Mayfly Populations Research Articles

AOBLMOA: A Hybrid Biomimetic Optimization Algorithm for Numerical Optimization and Engineering Design Problems.

The Mayfly Optimization Algorithm (MOA), as a new biomimetic metaheuristic algorithm with superior algorithm framework and optimization methods, plays a remarkable role in solving optimization problems. However, there are still shortcomings of convergence speed and local optimization in this algorithm. This paper proposes a metaheuristic algorithm for continuous and constrained global optimization problems, which combines the MOA, the Aquila Optimizer (AO), and the opposition-based learning (OBL) strategy, called AOBLMOA, to overcome the shortcomings of the MOA. The proposed algorithm first fuses the high soar with vertical stoop method and the low flight with slow descent attack method in the AO into the position movement process of the male mayfly population in the MOA. Then, it incorporates the contour flight with short glide attack and the walk and grab prey methods in the AO into the positional movement of female mayfly populations in the MOA. Finally, it replaces the gene mutation behavior of offspring mayfly populations in the MOA with the OBL strategy. To verify the optimization ability of the new algorithm, we conduct three sets of experiments. In the first experiment, we apply AOBLMOA to 19 benchmark functions to test whether it is the optimal strategy among multiple combined strategies. In the second experiment, we test AOBLMOA by using 30 CEC2017 numerical optimization problems and compare it with state-of-the-art metaheuristic algorithms. In the third experiment, 10 CEC2020 real-world constrained optimization problems are used to demonstrate the applicability of AOBLMOA to engineering design problems. The experimental results show that the proposed AOBLMOA is effective and superior and is feasible in numerical optimization problems and engineering design problems.

An improved mayfly algorithm based on Kapur entropy for multilevel thresholding color image segmentation

Multilevel thresholding segmentation of color images plays an important role in many fields. The pivotal procedure of this technique is determining the specific threshold of the images. In this paper, an improved mayfly algorithm (IMA)-based color image segmentation method is proposed. Tent mapping initializes the female mayfly population to increase population diversity. Lévy flight is introduced in the wedding dance iterative formulation to make IMA jump from the local optimal solution quickly. Two nonlinear coefficients were designed to speed up the convergence of the algorithm. To better verify the effectiveness, eight benchmark functions are used to test the performance of IMA. The average fitness value, standard deviation, and Wilcoxon rank sum test are used as evaluation metrics. The results show that IMA outperforms the comparison algorithm in terms of search accuracy. Furthermore, Kapur entropy is used as the fitness function of IMA to determine the segmentation threshold. 10 Berkeley images are segmented. The best fitness value, peak signal-to-noise ratio (PSNR), structural similarity index (SSIM), and other indexes are used to evaluate the effect of segmented images. The results show that the IMA segmentation method improves the segmentation accuracy of color images and obtains higher quality segmented images.

A hybrid chameleon swarm algorithm with superiority of feasible solutions for optimal combined heat and power economic dispatch problem

Combined heat and power economic dispatch (CHPED) is a challenging important optimization task in the economic operation of power systems that aims to minimize the production cost by scheduling the generation and heat outputs to committed units. The interdependency of heat and power production of the CHPED task exhibits non-convexity and non-linear natures in its modeling and optimization. Therefore, this paper introduces a novel hybrid approach comprising chameleon swarm algorithm (CSA) and mayfly optimization (MO), named CSMO, for solving the CHPED problem. The proposed CSMO algorithm has a better capability to evade from the trapping in local optima with faster rate of convergence pattern than the traditional CSA. Also the proposed CSMO algorithm employs the MO’ phase to assist the CSA to search based on deeper exploration/exploitation capabilities as MO utilizes two populations of male and female mayflies with crossover-based matting process. The effectiveness of the proposed CSMO algorithm is validated on CEC 2017 benchmark functions and two systems of the CHPED problem. The obtained results are compared with some successful optimizers. The simulation outcomes are portrayed based on the number of occasions where CSMO performs superior/equal/inferior to the other optimizers by considering the smaller mean values obtained by each algorithm for all test suites. Accordingly, it is exposed that the occasions achieved by the proposed CSMO are 29/1/0, 30/0/0, 30/0/0, 28/2/0, and 30/0/0 against some implemented algorithms, i.e., ISA, GOA, GBO, EO, and the original CSA. Similarly, the number of occasions achieved by the proposed CSMO are 30/0/0, 30/0/0, 30/0/0, 30/0/0, 30/0/0, 29/1/0, and 22/2/6 when the simulations are portrayed against some competitors from literature including the PSO, FA, FFPSO, HPSOFF, HFPSO, HGSO, and Q-SCA, respectively. Furthermore, the results of total cost found by CSMO are 9257.07 $/h for system 1 and 10094.25 $/h for system 2 of the CHPED problem, with percentage of improvement 0.02% and 14.42% on the original CSA, respectively. In addition, further assessments based on the Wilcoxon test, and convergence characteristic are reported. Based on the recorded results, it is portrayed that the CSMO can efficiently deal with the CEC 2017 benchmark functions and CHPED problem.

