Conochironomus Freeman: an Afro-Australian Chironomini genus revised (Diptera: Chironomidae)

The chironomid genus Conochironomus is revised, with diagnoses provided for both sexes of adults and, for the first time, the immature stages. The Afrotropical genotype C.acutistilus Freeman and the newly described Australian species C.australiensis (for misidentified acutistilus in Australia), C.cygnus and C.kakadu are described in all stages. C.avicula Freeman is redescribed from the male, and C.deemingi is described as new from the male alone, both from the Afrotropical Region. The Australian species C.cervus is described as new, based on the pupa alone. Comments are made on the ecology and distribution. A previously little-recognized 'tropical' Gondwanan biogeographic explanation for Conochironomus distribution is postulated.     

Food preferences of tanypodinae larvae (Diptera: Chironomidae)

Analyses of the gut contents of larvae of three species of Tanypodinae, collected from four sites in north-east England and Scotland, invariably showed small particles (1–10 µm²), predominantly of detritus, to be more abundant than large particles (10–100 µm²), mostly algae and diatoms. No animal remains, such as carapaces, head capsules and chaetae, or vascular plant fragments were found in any of the intestines. In contrast, food-choice and growth experiments suggested that animal food (particularly Tubificidae and Chironominae larvae) was important in the tanypod diet. In the food-choice experiments, six different foods offered to small (4–7 mm long) and to large (8–12 mm long) larvae of Procladius choreus Meigen, were chosen in the following order: live Tubificidae spp.; detritus; live Chironominae larvae; a mixture of algae and diatoms; live Ostracoda spp.; and live Cladocera spp. However, when the results of the individual choices were examined, it was clear that the small larvae had consumed greater amounts of the small types of food (i.e. detritus, algae and diatoms) in comparison to the large larvae. In the growth experiment, those larvae of P. choreus reared solely on Tubificidae, detritus or Chironominae larvae thrived, while those fed on algae and diatoms, ostracods or cladocerans grew more slowly and fewer survived the experimental period.It was concluded that although Tanypodinae larvae are primarily predators with definite food preferences in ideal foraging conditions, in adverse conditions they will utilize a range of available stand-by foods, the most important of which appears to be detritus.     

Comparative morphology of the larval ventromental plates of European species of Chironomus Meigen (Diptera: Chironomidae)

Abstract. The ventromental plates of larvae of twenty-six cytologi-cally identified species of Chironomus Meigen from Europe are described. Variation in plate features, including size, striae, inner and outer hook series, and ventral surface ornamentation, is reported. A principal components analysis based on plate characters is undertaken, and the taxonomic composition of the resulting groupings is discussed.     

A new genus and species of Chironominae (Diptera: Chironomidae) with wood-mining larvae

Abstract  Xylochironomus kakadu , a new genus and species of wood-mining chironomid, is described from northern Australia. Formerly known by a code 'unknown genus K1', the larvae mine soft immersed timber in tropical Australia. The basal striae on the larval mandible are observed otherwise only in Chironomus Meigen and likely close relatives currently placed in Einfeldia Kieffer. The adult male could key as a tanytarsine, and all stages superficially resemble Polypedilum Kieffer, except for the bare squama and the non-tapered male tergite VIII, and the dorsal larval head sclerites. However, analyses of a morphological data matrix derived from all life history stages support no such relationships. Instead, a relationship to Paralauterborniella Lenz and Apedilum Townes, and at one remove, to Fissimentum Cranston & Nolte and Imparipecten Kieffer is postulated. Larval wood-mining among the early branching Chironomini is evidently frequent, but taxa appear not to form a monophyletic clade.     

