Chironomid community structure deduced from larvae and pupal exuviae of a chalk stream

Species abundances of Chironomidae (Insecta: Diptera) have often been excluded from studies of benthic river communities because of difficulties associated with sampling and identifying larvae. Chironomid pupal exuviae are easier to collect and identify and could be used to determine community structure if shown to be representative of local larval assemblages. Larvae were sampled along a 20 m chain secured over mid-channel gravels, upstream of two collection points for pupal exuviae. Proportional taxa abundances of pupal exuviae and larvae sampled from 130 m of stream were directly compared by a ² test of independence and also separately fitted to four models of species abundance distribution. Observed proportions of taxa were not independent of the life stage sampled. The greatest discrepancies occurred with species of pupal exuviae that were absent as larvae from the gravel. The log series model provided the best fit with both pupal and larval data. Collections of pupal exuviae had greater species richness and evenness than samples of larvae. This was considered to be a consequence of sampling larvae from the gravel habitat alone.     

The dragonfly delusion: why it is essential to sample exuviae to avoid biased surveys

Odonate populations and species numbers are declining globally. Successful conservation requires sound assessments of both odonate distributions and habitat requirements. Odonates have aquatic (larval) and terrestrial (adult) stages, but most surveys that are used to inform conservation managers are undertaken of the adult stage. This study investigates whether this bias towards adult records in odonate recording is misinterpreting the environmental quality of sites. The habitat focus is farmland ponds, a key feature of agricultural landscapes. We tested whether or not, adult, larval and exuvial surveys lead to similar conclusions on species richness and hence on pond quality. Results showed that pond surveys based upon larvae and exuviae are equally suitable for the reliable assessment of presence/absence of odonates, but that adult surveys are not interchangeable with surveys of larvae/exuviae. Larvae were also found at ponds with no emerging individuals due to changes in habitat quality, therefore presence of exuviae remains the only proof of life-cycle completion at a site. Ovipositing females were recorded at all ponds where exuviae were totally absent hence adult surveys over-estimate pond quality and low-quality ponds are functioning as ecological traps. Highly mobile and generalist species were recorded at more locations than other species. Adult surveys also bias recording towards genera, species and populations with non-territorial mate-location strategies. Odonate biodiversity monitoring would benefit from applying the best survey method (exuviae) to avoid wasting valuable financial resources while providing unbiased data, necessary to achieve conservation objectives.     

Temporal and spatial distribution of chironomid larvae and oligochaetes in two Dutch storage reservoirs

Long-term changes in distribution and taxonomic composition of chironomid larvae and oligochaetes in two water storage reservoirs in The Netherlands were studied. A succession among the chironomid species was observed. In the last 10–15 years chironomid densities varied. Compared with other lakes chironomid densities were high. Densities of chironomids were higher in the littoral zone than in the profundal zone. The opposite was found for oligochaetes. Densities and composition of the chironomid fauna in the two reservoirs were similar.Procladius, Tanytarsus andHarnischia dominated at all depths. However, pupal exuviae samples showed some differences in chironomid taxonomic composition between the two reservoirs. Orthocladiinae, rarely found in bottom samples, abounded in pupal exuviae samples.     

Diversity and seasonality of adult Trichoptera captured in a light-trap at Yuccabine Creek,a tropical Australian rainforest stream

Seventeen light-trap samples were taken over a 20 month period at Yuccabine Creek, an upland rainforest stream in north-eastern Queensland. Seventy-eight species of Trichoptera were recorded from a total catch of 6431 individuals. The fauna was dominated by the Hydroptilidae (25 species and 5131 individuals) and, though composed primarily of Torresian genera, some Bassian elements were recorded. A seasonal pattern of change of abundance was observed with the majority of tax a exhibiting maxima between December and January (summer) and minima between July and September (winter).     

