Chironomidae Analysis Method BY Ji Xiaowen Цзи Сяовэнь

目录页 CONTENTS PAGE P 1. Introduction P 2. Sediment Processing P 3. Identification P 4. Taxonomy систематика 分类学

Introduction Part 1

Part 1 Part 2 Part 3 Part 4 Chironomidae Among insects, the chitinous larval remains of the order Diptera (true flies) are most abundant in lake sediments, and thus have proven to be especially useful in palaoenvironmental studies. Within this large and diverse group, however, remains of the Chironomidae (non-biting midges) greatly exceed the remains of all other Diptera in abundance. Each of these families is principally aquatic in its larval form, although the Ceratopogonidae and Chironomidae comprise some terrestrial or semi-terrestrial species. Ephemeroptera (mayflies) Head capsules are the principal remains of the Chironomidae that can be recovered from lake sediments. Identification of the Chaoboridae relies instead upon the larval mandibles (нижняя челюсть/Unterkiefer/下颌骨). 4

Sediment Processing Part 2

Part 1 Part 3 Part 2 Part 4 5% KOH Sediments (1 or 2 cm 3) Potasssium hydroxide Sediment Processing Excessive NO mineral matter? (Calcareous or Siiceous) 95 µm Sieve Distilled water YES 5% HCl Hydrochloric acid Excessive mineral matter? NO Distilled water 95 µm Sieve Counting tray S YE Polythene tubes 40% HF Hydrogen flouride Handsorting＆ Slides 5% HCl 6

Part 1 Part 2 Part 3 Part 4 Sediment Processing The methods best used to isolate midge remains vary considerably depending on the nature of the sediments. The KOH solution may be gently heated to quickly deflocculate the sample. If only air-dried samples are available, the sediment should initially be put in hot water for 30 to 60 minutes, and deflocculated slowly (perhaps over several days) in a cold KOH solution. If the sample contains carbonates, most may be eliminated in cold 5% HCl. The reaction should be allowed to proceed until the sediments no longer effervesce when fresh HCl is applied. 7

Part 1 Part 2 Part 3 Part 4 Sediment Processing I Sand other coarse siliceous matter may be eliminated in cold, concentrated (approx. 50%) HF. In preparation for HF digestion, the sediment should be concentrated by centrifugation in polythene tubes; the HCl acid residues may then be decanted, and the HF applied. II The HF processing step is rarely necessary, and should normally be omitted. The extreme dangers of HF burns and systemic poisoning, even on exposure to small drops, dictate that HF always be handled cautiously, in a fume hood equipped with a HF resistant sash. II Following digestion, the HF is diluted with distilled water, and the sediment is again concentrated by centrifugation. Once the HF has been decanted, the sediment should be washed in 5% HCl to eliminate silicofluoride crystals, before being thoroughly rinsed with distilled water on a 95µm sieve. 8

Part 1 Part 2 Part 3 Part 4 Sediment Processing Ultimately, the midge remains must be hand-picked from the sediment concentrate. This is most easily achieved by examining small aliquots of the aqueous concentrate in a Bogorov counting tray at 25 to 50 ×. Remains caught in the meniscus are most easily collected at 25 × magnification, whereas remains that have settled to the bottom of the groove used to concentrate It is worth noting that all of the procedures should be sorted at 50 × magnification to ensure that the smallest, first or at least the remains are likely to damage head capsules, and second instar, remains are not result in the loss of some ofoverlooked. the mouthparts used in their identification; thus, whenever possible, the number of processing Although some analysts pick midge remains from ethanol, steps should be minimized. recent safety guidelines recommend that prolonged exposure to ethanol vapours should be avoided. Because there is ample opportunity for incidental sorting of head capsules. 9

Identification Part 3

Part 1 Part 2 Part 3 Part 4 Identification In order to be identified, the midge remains must ultimately be transferred to microscope cover glasses, and mounted in an appropriate medium. The standard procedure in my laboratory is to transfer the remains direcdy from the Bogorov counting tray into a bead of distilled water, resting on a No. 1 thickness, 12 mm round cover glass. After the bead of water has air dried, a drop of Entellan® is used to secure the cover glass to a microscope slide. Photomicrograph of a Dicrotendipes head capsule (scale bar is 50 m). VMP = ventromental plate 11

Part 1 Part 2 Part 3 Part 4 Identification Recently several researchers have independently addressed the question, “How many head capsules must be identified from a sample, to reliably infer past environmental conditions? ”. A consensus appears to be emerging that a minimum of 50, and preferably close to 100 individuals should be identified. This result will be model dependent. Because tolerance-down weighted and weighted averaging partial least squares models are more sensitive to the abundances of rare taxa, such models will likely require larger counts than simple weighted averaging models. 12

Taxonomy Part 4

Part 1 Part 2 Part 3 Part 4 Taxonomy Chironomids Schnell (1998) developed The keys have limited geographic coverage; thus the Holarctic fauna is relatively well known, but identification of larvae from other zoogeographic regions relies on a widely scattered literature. Verschuren (1997) provides the taxonomic basis for future work in east Africa, but no comparable compilation is available for the Neotropical, Oriental, or Australian faunal regions. 14

Part 1 Part 2 Part 3 Part 4 Taxonomy Chaoborus Uutala 1997 provides keys to distinguish among the mandibular remains of many of the common North American species, although some closely related species. Differentiation to subgenus is generally possible on the basis of the size, shape and position of the subordinate tooth associated with each mandible. Simuliidae/мошки/ Simuliiden/蚋科 Currie & Walker 1992 developed a key forsubfossils of North American species groups. Because of the importance of the hypostoma to larval identifications. Like the Chironomidae, black fly larvae are commonly differentiated on the basis of the teeth of the hypostoma. 15

Indictor potential Points：Midge remains were first used as palaeoenvironmental indicators by Gams (1927). Although their significance as hypolimnetic oxygen indicators and potentially as palaeoclimatic indicators. ü Their increased use in recent years can be traced to the development of increasingly large surface-sample data sets, documenting the distributions of midge taxa with respect to climate, salinity and lake productivity. ü To the development of models for quantitatively inferring past environmental conditions from their remains. ü These developments have provided a more solid basis for interpreting fossil stratigraphies. ü Today, midges are widely respected, especially as indicators of climatic change.

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