is a real challenger for beekeepers and scientists: fragile out of the hive, tenacious inside a bee colony. From all the research done on the topic, we have learned that a better understanding of ...this organism in its relationship with the bee but also for itself is necessary. Its biology relies mostly on semiochemicals for reproduction, nutrition, or orientation. Many treatments have been developed over the years based on hard or soft acaricides or even on biocontrol techniques. To date, no real sustainable solution exists to reduce the pressure of the mite without creating resistances or harming honeybees. Consequently, the development of alternative disruptive tools against the parasitic life cycle remains open. It requires the combination of both laboratory and field results through a holistic approach based on health biomarkers. Here, we advocate for a more integrative vision of
research, where in vitro and field studies are more systematically compared and compiled. Therefore, after a brief state-of-the-art about the mite's life cycle, we discuss what has been done and what can be done from the laboratory to the field against
through an integrative approach.
Investigating the expression of trade-offs between key life-history functions is central to our understanding of how these functions evolved and are maintained. However, detecting trade-offs can be ...challenging due to variation in resource availability, which masks trade-offs at the population level. Here, we investigated in the European earwig Forficula auricularia whether (1) weapon size trades off with three key immune parameters - hemocyte concentration, phenoloxidase and prophenoloxidase activity - and whether (2) expression and strength of these trade-offs depend on male body condition (body size) and/or change after an immune challenge. Our results partially confirmed condition dependent trade-offs between weapon size and immunity in male earwigs. Specifically, we found that after an immune challenge, weapon size trades off with hemocyte concentrations in low-condition, but not in good-condition males. Contrastingly, weapon size was independent of pre-challenge hemocyte concentration. We also found no trade-off between weapon size and phenoloxidase activity, independent of body condition and immune challenge. Overall, our study reveals that trade-offs with sexual traits may weaken or disappear in good-condition individuals. Given the importance of weapon size for male reproductive success, our results highlight how low-condition individuals may employ alternative life-history investment strategies to cope with resource limitation.
Beekeepers can use a variety of treatments against Varroa destructor, the parasitic mite of Apis mellifera. However, sustainable and easy-to-use solutions are still scarce, considering the complexity ...of reaching the parasite alone. Current treatments involve soft acaricides, although their mechanism of action is not well understood. We investigated the effects of organic acids such as tartaric, lactic, formic, and citric acids on the attachment abilities of V. destructor under laboratory conditions. Preventing parasites from gripping or holding on to their hosts is a crucial target for mite control strategies. We challenged grip skills through the Rotavar setup after the direct application of acids to mites’ arolia. We also tested the potential for mites to fall off honeybees after bee treatment. We found that tartaric, citric, and lactic acids were good candidates to impair the attachment of V. destructor twenty-four hours post-treatment. However, lactic acid remained the only candidate at a reasonable concentration to destabilise mites after the honey bee’s treatment without reducing their lifespan. While we conducted these experiments under artificial conditions, our results improved our comprehension of the organic acids’ potential impact on V. destructor. They can also help with the development of new methods for hive application for beekeepers worldwide.
1. Host plant quality affects herbivorous insect performance and consequently their susceptibility to natural enemies. Recently, it has been hypothesized that the immune function of herbivorous ...insects can be altered by their host plant, thus generating variation in their susceptibility to entomopathogens. Previous studies testing this hypothesis provided contradictory outcomes, mainly as a result of the differences in methodology such as measuring a single-immune parameter rather than considering trade-off-mediated interactions between immune defence systems of the insect. Here, we hypothesized that plant-mediated changes in insect immunity could result from the alteration of physiological immune effectors of the herbivore evident as trade-offs. 2. Larvae of an inbred strain of the European grape berry moth Eupoecilia ambiguella were reared on five artificial diets each based on a different grape variety (Chardonnay, Chasselas, Gewurztraminer, Merlot, Riesling) and tested for changes in the baseline concentration of haemocytes, activities of the prophenoloxidase (PPO) system and of antimicrobial peptides of their haemolymph. Immune responsiveness of larvae across diets was also assessed by measuring changes in haemocyte concentration and activity of the PPO system after a bacterial immune challenge. 3. We found that variation among diets significantly affected immune defences of larvae. The alteration of the E. ambiguella immune system appears plastic and partly mediated by existing physiological trade-offs between immune pathways, at least between induced antibacterial defences and the PPO system. 4. These results clearly show that host plant quality can affect immune defences and potentially disease resistance of E. ambiguella and that these changes in immunity may also result from intrinsic trade-offs between immune defence systems in insects.
To combat parasitism hosts often rely on their immune system, which is the last line of defense. However, the immune system may not always be effective, and other non-immunological defenses might be ...favored to reduce the cost of parasite infection. Here we report that larvae of the moth Lobesia botrana can rapidly accelerate their development and reach maturity earlier in response to cues perceived at a distance from parasitoids. Such a phenotypically plastic life history shift, induced by the perception of deadly enemies in the environment, is likely to be an adaptive defensive strategy to prevent parasitoid attack, and has important implications in host-parasite dynamics.
•Its non-targeted effect on leaf arthropods (beneficial/pest) is under-investigated.•We monitored its effect on 3 grapevine diseases and 5 arthropods over 2 years.•We found a strong interaction ...between treatments and years in all the organisms.•We found a general decreases of species density in copper treatment.
