De novo genome assembly of Bradysia cellarum (Diptera: Sciaridae), a notorious pest in traditional special vegetables in China.

Bradysia cellarum (Diptera: Sciaridae) is a destructive vegetable insect pest infesting more than 30 species of host plants from seven families in Asia and Europe. B. cellarum causes grave problems in Chinese chive, which originated in China and is cultivated widely in East Asia. The B. cellarum infestation results in economic losses and subsequent severe food safety problems in farm productions, insecticide resistance and environmental pollution. The genomic and molecular information of B. cellarum to delineate the biological features, insecticide resistance, evolution remains poorly understood. Herein, we decode the whole genome of B. cellarum to delineate the underlying molecular mechanisms causing insecticide resistance. We constructed a highly reliable genome for B. cellarum using PacBio, Illumina and 10X Genomics sequencing platforms. The genome size of B. cellarum was 375.91 Mb with a contig N50 of 1.57 Mb. A total of 16,231 genes were identified, among which 93.8% were functionally annotated, and 42.06% were repeat sequences. According to phylogenetic analysis, B. cellarum diverged from the common ancestor of Drosophila melanogaster and Musca domestica ~139.3-191.0 million years ago. Moreover, some important genes responsible for significant insecticide resistance, such as cytochrome P450s, ABC transporters and those involved in glutathione metabolism, were expanded in B. cellarum. We assembled a high-quality B. cellarum genome to provide valuable insights into their life history strategies, insecticide resistance and biological behaviours. It also lays the foundation for exploring gene structure and functional evolution, as well as comparative genomics of B. cellarum and other model insect species.

First Report of Rust Caused by Tranzschelia discolor on Peach Leaves in Shenzhou, China.

Peach (Prunus persica [L.] Batsch) as an economically important fruit tree is widely cultivated in Shenzhou, China. In September 2021, peach rust was observed in the peach tree in Shenzhou City, Hebei Province (lat. 38°02'56'' N, long. 115°54'57'' E, altitude 22 m). We investigated a peach orchard with a planting area of 1334 m2, where a total of 162 peach trees were planted, and found that about 10% of peach trees exhibited severe disease symptoms. The leaves of infected plant developed 100% disease symptoms, in which 50% of the infected leaves showed about 10 small pale-yellow spots on the front of leaves and reddish-brown pustules on the corresponding abaxial surface of leaves. Urediniospores varied from obovoid to clavate in shape, sometimes in irregular shape. They were orange-brown, echinulate near base with spines smaller towards apex and often smooth at apex, with germ pores 3-4 at equator, size ranging from 25.4 to 38.6 × 10.1 to 18.7 µm (n=100), and with wall 1 to 1.5µm thick at sides and 5-7 µm thick at apex. Golden capitate paraphyses were present, ranging from 25 to 40 µm in length, with a head in diameter of 12 to 14 µm and a tail in width of 5.2 to 6.5 µm. Based on the rust morphological characters, this pathogen was primarily identified as Tranzschelia discolor (Fuckel) Tranzschel & Litv. (Hiratsuka et al. 1992). For molecular identification, total DNA was extracted from 2 isolates, respectively, and the internal transcribed spacer (ITS) region was PCR-amplified using the primer set ITS5-u and ITS4-u (Pfunder et al. 2001). Obtained sequences were compared with sequences in the GenBank repository using BLAST algorithm. BLAST showed a 100% sequence identify to T. discolor (accession nos. AB097449、MT786217、KU712078、KY764179、MH599069). The sequence has been deposited in GenBank with (accession NO. ON950745 and ON950747). Thus, combining morphological observations and molecular identification, the isolate was identified as T. discolor. The pathogenicity was verified by inoculating the abaxial surface of peach leaves with a suspension of 1 × 106 urediniospores/ml. Peach leaves sprayed with sterile water were used as controls. The inoculated peach trees were placed in a greenhouse at 20°C under dark for 24 hours and maintained at 100% relative humidity to promote disease development. Next, the peach trees were grown in a greenhouse at 20°C with a 12 h day length and symptoms were observed on the leaves 14 days after inoculation. In contrast, the control leaves were asymptomatic. Previous studies reported that peach rust occurred in Oman, Korea and Brazil was caused by T. discolor. (Deadman M L, et al.2007, Shin, H D, et al. 2019, Vidal G S, et al. 2021). To our knowledge, this is the first report of T. discolor as a causal agent causing peach leaf rust in Northern China, which will enable us to rapidly diagnose this disease, identify the occurrence of this disease and develop adequate management strategies to control it in China.

