John W. McCreadie

Scale, time, space, and predictability : species distributions of preimaginal black flies (Diptera : Simuliidae)

Abstract This study examines species-specific distributions of preimaginal black flies (Diptera: Simuliidae) over two large spatial scales (within and across ecoregions) and two seasons (spring and summer). The study area in the western two-thirds of South Carolina, United States, was divided into three ecoregions (Mountains, Piedmont, Sandhills). The mean correct classification of species distributions among stream sites was 81.3%. Predictability of species distributions varied with spatial scale, location, and time. Species occurrence was not independent of ecoregion; distributions of 12 of the 13 species examined at this scale were predictable on the basis of changes in water column (temperature, percentage dissolved oxygen) and channel characters (velocity, streambed-particle size). However, with the exception of the Mountains during the summer, predicting species distributions within ecoregions was far less successful than predicting distributions across these regions; predictability was particularly poor in the Sandhills. Seasonal effects on predictability were most pronounced in the Mountains. As stream sites became more homogeneous, predictive capability declined. Species-level identifications, aided by cytogenetic techniques, were of paramount importance in recognizing the association between species distributions and stream conditions, emphasizing that considerable ecological information is lost when species are not considered. This study emphasizes the critical role of taxonomic resolution, linked with spatial and temporal scale of observation, in elucidating patterns of species assemblages. It also demonstrates that predictability of species distributions at a fixed scale can vary with geographic location and time.

Environmental factors associated with the distribution of Simulium perflavum (Diptera: Simuliidae) among streams in Brazilian Amazonia

To investigate the aquatic distribution of Simulium perflavum Roubaud, 97 streams were sampled (1995–1996) over a wide ( 12° 57′ S–04° 25′ N; 67° 42′–59° 56′ W) geographic area of Brazilian Amazonia. Simulium perflavum was collected in 40 (41.2%) of the streams sampled and reported for the first time from the states of Rondônia and Acre. Last instar larvae of S. perflavum were analyzed at the cytotaxonomic level, giving added certainty to the species-level identification. At each sampled site, 10 variables were measured (temperature, water velocity, depth, width, discharge, streambed-particle size, riparian vegetation, canopy cover, pH, presence of upstream impoundments). Principal component analysis (PCA) and logistic regression were used to determine significant associations between stream-site conditions and larval distribution. Based on stream-site characteristics the occurrence (presence/absence) of S. perflavum larvae could be correctly predicted 75.3% of the time. Larval distribution showed a significant (p < 0.001) positive association with small, slow, sandy bottomed, open, streams near impoundments. Results agree with similar work in the Nearctic region, suggesting that the general response of black fly distribution to environmental conditions might be universal in nature.

Spatial-temporal distribution of preimaginal blackflies in Neotropical streams

The current study investigates the spatial-temporal distribution of preimaginal blackflies in three a priori established, adjacent areas of Brazil and Venezuela. First we tested the hypothesis that the distribution of individual simuliid species, over two geographic scales, were predictable on the basis of several habitat parameters. Secondly, we determined if local species assemblages remain constant over two spatial axes, i.e., were species assemblages predictable within and between defined regions. Finally we compared the species assemblage between Venezuelan streams sampled in both the wet (October) and dry (February) seasons. As stream conditions changed across a north–south gradient, so did the occurrence of the most common species. This change in species composition from upland to lowland areas is consistent with the patterns of faunal change seen in North American simuliid assemblages. Discriminant Function Analysis showed a strong association between regional demarcations and stream site conditions. These results were paralleled by the strong correspondence between species assemblages and these regions. Thus each region presented both distinct stream environments and species assemblages. Monte Carlo analysis suggests that some if not all species are not only present in both the wet and dry season but that they are continuing to use the same stream sites. Three broad contingent rules for blackfly species assemblages in new world streams are put forward; (i) the ubiquitous nature of simuliids; (ii) species often distribute themselves along an axis of stream size and; (iii) there is a strong and consistent correspondence between regional characteristics of streams and the species assemblage.

Patterns of species richness for blackflies (Diptera: Simuliidae) in the Nearctic and Neotropical regions

Abstract.  1. Patterns of simuliid species richness were examined over a variety of scales at 532 stream sites in the Nearctic (394) and Neotropical (138) regions. In Nearctic streams, species richness of immature blackflies both within and across ecoregions and over two seasons was examined. Stream variables at each site included seston, width, depth, velocity, discharge, conductivity, pH, dissolved oxygen, water temperature, dominant streambed‐particle size, canopy cover, and riparian vegetation. These variables were subjected to a principal component analysis and derived principal components were related back to richness, using regression analysis. At the level of the stream reach, richness was not highly correlated with single‐point measurements of stream conditions.

