Soon-Do Bae

Susceptibility of Stink Bugs Collected in Soybean Fields in Milyang to Some Insecticides

The susceptibility of five stink bugs species collected soybean fields in Milyang in 2006 to seven insecticides was evaluated using electric auto-sprayer. The insecticide deltamethirn had the lowest median lethal concentration (LC50) of 0.4 to 2.3 ppm regardless of stink bugs species while phenthoate had the highest concentration for one-banded stink bug (Piezodorus hybneri), green stink bug (Nezara antennata), sloe bug (Dolycoris baccarum), and brown marmorated stink bug, (Halyomorpha halys); and fenthion for bean bug (Riptortus clavatus). The average LC50 for stink bugs to seven insecticides was lowest at 7.5 ppm for R. clavatus, followed by 16.6 ppm for H. halys, 17.6 ppm for D. baccarum, 19.1 ppm for N. antennata, and 28.4 ppm for P. hybneri. The relative tolerance ratio (TR), which is the TR of 90 percent lethal concentration (LC90) of stink bugs to the recommended concentration, was the lowest in fipronil for R. clavatus, P. hybneri and D. baccarum; fenitrothion for N. antennata; and fenthion for H. halys. The relative average TR was lowest at 0.09 for R. clavatus, followed by 0.26 for D. baccarum, 0.30 for N. antennata, 0.37 for P. hybneri, and 0.39 for H. halys. Therefore, insecticides susceptibility was highest for R. clavatus and lowest for P. hybneri while the relative average TR was lowest for R. clavatus and highest for H. halys. Accordingly, it is expected that stink bugs can be effectively controlled with by spraying insecticides in soybean field because the relative average TR value of stink bugs was below 1.0, indicating high susceptibility of stink bugs to insecticides.

The Effect of Seed-borne Mycoflora from Sorghum and Foxtail Millet Seeds on Germination and Disease Transmission

Abstract The seed-borne mycoflora of sorghum and foxtail millet collected from different growing areas in South Korea were isolated and taxonomically identified using dry inspection, standard blotter and the agar plate method. We investigated the in vitro and in vivo germination rates of disinfected and non-disinfected seeds of sorghum and foxtail millet using sterilized and unsterilized soil. The percent recovery of seed-borne mycoflora from the seed components of sorghum and foxtail millet seeds was determined and an infection experiment using the dominant species was evaluated for seedling emergence and mortality. A higher number of seed-borne fungi was observed in sorghum compared to that of foxtail millet. Eighteen fungal genera with 34 fungal species were identified from the seeds of sorghum and 13 genera with 22 species were identified from the seeds of foxtail millet. Five dominant species such as Alternaria alternata, Aspergillus flavus, Curvularia lunata, Fusarium moniliforme and Phoma sp. were recorded as seed-borne mycoflora in sorghum and 4 dominant species (Alternaria alternata, Aspergillus flavus, Curvularia lunata, Fusarium moniliforme) were observed in foxtail millet. The in vitro and in vivo germination rates were higher using disinfected seeds and sterilized soil. More seed-borne fungi were recovered from the pericarp compared to the endosperm and seed embryo. The percent recovery of seed-borne fungi ranged from 2.22% to 60.0%, and Alternaria alternata, Curvularia lunata and 4 species of Fusarium were isolated from the endosperm and embryo of sorghum and foxtail millet. Inoculation of the dominant seed-borne fungi showed considerable mortality of seedlings. All the transmitted seed-borne fungi might well be a primary source of infection of sorghum and foxtail millet crops.

Effects of a Mungbean Cultivar, Jangannogdu on Nymphal Development, Adult Longevity and Oviposition of Soybean Stink Bugs

Nymphal development, adult longevity, and oviposition of six different species of stink bugs were compared on seeds of a soybean cultivar, Taekwangkong, and two mung bean cultivars, Kyungseonnogdu and Jangannogdu in the insect rearing room (, 16L:8D). Nymphs of six species of stink bugs normally developed on Taekwangkong seed. While nymphs of Riptortus clavatus, Halyomorpha halys, and Dolycoris baccarum developed on seeds of Kyungseonnogdu and Jangannogdu normally, all nymphs of Plautia stali, Piezodorus hybneri and Nezara antennata died after 4th instars on Kyungseonnogdu and after 3rd instars on Jangannogdu. Each instar period tended to be increased as nymphal stages were progressed. Nymphal period was shortest on Taekwangkong seed, followed by Kyungseonnogdu and Jangannogdu, irrelevant to stink bugs species. Emergence rate, adult longevity, and preoviposition period of 6 stink bugs were different depending on the reared seeds. Of 6 different species examined, Riptortus clavatus, Halyomorpha halys, and Dolycoris baccarum which fed on Jangannodu did not emerge, Plautia stali, Piezodorus hybneri, and Nezara antennata which fed on Jangannodu did not oviposit.