Karyotype and morphology of larvae of Chironomus (Chironomidae, Diptera) from the Caspian Sea

Karyotype and morphology of Chironomus sp. larvae from the Caspian Sea have been described. 2n = 8. Chromosomal arm combination is AB, CD, EF, G (cytocomplex thummi). All chromosomes display conjugation of homologues. Centromere areas are of s-type. The nucleolar organizer and two Balbiani rings are disposed in arm C, and another Balbiani ring is in arm B. Half larvae have heterozygotic paracentric inversions in arm D. The larva belongs to salinarius form. One scleritis is colorless, an occipital scleritis is light and irregularly colored. Premandible has 4-5 cogs. Epipharingeal ridge has 18-23 dens. This new species is close to salinarius group, especially to Ch. albidus Konst., but differs from it at the larva stage in the structure of non-massive basal antenna segment, in the presence of large quantity of premandible denses, in light color of occipital scleritis, and in a series of morphometric rates. A similarity berween Ch. paraalbidus and Ch. albidus, on the one hand, and Boeotendipes, on the other one, has been found out.     

Organic matter processing by chironomid larvae (Diptera: Chironomidae)

In laboratory experiments, we used fluorescent dye markers to investigate processing of organic matter by larvae of Psectrocladius limbatellus (Holm.) (Diptera: Chironomidae). 59% of the organic matter used was incorporated into tubes, 39% was present in faecal pellets (both after 24 h), and 2% was found in the larval gut at the end of experiments. Ingested matter passed through the gut rapidly, resulting in the gut being emptied more than 20 times each day. Further 24-h experiments using dye-marked faecal pellets showed that 6% of pellets produced were re-ingested and 12% were incorporated into tubes. There was no preference for conditioned faecal pellets as food over those that had recently been egested and tubes also provided a food reserve on which larvae feed. Chironomid larvae recycle organic matter resulting in its mineralization and their ‘engineering’ has a dramatic effect on the substratum. This revised version was published online in July 2006 with corrections to the Cover Date.     

Some observations on the food of larvae of Procladius bellus (Diptera: Chironomidae)

Analysis of the gut contents of Procladius bellus (Loew) larvae collected in field samples indicated that it was a detrivitore‐omnivore. The observed dietary change from first and second instars (detritivore‐herbivores) to third and fourth instars (omnivores) did not suggest a change in feeding behaviour from detritivore to predator, but rather that the animal material was consumed along with larger detrital material. Small detrital material (1–15 μm) was an important dietary component and detritus in general contributed 50–70% of the overall diet. Diatoms and green algae contributed 15–20%, while blue‐green algae contributed about 10%. Animal material contributed about 5% to second and third instar larvae and 20% to fourth instar larvae.     

Utility of geometric morphometrics for inferring feeding habit from mouthpart morphology in insects: tests with larval Carabidae (Insecta: Coleoptera)

Feeding habits are important life‐history traits in animals; however, methods for their determination are not well established in many species. The larvae of the beetle family Carabidae are an example. The present study tested the utility of geometric morphometrics of mouthpart morphology to infer the feeding habits of carabid larvae. Using Pterostichus thunbergi as a model system, larval feeding habits were inferred using geometric morphometrics of mouthparts and the results were compared with those obtained from rearing experiments. The rearing experiments indicated that P. thunbergi larvae are carnivores that require snails as an essential part of the diet. Through geometric morphometrics, associations between mouthpart morphology and larval feeding habits were confirmed for species in which these two traits are known. A discriminant analysis using these associations classified P. thunbergi larvae as snail/slug feeders, which is a result compatible with the rearing experiments. Geometric morphometrics also revealed that morphological integration and ontogenetic shape change might play roles in the diversification of mouthpart morphology. Overall, these results demonstrate the utility of the geometric morphometrics of mouthparts to infer feeding habit and to clarify the mechanisms of mouthpart morphological diversification in the study group, and the results also serve as a basis for future studies of other insect groups.     