Population connectivity of aquatic insects in a dam‐regulated, desert river

AbstractHumans have exaggerated natural habitat fragmentation, negatively impacting species dispersal and reducing population connectivity. Habitat fragmentation can be especially detrimental in freshwater populations, whose dispersal is already constrained by the river network structure. Aquatic insects, for instance, are generally limited to two primary modes of dispersal: downstream drift in the aquatic juvenile life stages and flight during the terrestrial winged adult stage. Yet the impacts of large hydropower dams can make rivers uninhabitable for incoming (drifting) juvenile insects, with remaining refugia found only in tributaries. The ability of adult aquatic insects to traverse such river stretches in search of suitable tributary habitat likely depends on factors such as species‐specific dispersal ability and distance between tributaries. To explore the intersection of natural and human‐induced habitat fragmentation on aquatic insect dispersal ability, we quantified population genetics of three taxa with varying dispersal abilities, a caddisfly (Hydropsychidae, Hydropsyche oslari), a mayfly (Baetidae: Fallceon quilleri), and a water strider (Veliidae: Rhagovelia distincta), throughout tributaries of the Colorado River in the Grand Canyon, Arizona, USA. Using 2bRAD reduced genome sequencing and landscape genetics analyses, we revealed a strong pattern of isolation by distance among mayfly populations. This contrasts with caddisfly and water strider populations, which were largely panmictic. Analysis of thousands of informative single nucleotide polymorphisms showed that realized dispersal ability may not be accurately predicted by species traits for these widespread species. Principal components analysis revealed a strong division between caddisfly populations upstream and downstream of Havasu Creek (279 km through the 390 km study reach), suggesting that the geography of the Grand Canyon imposes a dispersal barrier for this species. Our use of genetic tools in the Grand Canyon to understand population structure has enabled us to elucidate dispersal barriers for aquatic insects. Ultimately, these data may be useful in informing effective conservation management plans for understudied organisms of conservation interest.

Population-level variation in neonicotinoid tolerance in nymphs of the Heptageniidae

Anthropogenic activities can have significant ecological and evolutionary consequences on populations and communities. In the United States, neonicotinoid insecticides are widespread across the agricultural Midwest and frequently detected in stream systems. Their effect on Heptageniidae mayflies is a major concern because they are highly sensitive to neonicotinoids and have some of the lowest reported tolerance values of any organism. Our objective was to evaluate population-level variation in neonicotinoid sensitivity. We did so by conducting 96 h half maximal effective concentration (EC5096-h) tests for the neonicotinoids clothianidin and thiamethoxam on populations of Stenacron, Stenonema, and Maccaffertium mayflies and testing for associations with agricultural landcover. Additionally, we collected water samples to assess temporal patterns of neonicotinoid presence in stream habitats. We found variation in neonicotinoid tolerance with EC50 values ranging from 4.9 μg/L to 32 μg/L and 19.8 μg/L to 86.5 μg/L for clothianidin and thiamethoxam, respectively. Agricultural landcover was associated with neonicotinoid tolerance for Stenacron and thiamethoxam but not for other comparisons. Moreover, water samples demonstrated that the amount of agricultural landcover was not a strong predictor of neonicotinoids presence in streams. Our data suggest that populations of Heptageniidae mayflies can vary substantially in neonicotinoid tolerance. Population-level variation should be considered in toxicity assessments and presents the potential for evolved tolerance.