Combined use of two defensive traits in pupae of Scymnus posticalis ladybirds

Coccinellid pupae have various defensive traits, such as keeping their final‐instar larval exuviae and secreting droplets containing defensive chemicals at the tips of glandular hairs. Although each of these traits has been described separately in different species, it is unclear how each defensive trait functions when more than one trait coexists. We found that pupae of the ladybird Scymnus posticalis have two different types of traits; they were partially covered with their own final‐instar larval exuviae, with thick wax structures, and had many glandular hairs secreting transparent droplets on the exposed parts of the body without waxy exuviae (head and medial parts of thoracic and abdominal dorsum). In this study, the defensive effects of these two traits were evaluated against two ant species, Tetramorium tsushimae and Lasius japonicus, which are potential predators. When encountering a pupa, neither ant species were able to make frequent physical contact with the exposed parts of the pupa because of the presence of the waxy exuviae. When touching the exposed body part that was covered with droplets, both ant species immediately stepped backward and then swept their antennae. The droplets suppressed ant feeding when mixed with sucrose solution, suggesting that the droplets contain repellent chemicals. These results indicate that the two traits of S. posticalis pupae (the larval waxy exuviae and the droplets) effectively play defensive roles against ants, functioning as a physical obstruction and a chemical repellent, respectively.     

Gear type,species composition and economic value of fisheries in the mangroves of Pak Phanang,Thailand

Fishing gear and methods, catch composition, annual catch numbers and the monetary value of fisheries based in the mangroves of Pak Phanang, Nakhon Si Thamarat province, Thailand, were studied from September 2004 to February 2005. The fishing gear and methods were surveyed by visual observation and interviews. Sample catches were taken for each type of fishing gear and method. Semi-closed questionnaire surveys were conducted among fishers, local traders, local administrative officers and related organizations to derive information on utilized species, gear and methods, fisher and fishery status, and trading and catch price. The Pak Phanang mangrove fishery has three types of multi-species capture gear: channel traps, gill nets and lift nets. It also has three kinds of single-species (group) gear/methods: crab traps, catfish hooks and hand capture using a long tail fishing boat. A total of 57 fish species in 27 families, and 23 shell fish species in 8 families were recorded from the catch samples. Penaeid shrimp (25%), and ambassid (31%) and mugilid (24%) fishes were the abundant groups in the channel traps, while ariid (36%) and mugilid (19%) fishes were abundant in the lift net catches. Ambassid (42%) fish dominated the gill net catches. Species richness (number of species) varied depending on sampling month and type of fishing gear. The total annual catch and its monetary value were estimated to be 442–551 tons and US $368,038–733,973, respectively. The estimated annual catch per unit area of mangrove was 63–79 kg ha⁻¹, which generated a market value of US $368,038–733,973, respectively. The estimated annual catch per unit area of mangrove was 63–79 kg ha⁻¹, which generated a market value of US 52–105.     

Reduced productivity of Culex pipiens and Cx. restuans (Diptera: Culicidae) mosquitoes in parking area catch basins in the northeast Chicago metropolitan area

From June to September, 2016, 100 catch basins in eight parking areas were monitored weekly for the presence of mosquito pupae in the operational area of the North Shore Mosquito Abatement District (NSMAD) located just north of Chicago, IL, U.S.A. Weekly results from these basins were compared to weekly samples taken from residential street catch basins, the most common type of catch basin treated seasonally by the NSMAD with larvicides. Over the 17 study weeks, residential street basins had a mean rate of productivity (pupae per basin‐visit) 12 times that of parking area catch basins. The two parking area sites with the highest mean rate of productivity were associated with county forest preserves. Productivity in both street and parking area basins was positively associated with the presence of three or more deciduous trees within 20 m of basins and if they were located directly adjacent to curbs. Alternatively, productivity was negatively associated with the proportion of impervious surface within 10 m of basins and weekly rainfall. Findings suggest that reduced catch basin larvicide applications may be appropriate in many parking area sites.     

