Chronic toxicity and biochemical response of Apis cerana cerana (Hymenoptera: Apidae) exposed to acetamiprid and propiconazole alone or combined.

Acetamiprid and ergosterol-inhibiting fungicide (EBI) are frequently applied to many flowering plants, while honey bees are pollinating agents or pollinators of the flowers. Hence honey bees are often exposed to these pesticides. But until now, the effects of theses combinations at field-realistic doses on honey bee health have been poorly investigated. In this study, we explore the synergistic mortality and some physiological effects in surviving honey bees after chronic oral exposure to acetamiprid and/or propiconazole in the laboratory. The results indicated that chronic combined exposure to acetamiprid and propiconazole produced a significant synergistic effect on mortality both for newly emerged bees (50% mortality in 7.2 days) and forager bees (50% mortality in 4.8 days). Honey bee weight of newly emerged bees was decreased after feeding food with a field concentration of acetamiprid and propiconazole, alone or combined for 10 days. Combination of acetamiprid and propiconazole also modulated the activities of P450s, GST and CAT in newly emerged bees and forager bees than either alone, but neither pesticide affected the activity of AChE. These results show that chronic combined exposure to pesticides of relatively low toxicity may caused severely physiological disruptions that could be potentially damaging for the honey bees.

Acute toxicity and sublethal effects of myclobutanil on respiration, flight and detoxification enzymes in Apis cerana cerana.

Myclobutanil is currently used on the flowering plants. Little is known about how Apis cerana cerana respond to myclobutanil exposure. Hence, the acute toxicity of myclobutanil and its sublethal effects on respiration, flight and detoxification enzymes [7-ethoxycoumarin O-deethylase (ECOD) and glutathione S-transferases (GSTs)] in A. cerana cerana were investigated. The results indicated that formulation grade myclobutanil showed moderate toxicity to A. cerana cerana either contact (LD50=4.697µg/bee) or oral (LD50=2.154µg/bee) exposure. Sublethal dose of myclobutanil significantly reduced the respiration rate of workers at 24h and 48h regardless of the exposure method. However, myclobutanil didn't significantly affect the take-off flight. After nurse bees exposure to the dose (LD5) of formulation-grade myclobutanil, ECOD activity was significantly induced when compared with control, but GST activity didn't change. In the forager bees, no enzyme markers response was obtained in this test. From the present study we can infer that myclobutanil disturb respiration and P450-mediated detoxification of the individual bees of A. cerana cerana. Thus, myclobutanil may has risk for A. cerana cerana, it should be cautiously used.

Development of a SCAR marker for molecular detection and diagnosis of Tilletia controversa Kühn, the causal fungus of wheat dwarf bunt.

Tilletia controversa Kühn (TCK) is an important quarantine pathogen that causes wheat dwarf bunt and results in devastating damage to wheat production. The fungus is difficult to be distinguished from T. caries and T. laevis, which cause wheat common bunt, based on morphological, physiological and symptomatological characteristics of the pathogens. The traditional detection of the fungus can be a long and tedious process with poor accuracy. The inter-simple sequence repeat (ISSR) technique has been used for identifying molecular markers for detection of TCK. Of 28 ISSR primers screened, ISSR-859 amplified a specific 678 bp DNA fragment from all TCK isolates but not from any isolates of the common bunt fungi or other pathogenic fungi tested. Based on the fragment sequence, a pair of sequence characterized amplified region (SCAR) primers was designed, which amplified a 372 bp DNA fragment specifically in TCK. The SCAR marker was detected using as low as 1 ng template DNA of TCK, and was also detected using broken teliospores and DNA from asymptomatic wheat samples. We developed the SYBR Green I and TaqMan Green I and TaqMan real-time polymorphism chain reaction methods to detect TCK with the detection limit of 0.1 fg with asymptomatic wheat samples. Further work is needed to develop a rapid test kit for this pathogenic fungus using the designed specific primers.

Microbiomes, diet flexibility, and the spread of a beetle parasite of honey bees.

Invasive pests may disturb and destructively reformat the local ecosystem. The small hive beetle (SHB), Aethina tumida, originated in Africa and has expanded to America, Australia, Europe, and Asia. A key factor facilitating its fast global expansion is its ability to subsist on diverse food inside and outside honey bee colonies. SHBs feed on various plant fruits and exudates in the environment while searching for bee hives. After sneaking into a bee hive, they switch their diet to honey, pollen, and bee larvae. How SHBs survive on such a broad range of food remains unclear. In this study, we simulated the outside and within hive stages by providing banana and hive resources and quantified the SHB associated microbes adjusted by the diet. We found that SHBs fed on bananas were colonized by microbes coding more carbohydrate-active enzymes and a higher alpha diversity than communities from SHBs feeding on hive products or those collected directly from bee hives. SHBs fed on bananas and those collected from the hive showed high symbiont variance, indicated by the beta diversity. Surprisingly, we found the honey bee core symbiont Snodgrassella alvi in the guts of SHBs collected in bee hives. To determine the role of S. alvi in SHB biology, we inoculated SHBs with a genetically tagged culture of S. alvi, showing that this symbiont is a likely transient of SHBs. In contrast, the fungus Kodamaea ohmeri is the primary commensal of SHBs. Diet-based microbiome shifts are likely to play a key role in the spread and success of SHBs.

