Baosheng Liu

Interaction of Xestia c-nigrum Granulovirus with Peritrophic Matrix and Spodoptera litura Nucleopolyhedrovirus in Spodoptera litura

Abstract Xestia c-nigrum granulovirus (XcGV) was tested for its ability to increase Spodoptera litura nucleopolyhedrovirus (SlNPV) infection in larvae of S. litura (F.). The interaction of XcGV with peritrophic matrix and SlNPV in S. litura also was studied to account for the synergism. In dose-response bioassays with a constant XcGV concentration of 5-mg/ml capsules and SlNPV concentration that varied from 103 to 107 polyhedral inclusion bodies (PIB) per larva, XcGV increased the virulence of SlNPV infection in fifth instars of S. litura. The lethal concentration of 50% individuals (LC50) of SlNPV combined with XcGV was 3.35 × 105PIB/ml, which was significantly lower than that of SlNPV alone (2.17 × 106). Compared with 107 PIB/ml SlNPV alone, the lethal time of 50% individuals (LT50) of 107 PIB/ml SlNPV combined with XcGV was not significantly shortened. In addition, no significant improvement in the activity and killing speed of SlNPV progeny was noted after propagation with XcGV, indicating that native characters of SlNPV associated with viral potency were not altered by XcGV. Investigation via environmental scanning electronic microscopy showed that the peritrophic matrix (PM) of S. litura exposed to XcGV or XcGV enhancin, or the combination treatment, was markedly disrupted. The outer surface of the PM was loose, or ruptured, which potentially facilitated the passage of virions through the PM. Therefore, it is reasonable to conclude that the synergy between XcGV and SlNPV was closely associated with the disruption of the PM in S. litura.

Interactions between Meteorus pulchricornis and Spodoptera exigua multiple nucleopolyhedrovirus

Abstract Baculoviruses may interact with parasitoids in the same host. A previous study has shown that infection of larvae with Spodoptera litura nucleopolyhedrovirus (SpltNPV) was deleterious to the survival and development of Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae). In this paper, the interactions between M. pulchricornis and Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) in Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), a permissive host of the virus and parasitoid, were investigated. The results showed that the effect of M. pulchricornis on SeMNPV and the effect of the virus on the parasitoid both depended on the concentration of the virus and the interval between viral infection and parasitism. Whether S. exigua was treated with the parasitoid and virus simultaneously or 1 day apart, the biological activities of 105, 106, and 107 OBs/mL SeMNPV were all significantly improved by M. pulchricornis. In contrast, the biological activity of 103 OBs/mL SeMNPV was significantly decreased when the host was exposed to the virus and parasitoid simultaneously. Regarding the impact of SeMNPV on M. pulchricornis, exposing the host to the parasitoid and SeMNPV with concentrations lower than 106 occlusion bodies (OBs)/mL produced no negative effects on the parasitoid. The results also showed that ingestion of SeMNPV by adult stage M. pulchricornis significantly increased the number of parasitoid offspring that successfully emerged from the host. Furthermore, M. pulchricornis was found to transmit SeMNPV among populations of S. exigua. Taken together, these findings indicate that M. pulchricornis integrated with an appropriate concentration of SeMNPV has the potential to improve the efficacy of biological control against S. exigua.

Molecular characterization of the piggyBac-like element, a candidate marker for phylogenetic research of Chilo suppressalis (Walker) in China

BackgroundTransposable elements (TEs, transposons) are mobile genetic DNA sequences. TEs can insert copies of themselves into new genomic locations and they have the capacity to multiply. Therefore, TEs have been crucial in the shaping of hosts’ current genomes. TEs can be utilized as genetic markers to study population genetic diversity. The rice stem borer Chilo suppressalis Walker is one of the most important insect pests of many subtropical and tropical paddy fields. This insect occurs in all the rice-growing areas in China. This research was carried out in order to find diversity between C. suppressalis field populations and detect the original settlement of C. suppressalis populations based on the piggyBac-like element (PLE). We also aim to provide insights into the evolution of PLEs in C. suppressalis and the phylogeography of C. suppressalis.ResultsHere we identify a new piggyBac-like element (PLE) in the rice stem borer Chilo suppressalis Walker, which is called CsuPLE1.1 (GenBank accession no. JX294476). CsuPLE1.1 is transcriptionally active. Additionally, the CsuPLE1.1 sequence varied slightly between field populations, with polymorphic indels (insertion/deletion) and hyper-variable regions including the identification of the 3′ region outside the open reading frame (ORF). CsuPLE1.1 insertion frequency varied between field populations. Sequences variation was found between CsuPLE1 copies and varied within and among field populations. Twenty-one different insertion sites for CsuPLE1 copies were identified with at least two insertion loci found in all populations.ConclusionsOur results indicate that the initial invasion of CsuPLE1 into C. suppressalis occurred before C. suppressalis populations spread throughout China, and suggest that C. suppressalis populations have a common ancestor in China. Additionally, the lower reaches of the Yangtze River are probably the original settlement of C. suppressalis in China. Finally, the CsuPLE1 insertion site appears to be a candidate marker for phylogenetic research of C. suppressalis.

Cloning of Two Acetylcholinesterase Genes and Analysis of Point Mutations Putatively Associated with Triazophos Resistance in Chilo auricilius (Lepidoptera: Pyralidae).

