Infestation Pressure Research Articles

Effects of grape phylloxera leaf infestation on grapevine growth and yield parameters in commercial vineyards: a pilot study

Grape phylloxera (Daktulosphaira vitifoliae) can infest both roots and leaves of Vitis species. In commercial vineyards planted with Vitis vinifera scions grafted on rootstocks, grape phylloxera infestation is generally limited to root feeding. Vineyards are, however, increasingly subjected to vineyard-wide foliar infestations that last throughout the growing season. While some vineyards are affected by the infestation pressure of external leaf-feeding populations, other annually affected V. vinifera vineyards do not have these in their vicinity. Much is known about the damage potential of grape phylloxera root feeding; however, data on how phylloxera leaf infestation affects V. vinifera grapevines in commercial vineyards are lacking. This study, therefore, aimed to assess whether grapevine growth and yield are affected due to leaf infestation as it occurred in three commercial vineyards in the study area. Treatments were based on phylloxera leaf infestation and additional defoliation. Single-leaf carbon acquisition was measured with gas exchange analyses on healthy and galled leaves. Pruning weight and internode length were measured to assess the effect of leaf infestation and the effect of plant growth and vigour on leaf gall outbreaks. Yield quantity and quality were measured, and grapes were vinified for sensory analyses. Furthermore, using enzymatic analyses, non-structural carbohydrates were analysed in perennial wood. A significant decrease in sugar content in grapes (10 %) and starch reserves in perennial wood (11 %) was found in the most heavily infested vineyard. Grape must of infested plants in another vineyard furthermore showed a significantly higher level of titratable acid (7.5 %). Significant infestation effects seen in one vineyard were not significant in the other two vineyards. No significant differences were seen for carbon acquisition, harvest quantity, wine sensory analysis, pruning weight or internode length. The overall effect of phylloxera leaf infestation in the studied vineyards was, therefore, marginal. Grapevine vigour did not differ between infested vines, insecticide-sprayed vines, and vines on which no leaf infestation outbreaks took place. By analysing phylloxera leaf infestation under field conditions, these preliminary results form a basis for future long-term field studies about phylloxera leaf feeding on Vitis vinifera within the context of other biotic and abiotic plant stresses.

Modelling salmon lice-induced mortality of wild salmon post-smolts is highly sensitive to calibration data

Salmon lice from fish farms in open net pens pose a threat to the survival of wild salmon post-smolts migrating through areas with high farm and lice densities. Reliable estimation of this mortality is fundamental for the sustainable management of aquaculture in such areas but is challenged by considerable uncertainty about several of the processes that link reported lice numbers in fish farms to post-smolt mortality. Utilising recent access to lice data from post-smolt trawling, we revised a virtual post-smolt model that estimates salmon lice-induced mortality of seaward-migrating wild salmon post-smolts. We also assessed the sensitivity of model results to model assumptions that differ among the virtual post-smolt models currently being used as management support in Norway. The spatiotemporal variation in infestation pressure along the entire Norwegian coast was calculated based on monitoring data for salmon lice, temperature and fish abundance in all Norwegian salmonid farm locations. The revised model integrates lice data from sentinel cage experiments and post-smolt trawling to quantify the spatiotemporal variation in infestation rate of wild post-smolts from the spatiotemporal infestation pressure, while also estimating the effect of calibration data type on infestation rate. Results show 10 times higher infestation rate in trawl-caught post-smolts than in post-smolts from sentinel cage experiments. Mortality estimates calibrated to trawl data are more sensitive to assumptions about possible density dependence in lice infestation rate than to assumptions about migration speed. These findings contribute to explaining why different virtual post-smolt models provide different estimates of salmon lice-induced mortality.