Efficient isolation method for high‐quality genomic DNA from cicada exuviae

In recent years, animal ethics issues have led researchers to explore nondestructive methods to access materials for genetic studies. Cicada exuviae are among those materials because they are cast skins that individuals left after molt and are easily collected. In this study, we aim to identify the most efficient extraction method to obtain high quantity and quality of DNA from cicada exuviae. We compared relative DNA yield and purity of six extraction protocols, including both manual protocols and available commercial kits, extracting from four different exoskeleton parts. Furthermore, amplification and sequencing of genomic DNA were evaluated in terms of availability of sequencing sequence at the expected genomic size. Both the choice of protocol and exuvia part significantly affected DNA yield and purity. Only samples that were extracted using the PowerSoil DNA Isolation kit generated gel bands of expected size as well as successful sequencing results. The failed attempts to extract DNA using other protocols could be partially explained by a low DNA yield from cicada exuviae and partly by contamination with humic acids that exist in the soil where cicada nymphs reside before emergence, as shown by spectroscopic measurements. Genomic DNA extracted from cicada exuviae could provide valuable information for species identification, allowing the investigation of genetic diversity across consecutive broods, or spatiotemporal variation among various populations. Consequently, we hope to provide a simple method to acquire pure genomic DNA applicable for multiple research purposes.     

黄海中南部不同断面鱼类群落结构及其多样性

基于2006年9月和12月、2007年3月和5月对黄海中南部不同断面的底拖网调查数据,对黄海中南部不同断面的鱼类群落结构、多样性、单位时间的渔获量分布及其与环境因子的关系进行了分析。结果表明,调查中共捕获鱼类109种,其中鲈形目种类最多(45种,占40.18%),其次是鲉形目(12种,占10.71%)、鲱形目(10种,占8.93%)和鲽形目(10种,占8.93%),主要由暖温种和暖水种组成,并且暖水种和暖温种在各断面渔获量中所占的比例随时间不同而有所差异。各断面主要鱼种除小黄鱼Larimichthys polyactis、带鱼Trichiurus lepturus、银鲳Pampus argenteus等种类外,以小型中上层鱼类(鳀Engraulis japonicus、黄鲫Setipinna taty等)和底层经济价值较低的鱼类(黄鮟鱇Lophius litulon、细纹狮子鱼Liparis tanakai等)为主,各断面优势种渔获量均占其总渔获量的50%以上,主要鱼种渔获量均占其总渔获量85%以上。渔获物的营养级主要分布在4.2—4.5、3.0—3.3和3.6—3.9,各营养级渔获量随时间和断面的不同有所变化。鱼类长度谱主要集中在3—24 cm,由南向北长度谱逐渐增大。各断面鱼类群落多样性指数差异不大,与底层温度和深度关系密切。     

Diel emergence patterns of drifting chironomid (Diptera) pupal exuviae in the Aude River (Eastern Pyrenees,France)

Two diel emergence patterns (April and October 1990) of chironomids from a hyporhithral site (4th–5th order) in the Aude River are described. In April, 62 species were collected with a mean hourly richness of 31 (±4). The Orthocladiinae (91%) largely dominated the emergence. The total number of exuviae captured by one drift-net varied from 1300 to 11600 per one hour period. There was a clear bimodal pattern with peaks post dawn (07.00–09.00 hrs) and around sunset (18.00 hrs).In October, the total number of exuviae captured was much lower and varied from 150 to 540 per one hour period with post dawn (06.00–08.00 hrs) and post sunset (18.00 hrs) peaks. Nevertheless, the total species richness (65) was higher as was the mean hourly richness (37±4). The Orthocladiinae (68%) dominated less because of increases in the Tanytarsini (15%) and Chiromini (14%). A diel rhythm appeared in autumn emergence. Most of the Orthocladiinae exuviae were collected during daylight hours, whereas most of the Chironomini and Tanytarsini were sampled during darkness. A majority of the exuviae with a length below 3 mm emerged during daylight, but most of the exuviae above 5 mm length emerged during darkness. The exuviae with an intermediate length (3–5 mm) had an amodal diel emergence pattern. In spring and autumn, the majority of species had a bimodal emergence pattern either by day (Orthocladiinae) or by night (Chironominae). But the smallest species had either an unimodal (Thiennemaniella vittata) or bimodal (Neozavrelia fuldensis) daytime emergence. The diel emergence patterns of 10 of the most frequently recorded species are presented.     