Seasonal Occurrence of Tobacco Cutworm, Spodoptera litura Fabricius and Beet Armyworm, Spodoptera exigua Hübner Using Sex Pheromone Traps at Different Locations and Regions in Yeongnam District

Seasonal occurrences of tobacco cutworm, Spodoptera litura and beet armyworm, Spodoptera exigua were observed using sex pheromone traps at different locations and climatic regions in Yeongnam district. In Gyeongnam province, S. litura male adults kept occur from mid or late March to mid or late November Whereas in Gyeongbuk province, S. litura occurred from mid or late April to early or mid November with exception at Uljin where it was late May to late October. According to the climatic regions, the peak occurrence of S. litura was middle September at the southern coast region, late August at the inland and the basin region, middle August at the inland mountainous region, and early September at the eastern middle coast region. The occurrence rate of S. litura was the highest at Jinju with 20.0% and the lowest at Changyeong with 8.6% in Cyeongnam province, while it was the highest at Sungju with 3.3% and the lowest at Uljin with 0.8% in Gyeongbuk province. In accordance with the climatic regions, the occurrence rate of S. litura was the highest at the inland region with 43.7%, and followed by the southern coast region (36.3%), the basin region (8.4%) and the inland mountainous region (7.0%), and was the lowest at the eastern middle coast legion with 4.6%. On the other hand, S. exigua occurred from early March to middle November with the exception of the eastern middle coast region including Pohang, Yeongdeog and U]ien in Cyeongbuk province where it occurred from mfd April to middle November. The peak occurrence of s. exigua was early August at the inland region, the basin region and the inland mountainous region, and was late of August at the southern coast region and the eastern middle coast region. The occurrence of S. exigua was the highest at Changyeong with 1.6% and the lowest at Busan with 0.4% in Gyeongnam province, while it was the highest at Sungju with 37.2% and the lowest at Uljin with 2.7% in Gyeongbuk province. The climatic regional occurrence rate of S. exigua was the highest at the basin region with 54.3%, and followed by the inland mountainous region (29.9%), the eastern middle coast region (9.3%) and the inland (3.9%), and was the lowest at the southern coast region with 2.6%. As a whole, S. litura occurred more in Gyeongnam province than Cyeongbuk province, while S. exigua occurred more in Gyeongbuk province than Gyeongnam province. According to the regions grouped by climatic differences, the occurrence of S. litura and S. exigua was the highest at the inland region in Gyeongnam province and at the basin region in Gyeongbuk province. The total number of S. litura captured by sex pheromone trap was 2.4 times higher than that of S. exigua. However, the first occurring time and the peak occurrence of S. exigua were slightly earlier than those of S. litura.

Attractiveness of stink bugs to color, height and location of aggregation pheromone trap.

Attractiveness of stink bugs to various colors, heights and locations of fish-net traps incorporated with aggregation pheromones was determined. Bean bug, Riptortus pedestris Fabricius, was most attracted to yellow color trap, followed by white, black, green, blue and brown. R. pedestris and one-banded stink bug, Piezodorus hybneri Gmelin, were most attracted to fish-net traps placed 80 cm above the ground regardless of sexes of two species of stink bugs. Between the sexes, however, R. pedestris females were more attracted to 40 and 80 cm above the ground than the males at those heights although the attraction was not significantly different at 120 and 160 cm heights. P. hybneri females tended to be attracted to 40 and 80 cm height traps but the attraction was the opposite at 120 and 160 cm heights. The highest attraction of R. pedestris was observed in a perilla field with no significant difference in the soybean field and border area in which no crop were cultivated between the perilla and soybean fields. R. pedestris was also more attracted to the sweet persimmon orchard than the soybean and medicinal crops fields, which was a significant difference between the two fields.

Reproductive Rate of Green Stink Bug, Nezara antennata Scott (Hemiptera: Pentatomidae) by the Size of Rearing Cages

The embryonic and postembryonic developments of Nezara antennata Scott were observed in 5 different rearing cages such as A (Cylindrical, ), B (Cylindrical, ), C (Rectangle, ), D (Cylindrical, 9cm in bottom & 11.5 cm in ) and E (Cylindrical, ) containing soybean and peanut seeds as food, and sponge soaked with water under laboratory condition of and 15L : 9D. Hatchability ranged from 93 to 97%. Nymphal duration was shortest of 6 days in the 1st instar and longest of 10 days in the 5th instar. The nymphal duration was 38 to 39 days observed in the rearing cages. Emergence rate was in the range from 53 to 62% with highest in A and B cages. Adult longevity was 65 to 75 days for male, and 67 to 74 days for female, and was longest in the B cage. Total number of eggs laid by female adult was in the range from 51 to 56 without significant difference in the rearing cages, and was the most in the B cage. Accordingly, the reproductive rate of N. antennata for 1 generation was within 25 to 33 times, and was highest in the B rearing cage. Therefore, it could be concluded that B cage is most suitable for stable rearing of N. antennata under laboratory condition.