Salmon louse infestation levels on sea trout can be predicted from a hydrodynamic lice dispersal model

AbstractThe abundance of the parasitic salmon louse has increased with the growth in aquaculture of salmonids in open net pens. This represents a threat to wild salmonid populations as well as a key limiting factor for salmon farming. The Norwegian ‘traffic light’ management system for salmon farming aims to increase aquaculture production while securing sustainable wild salmonid populations. However, this system is at present solely focusing on mortality in wild Atlantic salmon, while the responses of sea trout with different ecological characteristics are not included.We analyse lice counts on sea trout from surveillance data and use Bayesian statistical models to relate observed lice infestations to the environmental lice infestation pressure, salinity and current speed. These models can be used in risk assessment to predict when and where lice numbers surpass threshold levels for expected serious health effects in wild sea trout.We find that in production areas with the highest density of salmon farms (West coast), more than 50% of the sea trout experienced lice infestations above the levels of expected serious health effects.We also observed high lice infestations on sea trout in areas with salinities below louse tolerance levels, indicating that fish had been infested elsewhere but were returning to low‐saline waters to delouse. This behavioural response may over time disrupt anadromy in sea trout.The observed infestations on sea trout can be explained by the hydrodynamic lice dispersal model, which provides continuous estimates of lice exposure along the whole Norwegian coast. These estimates, which are used in Atlantic salmon research and management, can also be used for sea trout.Synthesis and applications. Wild sea trout, spending its entire feeding migration in fjords and coastal areas, is at higher risk than wild Atlantic salmon to lice infestations from industrial salmon farming. The high levels of lice infestation we observed on sea trout question the environmental sustainability of the current aquaculture industry in areas with intensive farming. We discuss the complex responses of sea trout to salmon lice and how the Norwegian ‘traffic light’ management system may include data on sea trout.

Weeds and Their Responses to Management Efforts in A Changing Climate

Crop production is a constant battle with weeds, in which weeds, generally, are victorious. Therefore, rather than channeling our efforts into the development of a “silver bullet” to control weeds, the focus should be on sustainable weed management in both natural- and agro-ecosystems. However, sustainable weed management can be a challenge in the context of global climate change. Over the past few decades, global climate change, mostly indicated by phenomena such as increased atmospheric temperature and elevated CO2 levels, is evident due to human activities and natural events. These phenomena also affect regional/local climate, resulting in significant influences on the agricultural systems of a particular region. Rising CO2 levels may give comparative advantages to C3 plants through increased photosynthesis, biomass production and yield, compared to C4 plants. Plants with C4 photosynthetic pathways, on the other hand, are likely to benefit more from rising global temperatures than C3 plants. Thus, the differential responses of C3 and C4 plants to climate change may alter crop–weed interactions and competition outcomes, most likely at the expense of the crop. Climate change will likely cause shifts in weed community compositions, their population dynamics, life cycle, phenology, and infestation pressure. Some weed species may go extinct, while some others may become more aggressive invaders. Weeds are, generally, colonizers and have some unique biological traits and ecological amplitudes that enable them to successfully dominate crops in a habitat with changed environmental conditions. Moreover, climate shifts, especially erratic rainfall and drought, may affect herbicide selectivity and efficacy or the success of bio-control agents resulting in an establishment of a mixed and complex population of C3 and C4 weed species adding to the complexity of weed management. Although elevated CO2 levels will stimulate the productivity of major C3 crops, most troublesome agricultural weeds will likely be more responsive to a rise in CO2 than crops, and thus may dominate the agro-ecosystem. It is predicted that, as temperature rises, the majority of the C4 weeds will flourish and will pose serious crop yield losses. Understanding and assessment of the impact of simultaneous changes in multiple climate factors and their complex interactions on crops and weeds are therefore necessary to formulate an adaptive weed management approach and build resilience. Moreover, strategic policies and strong actions need to be taken to reduce the root causes of CO2 and other greenhouse gas emissions to minimize the impact of climate change on weed biology and management.

