Cytogenetics of New Zealand blackflies of the genus Austrosimulium (Diptera: Simuliidae) 1. The cytogenetics of Austrosimulium australense

Abstract

This study undertakes a cytogenetic analysis of the New Zealand blackfly species Austrosimulium australense (Schiner). The principles of such an approach are outlined, and previous taxonomic studies of the genus Austrosimulium, in particular the taxonomic position of A. australense, are discussed. Populations from North Island localities covering a wide area were sampled and analysed for polymorphisms in the polytene chromosomes, taken from salivary glands of larvae. In all, 1018 larvae from 49 sites were analysed. A polytene chromosome map of A. australense is presented, with details of chromosomal inversions found in salivary gland cells. Three geographical zones are designated, according to the incidence of certain chromosomal polymorphisms.     

Cytogenetics of New Zealand blackflies of the genus Austrosimulium (Diptera: Simuliidae) II. Heterozygote deficiency and non-random association of inversion heterozygotes

We present population cytogenetic data from an analysis of polytene chromosomes of individuals of the common New Zealand blackfly Austrosimulium australense (Schiner). These data show that, in an area of the central North Island of New Zealand (Tarawera), there are, firstly, a number of abrupt changes in inversion polymorphisms between this area and adjacent collection sites. Secondly, there is non-random association of heterozygous inversion pairs in samples from the Tarawera area. Thirdly, we present evidence of a deficiency of heterozygotes for a number of inversions found in this area. We conclude that this may provide evidence for the existence of cryptic species within our samples. We discuss this possibility in terms of the morphological and genetical changes which are likely to occur at speciation, and briefly discuss the mounting evidence for the ubiquity of cryptic species in Diptera.Publication No. 10 from the Evolutionary Genetics Laboratory, University of Auckland.     

The water velocity preferences of Austrosimulium furiosum and Simulium ornatipes (Diptera: Simuliidae) larvae,and the implications for micro-habitat partitioning

The aquatic larvae of two simuliid species, Austrosimulium furiosum (Skuse) and Simulium ornatipes Skuse, which often occur together in Victorian streams, were shown in laboratory experiments to have preferences for different water velocities: larvae of A. furiosum preferred water velocities of 0.2–0.3 m s^–1, and S. ornatipes preferred water velocities of 0.9–1.3 m s ^–1 . Final instar larvae of both species selected slow water speeds of less than 0.25 m s ^–1 prior to pupation. Flow patterns around a cylinder in a laboratory stream were mapped, and the distribution of A. furiosum larvae within the wake, paired vortices and horseshoe vortex was recorded. Larvae selected areas with suitable water velocities and aligned with the flow, providing flow visualization of micro-current speed and direction. The potential for micro-habitat partitioning is discussed in relation to benthic sampling strategies.     

Identification of entomopathogenic Bacillus isolated from Simulium (Diptera, Simuliidae) larvae and adults.

Entomopathogenic bacteria isolated from Simulium larvae and adults from breeding sites in the states of S?o Paulo and Rio de Janeiro, Brazil, were identified as 18 strains of Bacillus thuringiensis and one of B. sphaericus. Most of these strains were serotyped according to their flagellar antigens. However, nine of the B. thuringiensis samples, could not be serotyped and were designated as "autoagglutinating"; they were also shown to be toxic in preliminary tests against Aedes aegypti larvae. Additionally, B. sphaericus was also shown to be toxic towards Culex quinquefasciatus larvae.     

Size selection of latex beads by blackfly larvae (Diptera: Simuliidae) in the laboratory

In laboratory experiments, blackfly larvae collected from a lake outlet, a woodland and a meadow stream were tested for size selection of latex beads of < Ito > 100 μm diameters. 3 suspensions of varying proportions for each size category were supplied to these blackfly larvae in common experiments. Comparisons between the size frequency distributions of particles supplied and the particle compositions in the larval guts showed intra- and interspecific differences and were quantified by calculating Jacobs' electivity index. In all species selection of larger particles increased with the larger larval instars. Although there was a positive selectivity of small particles in some cases, the ingested proportion of large particles increases volumes and biomasses of gut content and may be more important for larval growth than small particles.     

Five Simuliidae (Diptera) from West Cameroon

The male, female, pupa and larva of a new phoretic species of Simulium are described. A new species-group is established for this species and S.diceros, and its systematic position is discussed. Two other new species of Simulium are described from pupal material, and new forms of S.palmeri and S.berghei are recorded.     

