Genome of the hoverfly Eupeodes corollae provides insights into the evolution of predation and pollination in insects

Chromosome-level genome assembly of marmalade hoverfly Episyrphus balteatus (Diptera: Syrphidae)

Episyrphus balteatus can provide dual ecosystem services including pest control and pollination, which the larvae are excellent predators of aphid pest whereas adults are efficient pollinator. In this study, we assembled a high-quality genome of E. balteatus from northern China geographical population at the chromosome level by using Illumina, PacBio long reads, and Hi-C technologies. The 467.42 Mb genome was obtained from 723 contigs, with a contig N50 of 9.16 Mb and Scaffold N50 of 118.85 Mb, and 90.25% (431.75 Mb) of the assembly was anchored to 4 pseudo-autosomes and one pseudo-heterosome. In total, 14,848 protein-coding genes were annotated, and 95.14% of genes were fully represented in NR, GO, KEGG databases. Besides, we also obtained the mitochondrial genome of E. balteatus of 16, 837 bp in length with 37 typical mitochondrial genes. Overall, this high-quality genome is valuable for evolutionary and genetic studies of E. balteatus and other Syrphidae hoverfly species.

The chromosome-level genome assembly of Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae)

Aphidoletes aphidimyza is widely recognized as an effective predator of aphids in agricultural systems. However, there is limited understanding of its predation mechanisms. In this study, we generated a high-quality chromosome level of the A. aphidimyza genome by combining PacBio, Illumina, and Hi-C data. The genome has a size of 192.08 Mb, with a scaffold N50 size of 46.85 Mb, and 99.08% (190.35 Mb) of the assembly is located on four chromosomes. The BUSCO analysis of our assembly indicates a completeness of 97.8% (n = 1,367), including 1,307 (95.6%) single-copy BUSCOs and 30 (2.2%) duplicated BUSCOs. Additionally, we annotated a total of 13,073 protein-coding genes, 18.43% (35.40 Mb) repetitive elements, and 376 non-coding RNAs. Our study is the first time to report the chromosome-scale genome for the species of A. aphidimyza. It provides a valuable genomic resource for the molecular study of A. aphidimyza.

A high-quality genome of the convergent lady beetle, Hippodamia convergens

Here, we describe a high-quality genome assembly and annotation of the convergent lady beetle, Hippodamia convergens (Coleoptera: Coccinellidae). The highest quality unmasked genome comprises 619 megabases (Mb) of chromosomal DNA, organized into 899 contigs, with a contig N50 score of 89 Mbps. The genome was assessed to be 96% complete (BUSCO). Reconstruction of a whole-genome phylogeny resolved H. convergens as sister to the Harlequin lady beetle, Harmonia axyridis, and nested within a clade of several known agricultural pests.

Different Sensitivity of Flower-Visiting Diptera to a Neonicotinoid Insecticide: Expanding the Base for a Multiple-Species Risk Assessment Approach

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 (Sphaerophoria rueppellii, Eristalinus aeneus) and one tachinid fly (Exorista larvarum) 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 (LD50) for the three species. The methodology consisted in applying 1 µL of the test solution on the thorax of each insect. Sphaerophoria rueppelli was the most sensitive species (LD50 = 10.23 ng/insect), and E. aeneus (LD50 = 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 Apis mellifera 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.

Episyrphus balteatus symbiont variation across developmental stages, living states, two sexes, and potential horizontal transmission from prey or environment

Introduction

Episyrphus balteatus is one representative Syrphidae insect which can provide extensive pollination and pest control services. To date, the symbiont composition and potential acquisition approaches in Syrphidae remain unclear.

Methods

Herein, we investigated microbiota dynamics across developmental stages, different living states, and two sexes in E. balteatus via full-length 16S rRNA genes sequencing, followed by an attempt to explore the possibility of symbiont transmission from prey Megoura crassicauda to the hoverfly.