Ecology of Symbiotes of Larval Black Flies (Diptera: Simuliidae): Distribution, Diversity, and Scale

ABSTRACT Symbioses are major drivers in ecology and evolution. Although nearly omnipresent in flowing waters, they remain poorly studied in these systems. To examine fundamental aspects of the ecology of symbioses in flowing-water systems, we use larval black flies as hosts and various fungi, nematodes, and protists as symbiotes, focusing on aspects of distribution, diversity, and scale. Most symbiotes of larval black flies are considered parasitic, although the dynamic nature of the relationship is becoming apparent for some systems in which it shifts along a continuum involving commensalism, mutualism, and parasitism. Perspective also is moving from a pairwise view of symbiotic associations to a multispecies network of interactions. Distributions of symbiotes are related to scale-dependent processes that influence the hosts and the stream habitats of the hosts; thus, characteristics of streams, as well as hosts, can be useful in predicting spatial patterns of symbiotes. As the taxonomy of symbiotes improves, so too does the understanding of ecological relationships of symbiosis, such as host specificity and patterns of diversity along spatial and temporal scales.

Parasites of Larval Black Flies (Diptera: Simuliidae) and Environmental Factors Associated with Their Distributions

A total of 26,673 midto late-instar larval black flies were collected from 115 stream sites in South Carolina. Host larvae with patent, externally visible infections of nematodes, fungus, or microsporidia were identified to species either morphologically or cytologically. Six parasite taxa were identified: nematodes of the family Mermithidae; the fungus Coelomycidium simulii; and the microsporidia Janacekia debaisieuxi, Polydispyrenia simulii, Amblyospora bracteatalvarians, and Caudospora simulii. Of 43 species of black flies, 25 harbored at least one of these parasite taxa. Records from museum specimens increased the number of infected host species in South Carolina to 34 species. Prevalence of patent infections for each parasite taxon was low, ranging from 0.1 to 6.5% of all larvae. The distribution of nematodes among stream sites was nonrandom and correlated with season, host abundance, and stream-site conditions. The association of nematode distributions with stream parameters might reflect environmental influences on the nematodes during their free-living period and on host susceptibility to infection. Additional keywords: Mermithidae, Coelomycidium simulii, microsporidia Larval black flies (Diptera: Simuliidae) are a major component of the macroinvertebrate fauna in streams and rivers (Adler & McCreadie 1997). They anchor themselves to a silken pad spun on solid substrates (e.g., rocks, trailing vegetation) and filter food from the water column or graze it from the substrate. Larval and pupal development is temperature dependent and requires from one week to half a year (Crosskey 1990). After emergence from the pupa, females of most species mate, acquire sugar for energy and a vertebrate bloodmeal for egg maturation, and find a suitable stream for oviposition. Larvae are hosts of a variety of parasites, especially mermithid nematodes (Mermithidae), microsporidian protozoans (Microspora), and the chytrid fungus Coelomycidium simulii DEBAISIEUX. Preparasitic mermithid nematodes crawl about on the stream substrate and use a protrusible stylet to penetrate the host body (Molloy 1981). Infected host larvae are recognized by the presence of one or more coiled worms visible through the abdominal cuticle. Mermithids either exit and kill the host while it is still in the larval stage or pass into the adult stage, exiting shortly thereafter (Crosskey 1990). Postparasitic worms molt to adults, mate, and deposit eggs in the streambed (Poinar 1981). a Author for correspondence. E-mail: jmccrd@clemson.edu Microsporidian infections cause pathological changes, primarily to the host fat body (Weiser & Undeen 1981). Patent infections are recognized by the presence of large, irregular cysts that distend the host abdomen. Life cycles of microsporidia that attack black flies are not well understood, but larval hosts become infected both by transovarial transmission and by ingesting the free-living spores (Crosskey 1990). Spores might require some form of environmental conditioning before they become infective, and alternate hosts might be required to complete the life cycle (Jamnback 1973; Lacey & Undeen 1987). Larvae with patent infections of the fungus C. simulii are packed with minute, spherical thalli throughout the body cavity. Thalli give rise to spores that are released into the water column after the death of the host (Tarrant 1984). An intermediate host might be required to complete the life cycle (Lacey & Undeen 1987). In the present study, we survey selected parasites of larval black flies in South Carolina. Given that nematodes have free-living stages, we ask whether these parasites occupy a restricted range of stream conditions within the broader range of conditions under which their hosts are found. In other words, can occurrence (presence/absence) of nematodes in a particular host species, at a particular location, be predicted This content downloaded from 157.55.39.84 on Wed, 15 Jun 2016 06:30:20 UTC All use subject to http://about.jstor.org/terms Parasites of larval black flies by local stream conditions? Our objective is to examine factors that can explain parasite distributions, with the tenet that patterns of distribution can provide insight into the basic ecology of these organisms. Other parasites (microsporidia, C. simulii) were collected in numbers too low to address these questions.