Long-term effects of hydromorphological stream restoration on changes in microhabitats of Ephemera danica (Ephemeroptera) and its population

Abstract Relationships between various techniques of stream restoration and selected characteristics of larvae of Ephemera danica (Muller 1764), were investigated along a small lowland watercourse, the Kwacza (N Poland). Effects of stream restoration were assessed on the basis of abundance, biomass, and body length of mayfly larvae as well as their biological condition (i.e. relation of mean body weight and length) within a decade (2007–2017) at each of 10 various hydrotechnical constructions along a 2.5-km stretch of the watercourse. Our results show that hydromorphological changes in the stream bed were strong stress factors for the mayfly population, especially in the first year of monitoring. In the following years, the applied restoration techniques created windows of opportunity for the population of E. danica which were successfully used by this species, as it increased in abundance and body length and colonized the whole restored stretch of the stream. Finally, 10 years after the river bed transformation, mayfly density increased 4-fold, while larval body length and biomass increased about 40-fold, as compared with the pre-restoration period. The improved habitat conditions of E. danica were observed in the sections where stream banks were strengthened with tree trunks, double groynes, and double semi-palisades to protect the banks against erosion. Surprisingly, the highest increase in larval abundance was recorded in a by-pass zone, an isolated part of the stream bed, which played the role of a refuge. Using redundancy analysis (RDA), we found that the mayfly population development after the stream restoration was primarily due to modified water velocities in the transformed sections and changes in water quality (e.g. higher pH, lower concentrations of N-NO3−). We inferred that the modification of the stream bed has contributed to favourable changes in the studied mayfly population, which constitutes an important food base for the fish fauna.

Risks of Mixtures of Oil Sands Contaminants to a Sensitive Mayfly Sentinel, Hexagenia

Tailings ponds in northeastern Alberta, Canada contain massive amounts of oil sands process water (OSPW) that cannot currently be released due to the toxicity of some components. Limited space and the need for reclamation of oil sands operation sites will necessitate the release of OSPW in the near future. Knowledge of the composition and toxicity of OSPW is lacking yet is crucial for both risk assessment and management planning. This study examines chronic toxicity of a mixture of OSPW components sodium naphthenate and naphthenic acid (NA) to nymphs of the mayfly Hexagenia spp. in control and polycyclic aromatic hydrocarbons (PAH)-spiked sediment treatments. The objective of this study was to determine whether the addition of the PAH-spiked sediment significantly contributed to or masked responses of these sensitive mayflies to mixtures of NA. Mean survival in nymphs exposed to NA and PAH-spiked sediment treatments was reduced by 48% compared to those exposed to the NA mixture alone. Lethal responses were observed in all of the PAH-spiked sediment treatments. However, within PAH-spiked and control sediment treatments, there was no significant difference in nymph survival due to NA concentration, indicating that changes in survivorship were predominantly a reflection of increased mortality associated with sediment PAHs and not to the NA mixture treatment. Sublethal effects on body segment ratios suggest that mayflies exposed to NA and PAH-spiked sediment, as well as those exposed to the highest NA concentration tested (1 mg/L) and control sediment, made developmental trade-offs in order to emerge faster and escape a stressful environment. These results reveal that the release of OSPW to the surrounding environment could cause a reduction in mayfly populations. Mayflies provide ecosystem services and are an important food source for higher trophic levels in both the aquatic and terrestrial communities.

Method to improve the survival of night-swarming mayflies near bridges in areas of distracting light pollution.