Cytotaxonomy of four species in the Simulium perflavum species group (Diptera: Simuliidae) from Brazilian Amazonia

Polytene chromosomes of four members of the Simulium perflavum species group in Brazil are described, and a standard map for the species group is presented. Simulium rorotaense Floch & Abonnenc, S. perflavum Roubaud and an undescribed species (S.‘X’) are chromosomally conservative, each representing a single species with a unique preimaginal habitat. Chromosomal, morphological and ecological evidence indicates that S. maroniense Floch & Abonnenc, previously considered synonymous with S. rorotaense, is a good species. Independent morphological and chromosomal analyses yielded 99.4% agreement in separating larvae of S. rorotaense and S. maroniense. The two species can be distinguished by gill morphology or by a subterminal inversion on the long arm of chromosome III. Simulium maroniense consists of at least four cytotypes, each with different sex chromosomes and autosomal polymorphism profiles and associated with a particular landscape type, altitude, temperature regime or geographical location. Simulium rorotaense and S. maroniense share one unique inversion, as do S. perflavum and S. ‘X’, indicating two pairs of sister species. The anthropogenic S. perflavum probably dispersed into Central Amazonia sometime after the mid-1970s.     

Evaluation of Bacillus thuringiensis as a biocide of blackfly larvae (Diptera: Simuliidae)

Thirteen strains of Bacillus thuringiensis were bioassayed against late-instar larvae of field-collected Simulium vittatum. All 13 strains caused significant blackfly mortality. The mortalities ranged from 64% for the HD 225 strain to 88% for HD 39 at 10 ppm for a 24-hr exposure period. A minimum 24 hr of exposure to a minimum concentration of 10 ppm was required to produce mortalities approximating 90%. The LC₅₀ values for the HD 39 and HD 225 strains were 1.1 and 1.0 ppm, respectively.     

Diel emigration and colonization responses of blackfly larvae (Diptera: Simuliidae) to ultraviolet radiation

1. Total counts of blackfly larvae densities over 30- and 57-h periods in experimental channels during May of 1996 & 1997 indicate that ultraviolet radiation (UV; 290–400 nm) may be important in stimulating emigration.
2. Under experimentally controlled solar UV exposure, larval densities at dawn in UV-shielded channels were 161% and 168% higher than in the UV-exposed channels. Larval densities in UV-exposed channels then decreased by 68.2% and 81.1% between dawn and early afternoon of the two days; density decreases in UV-shielded channels were slight, and not statistically significant, during the same periods.
3. Larvae within UV-exposed channels occupied shaded microhabitats during hours of intense solar radiation, suggesting that simuliid larvae can detect and respond to UV radiation over very short periods of time.
4. A cyclical pattern of UV-induced emigration during hours of increasing solar flux (06.30–13.30) and net immigration in the hours of decreasing solar flux and at night emerged. Thus stream invertebrates may be very sensitive to environmental changes, resulting in either increased UV flux or decreased shading of streams. Diel cycles in invertebrate densities should be taken into account in research designs and sampling protocols in order to identify and interpret correctly results of both periodic surveys and experiments.     

Three new chironomids (Diptera: Chironomidae) from the New Zealand seashore

The adults of Telmatogeton mortoni n.sp. (Clunioninae) and Smittia reinga n.sp. and Smittia whangaroa n.sp. (Orthocladiinae), from the northern New Zealand seashore, are described and figured.     

Feeding by blackfly larvae (Diptera: Simuliidae) forming dense aggregations at lake outlets

1. Larvae of Simulium noelleri formed dense aggregations (>60 larvae cm^?2) at a lake outlet where water passed in a very thin film vertically over wooden planks. Despite the high densities there was sufficient space between larvae to allow water to flow within an aggregation as well as over its surface. 2. Small larvae, occluded within an aggregation, had a faster midgut throughput rate than larger larvae. Both had rates that were similar to those recorded in the literature for a range of habitats and species. The same relationship of throughput rate and larval size was maintained from upstream to downstream across 20cm of an aggregation. 3. Material passed through the midgut of larvae of a given size at a constant rate, indicating that assimilation efficiency of the whole gut contents was low. 4. By colour-banding larval gut contents with fluorescent dye it was possible to demonstrate that faecal pellets are a component of the larval diet in the dense aggregations, especially of small larvae. 5. The abundance of four easily identifiable components of the lake seston were measured from water samples above, and below, a larval aggregation. Particles with a mean diameter of 40 μm, or greater, showed significant reductions in numbers over a stream length of 6cm. Particles of smaller size showed reductions but these were not significant.     