A phylogenetic interpretation of the Brachycera (Diptera) based on the larval mandible and associated mouthpart structures

Abstract. Based on outgroup comparison, the various components of the larval mandible of the Brachycera and their homologies are described. The final instar larval mandible of the Brachycera ground plan is comprised of a distal pointed hook and an inverted 'U'-shaped basal sclerite. The phylogenetic implications of the larval mandibular homologies and associated mouthpart structures for the current cladistic hypotheses of the Nematocera (Wood & Borkent, 1989) and orthorrhaphous Brachycera (Woodley, 1989) are evaluated.
A cladistic analysis of larval mouthpart characters largely supports the hypotheses of Wood & Borkent and Woodley. The presence of a pharyngeal filter is tentatively proposed as a synapomorphy of the Diptera exclusive of the Tipulomorpha and Bibionomorpha. Evidence is presented supporting a sister-group relationship between the Psychodomorpha ( sensu Wood & Borkent, 1989) and the Brachycera. The placement of the Pantophthalmidae in the Stratiomyomorpha is supported by the apomorphic development of the mandibular-maxillary complex and pharyngeal filter with posterior grinding mill. Additional larval mouthpart characters are proposed supporting the concept of the Eremoneura (Empidoidea + Cyclorrhapha). The ground plan of the Empidoidea appears to be characterized by the apomorphic development of a four-component mandible, in which the basal sclerite is subdivided into two connecting sclerites and a ventral sclerite. Morphological evidence is presented supporting the mandibular origin of the mouthhooks of the Cyclorrhapha.     

Incidence of deformed chironomid larvae (Diptera: Chironomidae) in Swedish lakes

The occurrence of deformed mouth parts in recent and subfossil material of mostly Chironomus, Micropsectra and Tanytarsus increased from less than 1 % of the larvae at unpolluted sites or time periods to figures in the range of approx. 5–25% at strongly polluted sites. Deformities occurred in species that are widely separate in taxonomic position and way of living. Several heavy metals are suspected causative agents. Deformities in various mouth parts are illustrated by SEM photographs.     

An ultrastructural study of the larval integument of the midge,Chironomus riparius meigen (Diptera: Chironomidae)

Summary The larval integument of the midge, Chironomus riparius Mg., is unusually thin although it conforms with the normal insect pattern. The cuticle of the post-cephalic segments is about 3 m thick and overlies an epidermis which has an irregular basal plasma membrane resulting in spaces occurring between it and the basement membrane. The ventral tubuli have a similar epidermis but the cuticle is somewhat thinner. The anal papillae have the thinnest cuticular covering with a uniquely folded epicuticle of variable thickness, and their epidermis has the characteristics of a transporting epithelium. No evidence of pore canals could be found in the cuticle of any part except the head capsule which has a remarkably smooth epicuticle and a distinct layer which may represent the exocuticle. There are no spaces between the basement membrane and basal plasma membrane of the epidermis in the head. Ultrastructural evidence would suggest that gaseous exchange can occur across most of the post-cephalic integument.The author is indebted to Mrs. L. Rolph and Mr. R.L. Jones for their technical assistance     

Fatty acid composition of aquatic insect larvae Stictochironomus pictulus (Diptera: Chironomidae): evidence of feeding upon methanotrophic bacteria

Larvae of the chironomid Stictochironomus pictulus were collected from Lake Biwa, central Japan. Both the fatty acid composition of the total lipid fraction and the carbon stable isotope ratios of whole larvae were determined. Larvae showed δ¹³C values of −57.4‰ to −62.4‰, similar to the values of methane recorded from the lake sediments. A high level of monounsaturated fatty acids (MUFAs; approximately 50% of total fatty acids) and an extremely low level of n-3 series polyunsaturated fatty acids (PUFAs) in the total lipids of S. pictulus indicated a predominantly bacterial nutrition for this species. Moreover, chironomid tissues contained large amounts of the Type I methanotroph group-specific fatty acid, 16:1(n-8) (approximately 8% of total fatty acids). This is the first time such a fatty acid biomarker has been described from freshwater invertebrates. The data suggest that S. pictulus larvae directly feed upon methanotrophic bacteria.     

