Interaction of Insecticides and Fungicides in Bees

Sublethal exposure to thiamethoxam and pyraclostrobin affects the midgut and Malpighian tubules of the stingless bee Frieseomelitta varia (Hymenoptera: Apidae: Meliponini)

The stingless bee Frieseomelitta varia Lepeletier 1836 (Hymenoptera: Apidae) is an essential pollinator in natural and agricultural ecosystems in the Neotropical region. However, these bees may be exposed to pesticides during foraging, which can affect both individuals and their colonies. One example comes from the use of pyraclostrobin (a fungicide) and thiamethoxam (an insecticide) for pest control in pepper crops, which F. varia visits. This study aimed to evaluate the isolated and combined sublethal effects of thiamethoxam (TMX) (0.000543 ng a.i./µL) and pyraclostrobin (PYR) (1.5 ng i.a./µL) on the morphology of the midgut and Malpighian tubules of F. varia workers. Results showed that both pesticides, regardless of the exposure time (through feeding during 48 h or 96 h), disturbed the morphology of the analyzed organs. Specifically, F. varia exposed orally to sublethal concentrations of thiamethoxam and pyraclostrobin, either alone or in combination, exhibited a higher rate of damage to the midgut (e.g., vacuolization, apocrine secretion, and cellular elimination) compared to the bees in the control groups, both after 48 h and 96 h of exposure. In Malpighian tubules, vacuolation is the only damage present. As the observed morphological alterations likely compromise the excretion and absorption functions, exposure to pyraclostrobin and thiamethoxam may lead to disturbances at both the individual and colony levels. These results highlight the urgent need for a future reassessment of the safety of fungicides and insecticides regarding their potential effects on bee populations.

Acute toxicity of the fungicide captan to honey bees and mixed evidence for synergism with the insecticide thiamethoxam

Honey bees are commonly co-exposed to pesticides during crop pollination, including the fungicide captan and neonicotinoid insecticide thiamethoxam. We assessed the impact of exposure to these two pesticides individually and in combination, at a range of field-realistic doses. In laboratory assays, mortality of larvae treated with captan was 80-90% greater than controls, dose-independent, and similar to mortality from the lowest dose of thiamethoxam. There was evidence of synergism (i.e., a non-additive response) from captan-thiamethoxam co-exposure at the highest dose of thiamethoxam, but not at lower doses. In the field, we exposed whole colonies to the lowest doses used in the laboratory. Exposure to captan and thiamethoxam individually and in combination resulted in minimal impacts on population growth or colony mortality, and there was no evidence of synergism or antagonism. These results suggest captan and thiamethoxam are each acutely toxic to immature honey bees, but whole colonies can potentially compensate for detrimental effects, at least at the low doses used in our field trial, or that methodological differences of the field experiment impacted results (e.g., dilution of treatments with natural pollen). If compensation occurred, further work is needed to assess how it occurred, potentially via increased queen egg laying, and whether short-term compensation leads to long-term costs. Further work is also needed for other crop pollinators that lack the social detoxification capabilities of honey bee colonies and may be less resilient to pesticides.

Transfer and bioaccumulation of pesticides in terrestrial arthropods and food webs: State of knowledge and perspectives for research

Arthropods represent an entry point for pesticide transfers in terrestrial food webs, and pesticide accumulation in upper chain organisms, such as predators can have cascading consequences on ecosystems. However, the mechanisms driving pesticide transfer and bioaccumulation in food webs remain poorly understood. Here we review the literature on pesticide transfers mediated by terrestrial arthropods in food webs. The transfer of pesticides and their potential for bioaccumulation and biomagnification are related to the chemical properties and toxicokinetic of the substances, the resistance and detoxification abilities of the contaminated organisms, as well as by their effects on organisms' life history traits. We further identify four critical areas in which knowledge gain would improve future predictions of pesticides impacts on terrestrial food webs. First, efforts should be made regarding the effects of co-formulants and pesticides mixtures that are currently understudied. Second, progress in the sensitivity of analytical methods would allow the detection of low concentrations of pesticides in small individual arthropods. Quantifying pesticides in arthropods preys, their predators, and arthropods or vertebrates at higher trophic level would bring crucial insights into the bioaccumulation and biomagnification potential of pesticides in real-world terrestrial food webs. Finally, quantifying the influence of the trophic structure and complexity of communities on the transfer of pesticides could address several important sources of variability in bioaccumulation and biomagnification across species and food webs. This narrative review will inspire future studies aiming to quantify pesticide transfers in terrestrial food webs to better capture their ecological consequences in natural and cultivated landscapes.