Results

Overall, Proteobacteria and Firmicutes were the dominant bacteria phyla with fluctuating relative abundances across the life stage. Cosenzaea myxofaciens is dominant in adulthood, while Enterococcus silesiacus and Morganella morganii dominate in larvae and pupae of E. balteatus, respectively. Unexpectedly, Serratia symbiotica, one facultative endosymbiont commonly harbored in aphids, was one of the predominant bacteria in larvae of E. balteatus, just behind Enterococcus silesiacus. In addition, S. symbiotica was also surprisingly most dominated in M. crassicauda aphids (92.1% relative abundance), which are significantly higher than Buchnera aphidicola (4.7% relative abundance), the primary obligate symbiont of most aphid species. Approximately 25% mortality was observed among newly emerged adults, of which microbiota was also disordered, similar to normally dying individuals. Sexually biased symbionts and 41 bacteria species with pairwise co-occurrence in E. balteatus and 23 biomarker species for each group were identified eventually. Functional prediction showed symbionts of hoverflies and aphids, both mainly focusing on metabolic pathways. In brief, we comprehensively explored the microbiome in one Syrphidae hoverfly using E. balteatus reared indoors on M. morganii as the model, revealed its dominated symbiont species, identified sexually biased symbionts, and found an aphid facultative endosymbiont inhabited in the hoverfly. We also found that the dominated symbiotic bacteria in M. crassicauda are S. symbiotica other than Buchnera aphidicola.

Discussion

Taken together, this study provides new valuable resources about symbionts in hoverflies and prey aphids jointly, which will benefit further exploring the potential roles of microbiota in E. balteatus.

Mutagenesis of Odorant Receptor Coreceptor Orco Reveals the Odorant-Detected Behavior of the Predator Eupeodes corollae

The successful mating of the hoverfly and the search for prey aphids are of great significance for biological control and are usually mediated by chemical cues. The odorant receptor co-receptor (Orco) genes play a crucial role in the process of insect odor perception. However, the function of Orco in the mating and prey-seeking behaviors of the hoverfly remains relatively unexplored. In this study, we characterized the Orco gene from the hoverfly, Eupeodes corollae, a natural enemy insect. We used the CRISPR/Cas9 technique to knock out the Orco gene of E. corollae, and the EcorOrco-/- homozygous mutant was verified by the genotype analysis. Fluorescence in situ hybridization showed that the antennal ORN of EcorOrco-/- mutant lack Orco staining. Electroantennogram (EAG) results showed that the adult mutant almost lost the electrophysiological response to 15 odorants from three types. The two-way choice assay and the glass Y-tube olfactometer indicated that both the larvae and adults of hoverflies lost their behavioral preference to the aphid alarm pheromone (E)-β-farnesene (EBF). In addition, the mating assay results showed a significant decrease in the mating rate of males following the knock out of the EcorOrco gene. Although the mating of females was not affected, the amount of eggs being laid and the hatching rate of the eggs were significantly reduced. These results indicated that the EcorOrco gene was not only involved in the detection of semiochemicals in hoverflies but also plays a pivotal role in the development of eggs. In conclusion, our results expand the comprehension of the chemoreceptive mechanisms in the hoverflies and offers valuable insights for the advancement of more sophisticated pest management strategies.

Effect of prey density on the performance of Eupeodes corollae and its predation rate against the cabbage aphid, Brevicorynae brassicae (L.)

Eupeodes corollae (F.) (Diptera: Syrphidae) is the most abundant syrphid fly which is distributed worldwide and is the sole predator of aphids. Therefore, the present study was conducted to evaluate the predation rate and functional response of E. corollae against the cabbage aphid, Brevicoryne brassicae (L.). The experiment was carried out under laboratory conditions at 25 ± 2°C with 60-70% relative humidity. The results revealed that age-specific net predation rate (qx) increased after the 4th day and a peak was recorded on the 10th day of pivotal age in the third larval instar. The stable host kill rate and finite host kill rate of E. corollae were 18.63 and 21.07, respectively, against the B. brassicae and predicted that a mean of 20.78 aphids was needed for E. corollae to produce one offspring. A negative linear coefficient (P < 0) indicated the type II functional response for all larval instars of E. corollae against the B. brassicae. At higher prey density, the prey consumption was significantly at par with second and third instar larvae of E. corollae as the prey consumption was increased with increasing the prey density, which then decreased after attaining the upper asymptote (76.40 and 81.40% consumption, respectively). The Roger's predator random equation for type II functional response was fitted to estimate attack rate (a) and handling time (Th). The maximum prey consumption was recorded for third instar of E. corollae with a higher attack rate (0.336 h-1) and lower handling time (0.514 h) against B. brassicae, followed by the second and first instar. Thus, it is concluded that the third larval instar of E. corollae was the voracious feeder and used as an efficient biocontrol agent in the IPM programme.