Optimal fine fescue mixture seeding dates in the northern United States

AbstractResearch is lacking on best establishment practices of fine fescues (Festuca spp.), such as optimal seeding timings, which are well known for other cool‐season turfgrasses. Our objective was to document establishment and determine optimal seeding timings for mixed stand of fine fescue in multiple cool‐season climate zones in the United States. From 2019 to 2020, an experiment was replicated across four locations in the northern United States to investigate nine monthly fine fescue mixture seeding timings from March through November. Fine fescue seedling emergence typically hastened as temperatures increased during the growing season, and emergence required 6.1–9.4 d when soil temperatures were within a range of 15–25 °C. Final grid count data across multiple sites indicated that seeding fine fescues in August, September, and at times, July, will likely produce the best establishment with the lowest weed infestation pressure, and there may be more flexibility in seeding timings in a Mediterranean climate, such as Oregon. Seeding fine fescues in the early‐spring or late‐autumn can be more unreliable because of greater likelihood of weed infestation, suboptimal growing conditions, and potential of a late‐autumn seeding to act as an unintended dormant seeding. Results indicate the weed invasion pressure of specific weeds will vary depending life cycle of weed and seeding time of year. Overall, seeding a fine fescue mixture in August or September will increase likelihood of success in cool‐season climate zones in the United States with a wider seeding window when planting in Mediterranean climates.

Parasitic copepod (Lernanthropus kroyeri) on caged sea bass (Dicentrarchus labrax): An estimation of abundance and internal infestation pressure

Infestation by parasitic copepods is a substantial problem in the cage culture of European sea bass (Dicentrarchus labrax). The Copepoda parasite, Lernanthropus kroyeri (Lernanthropidae), is one of the threats to the mariculture of sea bass. In the present study, we evaluated the data of abundance for L.kroyeri pre-adults and adult males (PAAM) and ovigerous adult females (AFo ) to estimate the internal infection pressure (IIP) in the same cage environment. The sea bass infested by L.kroyeri was collected from grow-out sea cages located in Gulluk Bay (Turkey) in September and October 2019. Mean fish weight and length of sea bass were 75.79±1.66g and 21.40±0.56cm, respectively. The fixed lag method was used to predict the abundance of L.kroyeri adult females. The overall prevalence of L.kroyeri was 60%. The mean abundance of PAAM and AFo varied from 0.8±0.24 to 2.5±0.67 and 2.9±0.40 to 4.3±0.55, respectively. The abundance of AF was strongly correlated with PAAM. The pattern of AFo and PAAM was interpreted as an indication of the continuous infestation of L.kroyeri on sea bass. Our results showed that the correlation of AFo abundance for five consecutive weeks was significant, representing the main determinative factor for the continuity of the parasitic load. In our approach, internal infestation pressure is the quantitative estimation of the potential infective copepodids, which are mainly characterized by AF abundance and the prevalence. We predicted that the internal infestation pressure could be high, even exceeding the 50.000×106 potential infective copepodids for one sea cage with the fish density of 20 sea bass/m3 .

Estimating the dispersal of Lepeophtheirus salmonis sea lice within and among Atlantic salmon sites of the Bay of Fundy, New Brunswick.

The objective of this study was to estimate the impact of infestation pressures on the abundance of the parasitic sea louse, Lepeophtheirus salmonis, in the Bay of Fundy, New Brunswick (NB), Canada, using the Fish‐iTrends database for the years 2009–2018. Infestation pressures were calculated as time‐lagged weighted averages of the abundance of adult female (AF) sea lice within a site (internal infestation pressure: IIP) and among sites (external infestation pressure: EIP). The EIP weights were calculated from seaway distances among sites and a Gaussian kernel density for bandwidths of 5 to 60 km. The EIP with a bandwidth of 10 km had the best fit, as determined with Akaike's information criterion, and historical AF sea lice abundance. This estimated dispersal distance of 10 km was similar to previous studies in Norway, Scotland and in New Brunswick. The infestation pressures estimated from empirical AF sea lice abundance within and among sites significantly increased the abundance of AF sea lice (p < .001). This study concludes that sea lice burdens within Atlantic salmon farms in the Bay of Fundy, NB, are affected by within site management and could be improved by synchronizing treatments between sites.