Biological effects of a copper-based fungicide on the fruit fly, Drosophila melanogaster

The increased consumption of pesticides can have a negative environmental impact by increasing the essential metals to toxic levels. Bordasul® is a commonly used fungicide in Brazil and it is composed of 20% Cu, 10% sulfur, and 3.0% calcium. The study of fungicides in vivo in non-target model organisms can predict their environmental impact more broadly. The Drosophila melanogaster is a unique model due to its ease of handling and maintenance. Here, the potential toxicity of Bordasul® was investigated by assessing the development, survival, and behavior of exposed flies. Exposure to Bordasul® impaired the development (p < 0.01) and caused a significant reduction in memory retention (p < 0.05) and locomotor ability (p < 0.001). Fungicides are needed to assure the world's food demand; however, Bordasul® was highly toxic to D. melanogaster. Therefore, Bordasul® may be potentially toxic to non-target invertebrates and new environmentally-safe biofertilizers have to be developed to preserve the biota.

Olfactory Learning Behavior and Mortality of the Honey Bee Apis mellifera jemenitica in Response to Pyrethroid Insecticide (Deltamethrin)

Honey bees are constantly threatened due to the wide use of pesticides. This study presents the effects of deltamethrin on the mortality, olfactory learning, and memory formation of the native Saudi bee Apis mellifera jemenitica. Topical and oral application of realistic field and serial dilutions of deltamethrin (250, 125, 62.5, and 25 ppm) caused significant mortality at 4, 12, 24, and 48 h posttreatment. Bee mortality increased with the increasing concentration of insecticide at all tested posttreatment times. Highest mortality was observed at 24 h and 48 h after both exposure routes. Food consumption gradually decreased with increasing concentration of deltamethrin during oral exposure. The LC50 of deltamethrin was determined at 12, 24, and 48 h for topical (86.28 ppm, 36.16 ppm, and 29.19 ppm, respectively) and oral (35.77 ppm, 32.53 ppm, and 30.78 ppm, respectively) exposure. Oral exposure led to significantly higher bee mortality than topical exposure of deltamethrin at 4 h and 12 h, but both exposure routes were equally toxic to bees at 24 h and 48 h. The sublethal concentrations (LC10, LC20, and LC30) of deltamethrin significantly impaired the learning during conditioning trials, as well as the memory formation of bees at 2, 12, and 24 h after topical and oral exposure. Thus, deltamethrin inhibits learning, and bees were unable to memorize the learned task.

Combined effect of a neonicotinoid insecticide and a fungicide on honeybee gut epithelium and microbiota, adult survival, colony strength and foraging preferences

Fungicides, insecticides and herbicides are widely used in agriculture to counteract pathogens and pests. Several of these molecules are toxic to non-target organisms such as pollinators and their lethal dose can be lowered if applied as a mixture. They can cause large and unpredictable problems, spanning from behavioural changes to alterations in the gut. The present work aimed at understanding the synergistic effects on honeybees of a combined in-hive exposure to sub-lethal doses of the insecticide thiacloprid and the fungicide penconazole. A multidisciplinary approach was used: honeybee mortality upon exposure was initially tested in cage, and the colonies development monitored. Morphological and ultrastructural analyses via light and transmission electron microscopy were carried out on the gut of larvae and forager honeybees. Moreover, the main pollen foraging sources and the fungal gut microbiota were studied using Next Generation Sequencing; the gut core bacterial taxa were quantified via qPCR. The mortality test showed a negative effect on honeybee survival when exposed to agrochemicals and their mixture in cage but not confirmed at colony level. Microscopy analyses on the gut epithelium indicated no appreciable morphological changes in larvae, newly emerged and forager honeybees exposed in field to the agrochemicals. Nevertheless, the gut microbial profile showed a reduction of Bombilactobacillus and an increase of Lactobacillus and total fungi upon mixture application. Finally, we highlighted for the first time a significant honeybee diet change after pesticide exposure: penconazole, alone or in mixture, significantly altered the pollen foraging preference, with honeybees preferring Hedera pollen. Overall, our in-hive results showed no severe effects upon administration of sublethal doses of thiacloprid and penconazole but indicate a change in honeybees foraging preference. A possible explanation can be that the different nutritional profile of the pollen may offer better recovery chances to honeybees.