The oviposition preference and offspring performance of Aethina tumida (Coleoptera: Nitidulidae).

Given the rapid spread and potential harm caused by the small hive beetle, Aethina tumida (Coleoptera: Nitidulidae) in China, it has become imperative to comprehend the developmental biology of this invasive species. Currently, there is limited knowledge regarding the impact of A. tumida female oviposition site preference on larval growth and development. To examine this, we investigated the ovipositional preference of adult female A. tumida on bee pupae, beebread, banana, and honey through a free choice test. Furthermore, we assessed the impact of these food resources on offspring performance, which included larval development time, survival, wandering larvae weight, emerged adult body mass, reproduction, and juvenile hormone titer. Our results showed that A. tumida females exhibited a strong preference for ovipositing on bee pupae compared to other diets, while showing reluctance toward honey. Moreover, A. tumida larvae that were fed on bee pupae displayed accelerated growth compared to those fed on other diets. Furthermore, A. tumida fed on bee pupae exhibited higher weights for wandering larvae, and emerged adult, increased pupation rates, enhanced fecundity and fertility, as well as a larger number of unilateral ovarioles during the larval stage when compared to those fed on other diets. Overall, the results indicate that the oviposition preferences of A. tumida females are adaptive, as their choices can enhance the fitness of their offspring. This finding aligns broadly with the hypothesis of oviposition preference and larval performance. This study can provide a foundation for the development of attractants aimed at promoting the oviposition of the A. tumida adults.

Gut microbiota composition and gene expression changes induced in the Apis cerana exposed to acetamiprid and difenoconazole at environmentally realistic concentrations alone or combined.

Apis cerana is an important pollinator of agricultural crops in China. In the agricultural environment, A. cerana may be exposed to acetamiprid (neonicotinoid insecticide) and difenoconazole (triazole fungicide), alone or in combination because they are commonly applied to various crops. At present, our understanding of the toxicological effects of acetamiprid and difenoconazole on honey bee gut microbiomes is limited. The primary objective of this study was to explore whether these two pesticides affect honey bees' gut microbiota and to analyze the transcriptional effects of these two pesticides on honey bees' head and gut. In this study, adults of A. cerana were exposed to acetamiprid and/or difenoconazole by contaminated syrup at field-realistic concentrations for 10 days. Results indicated that acetamiprid and/or difenoconazole chronic exposure did not affect honey bees' survival and food consumption, whereas difenoconazole decreased the weight of honey bees. 16S rRNA sequencing suggested that difenoconazole and the mixture of difenoconazole and acetamiprid decreased the diversity index and shaped the composition of gut bacteria microbiota, whereas acetamiprid did not impact the gut bacterial community. The ITS sequence data showed that neither of the two pesticides affected the fungal community structure. Meanwhile, we also observed that acetamiprid or difenoconazole significantly altered the expression of genes related to detoxification and immunity in honey bees' tissues. Furthermore, we observed that the adverse effect of the acetamiprid and difenoconazole mixture on honey bees' health was greater than that of a single mixture. Taken together, our study demonstrates that acetamiprid and/or difenoconazole exposure at field-realistic concentrations induced changes to the honey bee gut microbiome and gene expression.

Xylocopa caerulea and Xylocopa auripennis harbor a homologous gut microbiome related to that of eusocial bees.

Background: Eusocial bees, such as bumblebees and honey bees, harbor host-specific gut microbiota through their social behaviors. Conversely, the gut microbiota of solitary bees is erratic owing to their lack of eusocial activities. Carpenter bees (genus Xylocopa) are long-lived bees that do not exhibit advanced eusociality like honey bees. However, they often compete for nests to reproduce. Xylocopa caerulea and Xylocopa auripennis are important pollinators of wild plants on Hainan Island. Whether they have host-specific bacteria in their guts similar to eusocial bees remains unknown. Methods: We targeted the bacterial 16S rRNA V3-V4 region to investigate the diversity of bacterial symbionts in the fore-midgut and hindgut of two carpenter bees, X. caerulea and X. auripennis. Results: A maximum of 4,429 unique amplicon sequence variants (ASVs) were detected from all samples, belonging to 10 different phyla. X. caerulea and X. auripennis shared similar bacterial community profiles, with Lactobacillaceae, Bifidobacteriaceae, and Orbaceae being dominant in their entire guts. X. caerulea and X. auripennis harbor a highly conserved core set of bacteria, including the genera Candidatus Schmidhempelia and Bombiscardovia. These two bacterial taxa from carpenter bees are closely related to those isolated from bumblebees. The LEfSe analysis showed that Lactobacillaceae, Bifidobacteriaceae, and the genus Bombilactobacillus were significantly enriched in the hindguts of both carpenter bees. Functional prediction suggested that the most enriched pathways were involved in carbohydrate and lipid metabolism. Conclusions: Our results revealed the structure of the gut microbiota in two carpenter bees and confirmed the presence of some core bacterial taxa that were previously only found in the guts of social bees.

