Life cycle, microdistribution, larval dynamics, and drift patterns in a stream caddisfly Limnocentropus insolitus (Trichoptera, Limnocentropodidae)

Spatiotemporal variability in Newfoundland capelin (Mallotus villosus) larval abundance and growth: Implications for recruitment

BackgroundDams are important to ensure food security and promote economic development in sub-Saharan Africa. However, a poor understanding of the negative public health consequences from issues such as malaria could affect their intended advantages. This study aims to compare the malaria situation across elevation and proximity to dams. Such information may contribute to better understand how dams affect malaria in different eco-epidemiological settings.MethodsLarval and adult mosquitoes were collected from dam and non-dam villages around the Kesem (lowland), Koka (midland), and Koga (highland) dams in Ethiopia between October 2013 and July 2014. Determination of blood meal sources and detection of Plasmodium falciparum sporozoites was done using enzyme-linked immunosorbent assay (ELISA). Five years of monthly malaria case data (2010–2014) were also collected from health centers in the study villages.ResultsMean monthly malaria incidence was two- and ten-fold higher in the lowland dam village than in midland and highland dam villages, respectively. The total surface area of anopheline breeding habitats and the mean larval density was significantly higher in the lowland dam village compared with the midland and highland dam villages. Similarly, the mean monthly malaria incidence and anopheline larval density was generally higher in the dam villages than in the non-dam villages in all the three dam settings. Anopheles arabiensis, Anopheles pharoensis, and Anopheles funestus s.l. were the most common species, largely collected from lowland and midland dam villages. Larvae of these species were mainly found in reservoir shoreline puddles and irrigation canals. The mean adult anopheline density was significantly higher in the lowland dam village than in the midland and highland dam villages. The annual entomological inoculation rate (EIR) of An. arabiensis, An. funestus s.l., and An. pharoensis in the lowland dam village was 129.8, 47.8, and 33.3 infective bites per person per annum, respectively. The annual EIR of An. arabiensis and An. pharoensis was 6.3 and 3.2 times higher in the lowland dam village than in the midland dam village.ConclusionsThis study found that the presence of dams intensifies malaria transmission in lowland and midland ecological settings. Dam and irrigation management practices that could reduce vector abundance and malaria transmission need to be developed for these regions.

Comparing methods for estimating larval sea lamprey (Petromyzon marinus) density in the St. Marys River for the purposes of control

Measures of larval lake whitefish length and abundance as early predictors of year-class strength in Lake Michigan

Malaria remains a global public health threat. This study investigated the larval habitat of Anopheles mosquito in Osun State, Nigeria and its public health implication. Four larval habitat types were encountered: Ground pool, gutter, container and abandoned tires. 158 specific larval habitats were identified. Inisa 53(33.5%) had the highest larval habitat abundance while Ila had the lowest, 5(3.2%) (p > 0.05). Inisa 45(28.5%) had the highest distribution of ground pool while Ila 5 (3.2%) had the lowest (p > 0.05). Ejigbo 3 (1.9%) recorded the highest number of gutters while Ila 0(0%) had none (p > 0.05). Inisa and Ijebu-Ijesha both recorded the highest larval habitats, 2(1.3%) and 2(1.3%) for containers. Ipetumodu had the highest, 1540(28.8%) relative larval abundance while Ila had the lowest, 584(10.9%) (p < 0.05). Ground pool harbored the highest larvae with larval density of between 0.5 and 6.5 larvae per dip, while gutter had larval density between 0.5 and 1.5 larvae per dip (p > 0.05). The mean larval density was greater than one larva per dip but less than five larvae per dip in the ground pool and gutter but less than 1 in gutter at Ejigbo. Ipetumodu had the highest mean larval density for the ground water pool while gutter at Ejigbo had the lowest (p < 0.05). Ijebu-Ijesha had the highest mean larval density for the gutter. The ground pool had higher mean larval density as compared to gutter (p < 0.05). This study identified the necessity for Anopheles mosquito surveillance through environmental management for effective vector control towards malaria and other Anopheles-borne disease control and eradication in the state.

