Evolutionary analysis and biological characterization of a novel alphabaculovirus isolated from Mythimna separata.

Baculoviruses are insect-specific pathogens. Novel baculovirus isolates provide new options for the biological control of pests. Therefore, research into the biological characteristics of newly isolated baculoviruses, including accurate classification and nomenclature, is important. In this study, a baculovirus was isolated from Mythimna separata and its complete genome sequence was determined by next-generation sequencing. The double-stranded DNA genome was 153 882 bp in length, encoding 163 open reading frames. The virus was identified as a variant of Mamestra brassicae multiple nucleopolyhedrovirus (MbMNPV) and designated Mamestra brassicae multiple nucleopolyhedrovirus CHN1 (MbMNPV-CHN1) according to ultrastructural analysis, genome comparison and phylogenetic analysis. Phylogenetic inference placed MbMNPV-CHN1 in a clade containing isolates of MacoNPV-A, MacoNPV-B and MbMNPV, which we have designated the Mb-McNPV group. The genomes of isolates in the Mb-McNPV group exhibited a high degree of collinearity with relatively minor differences in the content of annotated open reading frames. The development of codon usage bias in the Mb-McNPV group was affected mainly by natural selection. MbMNPV-CHN1 shows high infectivity against seven species of Lepidoptera. The yield of MbMNPV-CHN1 in the fourth- and fifth-instar M. separata larvae was 6.25×109-1.23×1010 OBs/cadaver. Our data provide insights into the classification, host range and virulence differences among baculoviruses of the Mb-McNPV group, as well as a promising potential new baculoviral insecticide.

[Identification and biological characteristics of a pathogen causing leaf blight of Rehmannia glutinosa].

Leaf blight outbroke in Rehmannia glutinosa plantation in Wenxian county, Henan province in 2019. R. glutinosa plants with diseased leaves were collected from the plantation, and three strains were isolated from the diseased leaf samples. Pathogenicity test, morphological observation, and phylogenetic analysis of ITS, EF1-α, and Tub suggested that they were respectively Fusarium proliferatum, F. oxysporum, and F.acuminatum. Among them, F. acuminatum, as a pathogen of R. glutinosa leaf disease, had never been reported. To clarify the biological characteristics of F. acuminatum, this study tested the influence of light, pH, temperature, medium, carbon source, and nitrogen source on the mycelial growth rate of the pathogen during a 5-day culture period, and explored the lethal temperature. The results showed that the mycelia grew well under the photoperiod of 12 h light/12 h darkness, at 5-40 ℃(optimal temperature: 25 ℃), at pH 4-11(optimal pH: 7.0), on a variety of media(optimal medium: oatmeal agar), and in the presence of diverse carbon and nitrogen sources(optimal carbon source: soluble starch; optimal nitrogen source: sodium nitrate). The lethal temperature was verified to be 51 ℃(10 min). The conclusion is expected to lay a scientific basis for diagnosis and control of R. glutinosa leaf diseases caused by F. acuminatum.

Improved effects of Helicoverpa armigera nucleopolyhedrovirus integrated with Campoletis chlorideae against H. armigera and impact of the virus on the parasitoid.

BACKGROUND: Combined use can be an effective measure to improve pest control by viruses and parasitic wasps. However, not all combinations of natural enemies show improved effects. Helicoverpa armigera nucleopolyhedrovirus (HearNPV) and Campoletis chlorideae Uchida are two important natural enemies of Helicoverpa armigera. This study aimed to investigate the combined effects of C. chlorideae and HearNPV against H. armigera larvae and the impact of HearNPV on C. chlorideae. RESULTS: The combination of HearNPV and C. chlorideae exerted increased mortality on H. armigera when C. chlorideae parasitized larvae one day after infection with HearNPV. C. chlorideae could distinguish between HearNPV-infected and noninfected larvae. Besides influencing host selection of C. chlorideae, HearNPV infection had negative effects on the development and reproduction of C. chlorideae. The developmental time of C. chlorideae was significantly prolonged and the percentage of emergence and adult eclosion of C. chlorideae was lower in infected hosts. The adult wasps were also smaller in body size, and female adults had fewer eggs when they developed in virus-infected hosts. CONCLUSIONS: HearNPV combined with C. chlorideae could improve the efficacy of biological control against H. armigera. The results provided valuable information on the importance of timing in the combined use of HearNPV and C. chlorideae for the biological control of H. armigera. © 2023 Society of Chemical Industry.

Sublethal Effects of Thiamethoxam on Biological Traits and Detoxification Enzyme Activities in the Small Brown Planthopper, Laodelphax striatellus (Fallén).

The small brown planthopper (Laodelphax striatellus (Fallén), Hemiptera: Delphacidae), is an important agricultural pest of rice, and neonicotinoid insecticides are commonly used for controlling L. striatellus. However, the sublethal effects of thiamethoxam on L. striatellus remain relatively unknown. In this study, an age-stage life table procedure was used to evaluate the sublethal effects of thiamethoxam on the biological parameters of L. striatellus. Additionally, activities of carboxylesterase, glutathione S-transferase, and cytochrome P450 monooxygenase in the third instar nymphs were analyzed. The results indicated that the survival time of F0 adults and the fecundity of female adults decreased significantly after the third instar nymphs were treated with sublethal concentrations of thiamethoxam (LC15 0.428 mg/liter and LC30 0.820 mg/liter). The developmental duration, adult preoviposition period, total preoviposition period, and mean generation time of the F1 generation increased significantly, whereas the fecundity of the female adults, intrinsic rate of increase (ri), and finite rate of increase (λ) decreased significantly. The oviposition period was significantly shorter for the insects treated with LC30 than for the control insects. Neither sublethal concentrations had significant effects on the adult longevity, net reproduction rate (R0), or gross reproduction rate (GRR) of the F1 generation. The activities of carboxylesterase, glutathione-S-transferase, and cytochrome P450 monooxygenase increased significantly after the thiamethoxam treatments. These results indicate that sublethal concentrations of thiamethoxam can inhibit L. striatellus population growth and enhance detoxification enzyme activities.