Sublethal Effects of Four Insecticides Targeting Cholinergic Neurons on Partner and Host Finding in the Parasitic Wasp Nasonia vitripennis

Lethal and sublethal effects of pesticides on nontarget organisms are one of the causes of the current decline of many insect species. However, research in the past decades has focused primarily on pollinators, although other beneficial nontarget organisms such as parasitic wasps may also be affected. We studied the sublethal effects of the four insecticides acetamiprid, dimethoate, flupyradifurone, and sulfoxaflor on pheromone-mediated sexual communication and olfactory host finding of the parasitic wasp Nasonia vitripennis. All agents target cholinergic neurons, which are involved in the processing of chemical information by insects. We applied insecticide doses topically and tested the response of treated wasps to sex pheromones and host-associated chemical cues. In addition, we investigated the mating rate of insecticide-treated wasps. The pheromone response of females surviving insecticide treatment was disrupted by acetamiprid (≥0.63 ng), dimethoate (≥0.105 ng), and flupyradifurone (≥21 ng), whereas sulfoxaflor had no significant effects at the tested doses. Olfactory host finding was affected by all insecticides (acetamiprid ≥1.05 ng, dimethoate ≥0.105 ng, flupyradifurone ≥5.25 ng, sulfoxaflor ≥0.52 ng). Remarkably, females treated with ≥0.21 ng dimethoate even avoided host odor. The mating rate of treated N. vitripennis couples was decreased by acetamiprid (6.3 ng), flupyradifurone (≥2.63 ng), and sulfoxaflor (2.63 ng), whereas dimethoate showed only minor effects. Finally, we determined the amount of artificial nectar consumed by N. vitripennis females within 48 h. Considering this amount (∼2 µL) and the maximum concentrations of the insecticides reported in nectar, tested doses can be considered field-realistic. Our results suggest that exposure of parasitic wasps to field-realistic doses of insecticides targeting the cholinergic system reduces their effectiveness as natural enemies by impairing the olfactory sense. Environ Toxicol Chem 2023;42:2400-2411. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Fungicides and insecticides can alter the microbial community on the cuticle of honey bees

Honey bees are crucial for our ecosystems as pollinators, but the intensive use of plant protection products (PPPs) in agriculture poses a risk for them. PPPs do not only affect target organisms but also affect non-targets, such as the honey bee Apis mellifera and their microbiome. This study is the first of its kind, aiming to characterize the effect of PPPs on the microbiome of the cuticle of honey bees. We chose PPPs, which have frequently been detected in bee bread, and studied their effects on the cuticular microbial community and function of the bees. The effects of the fungicide Difcor® (difenoconazole), the insecticide Steward® (indoxacarb), the combination of both (mix A) and the fungicide Cantus® Gold (boscalid and dimoxystrobin), the insecticide Mospilan® (acetamiprid), and the combination of both (mix B) were tested. Bacterial 16S rRNA gene and fungal transcribed spacer region gene-based amplicon sequencing and quantification of gene copy numbers were carried out after nucleic acid extraction from the cuticle of honey bees. The treatment with Steward® significantly affected fungal community composition and function. The fungal gene copy numbers were lower on the cuticle of bees treated with Difcor®, Steward®, and PPP mix A in comparison with the controls. However, bacterial and fungal gene copy numbers were increased in bees treated with Cantus® Gold, Mospilan®, or PPP mix B compared to the controls. The bacterial cuticular community composition of bees treated with Cantus® Gold, Mospilan®, and PPP mix B differed significantly from the control. In addition, Mospilan® on its own significantly changed the bacterial functional community composition. Cantus® Gold significantly affected fungal gene copy numbers, community, and functional composition. Our results demonstrate that PPPs show adverse effects on the cuticular microbiome of honey bees and suggest that PPP mixtures can cause stronger effects on the cuticular community than a PPP alone. The cuticular community composition was more diverse after the PPP mix treatments. This may have far-reaching consequences for the health of honey bees.