Some carotenoids in Chironomus annularius Meig. larvae (Diptera : Chironomidae)

Summary The author investigated the presence of various carotenoids in the body of the larvae of the Chironomus annularius MEIG. moquito (Diptera: Chironomidae) by means of columnar and thin-layer chromatography.The investigations revealed the presence of the following carotenoids in the larvae: -carotene, -carotene, canthaxanthin, cryptoxanthin, lutein, astacene and a kind of xanthophyl which was not possible to identify more closely.     

Morphological deformations of hard-chitinized mouthpart structures in larvae of the genus Chironomus (Diptera,Chironomidae) as the index of organic pollution in freshwater ecosystems

Deformations of hard-chitinized mouthpart structures (mentum and mandibles) in larvae of the genus Chironomus affected by organic pollution have been studied. A system for the quantitative assessment of these structures has been developed. Indices for the severity of mental and mandibular deformation have been calculated. They allow one to determine the pollution of freshwater ecosystems by toxic organic substances.     

Larval mouthpart deformities in Procladius paludicola Skuse (Diptera: Chironomidae) from the Murray and Darling Rivers,Australia

A high incidence of ligula (mouthpart) deformities is reported for the larvae of Procladius paludicola Skuse (Diptera: Chironomidae) collected from sites on the Murray and Darling Rivers, Australia. This is the first report of deformities in Australian freshwater insects, and is discussed in relation to known toxic pollutants within the catchment.     

Identification of instars and species in some larval Polypedilum (Polypedilum) (Diptera: Chironomidae)

Instars II and III of Polypedilum aviceps Townes, Polypedilum convictum (Walker), and Polypedilum illinoense (Malloch) can be identified to species by associating them with instar IV because key taxonomic characters remain relatively unchanged from instar to instar. Instars I cannot be identified to species or genus unless they are associated with older, identifiable larvae reared from the same egg masses. No single character evaluated on slide material can be used to clearly separate instars in all three species. Larvae of P. aviceps can be separated into instars based on any four of seven characters; P. convictum by either of two characters; and, P. illinoense by a combination of two characters. Changes in structures of instars II, III, and IV are described for all three species. Growth ratios for some structures are compared and discussed with regard to Dyar's Rule.     

Particulate material and midge larvae (Chironomidae: Diptera) in an upland river

The density of midge larvae (Chironomidae), which dominate the stone-surface fauna (81.3 ± 4.9% of the community by number) in an upland stream in northeast England is regulated by the amount of particulate material available. The amount of material depends on the deposition of suspended particles and on epilithic algal growth. Spates, characteristic of this type of stream, result in scouring and denudation of rock surfaces, preventing the build-up of epilithic material and limiting larval densities by regulating the availability of food and tube-building material. Detritus is the main type of particle in suspension throughout the year (66 ± 6%); detritus and diatoms the chief epilithic kind (65 ± 4 and 29 ± 4% respectively). The probable effects of flow amelioration, resulting from the formation of the proposed Kielder Reservoir are discussed.     

Effects of fish predation on larval chironomid (Diptera: Chironomidae) communities in an arctic ecosystem

Chironomid communities were analyzed in systems with three types of predator regimes to determine hierarchical effects of predation; ponds without fish present, lakes with slimy sculpin (Cottus cognatus) present, and lakes with slimy sculpin present along with burbot (Lota Iota) and lake trout (Salvelinus namaycush). Samples were collected by coring bare sediment habitats in 4 systems of each type near the Toolik Lake field station in northern Alaska. Lakes with burbot and lake trout present in addition to slimy sculpin displayed significantly higher (P<0.05) biomass, density, richness, and diversity. This is likely due to the increased complexity of the predator regime. Ponds without fish had a significantly greater percentage of predacious chironomids present.     

Larval morphology and Karyotype of Cladopelma viridula (Diptera, Chironomidae)

The larval morphology and karyotype of Cladopelma viridula are described.