The influence of diel cycle,tidal direction and trawl alignment on beam trawl catches in an equatorial estuary

Synopsis Using a 3 m beam trawl, catch variation in the fish and prawn assemblage of the Labu estuary, Papua New Guinea was investigated during July and December 1981 and September 1984. About six times more organisms, three and a half times the biomass and twice as many species were caught per trawl at night than during the day. The greatest number of species, individuals and biomass were caught just after dusk. With the exception ofSecutor ruconius, there was no significant difference in the catches trawled at ebbing and flooding tides. Over twice as many individuals ofS. ruconius were caught during ebbing tides. Alignment of trawl direction in relation to the tidal current did not have a significant effect on the fish catch, but affected the prawn (Metapenaeus demani) catch. It is postulated that most species are not carried to and fro by tidal currents, but maintain their position in the estuary with respect to the substratum. Only prawns appeared to be carried by the currents. This study indicates that the most representative trawl results in terms of species diversity and abundance in shallow estuaries may be obtained at night and, that in estuaries with a small tidal range, tidal direction and velocity have little influence on catch. It also indicates that analyses of demersal nekton assemblages from daytime only estuarine trawl surveys must be approached with caution.Lizard Island Research Station     

Chironomid pupal exuviae and larvae of two storage reservoirs in The Netherlands

For three years chironomid larvae were collected bimonthly with a grab sampler in two deep storage reservoirs in The Netherlands. Chironomid pupal exuviae were collected monthly, from April to November, with a handnet. Net samples yielded more taxa than grab samples. The taxa found in net samples originated from more habitats, than taxa found in grab samples. The relative contribution of Orthocladiinae was much larger in net samples. Based on the results obtained in the two reservoirs, some advantages and disadvantages of both sampling methods are discussed.     

Fish sampling in the marine-dominated Kariega Estuary,South Africa,using a demersal otter trawl: day/night effects

Very few demersal fish assemblage studies using otter trawls in estuaries have been done in South Africa and none of these have tested for the effects of diel period. This study aimed to test whether diel period affects otter trawl catches in the clear, permanently open Kariega Estuary in terms of both species composition and abundance. Fish were sampled by day and night from 30 October to 1 November 2007 at 15 sites using an otter trawl. More species were collected at night, when there were higher catch rates for all key species, with the exception of Rhabdosargus holubi, which was more abundant during the day. Overall assemblages collected by day and by night were similar, with six species accounting for over 90% of the catch in both day and night samples. Both day and night samples reflected differences related to region, with the highest mean CPUE during day and night sampling being recorded in the head region.     

Emergence patterns of riverine dragonflies (Odonata: Gomphidae) in Hungary: variations between habitats and years

In this paper the results of a six-year study on riverine dragonflies (Odonata: Gomphidae) emergence based on the systematic collection of exuviae are presented. The exuviae were counted to determine variations in species composition, abundance and emergence pattern of gomphids at four different sites along the rivers Tisza and Szamos, as well as at a selected site in five different years. While the number of species decreased, the abundance of exuviae increased downstream the river Tisza. The total numbers of exuviae differed significantly between the dammed and non-dammed sites. The emergence of gomphids varied in initiation, synchronisation and also in duration between sites as well as between years. The onset of emergence was dependent mainly on the species-specific temperature sums, consequently earlier or later emergence resulted from the differences in the spring water temperature. The duration of emergence in G. flavipes and G. vulgatissimus was twice as long at the dammed site, characterised by a higher larval density, as at the other sites. In the degree of synchrony G. flavipes showed the emergence characteristics both of the spring and the summer species. Such interyear variations at the same site might have been attributed to the differences in annual fluctuations in the water temperature, indicating that rising temperatures may influence not only the onset of emergence but the synchrony as well.     