Fungicides modify pest insect fitness depending on their genotype and population

Fungicides are the most sold pesticide group, with an 8% increase in sales in Europe within the last decade. While adverse short-term fungicide effects on non-target insect species have been reported, the long-term effects and their impact on fitness are unclear. As the effects may depend on both the fungicide and the genetic background of the species, we investigated the effects of the commonly used fungicide, fluazinam, on the Colorado potato beetle's life history traits, and whether the effects were dependent on a previously characterized insecticide resistance mutation (S291G in acetylcholinesterase-2 gene) in different populations. Our findings show that fungicide exposure can have both negative and positive, long-lasting effects on beetles, depending on the parental insecticide resistance status and population. In the Belchow population, individuals carrying resistance mutation had higher survival, but they produced offspring with lower egg-hatching rates. While, in the Vermont population, fungicide exposure increased the body mass and offspring quality in the beetles carrying resistance mutation but did not affect the beetles' survival. Our results suggest that commonly used fungicides can have both negative and positive effects on pest insects' life-history, however, their impact may differ depending on the population and parental genetic background.

The fungicide tebuconazole modulates the sodium current of human NaV1.5 channels expressed in HEK293 cells

The fungicide Tebuconazole is a widely used pesticide in agriculture and may cause cardiotoxicity. In our present investigation the effect of Tebuconazole on the sodium current (INa) of human cardiac sodium channels (NaV1.5) was studied using a heterologous expression system and whole-cell patch-clamp techniques. Tebuconazole reduced the amplitude of the peak INa in a concentration- and voltage-dependent manner. At the holding potential of -120 mV the IC50 was estimated at 204.1 ± 34.3 μM, while at -80 mV the IC50 was 0.3 ± 0.1 μM. The effect of the fungicide is more pronounced at more depolarized potentials, indicating a state-dependent interaction. Tebuconazole caused a negative shift in the half-maximal inactivation voltage and delayed recovery from fast inactivation of INa. Also, it enhanced closed-state inactivation, exhibited use-dependent block in a voltage-dependent manner. Furthermore, Tebuconazole reduced the increase in late sodium current induced by the pyrethroid insecticide β-Cyfluthrin. These results suggest that Tebuconazole can interact with NaV1.5 channels and modulate INa. The observed effects may lead to decreased cardiac excitability through reduced INa availability, which could be a new mechanism of cardiotoxicity to be attributed to the fungicide.

Effects of pesticide-adjuvant combinations used in almond orchards on olfactory responses to social signals in honey bees (Apis mellifera)

Exposure to agrochemical sprays containing pesticides and tank-mix adjuvants has been implicated in post-bloom mortality, particularly of brood, in honey bee colonies brought into California almond orchards for pollination. Although adjuvants are generally considered to be biologically inert, some adjuvants have exhibited toxicity and sublethal effects, including decreasing survival rates of next-generation queens. Honey bees have a highly developed olfactory system to detect and discriminate among social signals. To investigate the impact of pesticide-adjuvant combinations on honey bee signal perception, we performed electroantennography assays to assess alterations in their olfactory responsiveness to the brood ester pheromone (BEP), the volatile larval pheromone β-ocimene, and the alarm pheromone 2-heptanone. These assays aimed to uncover potential mechanisms underlying changes in social behaviors and reduced brood survival after pesticide exposure. We found that combining the adjuvant Dyne-Amic with the fungicide Tilt (propiconazole) and the insecticide Altacor (chlorantraniliprole) synergistically enhanced olfactory responses to three concentrations of BEP and as well exerted dampening and compensatory effects on responses to 2-heptanone and β-ocimene, respectively. In contrast, exposure to adjuvant alone or the combination of fungicide and insecticide had no effect on olfactory responses to BEP at most concentrations but altered responses to β-ocimene and 2-heptanone. Exposure to Dyne-Amic, Altacor, and Tilt increased BEP signal amplitude, indicating potential changes in olfactory receptor sensitivity or sensilla permeability to odorants. Given that, in a previous study, next-generation queens raised by nurses exposed to the same treated pollen experienced reduced survival, these new findings highlight the potential disruption of social signaling in honey bees and its implications for colony reproductive success.