Bordeaux mixture has been used for more than 150 years in viticulture and other agricultural applications because it is the most effective fungicide against grape downy mildew. However, the copper present in these mixtures is not degradable and can have environmental consequences. Even though the effect of Bordeaux mixture on downy mildew is well known, the non-target effects of this fungicide on leaf arthropod communities are poorly understood. In this study, we simultaneously monitored the direct effect of Bordeaux mixture on three grapevine leaf diseases and five leaf arthropods (beneficial and pest species) in the field over a four-month time period. We found a strong interaction between sampling year and treatment for all tested organisms. Overall, the presence of copper generally decreased both the occurrence of disease and densities of leaf arthropods. Thus, copper reduces some pest densities but also biological agent densities which might interfere with biological control. The effects and results presented here should prove valuable when implementing future crop management strategies and pest control procedures.
Background and Aims
Cover crop has become a common management practice in viticulture. It improves the structure and protects the soil, enhances natural enemy populations and also reduces the vigour ...of the vine. Here, we investigated the effect of cover crop in vineyards on grapevine diseases and arthropods present on leaves.
Methods and Results
We measured the presence of the pathogens Plasmopara viticola, Uncinula necator and Guignardia bidwellii and monitored six common beneficial/pest arthropods: Panonychus ulmi, Orthotydeus lambi, Typhlodromus pyri, Scaphoideus titanus and Phalangium opilio in vineyards with cover crop or bare soil in 2014 and 2015. The density of the two pests P. ulmi and S. titanus and the beneficial mite O. lambi was lower in cover crop, while the density of the beneficial predatory mite T. pyri was higher in cover crop. We found no influence of cover crop on P. opilio and on the presence of grapevine diseases.
Conclusions
These findings point to a simple way to increase the population of beneficial arthropods and reduce pest arthropods, which could help integrated pest management programs.
Significance of the Study
To our knowledge, this is the first study monitoring the cover crop influence on both diseases and arthropods. It would help growers to optimise space management between rows to enhance their natural enemy populations while reducing pesticide application.
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•We applied a non-lethal heat wave to an insect at two distinct larval instars.•We examined the role of post-stress nutrition in the insect response to the heat.•Heat wave was ...detrimental overall to the insect (development, immunity).•Poorly nutritive food exacerbated these negative effects driven by the heat wave.•Larval instars differed in their heat susceptibility in a trait-specific manner.
Organisms are increasingly confronted with intense and long-lasting heat waves. In insects, the effects of heat waves on individual performance can vary in magnitude both within (e.g. from one larval instar to another) and between life stages. However, the reasons underlying these stage-dependent effects are not fully understood. There are several lines of evidence suggesting that individual ability to withstand a heat stress depends on mechanisms based on nutrition and supporting energetically physiological stress responses. Hence, we tested the hypothesis that the efficiency of these food-based buffering mechanisms may vary between different larval instars of a phytophagous insect. Using larvae of the moth Lobesia botrana, we examined the importance of post-stress food quality in insect response to a non-lethal heat wave at two distinct larval instars. Three major conclusions were drawn from this work. First, heat waves induced an overall decline in larval performance (delayed development, depressed immunity). Second, food quality primarily mediated the insect’s ability to respond to the heat stress: the reduction in performance following heat wave application was mostly restricted to individuals with access to low-quality food after the heat stress. Third, larval instars differed in their susceptibility to this combination of thermal and food stressors, but conclusions about the instar being the most vulnerable differed in a trait-specific manner. In a global warming context, this study may shed additional light on the combination of direct and indirect (through alteration of plant nutritional value) effects of rising temperatures on the ecology and the evolution of phytophagous insects.
Offspring of species with facultative family life are able to live with and without parents (i.e. to adjust to extreme changes in their social environment). While these adjustments are well ...understood on a phenotypic level, their genetic underpinnings remain surprisingly understudied. Investigating gene expression changes in response to parental absence may elucidate the genetic constraints driving evolutionary transitions between solitary and family life. Here, we manipulated maternal presence to observe gene expression changes in the fat body of juvenile European earwigs, an insect with facultative family life. Because parents typically protect offspring against pathogens, expression changes were recorded in pathogen-free and pathogen-exposed environments. We found that manipulating maternal presence changed the expression of 154 genes, including several metabolism and growth-related genes, and that this change depended on pathogen presence. Specifically, localization and cell transporter genes were downregulated in maternal absence without pathogens but upregulated with pathogens. At least one immunity gene (pathogenesis-related protein 5) was affected by pathogen exposure regardless of maternal presence. Overall, our findings explicate how offspring adjust to parental deprivation on a molecular level and reveal that such adjustments heavily depend on pathogens in the environment. This emphasizes the central role of pathogens in family life evolution.
Beekeepers can use a variety of treatments against Varroa destructor, the parasitic mite of Apis mellifera. However, sustainable and easy-to-use solutions are still scarce, considering the complexity ...of reaching the parasite alone. Current treatments involve soft acaricides, although their mechanism of action is not well understood. We investigated the effects of organic acids such as tartaric, lactic, formic, and citric acids on the attachment abilities of V. destructor under laboratory conditions. Preventing parasites from gripping or holding on to their hosts is a crucial target for mite control strategies. We challenged grip skills through the Rotavar setup after the direct application of acids to mites’ arolia. We also tested the potential for mites to fall off honeybees after bee treatment. We found that tartaric, citric, and lactic acids were good candidates to impair the attachment of V. destructor twenty-four hours post-treatment. However, lactic acid remained the only candidate at a reasonable concentration to destabilise mites after the honey bee’s treatment without reducing their lifespan. While we conducted these experiments under artificial conditions, our results improved our comprehension of the organic acids’ potential impact on V. destructor. They can also help with the development of new methods for hive application for beekeepers worldwide.
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