River discharge/flow exerts fundamental driving effects on the river ecosystem and larval abundance dynamics. In the subtropical Pearl River, China, the species‐specific effects of river discharge on the occurrence of grass carp larvae remain unknown. We performed cross wavelet analysis, using data on the daily density of larvae collected from 2006 to 2013 at a fixed site downstream in the Pearl River, to explore the temporal correlation between river discharge/water temperature and larval density. We further used the conditional random forest and generalised additive models to determine relevant environmental effects on their relationship. Grass carp larvae appeared from late April to early October, but mainly during June and July. River discharge, but not water temperature, showed significant coherence and in‐phase relationship with larval density. For discharge in significant coherence with larval density, it ranged from 4,740 to 28,700 m3/s, with peak discharge from 4,900 to 30,900 m3/s, and the discharge fluctuation state from −16 to 10 days (where − indicates the falling stage and + the rising stage). Maximum daily temperature/water temperature, ammonia‐nitrogen concentration, peak discharge and discharge contributed the most to the variations in coherence and phase relationships between discharge and larval densities over the short timescale (&lt;32 days) and accounted for 22.4% of coherence variation, 19.7% of in‐phase degrees and 15% of variation in phase lagging. These suggest that a combination of ecological regulation and water environment control would be efficient to promote the recruitment of grass carp and relevant freshwater fish species.

We used field and mesocosm experiments to measure effects of southern redbelly dace (Phoxinus erythrogaster), a grazing minnow, on stream ecosystem structure and function. Ecosystem structure was quantified as algal filament length, algal biomass, size distribution of particulate organic matter (POM), algal assemblage structure, and invertebrate assemblage structure, whereas ecosystem function was based on gross and net primary productivity. Our experiments showed that moderate densities of Phoxinus temporarily reduced mean algal filament length and mean size of POM relative to fishless controls. However, there was no detectable effect on algal biomass or ecosystem primary productivity. Several factors could explain the lack of effect of Phoxinus on primary productivity including increased algal production efficiency in grazed treatments or increased grazing by other organisms in fishless treatments. The inability of Phoxinus to reduce algal biomass and system productivity contrasts with experimental results based on other grazing minnows, such as the central stoneroller (Campostoma anomalum), and questions the generality of grazer effects in stream ecosystems. However, environmental venue and the spatial and temporal scale of ecosystem measurements can greatly influence the outcome of these experiments.

BackgroundWater level management has been suggested as a potential tool to reduce malaria around large reservoirs. However, no field-based test has been conducted to assess the effect of water level management on mosquito larval abundance in African settings. The objective of the present study is to evaluate the effects of water level drawdown rates on mosquito larval abundance.MethodsTwelve experimental dams were constructed on the foreshore of the Koka Dam in Ethiopia. These were grouped into four daily water drawdown treatments, each with three replicates: no water-level drawdown (Group 1; Control), 10 mm.d-1 (Group 2), 15 mm.d-1 (Group 3) and 20 mm.d-1 (Group 4). Larval sampling was conducted weekly for a period of 6 weeks each in the main malaria transmission season (October to November 2013) and subsequent dry season (February to March 2014). Larval densities were compared among treatments over time using repeated measures Analysis of Variance (ANOVA).ResultsA total of 284 Anopheles mosquito larvae were collected from the experimental dams during the study period. Most (63.4%; n = 180) were collected during the main malaria transmission season while the remaining (36.6%; n = 104) were collected during the dry season. Larvae comprised four Anopheles species, dominated by Anopheles arabiensis (48.1% of total larval samples; n = 136) and An. pharoensis (33.2%; n = 94). Mean larval density was highest in control treatment dams with stable water levels throughout the study, and decreased significantly (P < 0.05) with increasing water drawdown rates in both seasons. During the main transmission season, anopheline larval density was generally lower by 30%, 70% and 84% in Groups 2, Group 3 and Group 4, respectively, compared with the control dams (Group 1). In the dry season, larval density was reduced by 45%, 70% and 84% in Groups 2, Group 3 and Group 4, respectively, when compared to the control dams.ConclusionIncreased water drawdown rates were associated with lower mosquito larval abundance. Water level management could thus serve as a potential control measure for malaria vectors around reservoirs by regulating the persistence of shallow shoreline breeding habitats. Dam operators and water resource managers should consider incorporating water level management as a malaria control mechanism into routine dam operations to manage the risk of malaria transmission to human populations around reservoirs.

Non-parasitic life cycle of the cattle tick Rhipicephalus (Boophilus) microplus in Panicum maximum pastures in northern Argentina