Numerous negative ecological effects of urban lighting have been identified during the last decades. In spite of the development of lighting technologies, the detrimental effect of this form of light pollution has not declined. Several insect species are affected including the night-swarming mayfly Ephoron virgo: when encountering bridges during their mass swarming, these mayflies often fall victim to artificial lighting. We show a simple method for the conservation of these mayflies exploiting their positive phototaxis. With downstream-facing light-emitting diode beacon lights above two tributaries of the river Danube, we managed to guide egg-laying females to the water and prevent them from perishing outside the river near urban lights. By means of measuring the mayfly outflow from the river as a function of time and the on/off state of the beacons, we showed that the number of mayflies exiting the river's area was practically zero when our beacons were operating. Tributaries could be the sources of mayfly recolonization in case of water quality degradation of large rivers. The protection of mayfly populations in small rivers and safeguarding their aggregation and oviposition sites is therefore important.

Evaluating factors driving population densities of mayfly nymphs in Western Lake Erie

Abstract Mayfly ( Hexagenia spp.) nymphs have been widely used as indicators of water and substrate quality in lakes. Thermal stratification and the subsequent formation of benthic hypoxia may result in nymph mortality. Our goal was to identify potential associations between recent increases in temperature and eutrophication, which exacerbate hypoxic events in lakes, and mayfly populations in Lake Erie. Nymphs were collected during April–May 1999–2014. We used wind and temperature data to calculate four measures of thermal stratification, which drives hypoxic events, during summers of 1998–2013. Bottom trawl data collected during August 1998–2013 were used to estimate annual biomass of fishes known to be predators of mayfly nymphs. We used Akaike's Information Criterion to identify the best one- and two-predictor regression models of annual population densities ( N /m 2 ) of age-1 and age-2 nymphs, in which candidate predictors included the four measures of stratification, predator fish biomass, competition, and population densities of age-2 (for age-1) and age-1 (for age-2) nymphs from the previous year. Densities of both age classes of nymphs declined over the time series. Population densities of age-1 and age-2 nymphs from the previous year best predicted annual population densities of nymphs of both age classes. However, hypoxic conditions (indicated by stratification) and predation both had negative effects on annual population density of mayflies. Compared with predation, hypoxia had an inconsistent effect on annual nymph density. The increases in temperature and eutrophication in Lake Erie, which exacerbate hypoxic events, may have drastic effects on the mayfly populations.

Polarized light pollution of matte solar panels: anti-reflective photovoltaics reduce polarized light pollution but benefit only some aquatic insects

Photovoltaic solar panels represent one of the most promising renewable energy sources, but are strong reflectors of horizontally polarized light. Polarized light pollution (PLP) associated with solar panels causes aquatic insects to prefer to oviposit on panels over natural water bodies, with potential to negatively impact their global populations as solar energy expands. We evaluate the hypothesis that anti-reflective coatings (ARCs) used to increase the energy efficiency of solar panels will reduce the amount of PLP they reflect, and their attractiveness to aquatic insects. We created artificial test surfaces that mimicked the optical properties of coated and uncoated solar panels and exposed them to wild populations of polarotactic mayflies (Ephemeroptera), horseflies (Tabanidae) and non-biting midges (Chironomidae) used as indicators of PLP. We evaluated the reflection-polarization properties of test surfaces from four different angles of view and under sunny and overcast skies in the visible and ultraviolet parts of the spectrum. Matte (i.e. ARC-coated) sunlit solar panels were strong sources of horizontally polarized light only when the sun was afront and behind, in contrast to uncoated panels which exceeded common polarization-sensitivity thresholds for aquatic insects from all four viewing directions. As predicted by these polarization patterns, horsefly numbers and water-seeking behaviors were significantly reduced by ARCs. Under overcast skies, both matte and shiny (i.e. uncoated) panels were insect-detectible sources of PLP. Matteness modestly reduced the degree of polarization of reflected light, but not sufficiently such that fewer chironomids were attracted to them. Mayflies actually preferred matte panels under overcast skies. ARCs are most likely to reduce PLP and benefit aquatic insects under sunny skies and when used in conjunction with white non-polarizing gridding, but may actually exacerbate the severity of their negative effects under overcast conditions. Consequently, even current ARC technology has a role to play in aquatic insect conservation, but strategic deployment of solar panels away from water bodies and temperate regions may trump these benefits.