Combining predatory mites and film mulching to control Bradysia cellarum (Diptera: Sciaridae) on Chinese chives, Allium tuberosum.

The subterranean insect Bradysia cellarum Frey (Diptera: Sciaridae) is a notorious and major pest of Chinese chives, Allium tuberosum Rottler ex Sprengle (Amaryllidaceae) in China. Current chemical control of B. cellarum results in low insecticide efficacy, high cost and pesticide resistance, therefore there is an urgent need for sustainable management. Here, greenhouse experiments were conducted to evaluate the potential biocontrol agent Stratiolaelaps scimitus Womersley (Acari: Laelapidae) against B. cellarum. The number of B. cellarum larvae in soil declined from 17.6 to 0 in 4 months after releasing predatory mites in high density (5,000 adults per row); treatment was less effective under low densities of 2500 adults per row. To determine whether S. scimitus can be used in combination with soil solarization by film mulching over 40 °C for 4 h, we also evaluated heat tolerance of S. scimitus in laboratory and its control efficacy against B. cellarum after high-temperature treatment mimicking the film mulching in greenhouse. As our results showed that egg hatchability of S. scimitus was 2.6% at 38 °C and adult survival rate was 2% at 40 °C for 4 h, respectively, we concluded S. scimitus was largely inviable and could not reproduce at 40 °C. This temperature was the baseline of soil solarization, suggesting predatory mites should be released after soil solarization. When using S. scimitus after soil solarization or when using soil solarization as single treatment, fly larvae declined similarly from initial density of 18 to 0 or 17.2 to 0, respectively, within a month. Thus, our study suggests the potential of S. scimitus as a biocontrol agent of B. cellarum in greenhouse, and the most effective strategy is to combine film mulching and predatory mites (after soil heating) to control B. cellarum in chive productions.

Effect of Spinosad Resistance on Transmission of Tomato Spotted Wilt Virus by the Western Flower Thrips (Thysanoptera: Thripidae).

Tomato spotted wilt virus (TSWV) is transmitted by Frankliniella occidentalis (Pergande) in a persistent-propagative manner. We previously observed significant results in terms of feeding behavior of spinosad-susceptible (Ivf03) and -resistant (Spin-R) strains of F. occidentalis using electrical penetration graph. TSWV transmission by the two strains was compared in the present study. The results showed that the titer of TSWV-N RNA (a part of S RNA of TSWV and encoding the nucleocapsid protein) in Ivf03 and Spin-R strains was not significantly different after a 48-h inoculation access period. The TSWV transmission rate did not significantly differ between the two strains and was 51.0% for Ivf03 and 44.4% for Spin-R. The virus transmission rate was significantly higher for males than females of both strains. The virus transmission rate for males and females of Ivf03 was 68.1 and 33.8%, respectively; however, in case of Spin-R, it was 60 and 28.8% for males and females, respectively. Additionally, number of probes and duration of probes were generally greater for viruliferous females of Ivf03 than for viruliferous females of Spin-R but the total number and duration of noningestion probes did not significantly differ between males of the two strains. The latter finding behavior may help explain the similar transmission rates for the susceptible and resistant strains.

Both host and diet shape bacterial communities of predatory mites.

Microbial communities, derived from food, ambient, and inner, can affect host ecological adaption and evolution. Comparing with most phytophagous arthropods, predators may have more opportunities to develop specific microbiota depending on the level of prey specialization. To explore how diet sources affect host microbial communities and vary across predator species, we considered 3 types of predators from Phytoseiidae (Acari: Mesostigmata): polyphagous (Amblyseius orientalis Ehara, Neoseiulus barkeri Hughes, and Amblyseius swirskii Athias-Henrio), oligophagous (Neoseiulus californicus McGregor), and monophagous (Phytoseiulus persimilis Athias-Henriot) predatory mites. The polyphagous species were fed on 2 types of diets, natural prey and alternative prey. By using 16S rRNA sequencing, we found that diet was the main source of microbiota in predatory mites, while there was no clear pattern affected by prey specialization. Among 3 polyphagous predators, host species had a larger impact than prey on microbial composition. Unlike A. orientalis or N. barkeri which showed consistency in their microbiota, prey switching significantly affected ß-diversity of bacterial composition in A. swirskii, with 56% of the microbial alteration. In short, our results confirmed the substantial influence of diet on host microbial construction in predatory species, and highlighted species differences in shaping the microbiota which are not necessarily related to prey specialization.

