Characteristics biological activities of the novel acaricide flupentiofenox against phytophagous mites.

Flupentiofenox, which has a unique chemical structure, is a novel acaricide that has been developed by the Kumiai Chemical Industry Co., Ltd. Flupentiofenox exerted significant acaricidal activities against spider mites Tetranychus urticae and Panonychus citri at all developmental stages even at extremely low concentrations, as compared with its practical concentration (80 ppm) for use in mites and was effective against spider mite populations that are resistant to widely used commercial acaricides. These results suggested that flupentiofenox could be used effectively for the control and prevention of spider mite infestation. Additionally, flupentiofenox had a more rapid effect than acetyl CoA carboxylase inhibitors, but it had a relatively slower effect than mitochondrial electron transport inhibitors and glutamate-gated chloride channel modulators. Overall, flupentiofenox is assumed to have a new mode of action.

Two year field study to evaluate the efficacy of Mamestra brassicae nucleopolyhedrovirus combined with proteins derived from Xestia c-nigrum granulovirus.

Japan has only three registered baculovirus biopesticides despite its long history of studies on insect viruses. High production cost is one of the main hindrances for practical use of baculoviruses. Enhancement of insecticidal effect is one possible way to overcome this problem, so there have been many attempts to develop additives for baculoviruses. We found that alkaline soluble proteins of capsules (GVPs) of Xestia c-nigrum granulovirus can increase infectivity of some viruses including Mamestra brassicae nucleopolyhedrovirus (MabrNPV), and previously reported that MabrNPV mixed with GVPs was highly infectious to three important noctuid pests of vegetables in the following order, Helicoverpa armigera, M. brassicae, and Autographa nigrisigna. In this study, small-plot experiments were performed to assess concentrations of MabrNPV and GVPs at three cabbage fields and a broccoli field for the control of M. brassicae. In the first experiment, addition of GVPs (10 µg/mL) to MabrNPV at 106 OBs/mL resulted in a significant increase in NPV infection (from 53% to 66%). In the second experiment, the enhancing effect of GVP on NPV infection was confirmed at 10-times lower concentrations of MabrNPV. In the third and fourth experiments, a 50% reduction in GVPs (from 10 µg/mL to 5 µg/mL) did not result in a lowering of infectivity of the formulations containing MabrNPV at 105 OBs/mL. These results indicate that GVPs are promising additives for virus insecticides.

Mamestra brassicae nucleopolyhedrovirus infection and enhancing effect of proteins derived from Xestia c-nigrum granulovirus in larvae of Mamestra brassicae and Helicoverpa armigera (Lepidoptera: Noctuidae) on cabbage.

The insecticidal effect of Mamestra brassicae nucleopolyhedrovirus (MabrNPV) T5 against Mamestra brassicae (L.) and Helicoverpa armnigera (Hiibner) (Lepidoptera: Noctuidae), important pests of various vegetables and ornamental crops in Japan as well as many other countries, and the enhancing activity of proteins derived from occlusion bodies of Xestia c-nigrum granulovirus (XecnGV) a-4, which was named GVPs, on the infectivity of MabrNPV were evaluated in a bioassay with second-instar larvae fed on virus-applied cabbage, Brassica oleracea L. var. capitata, plants. The lethal concentrations of MabrNPV achieving 95% mortality (LC95) were estimated to be 7.7 x 10(5) and 1.8 x 10(5) OBs per ml for M. brassicae and H. armigera, respectively, with MabrNPV-alone treatment. Because the mean areas of cabbage leaf consumed by one larva in 60 h were not significantly different between M. brassicae and H. armigera, we conclude that MabrNPV is more infectious to H. armigera than to M. brassicae. When larvae were fed on cabbage plants treated with 10(4) OBs per ml MabrNPV and various concentrations of the GVPs, the mortality of the two noctuid larvae increased in relation to GVP concentration. The requisite concentrations of the GVPs achieving 95% mortality with the MabrNPV for M. brassicae and H. armigera were estimated to be 5.93-8.30 and 1.94-3.48 microg/ml, respectively. In a comparison of the MabrNPV-alone treatment with equivalent 95% mortality, addition of GVPs increased the rate of larval death at younger instars, especially in M. brassicae. Our results indicate that GVPs are a potentially useful additive for improving the insecticidal efficacy of MabrNPV.