Genetic isolation among mountains but not between stream types in a tropical high‐altitude mayfly

Summary Glaciers that directly feed high‐altitude streams create unique environmental conditions that contribute substantially to regional‐scale lotic habitat diversity and biodiversity, including intra‐specific genetic diversity (as population structure) between glacier‐fed and other types of streams (e.g. groundwater‐fed). However, these population‐genetic patterns are thus far only understood for macroinvertebrates in the temperate zone, where strong seasonality and narrow temporal windows for emergence and mating could help drive patterns of genetic differentiation between streams with contrasting temperature, flow, or other environmental characteristics influencing life‐history patterns. Our primary objective was to assess population‐genetic structure between groundwater‐(GW) and glacier runoff‐fed (RO) streams in high‐altitude tropical (relatively aseasonal) basins of the Ecuadorian Andes. Our focal species was Andesiops peruvianus, a baetid mayfly confamilial with well‐studied temperate alpine mayflies. We pursued secondary objectives of evaluating broader scale population‐genetic patterns across mountain ranges for the first time in high‐altitude tropical streams, and evaluating genetic evidence for recovery from population bottlenecks in this volcanically active region. For the primary objective, we collected A. peruvianus (mean N = 16.5 per reach) and a suite of environmental variables from six intra‐basin pairs of GW/RO stream reaches at altitudes 4000–4300 m a.s.l. on three glaciated volcanoes representing two parallel sub‐ranges of the Ecuadorian Andes. We tested for significant GW/RO pairwise differences in haplotype distribution and genetic diversity obtained by sequencing the barcoding region of the mitochondrial cytochrome oxidase I gene. For the broader scale sub‐objectives, we added two unpaired populations (total N = 231) and evaluated genetic structure at nested spatial scales of streams/basins/mountains, and we tested for differences between mountains. We also measured Tajima's D and Fu's FS to evaluate evidence for demographic instability at the scale of individual mountains, each with a different volcanic history. We found no evidence for population structure between GW and RO streams within basins. Population structure among basins within mountains was significant, but only in areas where streams occupied deep, physically isolating canyons. Comparisons between all possible pairs of the three mountains revealed significant structure, but pairwise ΦST was an order of magnitude greater between pairs of mountains occupying different ranges than for the pair in the same range. Indeed, no haplotypes were shared between the two Andean sub‐ranges. All three mountains, regardless of recent volcanic history, showed a significant signature of recovery from recent bottleneck. Our results suggest that strong environmental differences between glacial runoff and groundwater stream types do not isolate these tropical, high‐altitude mayfly populations. Rather, populations are panmictic within basins. Broader scale patterns among mountains suggest that dispersal and gene flow in these tropical streams proceed similarly to temperate alpine systems; that is, relatively strong isolation among mountains but reasonable capacity for gene flow between headwaters in close proximity on a single mountain. A notable difference from the temperate studies is that mayfly populations in Ecuadorian high‐altitude streams appear to be demographically unstable, regardless of the recent volcanic eruption history of the mountain they occupy. Frequent eruptions in this volatile region might affect streams across areas more extensive than a single mountain.

Burrowing mayfly populations in Chequamegon Bay, Wisconsin: 2002 and 2012

Burrowing mayflies (Ephemeroptera: Ephemeridae) are sensitive to pollution and have been used as environmental indicators in the Great Lakes. Hexagenia limbata and Ephemera simulans population abundance and biomass estimates from Chequamegon Bay, Lake Superior, were compared between the years 2002 and 2012 as well as inside and outside the Northern States Power Lakefront Superfund site. Mean abundance was similar and mean biomass of Ephemeridae was slightly less in 2012 than in 2002, most likely due to the occurrence of E. simulans in 2012, a smaller species not collected in 2002. In 2012, mean ephemerid abundance and biomass outside the Superfund site was significantly higher than inside the Superfund site. Biomass was higher in clay, clay with sand, and sand with clay substrates than in fine sand, coarse sand, or wood debris substrates. Substrate in the Superfund site was predominantly wood debris. Future monitoring of ephemerid populations in Chequamegon Bay, and particularly in the Superfund site as clean up begins, would be valuable to establish long-term population trends for these two species and potentially shed light on the habitat requirements of E. simulans, an understudied species in the Great Lakes.