Profitability of farm-scale management strategies against the boll weevil in the tropics: case study from the Colombian Caribbean

Decision making in pest management is a challenging task. While pest dynamics are often quite uncertain, such decisions are often based on tenuous assumptions of certainty (economic injury levels and marginal utility approximations). To overcome such assumptions and adequately consider uncertainty, we apply decision analysis to evaluate management strategies used by farmers in the Colombian Caribbean against the boll weevil (BW). We represent the decision to protect the crop using partial budget analysis. This allows us to capture key properties of BW control strategies, while accounting for uncertainty about pest infestation pressure, control effectiveness and cotton yield and price. Our results indicate that proactive pest management is more efficient than reactive control given the current BW infestation pressure. However, farmers may prefer the reactive strategy, since they have experienced seasons with low infestation pressure where no insecticide applications were required. The proactive strategy, in contrast, requires scheduled pesticide applications in all years. Results show that in seasons with high infestation pressure the expected revenues of the reactive strategy tend to decrease, mainly because more spray applications are required when fields are heavily infested by the weevil. Value of information analysis revealed that uncertainties related to the start of the infestation, loss damage rate and attainable yield have the greatest influence on the decision recommendation for crop protection. Narrowing these key knowledge gaps may offer additional clarity on the performance of the current management strategies and provide guidance for the development of strategies to reduce insecticide use. This is particularly important for the promotion of the proactive strategy, which, under the current infestation pressure, has potential to reduce insecticide use. While economic injury levels can only be applied to responsive measures, our approach of partial budget analysis under uncertainty allows us to assess and compare both responsive and preventive measures in the same methodological framework. This framework can be extended to non-pesticide control measures.

The Efficacy of Seed Treatments on Major Sugar Beet Pests: Possible Consequences of the Recent Neonicotinoid Ban

Sugar beet production remains unprotected after the ban on neonicotinoids, while pest pressure is increasing. Although the organic approach to agriculture is highly welcomed, the question remains whether it will be possible to grow sugar beet without pesticides. The aim of this study is to determine the efficacy of seed treatments with neonicotinoids on the main sugar beet pests, to determine the susceptibility of the pests under the specific climatic conditions and to discuss possible consequences of the ban of neonicotinoids on the future of sugar beet production in southeast Europe. The study was conducted in two different climatic regions in Croatia in two consecutive years. The tested variants were: seed coated with imidacloprid, seed coated with a combination of thiamethoxam and teflutrin and untreated control. Our results showed that seed coatings with imidacloprid and thiamethoxam provided satisfactory protection against wireworms, flea beetles and sugar beet weevils at low population pressure. These pests are regular pests of sugar beet in southern and eastern Europe and therefore need to be controlled. Caterpillars and aphids were present in low populations, so the efficacy of the insecticides tested cannot be determined with certainty. A further research program is needed to find alternative solutions and develop easily implementable strategies for all sugar beet pests. We would propose an authorization of neonicotinoids for seed treatment of sugar beet in the regions with high infestation pressure of the main sugar beet pests.

Parasite management in aquaculture exerts selection on salmon louse behaviour.

