Mamestra brassicae nucleopolyhedrovirus-K1 (MabrNPV-K1) was isolated from naturally infected Mamestra brassicae (Lepidoptera: Noctuidae) larvae in Korea. Restriction endonuclease fragment analysis using EcoRI, PstI, and BamHI estimated that the total genome size of MabrNPV-K1 is about 150 Kb. The full genome sequences of MabrNPV-K1 were determined, analyzed and compared to those of other baculoviruses. The MabrNPV-K1 genome consisted of 152,471 bp and had an overall G + C contents of 39.90 %. Computer-assisted analysis predicted 159 open reading frames (ORFs) of 150 nucleotides or greater that showed minimal overlap. The gene content and arrangement in MabrNPV-K1 were most similar to those of Mamestra configurata nucleopolyhedrovirus-B (MacoNPV-B), including three polh, p10 and lef-8 gene homologues. The MabrNPV-K1 genome contains four homologous repeat regions (hr1,hr2,hr3,hr4) that account for 3.1% of the genome. The genomic positions of MabrNPV-K1 regions hr1– hr4 are conserved with the genomic positions of MacoNPV-B hr1–hr4. This indicates that the position of MabrNPV–K1 hrs is conserved with regard to both the upstream and downstream genes. Given that hrs share higher similarity within a virus strain than any hrs between species, this evidence further indicates that hrs play a fundamental role in viral life cycle and replication process appears to be tightly linked to functional conservation. The dot plot analysis, percent identity of the gene homologues and a phylogenetic analysis suggested that MabrNPV-K1 is a Group II NPV that is closely related to MacoNPV but with a distinct genomic organization.

Mamestra brassicae (cabbage moth) is a common European moth of the order Lepidoptera and the family Noctuidae. The larval stage is highly polyphagous and is known to feed on more than 70 species of host plants from 22 families, including Brassica species, lettuce, onion, potato, pea, tomato and apple. M. brassicae has become a significant pest also in Asia due to the damage caused to agriculturally and economically important Brassica crops. It is difficult to control M. brassicae using chemical insecticide because of its rapid development of resistance. The objective of our study, therefore, was the mass production and formulation of a local strain of M. brassicae nucleopolyhedrovirus-K1 (MabrNPV-K1) for the development of viral insecticide to control it. In production efficiency of MabrNPV-K1 using M. brassicae larvae, the mortality of the 3rd instar larvae was 100% when inoculated with 1.0 × 105 PIBs/larva and the yield of MabrNPV-K1 was maximal. Regarding the mortality, yield of polyhedra, inoculation doses and required time, the 1.0 × 104 PIBs/larva at 30°C was determined as optimal conditions producing polyhedra efficiently. To formulate MabrNPV-K1, feeding toxicities of various supplements including spreader and ultraviolet (UV) -protectant were determined. Tinopal UNPA-GX which is UV-protectants was effective for protection of polyhedra from UV and showed the increased mortality when added with 1% concentration. Other supplements did not influence significantly the mortality of MabrNPV-K1. Formulated MabrNPV-K1 with several supplements showed higher pathogencity than un-formulated MabrNPV-K1.

This study was conducted to develop economic injury level (EIL) and economic threshold (ET) of Cabbage armyworm, Mamestra brassicae L. on cabbage (Brassica oleracea L. var). The changes of cabbage biomass and M. brassicae density were investigated after introduction of larval M. brassicae (2nd instar) at different densities: 0, 1, 2, 4, 8, and 16 larvae per plant at 40 d after planting for an open field experiment, and 0, 2, 5, 8 and 12 larvae per plant at 25 d after planting for a glass house experiment. In the field experiment, the yield loss of cabbage was not significantly different among treated-plots at 30 d after the larval introduction, showing an over-compensatory response of cabbage plants to M. brassicae attack. In the glasshouse experiment, however, the biomass of cabbage at 15 d after the larval introduction significantly decreased with increasing the initial introduced number of M. brassicae, resulting in 38.3, 36.7, 21.7, 23.3 and 16.7g in above treated-plots, respectively. The relationship between cumulative insect days (CID) and yield loss (%) of cabbage was well described by a nonlinear logistic equation. Using the estimated equation, EIL of M. brassicae on cabbage was estimated at 44 CID per plant based on the yield loss 14%, which take into account of an empirical gain threshold 5% and marketable rate 91% of cabbage. Also, ET was calculated at 80% of the EIL: 35 CID per plant. Until a more elaborate EIL-model is developed, the present result may be useful for M. brassicae management at early growth stage of cabbage.

도둑나방(Mamestra brassicae)은 배추, 무, 양배추 등 45종 107과의 식물을 가해하는 광식성 해충이며 연 2회 발생하나, 현재까지 국내에서는 등록된 적절한 약제나 천적이 없는 난방제해충이다. 이러한 도둑나방의 방제법을 개발하고자 도둑나방에 대하여 높은 병원성을 보이는 도둑나방 핵다각체병 바이러스(M. brassicae nucleopolyhedrovirus: MbNPV)를 국내에서 분리하고 바이러스 살충제의 개발을 위한 생물학적 및 분자생물학적 기초 특성을 조사하였다. MbNPV-K1의 다각체는 직경 약 1.8㎛의 부정형이고, 하나의 envelope에 다수의 nucleocapsid가 존재하는 MNPV(Multiple nucleocapsid nucleopolyhedrovirus)형태였다. 다각체 단백질은 Autographa californica 다각체 단백질의 분자량과 동일한 약 31 kDa의 단일 단백질로 나타났으며, 그 유전자의 염기서열을 확인한 결과 기존에 보고된 MbNPV와 동일한 염기서열을 보였다. 살충력을 조사하기 위한 생물검정은 외국에서 개발되어 상용화되고 있는 MbNPV 살충제인 Mamestrin을 대조구로 하여 도둑나방 3령충에 대하여 비교 조사하였다. 그 결과 MbNPV-K1의 반수치사농도(LC50)는 3.9 X 103 PIBs/larva로, 6.0 X 104 PIBs/larva 인 Mamestrin 보다 15배 높은 병원성을 나타냈다. 또한 반수치사일수(LT50)도 MbNPV-K1은 4.4~6.1일, Mamestrin 은 4.1~8.6일로 나타났다.

도둑나방(Mamestra brassicae L.)의 온도별 발육특성과 고랭지배추포장에서의 발생소장을 조사하였다. 15, 20, 22, 항온조건에서 알의 발육기간은 각각 9.2, 6.2, 5.0, 3.9일이었고, 유충의 발육기간은 각각 40.5, 30.1, 23.3, 21.2일이었다. 또한 알에서 성충으로 발육하기까지 각각 88.3, 63.0, 52.3, 42.8일이 소요되었다. 발육영점온도와 유효적산온도는, 알에 대해서 와 69.4 DD, 유충에 대해서 434.8 DD, 번데기에 대해서 와 344.8 DD이었다. 암컷의 총 산란수는 온도가 상승할수록 커졌는데, 에서 1262.1개, 에서 1663.8개, 에서 1763.2개를 낳았다. 또한 난괴당 알의 수는 온도별로 각각 99.4, 114.7, 167.9개였다. 도둑나방 성충은 대관령 고랭지 배추재배지역에서 6월 중순부터 8월 하순까지 발생하였으며, 일년에 2회 발생하였는데, 6월 하순과 8월 초순에 각각 최대발생량을 보였다.