Pesticide use is one of the main causes of pollinator declines in agricultural ecosystems. Traditionally, most laboratory studies on bee ecotoxicology test acute exposure to single compounds. ...However, under field conditions, bees are often chronically exposed to a variety of chemicals, with potential synergistic effects. We studied the effects of field-realistic concentrations of three pesticides measured in pollen and nectar of commercial melon fields on the solitary bee Osmia bicornis L. We orally exposed females of this species throughout their life span to 8 treatments combining two neonicotinoid insecticides (acetamiprid, imidacloprid) and a triazole fungicide (myclobutanil) via pollen and sugar syrup. We measured pollen and syrup consumption, longevity, ovary maturation and thermogenesis. Pesticide intake was three orders of magnitude higher via syrup than pollen. At the tested concentrations, no synergistic effects emerged, and we found no effects on longevity and ovary maturation. However, all treatments containing imidacloprid resulted in suppressed syrup consumption and drastic decreases in thoracic temperature and bee activity. Our results have important implications for pesticide regulation. If we had measured only lethal effects we would have wrongly concluded that the pesticide combinations containing imidacloprid were safe to O. bicornis. The incorporation of tests specifically intended to detect sublethal effects in bee risk assessment schemes should be an urgent priority. In this way, the effects of pesticide exposure on the dynamics of bee populations in agroecosystems will be better assessed.
Insects play an essential role as pollinators of wild flowers and crops. At the same time, pollinators in agricultural environments are commonly exposed to pesticides, compromising their survival and ...the provision of pollination services. Although pollinators include a wide range of species from several insect orders, information on pesticide sensitivity is mostly restricted to bees. In addition, the disparity of methodological procedures used for different insect groups hinders the comparison of toxicity data between bees and other pollinators. Dipterans are a highly diverse insect order that includes some important pollinators. Therefore, in this study, we assessed the sensitivity of two hoverflies (
,
) and one tachinid fly (
) to a neonicotinoid insecticide (Confidor
, imidacloprid) following a comparative approach. We adapted the standardized methodology of acute contact exposure in honey bees to build dose-response curves and calculate median lethal doses (LD
) for the three species. The methodology consisted in applying 1 µL of the test solution on the thorax of each insect.
was the most sensitive species (LD
= 10.23 ng/insect), and
(LD
= 18,176 ng/insect) the least. We then compared our results with those available in the literature for other pollinator species using species sensitivity distribution (SSD). Based on the SSD curve, the 95th percentile of pollinator species would be protected by a safety factor of 100 times the
endpoint. Overall, dipterans were less sensitive to imidacloprid than most bee species. As opposed to most bee species, oviposition and fecundity of many dipteran species can be reliably assessed in the laboratory. We measured the number of eggs laid following exposure to different insecticide doses and assessed the potential trade-off between oviposition and survival through the sublethal sensitivity index (SSI). Exposure to imidacloprid had a significant effect on fecundity, and SSI values indicated that oviposition is a sensitive endpoint for the three dipteran species tested. Future studies should integrate this information related to population dynamics in simulation models for environmental risk assessment.
Planting flower strips adjacent to crops is among the habitat-management practices employed to offer alternative floral resources to pollinators. However, more information is needed to understand ...their potential spill-over of pollinators on nearby insect-pollinated crops. Over the course of two consecutive years, the suitability of a flower mixture of 10 herbaceous plants for pollinators was evaluated on a weekly basis, in a randomized block design of two melon plots (10 × 10 m
) with or without 1 m-wide flower strips. Floral coverage and pollinator visits to the plant species, as well as pollinator visits and the yield and quality of the crop, were assessed. Additionally, the selected mixture was tested for 1 year in a commercial field in order to ascertain how far the flower strip could influence visitors in the crop. The most suitable species for a flower strip in central Spain based on their attractiveness, floral coverage and staggered blossom were
L.,
L.,
L. and
L. The flower strip can act as either pollinator competitor or facilitator to the crop, depending on their floral coverage and/or the predominant species during the crop bloom period. The concurrence of blooming of the rewarding plant
with the melon crop should be avoided in our area. In the commercial field, the bee visitation rate in the melon flowers decreased with the distance to the flower strip. No influence of the specific flower strip evaluated on crop productivity or quality was found.