A combination of the frequent fungicides boscalid and dimoxystrobin with the neonicotinoid acetamiprid in field-realistic concentrations does not affect sucrose responsiveness and learning behavior of honeybees

The increasing loss of pollinators over the last decades has become more and more evident. Intensive use of plant protection products is one key factor contributing to this decline. Especially the mixture of different plant protection products can pose an increased risk for pollinators as synergistic effects may occur. In this study we investigated the effect of the fungicide Cantus® Gold (boscalid/dimoxystrobin), the neonicotinoid insecticide Mospilan® (acetamiprid) and their mixture on honeybees. Since both plant protection products are frequently applied sequentially to the same plants (e.g. oilseed rape), their combination is a realistic scenario for honeybees. We investigated the mortality, the sucrose responsiveness and the differential olfactory learning performance of honeybees under controlled conditions in the laboratory to reduce environmental noise. Intact sucrose responsiveness and learning performance are of pivotal importance for the survival of individual honeybees as well as for the functioning of the entire colony. Treatment with two sublethal and field relevant concentrations of each plant protection product did not lead to any significant effects on these behaviors but affected the mortality rate. However, our study cannot exclude possible negative sublethal effects of these substances in higher concentrations. In addition, the honeybee seems to be quite robust when it comes to effects of plant protection products, while wild bees might be more sensitive.

Bees under interactive stressors: the novel insecticides flupyradifurone and sulfoxaflor along with the fungicide azoxystrobin disrupt the gut microbiota of honey bees and increase opportunistic bacterial pathogens

The gut microbiome plays an important role in bee health and disease. But it can be disrupted by pesticides and in-hive chemicals, putting honey bee health in danger. We used a controlled and fully crossed laboratory experimental design to test the effects of a 10-day period of chronic exposure to field-realistic sublethal concentrations of two nicotinic acetylcholine receptor agonist insecticides (nACHRs), namely flupyradifurone (FPF) and sulfoxaflor (Sulf), and a fungicide, azoxystrobin (Azoxy), individually and in combination, on the survival of individual honey bee workers and the composition of their gut microbiota (fungal and bacterial diversity). Metabarcoding was used to examine the gut microbiota on days 0, 5, and 10 of pesticide exposure to determine how the microbial response varies over time; to do so, the fungal ITS2 fragment and the V4 region of the bacterial 16S rRNA were targeted. We found that FPF has a negative impact on honey bee survival, but interactive (additive or synergistic) effects between either insecticide and the fungicide on honey bee survival were not statistically significant. Pesticide treatments significantly impacted the microbial community composition. The fungicide Azoxy substantially reduced the Shannon diversity of fungi after chronic exposure for 10 days. The relative abundance of the top 10 genera of the bee gut microbiota was also differentially affected by the fungicide, insecticides, and fungicide-insecticide combinations. Gut microbiota dysbiosis was associated with an increase in the relative abundance of opportunistic pathogens such as Serratia spp. (e.g. S. marcescens), which can have devastating consequences for host health such as increased susceptibility to infection and reduced lifespan. Our findings raise concerns about the long-term impact of novel nACHR insecticides, particularly FPF, on pollinator health and recommend a novel methodology for a refined risk assessment that includes the potential effects of agrochemicals on the gut microbiome of bees.