Calanoid copepods: an overlooked tool in the control of disease vector mosquitoes

Biological control can assist in the management of disease vector mosquitoes. However, we urgently require the identification of novel and effective agents to aid population management strategies. Quantifying interactions strengths between consumers and resources is central to our understanding of trophic stability, and is relevant within the biological control context. Previously, pPredatory biocontrol of disease vector mosquito species has previously focused extensively on cyclopoid copepods, but prey size refuge effects have been identified as a hindrance to their predatory efficacy. Calanoid copepods have yet to be comprehensively examined in the context of mosquito control, despite their high prevalence, diversity and distribution. Here, we apply functional responses (FRs; resource use as a function of resource density) to examine interaction strengthspredation efficiencies of a recently described ephemeral pond specialist species, the freshwater calanoid copepod Lovenula raynerae Suárez-Morales, Wasserman & Dalu 2015, using different size classes of larvae of the disease vector complex Culex pipiens as prey. Lovenula raynerae effectively consumed C. pipiens larvae across their ontogeny. A potentially population destabilising Type II FR was exhibited towards both early and late instar mosquitoes, indicative of a lack of prey refuge across ontogenetic stages. Attack rates were greatest and handling times lowest for early instar larvae compared to late instar larvae. These traits contrast to other copepods, commonly applied in biocontrol, which are only able to handle early instars, and in much smaller numbers. We thus advocate that calanoid copepods can exert particularly marked predatory impact on lower trophic groups, and that their use in disease vector mosquito control strategies should be further explored

Muddy waters: efficacious predation of container-breeding mosquitoes by a newly-described calanoid copepod across differential water clarities

Mosquito-borne diseases induce unrivalled morbidity and mortality in human populations. In recent times, greater urbanisation has facilitated vector population expansion, particularly of those which proliferate in container-style habitats. To combat increased associated disease risk, we urgently require innovative and efficacious control mechanisms to be identified and implemented. Predatory biological control of vectorially-important mosquitoes can be effective. Despite their high prevalence in freshwater ecosystems, predatory calanoid copepods have yet to be examined comprehensively for mosquito control. Moreover, environmental context-dependencies can cause substantial variations in natural enemy impacts on target populations. Accordingly, improved understanding of the effects of context-dependencies upon predatory biocontrol is needed. Here, we use functional responses (FRs) to examine the predatory impact of a newly-described species of calanoid copepod, Lovenula raynerae, upon larval Culex pipiens prey across variations in prey supply and water clarity. Using outdoor field trials, we assess the viability of L. raynerae in reducing mosquito survival in container-style habitats. Lovenula raynerae displayed destabilising Type II FRs towards larval mosquito prey across all water clarities tested, with overall predation rates remaining largely unaffected across all clarity treatments. In the outdoor experiment, L. raynerae applications resulted in substantial reductions in larval C. pipiens populations, with close to total eradication achieved following the experimental period under higher predator densities. These results demonstrate that environmental context such as water clarity may have little effect on vector control by calanoid copepods, which suggests a predatory reliance on hydromechanical signalling. Further, for the first time, we demonstrate the applicability of calanoid copepods to artificial container-style habitats where mosquitoes proliferate. Therefore, our results indicate that further examination into the applicability of this species group to aid vector biocontrol strategies is warranted

Combined impacts of warming and salinisation on trophic interactions and mortality of a specialist ephemeral wetland predator

Wetlands are of enormous importance for biodiversity globally but are under increasing risk from multiple stressors driven by ongoing anthropogenic environmental change. As the trophic structure and dynamics of ephemeral wetlands are poorly understood, it is difficult to predict how these biodiverse ecosystems will be impacted by global change. In particular, warming and salinisation are projected to have profound impacts on these wetlands in future. The present study examined the combined effects of warming and salinisation on species interaction strengths and mortality rates for two ephemeral wetland species. Using an ephemeral pond specialist copepod, Lovenula raynerae Suárez‐Morales, Wasserman, & Dalu, (2015) as a model predator species, we applied a functional response approach to derive warming and salinisation effects on trophic interactions with a prey species. Furthermore, the effects of a salinisation gradient on mortality rates of adult copepods were quantified. The predatory copepod exhibited type II functional responses towards larval Culex pipiens mosquito prey, owing to high predation rates at low prey densities. Increased temperatures generally resulted in greater predator feeding rates, whilst increased salinities reduced consumption. However, the effects of temperature and salinity interacted: temperature effects on functional responses were suppressed under heightened salinities. Substantial mortality was observed in both male and female adult L. raynerae at salinity levels exceeding 10 parts per thousand. Warming and salinisation substantially altered interaction strengths in ephemeral wetland ecosystems, with implications for ecosystem function and stability. Furthermore, we demonstrated salinisation thresholds for mortality in an ephemeral wetland specialist, showing that salinisation may threaten the persistence of endemic species. The ongoing effects of warming and salinisation may therefore interact to alter trophic dynamics and species composition in ephemeral wetlands. These stressors should be considered synergistically within management practices