The evolution of pest resistance to management strategies is a major challenge for farmed systems. Mitigating the effects of pest adaptation requires identifying the selective pressures imposed by these strategies. In Atlantic salmon (Salmo salar) aquaculture, barriers are used to prevent salmon louse (Lepeophtheirus salmonis) larvae (copepodids) from entering salmon cages. These barriers are effective against shallow‐swimming copepodids, but those swimming deeper can pass underneath and infest salmon. Laboratory experiments suggest that depth regulation in copepodids is a variable behavioural trait with a genetic basis. We used biological–hydrodynamic dispersal models to assess how this trait variation alters the dispersion of lice through the ocean environment and into farms. The dispersal of copepodids with 3 behavioural phenotypes (deep, mean or shallow) was modelled over winter–spring and spring–summer periods in a Norwegian fjord system with intensive aquaculture. The infestation pressure of each phenotype on barrier cages was estimated from their modelled depth distributions: copepodids deeper than 10 m were predicted to successfully pass underneath barriers. The deep phenotype was the most abundant below 10 m and reached infestation pressures 3 times higher than that of the mean phenotype. In contrast, the shallow phenotype infestation pressure reached less than half that of the mean phenotype. These differences in relative fitness indicate that barriers can impose strong directional selection on the swimming behaviour of copepodids. The strength of this selection varied seasonally and geographically, with selection for the deep phenotype stronger in winter–spring and at coastal locations than in spring–summer and within fjords. These findings can be applied across farms to slow louse adaptation, by limiting barriers during situations of strong selection, although this must be balanced against trade‐offs to short‐term efficacy. More broadly, our study highlights new ways in which dispersal models can address evolutionary questions crucial for sustainable parasite management in aquaculture.

State-space modeling for inter-site spread of sea lice with short-term population predictions

Accurate predictions for sea lice abundance can have a great impact on effective management of the parasite. Sea lice data are often from multiple production cycles coming from different aquaculture sites and exhibit strong process and observation variations, presenting challenges in developing effective prediction tools. Reliable predictions of sea lice abundance on aquaculture sites can save money and efforts in organizing effective control measures. A quantitative evaluation of different methods for estimating sea lice infestation pressure on aquaculture sites was presented in a preparatory paper (Elghafghuf et al., 2020). In the current work, we used the favored method for infestation pressure and predicted future sea lice abundances on different parasitic life stages at the site level using a multivariate state-space model fitted to data from aquaculture sites located near Grand Manan Island in the Bay of Fundy, New Brunswick, Canada. We employed a rolling prediction procedure that did not require the prediction model to be refitted to the data at each time of prediction and compared our results with those from a similar approach involving re-estimation of the model at each prediction. The accuracies of predictions were assessed based on hold-out samples of data, whereby the predictions were computed without prior knowledge of these observations. The results showed that the non-updated-model procedure gave short-term (six weeks) predictions with reasonable accuracy, albeit lower prediction errors could be obtained with the updated-model approach. The performance of the non-updated-model prediction, as well as its practical and computational advantages, suggests it to be well suited for user-friendly implementation linked to underlying database. Additionally, the research quantified the contributions of predictive covariates such as infestation pressures to the sea lice predictions.

The development of a sustainability assessment indicator and its response to management changes as derived from salmon lice dispersal modelling

Abstract Aquaculture is providing an increasingly larger proportion of the world’s protein for human consumption; however, its environmental impact is a bottleneck for sustainable expansion. In Norway, the government has enacted a framework where salmon lice-induced mortality in wild salmonid populations is used for assessing the environmental sustainability in production zones. Direct measurements of the level of lice-induced mortality on wild salmonids are difficult to acquire, thus comprehensive sustainability assessments are based on a set of evidence-based proxies. One such proxy is the infestation pressure from a bio-hydrodynamic model, from which we develop an index that summarize the sustainability of aquaculture in terms of lice infestation. This index is based on the proportion of areas with elevated lice loads, and is a novel approach used to investigate how sustainability could be achieved through scenario testing of different management strategies. The analyses identified a mismatch between legal and sustainable lice levels, but also a beneficial effect of reducing lice levels on farms. This study’s approach demonstrated how bio-hydrodynamic models might be used to assess sustainability and to predict the necessary reduction of lice larvae from farms to classify the entire Norwegian aquaculture industry as environmentally sustainable.