Unsuitability of introduced tiles for sampling blackfly larvae (Diptera: Simuliidae)*

SUMMARY. 1. Blackfly larvae were collected from twenty-one stations in five lake outlets in Southern Quebec. Tiles (total area=500cm²) were introduced in early March, and collected 4 weeks later: randomly selected rocks (30–500cm) from the surrounding area were collected at the same time. 2. Larval densities on tiles were significantly less variable than on rocks. The variance of density estimates on tiles averaged 36% of the observed variance on natural rocks, or 67% when variance on rocks was corrected for average rock size. 3. Tiles significantly overestimated densities on rocks in some streams, and significantly underestimated them in others. These differences could not be explained by microhabitat differences (distance from the lake, depth, current velocity) between rock and tile samples. The bias that tiles introduce in density estimates precludes their use in comparisons among sites.     

Cytotaxonomy, morphology and ecology of the Simulium nobile species group (Diptera: Simuliidae) in Thailand

The polytene chromosomes of 512 larvae of the Simulium nobile species group collected from 16 stream sites in northern, central and southern Thailand were examined. Band-by- band comparisons relative to the established standard chromosome map for the subgenus Simulium distinguished the 2 species of this group, S. nobile and S. nodosum. The differences are mainly due to the position of the nucleolar organizer, pseudochromocenter, and fixed and polymorphic inversions. S. nobile is a monomorphic species, while S. nodosum is a polymorphic species. The morphology of these taxa is described based on the gill filaments and the color of the antennae and female genitalia. S. nobile is distributed in southern Thailand at low altitudes, whereas the distribution of S. nodosum is in the north at higher altitudes.     

Three new mermithids (Nematoda) from Guatemalan blackflies (Diptera: Simuliidae)

Summary The following new species of Mermithidae (Nematoda) are described from Guatemalan blackflies: (a) Gastromermis cloacachilus from Gigantodax wrighti; (b) Isomernis vulvachila from Cnephia pacheco-lunai and (c) Mesomermis guatemalae from Simulium metallicum. All parasites were collected at Encuentros (Department of Totonicapan) in Guatemala. These are the first representatives of Gastromermis and Mesomermis from Central America and M. guatemalae represents the second mermithid species to be described from an American vector of Onchocerca volvulus, causal agent of river blindness. ac]19800728     

Growth,respiration, and assimilation of blackfly larvae (Diptera: Simuliidae) in a lake-outlet in Finland

Summary A field experiment on feeding-rate in blackfly larvae (Diptera: Simuliidae) was conducted in the River Teuronjoki near its origin from Lake Pääjärvi, Finland. Small larvae were seen to feed more rapidly than large larvae.The increase in mean body-tissue weight of the larvae in Teuronjoki was determined and, from this relationship, growth-rate day^-1 for the larvae was obtained.In the laboratory, respiration-rate was determined for larvae of known body-tissue weight. Experiments were conducted when animals were feeding to replicate, as closely as possible, the conditions in the field. Respiration costs were higher for small, than for large, larvae.Estimates of assimilation-rate could be obtained by addition of growthrate and respiration-rate for larvae of given body-tissue weight. As the weight of material ingested per unit of time was known it was therefore possible to calculate assimilation efficiency. The values given in this study are the lowest yet recorded for freshwater detritivores.The study was conducted at Lammi Biological Station, University of Helsinki, Finland     

Ecology and speciation in African Blackflies (Diptera:Simuliidae)

The simuliid fauna of the Ethiopian region is notably isolated, only two of its species occurring elsewhere; the region has 124 described species, and others still undescribed. Simuliid larvae and pupae are adapted to attachment in moving water; adult females may disperse over considerable distances. This paper considers three examples of evident speciation in an ecological context:(1) speciation on afromontane 'islands' (2) the Simulium naevei group and the adaptive significance of the association between the early stages and freshwater crabs; (3) the S. damnosum complex, which includes the widespread vectors of human onchocerciasis. Maps show the distribution of species in these three groups.     

Biology of the New Zealand genus Neolimnia (Diptera: Sciomyzidae)

Abstract

Data are presented on the life cycles of eight species of Neolimnia, an endemic New Zealand genus of snail-killing flies. Habitats, geographical distributions, biological features of adults and immature stages, including adult and larval behaviour and feeding habits, and phenology are discussed. Larvae of subgenus Pseudolimnia live in aquatic environments; those of N. (P.) repo, N. (P.) sigma, and N. (P.) ura prey on aquatic pulmonate snails, but those of N. (P.) tranquilla prey on aquatic prosobranch snails. Larvae of Neolimnia (Neolimnia) castanea, N. (N.) irrorata, N. (N.) obscura, and N. (N.) striata live in terrestrial environments, and apparently prey overtly on terrestrial snails in nature, but will also attack aquatic snails in laboratory rearings.