Estimating risks to aquatic life using quantile regression

One of the primary goals of biological assessment is to assess whether contaminants or other stressors limit the ecological potential of running waters. It is important to interpret responses to contaminants relative to other environmental factors, but necessity or convenience limit quantification of all factors that influence ecological potential. In these situations, the concept of limiting factors is useful for data interpretation. We used quantile regression to measure risks to aquatic life exposed to metals by including all regression quantiles (τ = 0.05–0.95, by increments of 0.05), not just the upper limit of density (e.g., 90th quantile). We measured population densities (individuals/0.1 m2) of 2 mayflies (Rhithrogena spp., Drunella spp.) and a caddisfly (Arctopsyche grandis), aqueous metal mixtures (Cd, Cu, Zn), and other limiting factors (basin area, site elevation, discharge, temperature) at 125 streams in Colorado. We used a model selection procedure to test which factor was most limiting to density. Arctopsyche grandis was limited by other factors, whereas metals limited most quantiles of density for the 2 mayflies. Metals reduced mayfly densities most at sites where other factors were not limiting. Where other factors were limiting, low mayfly densities were observed despite metal concentrations. Metals affected mayfly densities most at quantiles above the mean and not just at the upper limit of density. Risk models developed from quantile regression showed that mayfly densities observed at background metal concentrations are improbable when metal mixtures are at US Environmental Protection Agency criterion continuous concentrations. We conclude that metals limit potential density, not realized average density. The most obvious effects on mayfly populations were at upper quantiles and not mean density. Therefore, we suggest that policy developed from mean-based measures of effects may not be as useful as policy based on the concept of limiting factors.

The influence of recruitment on within-generation population dynamics of a mayfly

The relative contributions of recruitment and post-recruitment processes are pivotal to understanding the mechanisms influencing the population dynamics of organisms. We estimated recruitment by oviposition to populations of the mayfly Baetis bicaudatus in multiple streams of one drainage basin in western Colorado, USA, and subsequent changes in larval population densities of one cohort over one generation. Our goal was to compare the potential for recruitment limitation and post-recruitment processes to explain variation in population dynamics of one cohort in streams with predatory fish (brook trout) and fishless streams. We censused Baetis egg masses oviposited in 14 streams during summer 2001, and estimated larval densities of this cohort during September 2001, April and June 2002. There was substantial variability among streams in densities of eggs and subsequent larval densities, with qualitatively different larval dynamics in fish and fishless streams. In fishless streams egg densities were generally lower than in fish streams due to hydrogeomorphic habitat constraints; and increasing egg densities resulted in higher densities of early stage larvae. This pattern was consistent with recruitment limitation of population size of early stages, which persisted until April. In contrast, increasing egg densities in trout streams resulted in lower densities of early stage larvae, consistent with strong density-dependent losses due to post-recruitment processes. In both fish and fishless streams the loss rates of early stage larvae during winter were density-independent; but from April to June the pattern suggests strong density-dependent losses of larvae in fish streams, and weaker, although significant density-dependent losses in fishless streams as larvae developed to late instars from April to June. We conclude that recruitment can limit the population size of early larval stages of Baetis related to the availability of preferred oviposition sites for females; but post-recruitment processes eventually (in lower risk environments) or almost immediately swamp the effects of recruitment on population dynamics especially in fish streams. This study illustrates that the relative influences of recruitment limitation and post-recruitment processes on mayfly population dynamics varies across life stages and among environments with different habitat constraints and predation risks.