Crop rotations with temporary grassland shifts weed patterns and allows herbicide-free management without crop yield loss

Weeds are a concern to farmers mainly by reducing crop yield, especially in organic farming where herbicides are not an option. Additionally, reducing reliance on herbicides is among the goals to achieve sustainable crop production. By investigating alternatives for weed control, several studies have shown that grassland is more competitive with weeds than cash crops and adopting diversified crop rotations reduces overall weed infestation. However, in many of those studies the effect of the rotation is confounded with herbicide use. Moreover, there is a gap in understanding how diversified rotations influence the weed community and how changes in that weed community impact yield of the subsequent cash crop. Here, using a 4-year herbicide-free experiment in southern Brazil, we compared a grassland-cropping rotation (i.e., 3-year perennial tropical grassland before maize cultivation) vs. a crop-based rotation (i.e., sunflower-maize) to clearly characterize how a more diversified crop rotation changed weed patterns and weed interference in maize. We demonstrate the higher suppressive effect on weeds of a grassland-cropping rotation compared with a crop-based rotation, clearly evidenced in the early season of maize growth, in which the crop-based rotation had about twice as many number of weeds as the grassland-cropping rotation. However, there was no difference in seedbank size between both rotations. Weed community composition was not affected (i.e. rotations had 98% similarity in species composition), but weed assemblage was drastically changed with different rates of species-specific infestation in each rotation. The crop-based rotation selected weeds with rapid light acquisition ability (higher specific leaf area) that added to higher early season weed infestation and higher competitive pressure of weeds resulted in maize grain yield losses, whereas there was no significant weed interference on maize grain yield in the grassland-cropping rotation. The strategy of including a tropical grassland in rotation with cash crops as a herbicide-free weed management tool reduces overall weed infestation and prevents selection of weeds that cause a significant yield reduction in maize and represents an economically viable alternative.

A statistical mechanistic approach including temperature and salinity effects to improve salmon lice modelling of infestation pressure

Salmon lice Lepeophtheirus salmonis pose a major threat to the sustainable development of salmonid farming. To investigate effects of farm-origin salmon lice on wild salmonids, salmon lice dynamics are typically simulated using models that depend on experimentally determined rates of development, reproduction, mortality and infestation. Several recent studies provide new estimates of how these demographic rates depend on temperature and salinity. Here, we review and synthesize these studies and test if updating a salmon lice infestation model based on the new insights improves predictions of salmon lice infestations on salmon post-smolts in experimental cages in the sea. This model predicts spatiotemporal variation in infestation pressure based on weekly monitoring data of salmon lice and sea temperature in all salmonid fish farms in Norway, here supplemented by temperature and salinity data from a regional ocean model. Using data from 2012-2017 to select model formulation, we found the largest improvement in explanatory power by incorporating a salinity-dependent infestation rate. Updating functions for temperature-dependent egg production and infestation rates led to smaller improvements. Moreover, results suggest additional effects of temperature and a possible temperature-salinity interaction effect, not captured by the modelled processes. Out-of-sample predictions for experimental cage data from 2018-2020 confirmed that the uncertainty was realistically quantified, but also showed that associations of salmon lice infestations with salinity and temperature had changed. These results provide a field evaluation of experimental data and point to a knowledge gap regarding the combined effects of temperature and salinity on salmon lice infestations.

System-specific salmon louse infestation thresholds for salmon farms to minimize impacts on wild sea trout populations

Salmon lice Lepeophtheirus salmonis from aquaculture can cause negative impacts on sea trout Salmo trutta and other wild salmonids. Long-term records from 5 Irish rivers were used to explore relationships between annual sea trout runs and estimated total number of lice on nearby salmon farms. It was hypothesised that local environmental conditions may result in system-specific differences in realised louse pressure on sea trout. Louse count was thus tested as an absolute number and as a relative pressure, i.e. standardised by farm. When the standardised total number of mobile lice on a given salmon farm in April was above baseline level (50th percentile of observed annual values on that farm), there was a high probability of a below-average sea trout run in the local river. Absolute louse counts did not show an important effect on runs. This finding suggests that salmon farm louse production in spring can have a strong system-specific regulating effect on wild sea trout populations. Total number of lice on a farm was most strongly driven by changes in individual infestation rate, with a lesser effect of stocking density. Thresholds for number of mobile lice per farmed salmon required to maintain total louse count below the baseline varied with stocking density and among systems: greater density required lower infestation rate. Regulations relying on a generic louse threshold to trigger treatment are not sufficient to protect sea trout populations—stocking density and site characteristics must be considered to evaluate system-specific infestation pressure and impacts on wild salmonids.