Assessing multiple predator, diurnal and search area effects on predatory impacts by ephemeral wetland specialist copepods

Predator-prey interaction strengths can be highly context-dependent. In particular, multiple predator effects (MPEs), variations in predator sex and physical habitat characteristics may affect prey consumption rates and thus the persistence of lower trophic groups. Ephemeral wetlands are transient ecosystems and predatory copepods are often numerically dominant. We examine the interaction strengths of a specialist copepod Paradiaptomus lamellatus towards mosquito prey in the presence of conspecifics using a functional response (FR) approach. Further, we examine sex variability in predation rates of P. lamellatus under circadian and surface area variations. Then, we assess the influence of a co-occurring heterospecific predatory copepod, Lovernula raynerae, on total predation rates. We demonstrate MPEs affecting consumption, with negative non-trophic interaction strength and thus antagonism displayed between conspecific predatory units of P. lamellatus. This antagonism was present irrespective of prey density. Furthermore, we show differences between sexes in interaction strengths, with female P. lamellatus significantly more voracious than males, irrespective of time of day and experimental arena surface area. Predation rates by P. lamellatus were significantly lower than the heterospecific calanoid copepod L. raynerae, whilst heterospecific copepod groups exhibited the greatest predatory impact. Our results provide insights into the predation dynamics by specialist copepods, wherein species diversity and sex affect interaction strengths. In turn, this may influence population-level persistence of lower trophic groups under shifting copepod predator composition

Quantifying reproductive state and predator effects on copepod motility in ephemeral ecosystems

Ephemeral wetlands in arid environments are unique ecosystems with atypical trophic structuring, often dominated by invertebrate predation. Copepod behavioural traits and vulnerabilities to predation can vary substantially according to reproductive status. Gravid female copepods may be more vulnerable to predation due to reduced escape speeds or higher visibility to predators. Here, we quantify how reproductive status modulates horizontal motility rates of the predatory ephemeral pond specialist copepod Lovenula raynerae, and the responsiveness of the copepod to predator cues of the notonectid Anisops debilis. Males exhibited significantly higher motility rates than gravid female copepods, however chemical predator cues did not significantly influence activity rates in either sex. The lack of responsiveness to predator cues by specialist copepods in ephemeral wetlands may result from a lack of predation pressure in these systems, or due to time stress to reproduce during short hydroperiods. In turn, this could increase predation risk to copepods from externallyrecruited top predators in ephemeral wetlands, and potentially contribute to the development of skewed sex ratios in favour of females

Sex demographics alter the effect of habitat structure on predation by a temporary pond specialist

Habitat structure can profoundly influence the strength of interactions between predators and prey. Spatio-temporal habitat structure in temporary wetland ecosystems is particularly variable because of fluctuations in water levels and vegetation colonisation dynamics. Demographic characteristics within animal populations may also alter the influence of habitat structure on biotic interactions, but have remained untested. Here, we investigate the influence of vegetation habitat structure on the consumption of larval mosquito prey by the calanoid copepod Lovenula raynerae, a temporary pond specialist. Increased habitat complexity reduced predation, and gravid female copepods were generally more voracious than male copepods in simplified habitats. However, sexes were more similar as habitat complexity increased. Type II functional responses were exhibited by the copepods irrespective of habitat complexity and sex, owing to consistently high prey acquisition at low prey densities. Attack rates by copepods were relatively unaffected by the complexity gradient, whilst handling times lengthened under more complex environments in gravid female copepods. We demonstrate emergent effects of habitat complexity across species demographics, with predation by males more robust to differences in habitat complexity than females. For ecosystems such as temporary ponds where sex-skewed predator ratios develop, our laboratory findings suggest habitat complexity and sex demographics mediate prey risk