Benefits and costs ofLeptophlebia(Ephemeroptera) mayfly movements between river channels and floodplain wetlands

Dramatic drift of nymphs of the mayflies Leptophlebia Westwood, 1840 and Siphlonurus Eaton, 1868 (47 600 individuals/trap per hour) was observed between a southeastern USA river and adjacent floodplain following natural flooding events. Active movements of these nymphs against the water flow were also detected. Large numbers of leptophlebid nymphs reside in floodplains during the winter and spring, but how and why they colonize and develop in temporary habitats is uncertain. We detected few environmental advantages (i.e., temperature, food abundance or quality) for mayflies in floodplains compared with river habitats. Despite this, experiments indicated that mayflies had 36% higher growth rates in the floodplain than in the river and demonstrated tolerance to short-term drying (up to 12 d). Migration entails costs of migrating against flows during daylight when vulnerability to predation is high, colonizing a habitat subject to drying, hypoxia, and supporting amphibian predators, with few apparent benefits. Dispersal into wetlands may be attributed to avoiding swift river flows or exploiting largely fishless habitats. However, dispersal could be an evolutionary relic of behavior beneficial in more northerly habitats; our study populations of Leptophlebia mayflies were at the southern extreme of their range and perhaps operating suboptimally. Our results emphasize the importance of river–floodplain linkages to the ecology of both habitats.

Insecticide susceptibility of Ephemera orientalis (Ephemeroptera: Ephemeridae) and two mosquito species, Anopheles sinensis and Culex pipiens in the Republic of Korea

Field-collected populations of mayflies, Ephemera orientalis were tested for susceptibility to 10 different insecticides using a direct-contact mortality bioassay. Ephemera orientalis subimagoes were susceptible to the insecticides chlorpyrifos, fenitrothion and chlorfenapyr with LD 50 values of 69.7, 78.8 and 81.9 μg/♀, and adults had LD 50 values of 71.9, 78.8 and 85.4 μg/♀, respectively. Susceptibility ratios (SRs) of subimagoes and adults of E. orientalis to the 10 insecticides were 1.0 to1.2 folds. The mayflies showed higher susceptibility to organophosphates than to pyrethroids. The SRs of Anopheles sinensis to E. orientalis were 514 to 1438 folds higher for organophosphates (LD 50 values of 0.05 to 0.23 μg/♀) and 62 to 1155 folds higher for pyrethroids (LD 50 values of 0.13 to 2.41 μg/♀). The SRs of Culex pipiens to E. orientalis were 606 to 3595 folds higher for organophosphates with LD 50 values of 0.02–0.17 μg/♀ and 81 to 1365 folds higher for pyrethroids with LD 50 values of 0.11–1.83 μg/♀. These results indicate that the use of ineffective insecticides will result in unsatisfactory control against field populations of the subimagoes and adults of E. orientalis.

Loss of genetic diversity in the North American mayfly Ephemerella invaria associated with deforestation of headwater streams

Summary 1. Terrestrial dispersal by aquatic insects increases population connectivity in some stream species by allowing individuals to move outside the structure of the stream network. In addition, individual survival and reproductive success (as well as dispersal) are tightly linked to the quality of the terrestrial habitat. 2. In historically forested catchments, deforestation and altered land use have the potential to interfere with mayfly dispersal or mating behaviours by degrading the quality of the terrestrial matrix among headwater streams. We hypothesised that loss of tree cover in first-order catchments would be associated with an increase in population substructure and a decrease in genetic diversity of mayfly populations. 3. To test this hypothesis, we investigated spatial patterns of genetic variation in the common mayfly Ephemerella invaria across a gradient of deforestation in the central piedmont region of eastern United States. Intraspecific genetic diversity and population substructure were estimated from data obtained using fluorescent amplified fragment length polymorphism (AFLP) markers. 4. We found that mayfly populations had low population substructure within headwater stream networks and that genetic diversity was strongly negatively correlated with mean deforestation of the first-order catchments. The large-scale pattern of population substructure followed a pattern of isolation by distance (IBD) in which genetic differentiation increases with geographical distance, but assignment tests placed a few individuals into populations 300 km away from the collection site. 5. Our results show that loss of genetic diversity in this widespread aquatic insect species is co-occurring with deforestation of headwater streams. 6. Most arguments supporting protection of headwater streams in the United States have centred on the role of these streams as hydrological and biogeochemical conduits to downstream waters. Our work suggests that headwater stream land use, and specifically tree cover, may have a role in the maintenance of regional genetic diversity in some common aquatic insect species.