Fine structure of the compound eyes of the crepuscular moth Grapholita molesta (Busck 1916) (Lepidoptera: Tortricidae).

Morphological organization, ultrastructure and adaptational changes under different light intensities (10000, 100, 1, and 0.01 mW/m2) of the compound eye of the oriental fruit moth Grapholita molesta (Busck 1916) were investigated. Its superposition type of eyes consist of approximately 1072 ommatidia in males and 1029 ommatidia in females with ommatidial diameters of around 15 µm. Each ommatidium features a laminated corneal lens densely covered by corneal nipples of 256 nm in height. Crystalline cones are formed by four cone cells, proximally tapering to form a narrow crystalline tract with a diameter of 1.5 µm. Eight retinula cells, two primary and six secondary pigment cells per ommatidium are present. The 62.3 µm long rhabdom is divided into a thin 1.8 µm wide distal and a 5.2 µm wide proximal region. Distally the fused rhabdom consists of the rhabdomeres of seven retinula cells (R1-R7) and connects with the crystalline cone. In the proximal rhabdom region, the pigment-containing retinula cell R8 occupies a position in centre of the rhabdom while R1-R7 cells have taken peripheral positions. At this level each ommatidial group of retinula cells is surrounded by a tracheal tapetum. In response to changes from bright-light to dim-light adaptations, the pigment granules in the secondary pigment cells and retinula cells migrate distally, with a decrease in the length of crystalline tract.

The effects of circularly polarized light on mating behavior and gene expression in Anomala corpulenta (Coleoptera: Scarabaeidae).

Light is an important abiotic factor affecting insect behavior. In nature, linearly polarized light is common, but circularly polarized light is rare. Left circularly polarized (LCP) light is selectively reflected by the exocuticle of most scarab beetles, including Anomala corpulenta. Despite our previous research showing that this visual signal probably mediates their mating behavior, the way in which it does so is not well elucidated. In this study, we investigated how LCP light affects not only mating behavior but also gene expression in this species using RNA-seq. The results indicated that disruption of LCP light reflection by females of A. corpulenta probably affects the process by which males of A. corpulenta search for mates. Furthermore, the RNA-seq results showed that genes of the environmental signaling pathways and also of several insect reproduction-related amino acid metabolic pathways were differentially expressed in groups exposed and not exposed to LCP light. This implies that A. corpulenta reproduction is probably regulated by LCP light-induced stress. Herein, the results show that LCP light is probably perceived by males of the species, further mediating their mating behavior. However, this hypothesis needs future verification with additional samples.

High innate preference of black substrate in the chive gnat, Bradysia odoriphaga (Diptera: Sciaridae).

The chive gnat, Bradysia odoriphaga, is a notorious pest of Allium species in China. Colour trapping is an established method for monitoring and control of Bradysia species. In order to clarify the effect of colour preference of B. odoriphaga for the perched substrate, multiple-choice tests were used to assess the response of the chive gnat to different colour hues and brightness levels under different intensities of white illumination and two spectrally different illuminations. Given the choice among four colours differing in hue under different intensities of white illumination and two spectrally different illuminations, chive gnat adults significant preferred the black substrate, a lesser preference to brown and green substrates, and the least preference to orange substrate irrespective of illumination. Given the choice among four levels of brightness under the same illumination conditions as those in the previous experiment (different intensities of white illumination and two spectrally different illuminations), chive gnats preferred black substrate over dark grey, light grey and white substrates. Meanwhile, both virgin and mated adults significantly preferred black over other colour hues and brightness. Based on our results, we conclude that the chive gnat adults significantly prefer black substrates irrespective of colour hues and brightness. This behaviour does not alter with ambient light condition changes. No difference observed between choices of female and male adults. Our results provide new insight for understanding the colour choice behaviour in chive gnat and pave a way to improve monitoring and control of chive gnats and management.