Crkva sv. Križa u Križevcima

When invasive species become integrated within a food web, they may have numerous direct and indirect impacts on the native community by creating novel trophic links, and modifying or disrupting existing ones. Here we discuss these impacts by drawing on examples from freshwater ecosystems, and argue that future research should quantify changes in such trophic interactions (i.e. the links in a food web), rather than simply focusing on traditional measures of diversity or abundance (i.e. the nodes in a food web). We conceptualise the impacts of invaders on trophic links as either direct consumption, indirect trophic effects (e.g. cascading interactions, competition) or indirect nontrophic effects (e.g. behaviour mediated). We then discuss how invader impacts on trophic links are context-dependent, varying with invader traits (e.g. feeding rates), abiotic variables (e.g. temperature, pH) and the traits of the receiving community (e.g. predators or competitors). Co-occurring invasive species and other environmental stressors, such as climate change, will also influence invader impacts on trophic links. Finally, we discuss the available methods to identify new food web interactions following invasion and to quantify how invasive species disrupt existing feeding links. Methods include direct observations in the field, laboratory trials (e.g. to quantify functional responses) and controlled mesocosm experiments to elucidate impacts on food webs. Field studies which use tracer techniques, such as stable isotope analyses, allow diet characterisation of both invaders and interacting native species in the wild. We conclude that invasive species often drastically alter food webs by creating and disrupting trophic links, and future research should be directed particularly towards disentangling the effects of invaders from other environmental stressors

Functional responses can unify invasion ecology.

We contend that invasion ecology requires a universal, measurable trait of species and their interactions with resources that predicts key elements of invasibility and ecological impact; here, we advocate that functional responses can help achieve this across taxonomic and trophic groups, among habitats and contexts, and can hence help unify disparate research interests in invasion ecology

Determinants of Arsenicosis Patients’ Perception and Social Implications of Arsenic Poisoning through Groundwater in Bangladesh

Adverse human health effects ranging from skin lesions to internal cancers as well as widespread social and psychological problems caused by arsenic contaminated drinking water in Bangladesh may be the biggest arsenic calamity in the world. From an arsenicosis patients survey, this paper empirically analyzes the determinants of arsenicosis patients’ perception about chronic arsenic poisoning and social and psychological implications of arsenicosis. In this study, cross-sectional data were collected from the Matlab and Hajiganj Upzillas of Chandpur district which are known to be highly contaminated with arsenic in their underground water. Respondents informed that arsenic poisoning causes a wide range of social and psychological problems. Female respondents were less vulnerable in the case of social problems (p < 0.01) and more vulnerable for the psychological problems (p < 0.001) of arsenicosis than male respondents. The results based on logit analysis showed that education (p < 0.01) and household income (p < 0.05) were significantly correlated to respondents’ perception about arsenicosis. The arsenicosis related special program (s) needs a clear understanding of people’s perception about arsenic exposure for abating the health burden as well as social and psychological problems

Interspecific variation, habitat complexity and ovipositional responses modulate the efficacy of cyclopoid copepods in disease vector control

The use of predatory biological control agents can form an effective component in the management of vectors of parasitic diseases and arboviruses. However, we require predictive methods to assess the efficacies of potential biocontrol agents under relevant environmental contexts. Here, we applied functional responses (FRs) and reproductive effort as a proxy of numerical responses (NRs) to compare the Relative Control Potential (RCP) of three cyclopoid copepods, Macrocyclops albidus, M. fuscus and Megacyclops viridis towards larvae of the mosquito Culex quinquefasciatus. The effects of habitat complexity on such predatory impacts were examined, as well as ovipositional responses of C. quinquefasciatus to copepod cues in pairwise choice tests. All three copepod species demonstrated a population destabilising Type II FR. M. albidus demonstrated the shortest handling time and highest maximum feeding rate, whilst M. fuscus exhibited the highest attack rate. The integration of reproductive effort estimations in the new RCP metric identifies M. albidus as a very promising biocontrol agent. Habitat complexity did not impact the FR form or maximum feeding rate of M. albidus, indicating that potentially population destabilising effects are robust to habitat variations; however, attack rates of M. albidus were reduced in the presence of such complexity. C. quinquefasciatus avoided ovipositing where M. albidus was physically present, however it did not avoid chemical cues alone. C. quinquefasciatus continued to avoid M. albidus during oviposition when both the treatment and control water were dyed; however, when an undyed, predator-free control was paired with dyed, predator-treated water, positive selectivity towards the treatment water was stimulated. We thus demonstrate the marked predatory potential of cyclopoid copepods, utilising our new RCP metric, and advocate their feasibility in biological control programmes targeting container-style habitats. We also show that behavioural responses of target organisms and environmental context should be considered to maximise agent efficacy