Ecosystem engineering by beavers affects mayfly life histories

1. The North American beaver has been studied as a model ecosystem engineer for many decades. Previous studies have documented physical, chemical and biological impacts attributed to beaver engineering in both aquatic and terrestrial environments. This study focused on the effects of ecosystem engineering by beavers on life histories of a common mayfly and on the potential consequences for mayfly populations. 2. We studied 18 montane beaver ponds of varying size and shape in western Colorado near the Rocky Mountain Biological Laboratory. Our goal was to test whether variation in beaver pond morphology (pond size and shape) explains downstream changes in stream temperature, mayfly size and timing of emergence. 3. Downstream water temperatures varied predictably with pond morphology, being colder downstream of high-head dams and warmer downstream of low-head dams. Pond morphology was also a significant predictor of variation in the size of mature female Baetis bicaudatus (the most abundant mayfly), with larger females emerging downstream of high-head dams and smaller females downstream of low-head dams. The size of male B. bicaudatus was not significantly related to pond morphology or stream temperature. There was no relationship between pond morphology and variation in the timing of emergence of Baetis (males or females) between upstream and downstream reaches. 4. Our results have implications for the effects of beaver ponds on Baetis individual fitness because large Baetis females are more fecund. Therefore, predictable female size variation associated with beaver pond morphology makes it possible to model the effects of beaver activity on local contributions of Baetis to the regional pool of reproductive adults at the catchment scale. Additionally, predictable changes in the size of emerging mayflies may have important consequences for the magnitude of aquatic to terrestrial resource subsidies in beaver-modified systems.

Emergent body size of mayfly survivors

Summary1. Employing field‐deployed mesocosms, we examined the effects of 12‐h pulse and 20‐day press (continuous) exposures of the common agricultural insecticide, imidacloprid, on nymph abundance, emergence patterns and adult body size of Epeorus spp. (Heptageniidae) and Baetis spp. (Baetidae).2. In press exposures, reduced nymph density was driven by reduced survivorship; in pulse exposures, reduced nymph density may reflect increased emergence because of stress.3. Once exposed to imidacloprid, Epeorus and Baetis mayflies developed less and emerged smaller than their control counterparts. Concentrations as low as 0.1 μg L−1 (12‐h pulse) reduced head length in Baetis and thorax length in Epeorus.4. In all of the Baetis and Epeorus examined, effects were only found in males. Male survivorship and body size can affect population dynamics. Sublethal doses of this widely applied agricultural insecticide have the potential to reduce reproductive success of mayfly populations.

The use of in situ and stream microcosm experiments to assess population‐ and community‐level responses to metals

We conducted field and stream microcosm experiments to assess population-level (density, size distribution) and community-level (species richness metrics, multivariate analysis of community composition) responses of macroinvertebrates to heavy metals in the Arkansas River, a mining-polluted stream in Colorado, USA. Experiments were conducted in spring and summer to coincide with early and late developmental stages (i.e., instars) of the mayfly Rhithrogena hageni. Results of field experiments showed significant mortality at metal-contaminated sites during summer when mayfly populations were dominated by small, early instars (mean dry wt = 0.13 mg). In contrast, no significant mortality was observed in spring when organisms were larger (mean dry wt = 1.78 mg). Multivariate analyses based on abundance of dominant taxa clearly separated reference and metal-impacted stations in summer experiments but showed little separation in spring. We observed no significant effects of metals on species richness, number of mayfly species, or EPT (species richness of Ephemeroptera, Plecoptera, and Trichoptera) in.either field experiment. Using stream microcosms, we established concentration-response relationships between heavy metals and R. hageni density, species richness, mayfly richness, and EPT. Density of R. hageni was generally more sensitive to metals than measures of species richness, and summer populations of R. hageni were more sensitive to metals than spring populations. Because the presence of large, relatively tolerant individuals in spring coincided with periods of higher metal concentrations, R. hageni was protected from toxic effects in this system. We conclude that phenology and developmental stage are important factors influencing responses of some aquatic macroinvertebrates to metals. Thus, timing bioassessments to coincide with the presence of these sensitive life stages can improve our ability to detect subtle contaminant effects.