Integrated Pest Management programs do not always prioritize natural enemies when selecting control methods; too often these important pest reducing agents are negatively affected by the action of ...other methods in agroecosystems. The aim of this research was to evaluate side effects of a bioinsecticide, developed from the mixture of cedar (
Cedrus atlantica
), eucalyptus (
Corymbia citriodora
) and lemon grass (
Cymbopogon citratus
) essential oils (EOs), in a ratio of 1:1:1, on
Psyttalia concolor
(Szèpligeti) (Hymenoptera: Braconidae) which is a parasitoid of some pests of the Tephritidae family, as
Ceratitis capitata
. The LD
50
of the EOs mixture for
C. capitata
females was 3.09 µl/g, whereas the LD
50
for
P. concolor
females was 20.45 µl/g which suggests the natural enemy is more tolerant to the EOs mixture.
P. concolor
parasitized L3 larvae of
C. capitata
through a voile treated with the mixture of EOs at 1.8% without causing any deleterious effects neither on the percentage of attacked hosts nor on the emergence rate, whereas at the highest concentration tested, 4.8%, decreased both parameters during the 2 first days after treatment. Semi-field assays showed that mixture of EOs was harmless to
P. concolor
when released 4 h after treatment whereas killed 55 ± 3.9% males and 37.5 ± 1.6% females of
C. capitata
. The mixture of EOs used jointly with lambda-cyhalothrin or kaolin, both compounds applied against
C. capitata
in conventional and organic farming, respectively, did not increase the toxicity and/or persistence against the pest.
The recent EU ban of the three most widely used neonicotinoids (imidacloprid, thiamethoxam and clothianidin) to all outdoors applications has stimulated the introduction of new insecticides into the ...market. Sulfoxaflor is a new systemic insecticide that, like neonicotinoids, acts as a modulator of nicotinic acetylcholine receptors. In agro-environments, bees can be exposed to this compound via contaminated pollen and nectar for long periods of time. Therefore, it is important to assess the potential effects of chronic exposure to sulfoxaflor, alone and in combination with fungicides, on pollinators. In this study, we tested the effects of chronic exposure to two field concentrations of sulfoxaflor (20 and 100 ppb) alone and in combination with four concentrations of the fungicide fluxapyroxad (7500, 15,000, 30,000 and 60,000 ppb) on syrup consumption and longevity in females of the solitary bee Osmia bicornis L. Exposure to 20 ppb of sulfoxaflor, alone and in combination with the fungicide, stimulated syrup consumption, but did not affect longevity. In contrast, syrup consumption decreased in bees exposed to 100 ppb, all of which died after 2–6 days of exposure. We found no evidence of synergism between the two compounds at any of the two sulfoxaflor concentrations tested. Comparison of our findings with the literature, confirms that O. bicornis is more sensitive to sulfoxaflor than honey bees. Our results highlight the need to include different bee species in risk assessment schemes.
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•Chronic oral exposure to 100 ppb of sulfoxaflor reduces the survival of Osmia bicornis.•The chronic exposure up to 60,000 ppb of fluxapyroxad does not reduce bee survival.•Syrup consumption increases at 20 ppb of sulfoxaflor and decreases at 100 ppb.•We found no synergistic interaction between sulfoxaflor and fluxapyroxad.
Residues detected in pollen collected by honey bees are often used to estimate pesticide exposure in ecotoxicological studies. However, for a more accurate assessment of pesticides effect on foraging ...pollinators, residues found directly on flowers are a more realistic exposure approximation. We conducted a multi-residue analysis of pesticides on pollen and nectar of melon flowers collected from five fields. The cumulative chronic oral exposure Risk Index (RI) was calculated for Apis mellifera, Bombus terrestris and Osmia bicornis to multiple pesticides. However, this index could underestimate the risk since sublethal or synergistic effects are not considered. Therefore, a mixture containing three of the most frequently detected pesticides in our study was tested for synergistic impact on B. terrestris micro-colonies through a chronic oral toxicity test. According to the result, pollen and nectar samples contained numerous pesticide residues, including nine insecticides, nine fungicides, and one herbicide. Eleven of those were not applied by farmers during the crop season, revealing that melon agroecosystems may be pesticide contaminated environments. The primary contributor to the chronic RI was imidacloprid and O. bircornis is at greatest risk for lethality resulting from chronic oral exposure at these sites. In the bumblebee micro-colony bioassay, dietary exposure to acetamiprid, chlorpyrifos and oxamyl at residue level concentration, showed no effects on worker mortality, drone production or drone size and no synergies were detected when pesticide mixtures were evaluated. In conclusion, our findings have significant implications for improving pesticide risk assessment schemes to guarantee pollinator conservation. In particular, bee pesticide risk assessment should not be limited to acute exposure effects to isolated active ingredients in honey bees. Instead, risk assessments should consider the long-term pesticide exposure effects in both pollen and nectar on a range of bees that reflect the diversity of natural ecosystems and the synergistic potential among pesticide formulations.
