Sungwoo Bae

IkB genes encoded in Cotesia plutellae bracovirus suppress an antiviral response and enhance baculovirus pathogenicity against the diamondback moth, Plutella xylostella.

An endoparasitoid wasp, Cotesia plutellae, parasitizes larvae of the diamondback moth, Plutella xylostella, with its symbiotic polydnavirus, C. plutellae bracovirus (CpBV). This study analyzed the role of Inhibitor-kB (IkB)-like genes encoded in CpBV in suppressing host antiviral response. Identified eight CpBV-IkBs are scattered on different viral genome segments and showed high homologies with other bracoviral IkBs in their amino acid sequences. Compared to an insect ortholog (e.g., Cactus of Drosophila melanogaster), they possessed a shorter ankyrin repeat domain without any regulatory domains. The eight CpBV-IkBs are, however, different in their promoter components and expression patterns in the parasitized host. To test their inhibitory activity on host antiviral response, a midgut response of P. xylostella against baculovirus infection was used as a model reaction. When the larvae were orally fed the virus, they exhibited melanotic responses of midgut epithelium, which increased with baculovirus dose and incubation time. Parasitized larvae exhibited a significant reduction in the midgut melanotic response, compared to nonparasitized larvae. Micro-injection of each of the four CpBV genome segments containing CpBV-IkBs into the hemocoel of nonparasitized larvae showed the gene expressions of the encoded IkBs and suppressed the midgut melanotic response in response to the baculovirus treatment. When nonparasitized larvae were orally administered with a recombinant baculovirus containing CpBV-IkB, they showed a significant reduction in midgut melanotic response and an enhanced susceptibility to the baculovirus infectivity.

Analysis of migration of the oriental fruit moth, Grapholita molesta, in apple-cultivating areas based on population monitoring using sex pheromone and RAPD molecular marker.

Local and seasonal populations of the oriental fruit moth, Grapholita molesta, were monitored with sex pheromone trapping and RAPD (random amplified polymorphic DNA) molecular marker to analyze their movement in apple orchards. To detect their movements among farms, pheromone traps were placed at regions between apple farms (`outside-farms`) as well as within-farms (`inside-farms`). Four seasonal adult peaks were evident in apple-cultivating fields from April to October in both trappings of inside- or outside-farms. After overwintering generation, populations of inside-farms were significantly reduced with frequent insecticide applications, compared to populations of outside-farms. Within apple farms, G. molesta tended to be unevenly distributed because of significant sublocal preference. Active movements of local and seasonal populations of G. molesta were supported by gene flow analysis using RAPD marker. Monitoring data using sex pheromone and seasonal reduction in initial genetic differentiation detected in the overwintering populations suggest that there must be significant movement of G. molesta among different orchards in apple-cultivating areas.

Genetic Differentiation of Overwintering Populations of Oriental Fruit Moth, Grapholita molesta, and Their Movement

Spring phonology of the oriental fruit moth, Grapholita molesta, was monitored using sex pheromone traps in apple cultivating areas. Their occurrence was earlier in southern areas and their population sizes were significantly different among orchards even in a local cultivating zone. The overwintering populations appeared to move between local orchards, based on the fact that monitoring data obtained at the sites between orchards were similar to those of nearby orchards. However, within orchards, these adult movements appeared to decrease and showed skewed occurrences at the side of upwind direction or close to neighboring orchards. At initial occurrence peak(April 20-25), the ovenvintering populations of the different localities were collected and analyzed in their genetic distances. PCR-RAPD analysis indicated that there were significant genetic differences among the overwintering populations of G. molesta. This genetic differentiation of overwinterin populations may be due to genetic bottleneck following differential selection pressures against the subpopulations of G. molesta during winter on the basis of the RAPD analysis that each early spring population was significantly different to its previous fall population in the same locality.

Development of Wax-typed Pheromone Dispenser for Mating Discruption of the Oriental Fruit Moth, Grapholita molesta, and Its Application Technique

A wax-typed pheromone dispenser has been developed and applied to control outbreak of the oriental fruit moth, Grapholita molesta, in apple orchard. To optimize its application technique, this study analyzed effect of different amounts of the pheromone dispenser on mating disruption(`MD`) of G. molesta. Different pheromone dispenser amounts significantly influenced the MD effect assessed by cumulative male adult catches monitored respectively by sticky delta trap and food trap, and resulted in differential damage on host plants. In a field test during entire growing season, a standard amount(120 g per 0.117 ha) of wax-typed pheromone dispenser was proved to be effective to suppress outbreak of G. molesta adults and to prevent host plant damage as much as a current commercial MD product(). This study also demonstrated an effectiveness of deployment of food trap barriers around MD-treated area to prevent immigration of mated females from outside untreated areas. These results indicate that the wax-typed pheromone dispenser can be applied to control field G. molesta populations and its co-application with fuod trap barriers would be optimal to maximize MD efficacy.

Efficacy Test of Mating Disruptors Using Food Trap of Oriental Fruit Moth, Grapholita molesta (Busck)

This study was performed to estimate the efficacy of three commercial mating disruptors for the control of oriental fruit moth, Grapholita molesta (Busck), using a food-baited trap to collect field females. Mated female ratios estimated in the mating disruptor-treated areas were compared with the estimates of male trap captures, and both estimates were evaluated on the basis of crop damage measured by shoot tip damage caused by G. molesta. Both males and females were attracted to the food trap-baited with terpinyl acetate in apple orchard. Spermatophore of G. molesta was similar to female bursa copulatrix in size. Though there was more than 95% reduction in male trap captures indicating significant mating disruption, significant crop damage occurred on apple leaf buds, in which more than 35% of captured females were mated. This study demonstrates that assessment of the mated females would be more reasonable to represent the efficacy of mating disruptor(s) than the assessment of the male captures in G. molesta.