Evaluation of Apple and Orange Fruits as Food Sources for the Development of Halyomorpha halys (Hemiptera: Pentatomidae)

Halyomorpha halys (Stl) (Hemiptera: Pentatomidae) is a typical polyphagous stink bug causing losses in several host plants including leguminous crops and fruits. Nutritional status of fruits such as apple and orange for the development of H. halys is not yet clear. We evaluated fruits of apple and orange with or without soybean-peanuts as food sources to investigate development, mortality and fecundity of the stink bug in a controlled condition. Those only fed on water could not develop into third instars. H. halys could not develop into fourth instar on apple only food. However, on an orange only food, 14% of H. halys emerged as adults. Those fed on orange only food had the longest development period (74.2 d). Total mortality of those fed on foods consisting of soybean-peanut ranged from 38 to 44%. In an average a female laid 169~190 eggs in a lifetime and those eggs had 81~83% hatchability. Results indicated that the apple fruit as a solo food source is an incomplete food for H. halys development while orange could support development of only few of the bugs.

Preference of Adult Alfalfa Weevil, Hypera postica (Gyllenhal), (Coleoptera: Curculionidae), to Different Seedlings of Upland Crops

Occurrence of adult alfalfa weevil, Hypera postica Gyllenhal, was observed at Chinese milk vetch field, and host plant preference of its generation adult was observed at greenhouse and Chinese milk vetch field. The over-wintered adult of the weevil appeared from late March and peaked in mid April while the generation adult appeared from late April and peaked in late May. However, the occurrence of over-wintered adult was very low contrary to the generation adult which was very high with some variations among observed years. In greenhouse, host plant preference of adult generation of H. postica was evaluated with 11 different seedlings. H. postica was found to occur in significantly higher number on Chinese cabbage seedling followed by soybean, and kale at 7 days after releasing(DAR). Corn, crown daisy and sorghum were found to be the least preferred with nil occurrence of the weevil. Seedlings damage rate by H. postica feeding at 7DAR was the most severe on Chinese cabbage(60.0%) followed by soybean(50.0%), kale(30.0%), foxtail millet(16.7%), proso millet(13.3%) and lettuce(3.3%) significantly. Also, seedlings damage rate by H. postica at 7DAR in Chinese milk vetch field had shown the similar trend with Chinese cabbage(46.7%), soybean(43.3%), kale(23.3%), foxtail millet(13.3%) and proso millet(13.3%) in greenhouse significantly. Accordingly, results on host plant preference of H. postica from this study can be used as a basic information for safe cultivation of upland crops at near or around green manure crop field.

Effects of Temperature on the Development and Longevity of the Gray Field Slug, Deroceras reticulatum Müller (Stylommatophora: Limacidae)

The egg size and weight of the gray field slug, Deroceras reticulatum Muller, was mm and 3.3 mg at , respectively. Its weight increased from newly laid eggs to adults for 17 weeks at four temperature regimes and was heaviest at , followed by 24, 16 and . Likewise, hatching rate of the egg batches was highest with 95% at , followed by 24, 16 and with significant differences. The number of eggs in the batches was increased with 20 at while it was only 10 at . The average accumulated egg-laying days was longest with 15 days at while shortest with 9 days at . The range of egg-laying period was shortest with 84-134 days at and longest at . Thus, the total number of eggs laid by adult D. reticulatum was highest with 217 at and lowest with 105 at . The egg period was 12-19 days while the juvenile period and adult longevity were 51-68 days and 85-134 days, respectively. The life span of D. reticulatum from egg to adult was longest with 216 days at , followed by 193 days at , 170 days at and 151 days at . Accordingly, the most favorable temperature for the oviposition, development and longevity of D. reticulatum is .

First report of Maize yellow mosaic virus infecting Panicum miliaceum and Sorghum bicolor in South Korea

Maize yellow mosaic virus (MaYMV) is a tentative new Polerovirus, which was recently identified from maize (Zea mays) in China (Chen et al. 2016). MaYMV has also been reported to infect sugarcane (Saccharum spp.) and itch grass (Rottboellia cochinchinensis), and it has been reported in Asia, Africa and South America (Goncalves et al. 2017; Palanga et al. 2017; Yahaya et al. 2017). In this study, MaYMV was detected in Panicum miliaceum and Sorghum bicolor using Illumina HiSeq2500 system by Theragen Etex Bio Institute (Suwon, Korea) and SG-VIPdb by SeqGenesis (Daejeon, Korea), as described by Lim et al. (2015). Twenty samples of P. miliaceum and sixty three samples of S. bicolor were collected from July to September and from June to October, 2016, respectively, in South Korea. The high-throughput RNA sequencing of the samples mixed into one pool resulted in a single large contig (5606-nt) with nearly complete MaYMV genome coverage. The contig was assembled from a total of 234,537 reads; the maximum, minimum...