In vivo characterization of two granuloviruses in larvae of Mythimna separata (Lepidoptera: Noctuidae).

The pathogenicity of two granuloviruses (GVs), Xestia c-nigrum GV (XecnGV) and Pseudaletia unipuncta GV (PsunGV), was examined in Mythimna separata. Partial sequencing of the genome of PsunGV indicated that it is related closely to XecnGV, but considered to be a different species. PsunGV and XecnGV showed similar pathogenicity in terms of dose-mortality response and pattern of host mass changes following infection. Both GVs killed infected larvae in 2-3 weeks. Temporal changes in the concentrations of GV-specific DNA in the larval haemolymph were measured by using a real-time quantitative PCR. Viral DNA concentration increased quickly and reached a plateau at 60-72 h post-inoculation. Rates of budded virus (BV) production of each GV were estimated on the basis of viral DNA concentrations by a modified Gompertz model. The slopes of the estimated BV growth curves of both XecnGV and PsunGV in M. separata larvae were equivalent to that of Mamestra brassicae nucleopolyhedrovirus (NPV) in its original host, reported in our previous study. This suggested that BV production is not a major factor in the slower killing speed of GVs in comparison to NPVs. The GV-infected larvae survived for an additional 10 days or more after reaching a maximum level of BV concentration, and kept growing without pupation. These findings also suggested that the GVs have a unique mechanism to regulate the growth of host larvae.

Enhancement of nucleopolyhedrovirus infectivity against Mamestra brassicae (Lepidoptera: Noctuidae) by proteins derived from granulovirus and a fluorescent brightener.

The synergistic enhancement of nucleopolyhedrovirus (NPV) infection by granuloviruses (GVs) is well documented; and a GV granule protein, named viral enhancin, has been identified as an active contributor to this effect. We detected the presence of two proteins with molecular mass of 93 and 108 kDa in granules of a GV isolated from Xestia c-nigrum (L.) (XecnGV) as candidates for enhancin, and we confirmed that at least the 108-kDa protein enhances the infectivity of Mamestra brassicae nucleopolyhedrovirus (MabrNPV). We tested the effect of virion-free proteins obtained from XecnGV granules (GVPs) on MabrNPV infection, and we made a comparison with an enhancing chemical, the stilbene-derived fluorescent brightener Tinopal. Bioassay was performed employing the diet contamination method, by using second instars of Mamestra brassicae (L.) (Lepidoptera: Noctuidae). The enhancing effects of GVPs (0.1 mg/g diet) and Tinopal (1 mg/g diet) were estimated to be 70.7-81.5-fold and 26.9-33.7-fold, respectively, as calculated from the LC50 values of MabrNPV with or without the additives. The additives reduced the lethal time of MabrNPV-infected larvae and they caused death at a younger instar. These results suggest that GVPs can enhance MabrNPV infection as effectively as Tinopal.

In vivo characterization of a group II nucleopolyhedrovirus isolated from Mamestra brassicae (Lepidoptera: Noctuidae) in Japan.

A Japanese isolate of Mamestra brassicae nucleopolyhedrovirus (MabrNPV) was identified phylogenetically as a group II nucleopolyhedrovirus (NPV) that is related closely to other NPVs isolated from Mamestra spp. based on nucleotide sequence data of its polh, egt and lef-3 genes. The multiplication of MabrNPV in M. brassicae larvae was characterized following inoculation at various doses and in combination with the fluorescent brightener Tinopal by measuring temporal changes in the concentrations of its viral DNA using real-time quantitative PCR. The growth curves of budded-virus replication were analysed by fitting the data of viral DNA concentration in the host haemolymph to a modified Gompertz model. When fifth-instar larvae were inoculated with an LD95 equivalent dose of MabrNPV and Tinopal, the time lag between the onset of primary and secondary infection was estimated to be 25 h. Another 65 h was required to reach a plateau titre equivalent to a level of 10(9) virions ml(-1) in the haemolymph. All larvae died during the sixth instar following this inoculation regime. In contrast, following inoculation with a 1000-fold higher dose of MabrNPV and Tinopal, the time lag between the onset of primary and secondary infection was only 20 h. Subsequently, the same plateau titre was reached after a further 20 h. Following this inoculation regime, most larvae died during the fifth instar. Quantification of viral DNA by real-time quantitative PCR and application of the Gompertz model are valuable for the characterization of baculovirus replication in vivo.