Ecology of aquatic Lepidoptera (Crambidae : Nymphulinae) in South Carolina, USA

An ecological study was conducted in May and June of 1995 and 1996 in South Carolina to determine the factors associated with distributions of aquatic Lepidoptera (Crambidae: Nymphulinae). Larvae were found at 65 lotic and lentic sites in three ecoregions (Piedmont, Sandhills, Coastal Plain). Nine species of aquatic Lepidoptera were collected from 12 species of aquatic vascular macrophytes. One to six plant species were used as hosts, depending on the species of lepidopteran; however, the number of host plants used by a lepidopteran was significantly correlated with the lepidopterans frequency of occurrence. Significant habitat associations were found for five species. Langessa nomophilalis (Dyar) was found under the widest range of temperature and width and occurred in both lotic and lentic habitats. Munroessa icciusalis (Walker) was found in lotic and lentic habitats and had the widest range of recorded depths. Parapoynx maculalis (Clemens) occurred at stream sites with lentic-like conditions. Parapoynx obscuralis (Grote) occupied the widest range of pH and was restricted to lotic habitats, and P. seminealis (Walker) was found in both lotic and lentic habitats. Additional species, collected at fewer than 8% of sites, included M. gyralis, P. allionealis, Synclita obliteralis, and S. tinealis. Overall, the distributions of aquatic Lepidoptera in South Carolina were nonrandom and predictable on the basis of habitat characteristics.

Size of the Larval Black Fly Simulium truncatum (Diptera: Simuliidae) in Relation to Distance from a Lake Outlet

ABSTRACT High abundance of filter-feeding lotic insects near lake outlets has been attributed to the high quality/quantity of seston available in this habitat. Accordingly, a decrease in food quality or quantity with increased distance from a lake outlet might be detectable as a decrease in insect size. We examined changes in larval size of the black fly Simulium truncatum within the first 120 m of a stream draining a small lake from the Avalon Peninsula, Newfoundland. The observed decrease in larval size with increased distance from the outlet was consistent with a decreasing food hypothesis. Laboratory experiments also showed that larval size was dependent on food supply.

Long-term emergence patterns of black flies (Diptera: Simuliidae) in northwestern Pennsylvania

Spatial and temporal patterns of black fly emergence at three sites over a 7-year to 11-year period are presented. This study is the longest, continuous collection of emerging black flies ever undertaken. Because ovipositing females were able to enter emergence traps, analysis of emergence patterns for the Simulium vittatum Zetterstedt and S. tuberosum Lundström complexes, was restricted to males. Year, season and stream temperature had significant effects on mean emergence for these complexes. Sampling stations on the same system and within close proximity exhibited synchronous emergence patterns, whereas streams in close proximity but in separate basins showed asynchronous patterns. Dissimilarities might reflect divergent temperature regimes. We suggest that emergence-trap data might provide a less variable picture of community structure than larval data.

Population ecology of cavernicoles associated with carrion in caves of Georgia, USA

The abundance of troglophilic Megaselia spp. (Diptera: Phoridae), trogloxenic Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae), and troglobitic Ptomaphagus whiteselli Barr (Coleoptera: Leiodidae) on carrion was studied in two caves in Georgia, USA. Phorid and leiodid abundance were statistically independent of location in the caves and of time the carrion was available for colonization in a cave. Calliphorid abundance was linked to location in the cave and duration the carrion remained in the cave. The colonization patterns on carrion by cavernicoles differed between permanent and transient cave-dwelling species. Variation could be due to the different reproductive strategies of each species.