Species composition,seasonal abundance and population dynamics of predatory spiders from cotton field plots of irrigated and semi-arid regions of Punjab,Pakistan

The purpose of the current study was to document the variety of predatory spider species present in the cotton fields of two major cotton-producing districts in Punjab, Pakistan, as well as the population dynamics of those spiders. The research was carried out between May and October 2018 and 2019. Manual picking, visual counting, pitfall traps, and sweep netting were the procedures used to collect samples on a biweekly basis. A total of 10,684 spiders comprising 39 species, 28 genera, and 12 families were documented. Araneidae and Lycosidae families contributed a major share to the overall catch of spiders, accounting for 58.55 percent of the total. The Araneidae family's Neoscona theisi ) was the most dominating species, accounting for 12.80% of the total catch and being the dominant species. The estimated spider species diversity was 95%. Their densities were changed over time in the study, but they were highest in the second half of September and the first half of October of both years. The cluster analysis distinguished the two districts and the sites chosen. There was a relationship between humidity and rainfall and the active density of spiders; however, this association was not statistically significant. It is possible to increase the population of spiders in an area by reducing the number of activities detrimental to spiders and other useful arachnids. Spiders are considered effective agents of biological control throughout the world. The findings of the current study will help in the formulation of pest management techniques that can be implemented in cotton growing regions all over the world.     

Analysis of chlordane-impacted streams using chironomid pupal exuviae (Diptera: Chironomidae)

A method of rapidly assessing streams and rivers using chironomid pupal exuviae was tested on a chlordane-impacted stream near St. Louis, Missouri. Various concentrations of chlordane were found in sediments of Grand Glaize Creek, most likely resulting from soil runoff around housing and business developments throughout the stream's course. Chironomid pupal exuviae and sediment samples were collected concurrently from Grand Glaize Creek on two separate occasions, once in 1988 and again in 1990. Cluster analysis of samples at sites, based on the percent abundances of taxa within habitats and by subfamilies, produced two distinct clusters; one grouping samples with lower chlordane concentrations and the other grouping samples with higher chlordane concentrations. Further analysis showed a trend towards lower percent abundances of taxa living in depositional and transitional/depositional zones (Chironominae and some Tanypodinae) at the higher chlordane site, while the lower chlordane sites had lower percent abundances of taxa within erosional and erosional/transitional zones (Orthocladiinae and some Tanypodinae). These findings support the hypothesis that taxa living in close association to fine organic sediments will be exposed to higher concentrations of chlordane in the stream and more negatively affected than taxa feeding and living in habitats removed from chlordane-bound sediments. Comparisons from the present study were made to related studies revealing similar patterns among the Chironomidae.     

Attachment of Vibrio cholerae serogroup O1 to zooplankton and phytoplankton of Bangladesh waters

Vibrio cholerae serogroup O1, the causative agent of cholera, is capable of surviving in aquatic environments for extended periods and is considered an autochthonous species in estuarine and brackish waters. These environments contain numerous elements that may affect its ecology. The studies reported here examined physical interactions between V. cholerae O1 and natural plankton populations of a geographical region in Bangladesh where cholera is an endemic disease. Results showed that four of five clinical V. cholerae O1 strains and endogenous bacterial flora were attached preferentially to zooplankton molts (exuviae) rather than to whole specimens. One strain attached in approximately equal numbers to both exuviae and whole specimens. V. cholerae O1 also attached to several phytoplankton species. The results show that V. cholerae O1 can bind to diverse plankton species collected from an area where cholera is an endemic disease, with potentially significant effects on its ecology.     