Summary 1. Channel complexity affects the physical structure, biotic communities and functioning of stream ecosystems. Large wood (LW) is a key element in the creation and maintenance of physically complex stream channels in forested areas. 2. In an attempt to enhance stream habitat quality and ecosystem functioning and to reduce inputs of organic matter to a downstream reservoir, LW was experimentally introduced into four mountain streams in the Basque Country (northern Spain), ranging in channel width from 3 to 13 m. Following a before–after/control–impact (BACI) design, streams were monitored during 1 year prior to wood addition and during 2 years after addition in one control and one experimental reach per stream. 3. Areal cover of benthic organic matter in the entire channel was measured from regular transects and the mass of stored organic matter from random Surber samples. Breakdown of organic matter was assessed in litter bag experiments performed with black alder leaves. When 50% of the initial mass in the bags remained, invertebrates associated with leaf bags were collected. 4. Wood placement produced a 2- to 70-fold increase in the storage of organic matter, especially in thick deposits upstream from wood jams, with values in excess of 2 kg AFDM per m2 in the small streams. The accumulation of organic matter produced by wood introduction decreased with increasing stream size. 5. Despite the large increase in the availability of organic matter, litter breakdown rates were unaffected by the experimental reaches, suggesting large increases in the total amount of organic matter consumed at the reach scale. 6. Numbers of invertebrates and shredders per gram of leaf litter did not respond to wood addition. Average body mass of invertebrates associated with leaf litter showed a non-significant decreasing trend, which might reflect increased recruitment. 7. Although the effects of wood addition can depend on wood stability and stream size, adding LW to restore channel complexity can improve environmental conditions for invertebrate communities and affect stream ecosystem functioning, enhancing the efficiency to use organic matter inputs on a reach scale.

Distribution of Culex (Microculex) (Diptera: Culicidae) in forest cover gradients

Seasonal population densities of Heliothis virescens (F.) and H. zea (Boddie) in the Imperial Valley of California were determined by pheromone-baited trap catches and by egg and larval densities in alfalfa, cotton, and lettuce. Moth populations were present from March to December; low densities during winter and early summer corresponded to conditions favoring winter diapause and summer estivation, respectively. The relative importance of each host in supporting moth populations varied seasonally. The dominant species in alfalfa was H. zea , whereas H. virescens was dominant in cotton and lettuce. The highest population of H. zea in alfalfa occurred in late spring and late summer, in cotton during early summer, and in lettuce during October. The highest populations of H. virescens in alfalfa were found during October, in cotton from July through October, and in lettuce from October through December. Populations in alfalfa and cotton were greater in commercial fields than pesticide-free untreated fields, whereas lettuce populations were greater in untreated fields. Larval mortality from parasitoids and viruses was infrequent except in alfalfa during late spring and early summer.

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.

BackgroundProblems associated with resistant mosquitoes and the effects on non-target species by chemicals, evoke a reason to find alternative methods to control mosquitoes, like the use of natural predators. In this regard, aquatic coleopterans have been explored less compared to other insect predators. In the present study, an evaluation of the role of the larvae of Acilius sulcatus Linnaeus 1758 (Coleoptera: Dytiscidae) as predator of mosquito immatures was made in the laboratory. Its efficacy under field condition was also determined to emphasize its potential as bio-control agent of mosquitoes.MethodsIn the laboratory, the predation potential of the larvae of A. sulcatus was assessed using the larvae of Culex quinquefasciatus Say 1823 (Diptera: Culicidae) as prey at varying predator and prey densities and available space. Under field conditions, the effectiveness of the larvae of A. sulcatus was evaluated through augmentative release in ten cemented tanks hosting immatures of different mosquito species at varying density. The dip density changes in the mosquito immatures were used as indicator for the effectiveness of A. sulcatus larvae.ResultsA single larva of A. sulcatus consumed on an average 34 IV instar larvae of Cx. quinquefasciatus in a 24 h period. It was observed that feeding rate of A. sulcatus did not differ between the light-on (6 a.m. – 6 p.m.), and dark (6 p.m. – 6 a.m.) phases, but decreased with the volume of water i.e., space availability. The prey consumption of the larvae of A. sulcatus differed significantly (P < 0.05) with different prey, predator and volume combinations, revealed through univariate ANOVA. The field study revealed a significant decrease (p < 0.05) in larval density of different species of mosquitoes after 30 days from the introduction of A. sulcatus larvae, while with the withdrawal, a significant increase (p < 0.05) in larval density was noted indicating the efficacy of A. sulcatus in regulating mosquito immatures. In the control tanks, mean larval density did not differ (p > 0.05) throughout the study period.Conclusionthe larvae of the dytiscid beetle A. sulcatus proved to be an efficient predator of mosquito immatures and may be useful in biocontrol of medically important mosquitoes.

In a quadrat sampling made in a 2.4-m stretch. Simulium ochraceum larvae were recovered only from shallow rapids. Lead plates were designed for collecting larvae attached on them. The highest larval density was recorded from the lowest depth (0.2-2.0cm) and the highest velocity (41-66cm/sec). The density increased with velocity increment, but decreased with depth increment. No larva was recorded in the stream of the current velocity less than 10cm/sec. Comparing among the five sampling stretches of 20m each, the increase in discharge was associated with increase both in depth and current velocity, but decrease in larval density, while increase in slope was associated with decrease in depth but increase in both current velocity and mean larval density.