Chromosome-level genome assembly of Dastarcus helophoroides provides insights into CYP450 genes expression upon insecticide exposure

BACKGROUND

Dastarcus helophoroides is an important natural enemy of cerambycids, and is wildly used in biological control of pests. Nevertheless, the absence of complete genomic information limits the investigation of the underlying molecular mechanisms. Here, a chromosome-level of Dastarcus helophoroides genome is assembled using a combination strategy of Illumina, PacBio, 10x™ Genomics, and Hi-C.

RESULTS

The final assembly is 609.09 Mb with contig N50, scaffold N50 and GC content of 5.46 Mb, 42.56 Mb and 31.50%, respectively, and 95.25% of the contigs anchor into 13 chromosomes. In total 14 890 protein-coding genes and 65.37% repeat sequences are predicted in the assembly genome. The phylogenetic analysis of single-copy gene families shared among 20 insect species indicates that Dastarcus helophoroides is placed as the sister species to clade (Nitidulidae+Curculionoidea+Chrysomeloidea) + Tenebrionoidea, and diverges from the related species ~242.9 Mya. In total 36 expanded gene families are identified in Dastarcus helophoroides genome, and are functionally related to drug metabolism and metabolism of xenobiotics by cytochrome P450. Some members of CYP4 Clade and CYP6 Clade are up-regulated in Dastarcus helophoroides adults upon insecticide exposure, of which expressions of DhCYP4Q, DhCYP6A14X1 and DhCYP4C1 are significantly up-regulated. The silencing of the three genes leads to adults more sensitive to insecticide and increased knocked-down rate, which may indicate their critical roles in stress resistance and detoxication.

CONCLUSION

Our study systematically integrated the chromosome-level genome, transcriptome and gene expression of Dastarcus helophoroides, which will provide valuable resources for understanding mechanisms of pesticide metabolism, growth and development, and utilization of the natural enemy in integrated control. © 2022 Society of Chemical Industry.

The genome sequence of the Vagrant Hoverfly, Eupeodes corollae (Fabricius, 1794)

We present a genome assembly from an individual female Eupeodes corollae (the Vagrant Hoverfly; Arthropoda; Insecta; Diptera; Syrphidae). The genome sequence is 648.2 megabases in span. Most of the assembly is scaffolded into four chromosomal pseudomolecules, including with the X sex chromosome. The mitochondrial genome has also been assembled and is 18.3 kilobases in length.

Conserved Odorant Receptor, EcorOR4, Mediates Attraction of Mated Female Eupeodes corollae to 1-Octen-3-ol

Odorant receptors (ORs) in insects are crucial for the detection of chemical signals. However, the functions of the conserved OR genes among insect species are rarely studied. In this study, we analyzed a well-conserved OR clade in Diptera insects and cloned a gene from this clade, EcorOR4, in the hoverfly Eupeodes corollae. Real-time quantitative PCR showed that EcorOR4 was highly expressed in the antennae and upregulated in the mated females, and in vitro functional characterization showed that EcorOR4 was narrowly tuned to 1-octen-3-ol. Electroantennogram assays revealed that the antennal response of mated females to 1-octen-3-ol was significantly higher than that of mated males, but no significant differences were observed between male and female virgins. Finally, a Y-tube olfactometer bioassay showed that 1-octen-3-ol is an attractant for only mated female E. corollae adults. These results demonstrate that EcorOR4 is involved in the detection of 1-octen-3-ol and that this compound may affect the host-finding and oviposition behavior in female E. corollae.