The surface wax composition of the exuviae and adults of Aleyrodes singularis

Long-chain aldehydes, alcohols, hydrocarbons and wax esters were major components of the external lipids of adult Aleyrodes singularis. In exuviae, acetate esters replaced the hydrocarbons as a major component. The major long-chain alcohol and aldehyde from adults were C32 and were essentially the exclusive components of the wax particles. The major alcohol from exuviae was C26 and the aldehydes were C26, C28, C30 and C32. The major acetate esters were C28 and C30 in both adults and exuviae. There were wax esters of similar carbon number in adults and exuviae although the exuviae had a greater amount of wax esters with unsaturated fatty acids. The fatty acid and alcohol composition of the wax esters differed markedly between adults and exuviae. Wax esters of adults had similar amounts of C16, C18, C20, C22 and C24 fatty acids while those from exuviae contained largely C16 and C18. The major alcohol in the wax esters of adults was C22 and those of exuviae were C26 and C28. The distribution of fatty acids and alcohols among wax esters of varying chain length also differed between adults and exuviae: in adults C22 was the major fatty acid found in the dominant wax ester, C44 and the C22 alcohol was the major alcohol and found in wax esters C42 and C44. In exuviae C16 and C18 were the major fatty acids found in most wax esters and a C28 alcohol was the major alcohol found in wax esters C44 and C46, the two dominant wax esters in exuviae. It was clear that the difference in chemistry of the wax esters between the adults and exuviae is not evident unless the acid and alcohol moieties are characterized.     

Diel variation in chironomid (Diptera: Insecta) exuviae abundance and taxonomic richness in near-pristine upland streams of the Greater Blue Mountains World Heritage Area,South-Eastern Australia

We assessed diurnal variation of Chironomidae exuviae in two small upland streams in temperate Australia, during summer. Understanding the diel periodicity of exuviae can be an important consideration for biomonitoring purposes or to investigate adult emergence patterns. We collected 1,813 floating exuviae, comprising 54 taxa from four subfamilies, from flowing water using a drift net. Unlike many northern hemisphere temperate studies, we observed that peak exuviae abundance (7.3 exuviae per m3) and taxon richness (1.7 taxa per m3) occurred in the dusk and night hours, with the lowest numbers (0.9 exuviae per m3) and taxon richness (0.6 taxa per m3) recorded in the late morning to early afternoon. We suggest that this could be an adaptation to avoid stressful weather during the heat of summer days, or it could be to avoid visual predators. The numerically dominant taxa exhibited peak abundance in the dusk/night samples which indicates predominant crepuscular/nocturnal patterns of adult emergence. This pattern was consistent across both streams surveyed. Our taxon inventory rose steeply during the first 24-h occasion, then at a reduced rate during the second and third days of sampling. For flowing water collections of exuviae that utilise drift-netting, we suggest that sampling at all sites includes at least three 24-h cycles and avoids periods of heavy rainfall and increased stream flow.     

Body size regulation in copepod crustaceans

Body size affects survival probabilities, reproductive output and individual fitness in many organisms. In freshwater zooplankton, traits ranging from demographic rates to community composition depend on body size, and predation is most often identified as the selection pressure determining body size. We examined the extent to which stage-specific growth trajectories and body sizes of copepod crustaceans are constrained, independent of selection. We used exuviae shed at each molt to quantify the relationship between size at molting and growth during the subsequent instar for two common, herbivorous calanoid copepods, Boeckella triarticulata and Diaptomus leptopus. Individuals of both species were raised under diets of different food quality or quantity, and at different temperatures. Size at molting varied little among individuals of both species, as a consequence of a persistent negative relationship between size at molting and subsequent (absolute) growth increment. Individuals that were small when they molted grew more during the subsequent instar than individuals that were large. This relationship was statistically significant for nearly all instars of both species raised in different food or temperature conditions, and not affected by food quality, food quantity or temperature. Our results indicate that body size is constrained or regulated over much of the copepod life cycle, independent of the effects of environmental conditions (food, temperature, predation). Received: 26 December 1998 / Accepted: 13 September 1999