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•Nineteen pesticides were detected, eleven of them had not been applied in the crops•Imidacloprid was the main contributor in the cumulative chronic risk index•Mason bees have the greatest risk of lethality associated with chronic oral exposure•Residue dose of one frequently mixture did not affect bumblebee micro-colonies
Abstract
Bee populations are exposed to multiple stressors, including land‐use change, biological invasions, climate change, and pesticide exposure, that may interact synergistically. We analyze the ...combined effects of climate warming and sublethal insecticide exposure in the solitary bee
Osmia cornuta
. Previous
Osmia
studies show that warm wintering temperatures cause body weight loss, lipid consumption, and fat body depletion. Because the fat body plays a key role in xenobiotic detoxification, we expected that bees exposed to climate warming scenarios would be more sensitive to pesticides. We exposed
O. cornuta
females to three wintering treatments: current scenario (2007–2012 temperatures), near‐future (2021–2050 projected temperatures), and distant‐future (2051–2080). Upon emergence in spring, bees were orally exposed to three sublethal doses of an insecticide (Closer, a.i. sulfoxaflor; 0, 4.55 and 11.64 ng a.i./bee). We measured the combined effects of wintering and insecticide exposure on phototactic response, syrup consumption, and longevity. Wintering treatment by itself did not affect winter mortality, but body weight loss increased with increasing wintering temperatures. Similarly, wintering treatment by itself hardly influenced phototactic response or syrup consumption. However, bees wintered at the warmest temperatures had shorter longevity, a strong fecundity predictor in
Osmia
. Insecticide exposure, especially at the high dose, impaired the ability of bees to respond to light, and resulted in reduced syrup consumption and longevity. The combination of the warmest winter and the high insecticide dose resulted in a 70% longevity decrease. Smaller bees, resulting from smaller pollen–nectar provisions, had shorter longevity suggesting nutritional stress may further compromise fecundity in
O. cornuta
. Our results show a synergistic interaction between two major drivers of bee declines, and indicate that bees will become more sensitive to pesticides under the current global warming scenario. Our findings have important implications for pesticide regulation and underscore the need to consider multiple stressors to understand bee declines.
In agricultural ecosystems, bees are exposed to combinations of pesticides that may have been applied at different times. For example, bees visiting a flowering crop may be chronically exposed to low ...concentrations of systemic insecticides applied before bloom and then to a pulse of fungicide, considered safe for bees, applied during bloom. In this study, we simulate this scenario under laboratory conditions with females of the solitary bee,
Osmia bicornis
L. We studied the effects of chronic exposure to the neonicotinoid insecticide, Confidor® (imidacloprid) at a realistic concentration, and of a pulse (1 day) exposure of the fungicide Folicur® SE (tebuconazole) at field application rate. Syrup consumption, survival, and four biomarkers: acetylcholinesterase (AChE), carboxylesterase (CaE), glutathione S-transferase (GST), and alkaline phosphatase (ALP) were evaluated at two different time points. An integrated biological response (IBRv2) index was elaborated with the biomarker results. The fungicide pulse had no impact on survival but temporarily reduced syrup consumption and increased the IBRv2 index, indicating potential molecular alterations. The neonicotinoid significantly reduced syrup consumption, survival, and the neurological activity of the enzymes. The co-exposure neonicotinoid-fungicide did not increase toxicity at the tested concentrations. AChE proved to be an efficient biomarker for the detection of early effects for both the insecticide and the fungicide. Our results highlight the importance of assessing individual and sub-individual endpoints to better understand pesticide effects on bees.
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