ABSTRACT Acetylcholinesterase (AChE) is the target of organophosphate (OP) and carbamate insecticides. Mutations in the AChE gene (ace) leading to decreased insecticide susceptibility is the main resistance mechanism in insects. In this study, two Chilo auricilius acetylcholinesterase genes, designated as Caace1 and Caace2, were cloned using RT-PCR and RACE. Caace1 cDNA is 2534 bp, with ORF of 2082 bp, and it encodes an acetylcholinesterase 1 (CaAChE1) protein comprising a calculated 693 amino acid (aa) residues. Caace2 cDNA contains 2280 bp, with a full-length ORF of 1917 bp, encoding acetylcholinesterase 2 (CaAChE2) comprising a calculated 638 aa residues. At the aa level, CaAChE1 displays the highest similarity (97%) with the Chilo suppressalis AChE1, and CaAChE2 shows the highest similarity with the C. suppressalis AChE2 (99%). From the restriction fragment length polymorphism (RFLP) PCR (RFLP-PCR) analysis, one mutation in Caace1, similar to the ace1 mutation associated with triazophos resistance in C. suppressalis, was detected. Detailed examination of field populations of C. auricilius indicated this resistance mutation in C. auricilius is still quite infrequent. Based on the assay of AChE activity and RFLP-PCR testing, an individual that contains resistance mutation has lower AChE activities, while the individual that does not contain the resistance mutation has higher AChE activities. This study provides a basis for future investigations into the mechanism of OP resistance in C. auricilius, as well as a guidance for C. auricilius control with reasonable choice of pesticides.

Synergistic and additive interactions of Serratia marcescens S-JS1 to the chemical insecticides for controlling Nilaparvata lugens (Hemiptera: Delphacidae)

Abstract The combined use of entomopathogens and chemical agents has been suggested as an alternative strategy to control pest insects. However, the effectiveness of combinations of entomopathogenic bacteria and insecticides against rice planthoppers is largely unknown. Here, we evaluated the separate and combined effects of an entomopathogenic bacterium, Serratia marcescens S-JS1, and spirotetramat or thiamethoxam insecticides against third-instar nymphs of Nilaparvata lugens Stål (Hemiptera: Delphacidae) under laboratory and greenhouse conditions. Under laboratory conditions, the combinations caused higher mortality in the third-instar nymphs of N. lugens and produced a synergistic or additive effect compared with the treatments with either bacterial suspension or insecticide alone. Application of S-JS1 (1 × 109 cfu/ml) in combination with 20 mg/liter spirotetramat resulted in 80.5% of N. lugens nymphal mortality, compared with 52.7% in spirotetramat alone treatments, and interactions resulted in a synergistic responses. Other combination treatments of S-JS1 with either insecticide concentration all exhibited additive interactions. In further greenhouse tests, S-JS1 (1 × 109 cfu/ml) + spirotetramat (20 mg/liter) and S-JS1 (1 × 109 cfu/ml) + thiamethoxam (5 mg/liter) showed additive effects against the nymphs, and were found to be most effective relative to their individual treatments on days 5 and 9. Our results indicate that S. marcescens S-JS1 combined with insecticide may provide a promising new strategy for controlling N. lugens.

Differential Expression of P450 Genes and nAChR Subunits Associated With Imidacloprid Resistance in Laodelphax striatellus (Hemiptera: Delphacidae)

Abstract Imidacloprid is a key insecticide used for controlling sucking insect pests, including the small brown planthopper (Laodelphax striatellus, Fallén) (Hemiptera: Delphacidae), an important agricultural pest of rice. A strain of L. striatellus (YN-ILR) developed 21-fold resistance when selected with imidacloprid on a susceptible YN strain. An in vitro study on piperonyl butoxide synergism indicated that enhanced detoxification mediated by cytochrome P450s contributed to imidacloprid resistance to some extent, and multiple P450 genes showed altered expression in the imidacloprid-resistantYN-ILR strain compared with the susceptibleYN strain (CYP425B1-CYP6BD10 had 1.51- to 11.45-fold higher expression, CYP4CE2-CYP4DD1V2 had 0.12- to 0.57-fold lower expression). While there were no mutations in target nicotinic acetylcholine receptor (nAChR) genes, subunits of Lsα1, Lsβ1, and Lsβ3 in the YN-ILR strain showed 3.86-, 4.39-, and 2.59-fold higher expression and Lsa8 displayed 0.38-fold lower expression than the YN strain. Moreover, 21-fold moderate imidacloprid resistance in individuals of L. striatellus did not produce a fitness cost. The findings suggest that L. striatellus has the capacity to develop resistance to imidacloprid through P450 detoxification and potential target nAChR expression changes, and moderate imidacloprid resistance was not associated with a fitness cost.

Resistance monitoring and cross-resistance role of CYP6CW1 between buprofezin and pymetrozine in field populations of Laodelphax striatellus (Fallén)

Monitoring resistance and investigating insecticide resistance mechanisms are necessary for controlling the small brown planthopper, Laodelphax striatellus. The susceptibility to four common insecticides of L. striatellus collected from Jiangsu, Anhui, Zhejiang and Jilin provinces of China in 2015 was monitored. The results showed that all field populations remained susceptible to chlorpyrifos and thiamethoxam with resistance ratios (RRs) of 2.3- to 9.5 and 1.6- to 3.3, respectively, while the insects had developed moderate pymetrozine resistance with RRs of 18.7 to 34.5. Resistance against buprofezin had developed to an alarmingly high level in three southeastern provinces of China with RRs of 108.8 to 156.1, but in Jilin it had an RR of only 26.6. Moreover, in line with both the buprofezin and pymetrozine resistance levels, we found LsCYP6CW1 to be over-expressed in all field L. striatellus populations, which indicated that it might be important for cross-resistance between buprofezin and pymetrozine. RNA interference (RNAi) ingestion resulted in the effective suppression of LsCYP6CW1 expression, and significantly increased susceptibility to both buprofezin and pymetrozine compared with the control, which further confirmed that overexpression of LsCYP6CW1 was involved in the cross-resistance to buprofezin and pymetrozine in field L. Striatellus populations.