Phylogenetic Analysis of Small Hive Beetles From Native to Introduced Populations.

The small hive beetle (SHB), a social parasite of beehives, is native to sub-Saharan Africa and has spread to America, Europe, and Australia. Recently, these beetles invaded China, causing widespread colony collapses in the honeybee, Apis cerana. In this study, single nucleotide polymorphisms (SNPs) were identified in the beetle genome from its native range (Africa), a region that was invaded by SHBs nearly 30 years ago (America), and more recent invasions (Asia). The beetles in the United States formed the earliest branch and show signs of two decades of gene flow and local adaptation to differentiate this population from the native ones. The beetles in China were deep branched and showed the highest fixation index when compared to the US populations. The number of SNPs in overexpressed genes was significantly higher than the transcriptome. Gene-expression profiles presented here distinguish the characters between adult and larvae SHBs.

Bioactive characterization of multifloral honeys from Apis cerana cerana, Apis dorsata, and Lepidotrigona flavibasis.

Honey is a complex food product, and has been linked to a number of substantial health advantages. The aim of this study was to assess the phenolic compounds, organic acids, microbial community, antioxidant activity, and antimicrobial activity of multifloral honeys produced by Apis cerana cerana, A. dorsata, and Lepidotrigona flavibasis in Hainan province, China. Our results illustrated that chlorogenic acid was the major phenolic component in all honeys. L. flavibasis honey showed the greatest antioxidant activity (DPPH IC50 value, 7.66 mg/mL; FRAP value, 5217.06 µmol TE/kg), as well as the highest levels of proline (548.64 mg/kg), total flavonoid (11.67 mg QE/100 g), total phenolic (132.73 mg GAE/100 g), and Lactobacillus (96.28 %). Besides, all honeys were found to have a broad spectrum of antibacterial activity. Overall, our data imply that Hainan honeys, particularly stingless bee honeys, have been beneficial components of human diets.

Identification of sex chromosomes and primary sex ratio in the small hive beetle, a worldwide parasite of honey bees.

BACKGROUND: The small hive beetle (SHB), Aethina tumida, has emerged as a worldwide threat to honey bees in the past two decades. These beetles harvest nest resources, feed on larval bees, and ultimately spoil nest resources with gelatinous slime together with the fungal symbiont Kodamaea ohmeri. RESULTS: Here, we present the first chromosome-level genome assembly for the SHB. With a 99.1% representation of conserved (BUSCO) arthropod genes, this resource enables the study of chemosensory, digestive, and detoxification traits critical for SHB success and possible control. We use this annotated assembly to characterize features of SHB sex chromosomes and a female-skewed primary sex ratio. We also found chromosome fusion and a lower recombination rate in sex chromosomes than in autosomes. CONCLUSIONS: Genome-enabled insights will clarify the traits that allowed this beetle to exploit hive resources successfully and will be critical for determining the causes of observed sex ratio asymmetries.

Residual toxicity and sublethal effects of chlorantraniliprole on Plutella xylostella (lepidoptera: plutellidae).

BACKGROUND: The diamondback moth (DBM), Plutella xylostella (L.), is the most important pest of cruciferous vegetables in the world. Chlorantraniliprole is a novel anthranilic diamide insecticide registered for the control of lepidopteran pests. The dose response, residual toxicity and sublethal effects of chlorantraniliprole applied for 48 h at LC10 (0.02 mg L(-1) ) and LC25 (0.06 mg L(-1) ) on P. xylostella were investigated. RESULTS: Leaf-dip bioassays showed that chlorantraniliprole had a high level of toxicity against larvae of P. xylostella, and the 48 h LC50 values were 0.23 and 0.25 mg L(-1) for a susceptible and field strain respectively. Chlorantraniliprole also had a long-lasting effect when the larvae were exposed to chlorantraniliprole field sprayed on radish seedlings. Sublethal effects of chlorantraniliprole were indicated by reduced pupation, pupal weight and adult emergence rates. There was also an increase in the duration of female preoviposition period, decreased fecundity and egg hatch and decreased survival rates of the offspring. The mean values of the net reproductive rate (R0), intrinsic rate of increase (r(m)), finite rate of increase (λ) were significantly lower in the treatment than in control groups. CONCLUSIONS: These results indicate that chlorantraniliprole is effective against P. xylostella. The sublethal concentrations of chlorantraniliprole may reduce the population growth of P. xylostella by decreasing its survival and reproduction, and by delaying its development.