Dynamics of Gastro-Intestinal Strongyle Parasites in a Group of Translocated, Wild-Captured Asiatic Wild Asses in Kazakhstan.

Asiatic wild ass (Kulan, Equus hemionus) population range and numbers became severely reduced and a reintroduction project is currently aiming to re-establish a population in the Central Steppe of Kazakhstan. Pre-emptive deworming is often recommended for equid translocations but eliminating parasites prior to translocation could cause disruptions in a balanced host-parasite relationship, adding an additional stressor to an already stressful intervention involving capture, transport, and adaptation to a new environment. Following a disease risk assessment, we decided against pre-emptive deworming and focused on monitoring the first group of nine translocated kulan in a large acclimatization enclosure prior to release. Over the 5-month acclimatization period, we regularly collected fecal samples and analyzed the shedding intensity of gastro-intestinal parasite eggs, obtained time budgets through behavioral observations, and visually assessed body condition. We identified strongyles (Strongylinae and Cyathostominae) and pinworms (Oxyuris equi) in fecal samples. All individuals shed strongyle eggs and two of the nine individuals had higher shedding intensities, but rarely reached levels for which deworming is recommended. All kulan appeared healthy throughout the observation period, aggressive interactions were very rare, and time budgets were very similar and dominated by feeding. Our results suggest that in translocation projects where the risk of introducing new parasites is minimal, pre-emptive treatment in wild equids can be replaced with non-invasive monitoring during the acclimatization period. We acknowledge that the small number of kulan, the large size of the enclosure, and the low temperatures during the animals stay in the acclimatization enclosure may all have reduced infestation pressure.

Geographical Distribution and Selection of European Honey Bees Resistant to Varroa destructor.

Simple SummaryThe parasitic mite Varroa destructor is a major challenge to honey bee populations worldwide. Some honey bee populations are resistant to the mite, but most of the commercially used stocks are not and rely on chemical treatment. In this article, we describe known varroa-resistant populations and the mechanisms which have been identified as responsible for survival of colonies without beekeeper intervention to control the mite. We review traits that have potential in breeding programs, discuss the role played by V. destructor as a vector for virus infections, and the changes in mite and virus virulence which could play a role in colony resistance. We also describe results of surveys carried out (mostly within Europe) on the presence of naturally surviving honey bee populations, on the commercial availability of mite resistant stock and on the traits considered in breeding programs. We found that there is a growing interest and awareness among beekeepers, but that there are very few commercially available resistant lines; some from breeding programs and some from naturally selected populations. The most commonly considered traits for assessing varroa resistance are linked to mite reproduction and specific hygienic behavior of the bees. Developing resistance to the varroa mite in honey bees is a major goal for apicultural science and practice, the development of selection strategies and the availability of resistant stock. Here we present an extended literature review and survey of resistant populations and selection programs in the EU and elsewhere, including expert interviews. We illustrate the practical experiences of scientists, beekeepers, and breeders in search of resistant bees. We describe numerous resistant populations surviving without acaricide treatments, most of which developed under natural infestation pressure. Their common characteristics: reduced brood development; limited mite population growth; and low mite reproduction, may cause conflict with the interests of commercial beekeeping. Since environmental factors affect varroa mite resistance, particular honey bee strains must be evaluated under different local conditions and colony management. The resistance traits of grooming, hygienic behavior and mite reproduction, together with simple testing of mite population development and colony survival, are significant in recent selection programs. Advanced breeding techniques and genetic and physiological selection tools will be essential in the future. Despite huge demand, there is no well-established market for resistant stock in Europe. Moreover, reliable experience or experimental evidence regarding the resistance of stocks under different environmental and management conditions is still lacking.

