinal plate projecting dorsally from the floor of the pharynx, the bifurcated upper edge of the plate bears, one on each side, a row of lateral lamellae, each about 0·3 μm thick They are set vertically at regular intervals of just less than 1 μm The lateral lamellae of adjacent ridges are closely apposed and completely roof over the channels between the ridges Anteriorly the upper arms of the ridges are fused togetherThe lamellae form a sieve which retains particles of 0·6 μm and above in size as the relaxation of the pharyngeal dilator muscles allows the roof to descend so forcing liquid downward between the lamellae In Calliphora vicina (Syn C erythrocephala) the sieve concentrates a suspension of 2700 particles of 4–7 μm per mm3 between five and six times The natural food consists largely of bacteriaFungus spores and pollen grains of selected sizes were used to demonstrate the movements of particulate material in the pharynx and to define the upper size limit of the particles ingestedSwallowing is effected by simultaneous relaxation of the anterior dilator and transverse muscles of the pharynx, with contraction of the posterior dilator muscles; the transverse muscles are otherwise maintained in a state of contraction closing the posterior exit from the pharynxStarved third-instar larvae of C vicina can ingest 50% of their body weight in 6 minThe larvae of the Cyclorrhapha which possess pharyngeal ridges are essentially particle feeders The ridges form a sieve by means of which food is concentrated and the amount of non-nutritious liquid ingested is reduced The lack of pharyngeal ridges in larvae feeding on living material is correlated with the constant and high nutritive value of both the solid and the liquid fractions of the foodI should like to thank Dr P Tate for his help and encouragement during the course of this work which was carried out during the tenure of a Postgraduate Studentship awarded by the Agricultural Research Council Thanks are also due to the staff of the Plant Pathology subdepartment of the Botany School, Cambridge, for their help in obtaining fungus spores of suitable sizes

61 citations


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TL;DR: The major objectives of this article are to review the means by which filter-feeding insects obtain their food and to assess the role of these animals in aquatic ecosystems.
Abstract: suspended material (seston), including living organisms and both organic and inorganic detritus. Filter-feeding insects constitute important pathways for energy flow and are very important in the productivity of aquatic environments. Yet, some of these animals epitomize the complex relation­ ship between man and insects since biting adults of certain groups are among man's oldest adversaries. The major objectives of this article are to review the means by which filter-feeding insects obtain their food and to assess the role of these animals in aquatic ecosystems. Filter-feeding strate­ gies by other invertebrates in both marine and freshwater habitats have been partially reviewed elsewhere (82, 100, 101).

427 citations

Journal ArticleDOI
TL;DR: Compared with other forest ecosystems located at the similar latitude, the carbon fixation of the old-growth forest was larger, likely due to its complicated structure within the canopy and the presence of young-growth regeneration and successional stands and showed that other than in carbon neutral, old- growth forests of Tianmu Mountain in subtropical China had a strong capability in carbon sequestration.
Abstract: The old-growth, multiple ages, multispecies natural forest has played an important role in terrestrial ecosystem dynamics model and the global carbon budget. However, carbon fluxes of old forests in subtropical regions are rarely reported in China. In the present study, the CO₂ flux of an old-growth subtropical evergreen and deciduous broad-leaved mixed forest was observed using eddy covariance technique in Tianmu Mountain of Zhejiang Province. Based on the data sets which were observed from July 2013 to June 2014, the variations of net ecosystem exchange (NEE), eco-system respiration (Re), and gross ecosystem exchange (GEE) were analyzed. The results showed that during the study period, the monthly NEE all had a negative value (acted as a carbon sink) except for December and February (acted as a carbon source). The average monthly NEE was -61.52 g C · m⁻², the monthly carbon sequestration showed a double-peak curve and the maximum carbon sink was -149.40 g C · m⁻², which occurred in June while the maximum carbon source was 23.45 g C · m⁻², which occurred in February. The maximum of monthly mean CO₂ flux occurred in June with a value of -0.98 mg · m⁻² · s⁻¹, while the minimum value occurred in December with a value of -0.35 mg · m⁻² · s⁻¹. The NEE at the time point of positive and negative conversion had typical seasonal characteristics. The yearly NEE, Re, and GEE were -738.18, 931.05 and -1669.23 g C · m⁻², respectively. Compared with other forest ecosystems located at the similar latitude, the carbon fixation of the old-growth forest was larger, likely due to its complicated structure within the canopy and the presence of young-growth regeneration and successional stands. This showed that other than in carbon neutral, old-growth forests of Tianmu Mountain in subtropical China had a strong capability in carbon sequestration.

215 citations

Journal ArticleDOI
TL;DR: The nature and extent of the effects of veterinary parasiticides in dung of treated livestock, and how greater awareness of these nontarget effects has resulted in regulatory changes in the registration of veterinary products are described are described.
Abstract: Residues of veterinary parasiticides in dung of treated livestock have nontarget effects on dung-breeding insects and dung degradation. Here, we review the nature and extent of these effects, examine the potential risks associated with different classes of chemicals, and describe how greater awareness of these nontarget effects has resulted in regulatory changes in the registration of veterinary products.

201 citations

Journal ArticleDOI
TL;DR: The larvae of Megaselia scalaris (Diptera: Phoridae) exploit a broad spectrum of larval pabula and is favored as an experimental species for genetic, developmental, and bioassay studies.
Abstract: The larvae of Megaselia scalaris (Diptera: Phoridae) exploit a broad spectrum of larval pabula. Consequently, the species features in a range of situations that affect the resources or well-being of humans. Furthermore, M. scalaris is readily cultured in the laboratory and is therefore favored as an experimental species for genetic, developmental, and bioassay studies. However, the extensive but widely scattered literature, reviewed herein, is frequently ignored by specialists, which gives rise to the unwitting repetition of previous work as well as insupportable proposals.

169 citations

Journal ArticleDOI
TL;DR: Pure cultures of individual bacterial species isolated from the intestinal tract of larvae from turkey bedding supported development of flies to a much greater extent than those isolated from larvae from corn silage.
Abstract: The bacterial diversity in the intestinal tract of Musca domestica L. was examined in larvae collected from turkey bedding and corn silage. Aerobic culturing yielded 25 bacterial species, including 11 from larvae collected from turkey bedding and 14 from larvae collected from corn silage. Providencia rettgeri (Hadley, Elkins & Caldwell) was the only species common to both environments. Two mammalian pathogens, Yersinia pseudotuberculosis (Pfeiffer) and Ochrobactrum anthropi (Holmes), were isolated from the larval intestinal tracts. The majority of isolates represented facultatively anaerobic heterotrophs capable of fermentation. The significance of these bacteria for development of house fly larvae was evaluated by bioassays on trypticase soy egg yolk agar. Pure cultures of individual bacterial species isolated from the intestinal tract of larvae from turkey bedding supported development of flies to a much greater extent than those isolated from larvae from corn silage. House fly development was best supported by a Streptococcus sanguis (White) isolate. The significance of bacteria for development of house flies is discussed.

154 citations