Resistance development in insect pests against pesticides is one of the most important issues for pest management. Biological control is an attractive strategy for suppressing insects that have become resistant to chemical pesticides. The smaller tea tortrix Adoxophyes honmai (Lepidoptera: Tortricidae) is a serious pest of tea and has acquired resistance to various chemical pesticides, and baculovirus agents have been developed to control this pest in Japan. However, there was great concern about whether A. honmai might also acquire resistance against baculoviruses. To address this question, we developed a model resistant population and studied the mechanism of resistance in A. honmai against baculoviruses. A population of A. honmai that is resistant to nucleopolyhedrovirus (NPV) was selected by exposing a field-collected A. honmai population to the 70% lethal concentration (LC70) of NPV over multiple generations in the laboratory. After 155 generations, the selected strain (Resistant strain; R-strain) showed over 400,000-fold higher resistance to AdhoNPV than the non-selected strain (Susceptible strain; S-strain). In this presentation, mode of resistance of R-strain against baculoviruses were discussed.

Hyphantria cunea is a fall webworm is considered an agricultural pest. It is a major pest of many board-leaved trees. H. cunea nucleopolyhedrovirus (HcNPV) and H. cunea granulovirus (HcGV) were isolated from the fall webworm cadavers in Korea. To better understand HcNPV and HcGV, their genomic sequences were determined, analyzed and compared to two viruses together. The entire nucleotide sequence of the HcNPV genome was fully sequenced using 454 pyrosequencing. The genome of the HcNPV was 131,302 bp with a 45 % G+C content. Computer assisted analysis predicted 146 open reading frames (ORFs) of 50 or more amino acids that showed minimal overlap. Further more, when the phylogenetic relationship was analyzed, HcNPV was closely related to Orgyia pseudotsugata MNPV (OpMNPV) which belong to Group I NPV. The HcGV genome was 114,557 bp with a 39% G+C content and contained 130 putative ORFs of 50 or more amino acids. When phylogenetic relationships were analyzed, HcGV was closely related to Xestia c-nigrum granulovirus, which belong to the Type-II GV. HcNPV shares 48 ORFs with HcGV. The most significant difference between HcNPV and HcGV is fgf gene. HcNPV contains one fgf gene, whereas HcGV contains three fgf genes. The presence of fgf reduces the time and efficient systemic infection it takes the virus to kill its host. The difference of fgf number from HcNPV and HcGV suggested that different affect for the speed of systemic infection.

This study was conducted to investigate the insecticidal capacity of recombinant baculoviruses to Plutella xylostella and Spodoptera exigua larvae. For recombinant viruses, Bacillus thuringiensis cry1-5 crystal protein gene was introduced into the genome by fusion of polyhedrin-cry1-5 under the control of polyhedrin gene promoter. Recombinant AcPolh5-3006BiKTT and AcPolh5-3006 AvTox2 based on BiKTT and AvTox2, respectively, were constructed under the control of early promoter from Cotesia plutellae bracovirus. Mortality of S. exigua larvae was significantly higher when they fed on cabbage coated with ApEGFP (wild type) over 5.0×106 PIBs/ml. For AcPolh5-3006BiKTT and AcPolh5-3006AvTox2, mortality of P. xylostella and S. exigua larvae was significantly higher when they fed on cabbage coated with recombinant baculoviruses over 5.0×106 PIBs/ml and 1.0×104 PIBs/ml, respectively. The value of LD50 was lower in the treatments with AcPolh5-3006BiKTT (P. xylostella:1.2×106, S. exigua:1.3×104) or AcPolh5-3006AvTox2 (P. xylostella:2.3×106, S. exigua:1.4×104) than the treatments with ApEGFP (P. xylostella: not estimated, S. exigua:5.0×105). Survival time (ST50) of P. sylostella larvae was much shorter at AcPolh5-3006BiKTT (29.6h) than AcPolh5-3006AvTox2 (46.2h) while that of S. exigua larvae was much shorter at AcPolh5-3006AvTox2 (95.1h) than AcPolh5-3006BiKTT (101.9h) or ApEGFp (130.7h). The two recombinant baculoviruses were more effective in S. exigua larvae but slower speed of action.

We isolated two baculoviruses, Spodoptera litura granulovirus (SlGV) and S. litura nucleopolyhedrovirus (SlNPV) in the dead larvae of S. litura. The granule of SlGV were ovoidal shape with an approximate measure of 240-340 nm×140-180 nm, and each granule contained one single rod-shape virion with a mean size of 180-200 nm×20-40 nm. Whereas, the polyhedra of SlNPV were irregular in shape with a approximate diameter of 1.0-1.5 ㎛, and numerous virions comprised of the multinucleocapsid were contained in each polyhedra. The major component of occlusion bodies produced by SlGV and SlNPV were about 29 and 30 kDa, respectively. When the phylogenic relationship between these viruses were analyzed using the nucleotide sequences of granulin gene from SlGV and polyhedrin gene from SlNPV, they were not closely related to each other. We also found that the two viruses showed similar insecticidal activity against 2nd instar larvae of Spodotera litura in terms of dose-response, but SlGV showed much longer LT50 than that of SlNPV. The two baculoviruses might be cooperatively be applied as biological control agent for the control of S. litura

This study was conducted to investigate the insecticidal capacity of several recombinant baculoviruses to P. xylostella and S. exigua larvae. NeuroBactrus was constructed as follows: the cry1-5 of Bacillus thuringiensis 2385-1 was inserted into Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) genome by fusion of polyhedrin-cry1-5-polyhedrin under the control of polyhedrin gene promoter, and insect-specific neurotoxin from the scorpion Androctonus australis (AaIT) under the control of early promoter from Cotesia plutellae bracovirus was introduced by fusion of orf603 partial fragment in the opposite direction of polyhedrin gene, respectively. Other recombinant baculoviruses derived from the NeuroBactrus - NBt-DelA (deleted AaIT), NBt-Del5 (deleted cry1-5), and NBt-DelA5 (deleted AaIT and cry 1-5) - were manufactured in serial passages in vitro. The data were analyzed by SPSS. The value of LC50 was lower when P. xylostella larvae fed on cabbage coated with NeuroBactrus (4068.4) than when it fed on cabbage coated with AcMNPV (4.5x106). Survival time (ST50) of P. xylostella larvae (2.54days) was shorter when it fed on cabbage coated with NeuroBactrus than when it fed on cabbage coated with other recombinant baculoviruses (7.54days, 7.68days, and 8.26days) and AcMNPV (9.67days). S. exigua larvae presented the same results.

파밤나방 핵다각체병ㅂ이러스의 기주곤충 및 나비목해충에 대한 병원성과 10종 baculovirus의 파밤나방 유충에 대한 교차감염을 조사하여 방제에 이용하고자 시험을 수행하였다. 난에대한 중앙치사농도()는 2.855 다각체/ml로 유충보다 높았다. 령별 은 3령이 1.422 다각체/ml로 1령보다 1.16배, 5령보다 .11배의 높은 병원성을 나타냈다. 각 령의 중앙치사일수()은 1.56 다각체/ml에서 4.26~5.04일이었다. 8종 나비목 해충에 대한 파밤나방 핵다각체병바이러스의 병원성은 기주곤충인 파밤나방에서만 인정되었고 10종의 곤충간상바이러스 중 Autographa californica MNPV, Mamestra brassicae MNPV 및 Trichoplusia ni MNPV 등 3종이 파밤나방 유충에 대해 교차감염을 일으켰다.