Salmon lice-induced mortality of Atlantic salmon during post-smolt migration in Norway

Abstract The expansion of salmonid aquaculture has resulted in environmental challenges, including salmon lice that may infest both farmed and wild fish. For wild Atlantic salmon post-smolts that migrate from their rivers to the ocean, the first phase of their journey in the coastal zone, where aquaculture occurs, is critical when considering lice exposure. To evaluate the lice influence during the post-smot migration we have developed a migration model. An archive with spatiotemporal concentrations of lice larvae in Norwegian coastal waters has been established using a combination of state-of-the-art hydrodynamic and lice biology models. To estimate lice-induced mortality of wild salmon from Norwegian rivers, the infestation level on the virtual post-smolts was calibrated to match that observed on wild post-smolts genetically assigned their rivers of origin. The lice infestation pressure was modelled on post-smolts from 401 rivers covering all of Norway. Based on this, aquaculture-produced salmon lice-induced mortality of wild salmon post-smolts was estimated as &amp;lt;10% for 179 rivers, 10–30% for 140 rivers, and &amp;gt;30% for 82 rivers in 2019. Estimated mortalities were used together with other data sets to evaluate aquaculture sustainability in Norway. The aquaculture regulatory system represents a globally leading example of science-based management that considers the environmental impact.

Demographic characteristics of young-of-year freshwater mussel populations in ponds

We describe demographics of young-of-year (YOY) Pondmussels (Ligumia subrostrata) and Giant Floaters (Pyganodon grandis) in ponds during 2009 and 2011. YOY attained large size by approximately 6 months (Pondmussel, mean = 48.5 mm; Floater = 57.5), most individuals were sexually mature, and most females were gravid. Size and sex ratios varied among ponds. Pondmussel size was negatively related to mussel density, suggesting food competition; Floater size was not related to density. Size was not related to glochidial infestation pressure on fishes, suggesting that acquired immunity did not affect YOY performance. The percentage of gravid female Pondmussels varied between years from 27 to 100%, and 91% of female Floaters were gravid in 2011. Mean fecundity was high (Pondmussel = 34,311; Floater = 38,873). The proportion of gravid females and mean fecundity were not related to male density, showing that fertilization was efficient. Variation in size, sex ratios, and gravidity among ponds suggests that small differences in environmental conditions or demographic stochasticity can have large effects on populations. Rapid growth, early maturity, efficient fertilization, and high fecundity of YOY are contrary to traditional views of mussel life history, but these traits may allow Pondmussels and Floaters to rapidly colonize disturbed, unstable habitats.

The environmental effectiveness of sea lice regulation: Compliance and consequences for farmed and wild salmon

Wild Atlantic salmon populations are declining. Since the 1970s, the proportion returning to Norwegian rivers has been almost halved, while Norwegian sea farming has undergone massive industrialization and expansion. As the proliferation of sea lice is an important part of the explanation for the decline in wild salmon, Norway has enacted increasingly stricter regulatory thresholds for the average number of lice per farmed fish at production sites. This study shows that setting stricter thresholds has led to declining lice-levels within sea farms, but that more frequent de-lousing measures to ensure compliance leads to farmed-salmon welfare problems and higher mortality rates. Compliance with stricter thresholds has not lessened the sea-lice infestation pressure on surrounding, wild salmonid populations. The environmental effectiveness of such regulation is thus limited. This raises the important question of whether a regulatory regime focused on minimizing the average number of sea lice per farmed fish may do more harm than good, unless accompanied by a broader set of regulatory instruments targeting other variables that affect sea-lice infestations in the wild salmon habitat.