Yoo-Han Song

The Seasonal Occurrence of the Two Aphid Species, Myzus persicae and Aphis gossypii, and their Natural Enemies on Vegetable Crops in Chinju, Korea

Abstract We conducted a study on the population dynamic of the two major aphid species of green peach aphid, Myzus persicae (Sulzer), and cotton aphid, Aphis gossypii (Glover), as well as their natural enemies on the five major green house crops in Chinju greenhouse vegetable area in Korea. The green peach aphid was relatively the majority among all aphids collected from tomato, potato, and chinese cabbage, while the cotton aphid was major species on water melon and hot pepper. Both species reached their peaks in mid June, when the summer monsoon was not initiated, the temperature was relatively as low as 23°C, and the crops were young and favorable. The density of predators such as spiders, lady beetles and green lacewings and some other arthropods were very low in the early season and reached their pick three weeks after the aphids density peaked. This data indicated that the predators only follow aphid abundance but arrive too late to be effective as regulators of aphids population. About 9,255 samples of various aphids collected from the five crops, we found 39 parasitoids representing at least eight different species. Aphidiid sp. occupied 35.8% and hyperparasites occupied 56.5%. Lipolexis scutellaris species was very scarce and only occupied 2.6% from Aphis gossypii on watermelons. This information can be used for determining the impact of natural enemies under the mixture of greenhouse-open field vegetable production system.

Molecular Genetic Diagnosis of Four Fruit Fly Species (Tephritidae)

Abstract The true fruit flies (Diptera: Tephritidae) are major agricultural pests worldwide. In Korea, imported crops are carefully scrutinized to prevent infestation by exotic tephritids and rapid species identification is required to make quarantine decisions. At quarantine checkpoints, tephritids are most commonly intercepted at the larval stage, however larvae have few diagnostic morphological features. Here we describe a molecular genetic method using restriction enzyme digestions of PCR products from the mitochondrial gene, cytochrome oxidase I (COI). This technique provides a simple diagnostic marker for Korean fruit flies in the genus Bactrocera (B. depressa, pumpkin fruit fly; and B. scutellata, pumpkin flower fruit fly) and wide spread fruit flies (B. dorsalis, oriental fruit fly; and Ceratitis capitata, medfly). The restriction enzymes ApaI, NheI and SacI were used to digest the 815 bp PCR product into fragments that uniquely diagnose each species. The simplicity and relatively low cost of this molecular approach will facilitate rapid quarantine decisions concerning exotic fruit flies.

Overwintering Two Aphid Species, Lipaphis pseudobrassicae and Myzus persicae (Homoptera: Aphididae), in Southern Greenhouse Area in Korea

Abstract In southern Korea, the two aphid species, Myzus pessicae (Sulzer) and Lipaphis pseudobrassicae (Davis), had been known to have sexual phase to produce hibernating eggs on their alternate hosts. However, we have frequently found that they were still alive in the parthenogenetic form even in below freezing conditions in winter. This study had been focused on verifying the possibility of overwintering of the two important aphid species in the parthenogenetic morph, by comparing the population density changes within greenhouse and open field condition. In greenhouse condition, though not heated, both species successfully continued reproducing in a parthenogenetic form. In open field, L. pseudobrassicae successfully survived and reproduced on chinese cabbage and spinach even below freezing temperatures. M. persicae were also able to survive in the winter but not as much capability of reproduction as L. pseudobrassicae. This study provided the evidence that the aphid infestations in greenhouse can be mostly from overwintering populations in the parthenogenetic morph in southern greenhouse area of Korea.

Development of Western Cherry Fruit Fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), after Overwintering in the Pacific North West Area of USA

The western cherry fruit fly, Rhagoletis indifferens Curran (Diptera:Tephritidae), is the most important pest of cultivated cherries in the Pacific Northwest area of the United States, being widely distributed throughout Oregon, Washington, Montana, Utah, Idaho, Colorado and parts of Nevada. The control of R. indifferens has been based on calendar sprays after its first emergence because of their zero tolerance for quarantine. Therefore, a good prediction model is needed for the spray timing. This study was conducted to obtain the empirical population dynamic information of R. indifferens after overwintering in the major cherry growing area of the Pacific Northwest of the United States, where the information is critically needed to develop and validate the prediction model of the fruit fly. Adult fly populations were monitored by using yellow sticky and emergence traps. Larvae growth and density in fruits were observed by fruit sampling and the pupal growth and density were monitored by pupal collection traps. The first adult was emerged around mid May and a large number of adults were caught in early June. A fruit had more than one larva from mid June to early July. A large number of pupae were caught in early July. The pupae were collected in various period of time to determine the effect of pupation timing and the soil moisture content during the winter. A series of population density data collected in each of the developmental stage were analyzed and organized to provide more reliable validation information for the population dynamic models.