Search

The perilla seed bugs, Nysius plebeius Distant and Nysius hidakai Nakatani, are emerging pests of several field crop species including perilla crop in Korea. Here, we investigated the oviposition, nymphal mortality, development, adult emergence, adult longevity, adult weight and female ratio of N. plebeius and N. hidakai on multiple (MC) and double (DC) combinations of five crop seed species: perilla [Perilla frutescens (L.) Britton.], sesame (Sesamum indicum L.), sorghum [Sorghum bicolor (L.)], proso millet (Panicum miliaceum L.), and foxtail millet (Setaria italic L.) in no-choice test. The life-history variables of N. plebeius and N. hidakai were significantly influenced by the crop seed combinations. The most preferred crop seed combinations for oviposition were MC (perilla + sorghum + sesame + proso millet + foxtail millet), followed by DC (perilla + foxtail millet and perilla + sorghum), whereas the least preferred seed combination was DC (proso millet + foxtail millet). Both Nysius sp. were developed faster in MC (perilla + sorghum + sesame + proso millet + foxtail millet), with minimal nymphal mortality, higher adult emergence, longer adult longevity and heavier adult weight. The positive adult bug’s performance on the MC (perilla + sorghum + sesame + proso millet + foxtail millet) may be due to the nutrient contents and physicochemical components associated with the crop seeds. Further, the findings of this study are discussed in terms of bug's behavioral response to crop seed species combinations and management strategies of Nysius sp. as an alternative to chemical management.

Nysius species are one of the emerging pests of perilla crop in Korea. Seed weight loss and germination of perilla seeds caused by Nysius plebeius were studied by exposing perilla seeds cv. Deulsaem to six insect infestation levels (0, 5, 10, 15, 20, and 25 individual) for 3 and 5 days in the laboratory. The seed weight loss and germination rate were significantly affected by infestation levels and feeding durations. The feeding impacts on seeds increased with increasing in bug density and duration. The higher seed weight loss, and weak germination were recorded at higher bug density (25 individuals) for longer (5 days) feeding duration. The triphenyl tetrazolium chloride, TTC, showed lower seed viability for damaged seeds than undamaged seeds. The outcomes of the study are discussed in terms of impacts of perilla seed bugs infestation, and suggest longer field exposure of perilla seeds to seed bugs may bring lower yield with poor quality of seeds and low germination potential of seeds. Future studies should examine the changes in nutrient contents of seeds after exposed to perilla seed bugs.

The genus Nysius (Hemiptera: Lygaeidae) are polyphagous pests of various plants that damage seeds, foliage, and flowers. Here, we studied the life-table parameters and adult performances of Nysius plebeius Distant and Nysius hidakai Nakatani after exposure to five radiofrequencies: 0 (control), 5, 10, 20, and 30 kHz in infested perilla seeds. In addition, we measured the follow on effects of treatment for four generations (Parent, F1-, F2-, and F3-generation), for both Nysius species. Radiofrequency application significantly affected the life-table parameters of both Nysius species. Radiofrequency exposures affected bug oviposition, developmental period, adult weight, and longevity. Exposure also negatively affected the fecundity of subsequent generations; total developmental period from egg to adult emergence was longer while adult longevity was shorter in the radiofrequency treatments than in the untreated control. Low radiofrequency levels had the greatest effect on the life-table parameters of Nysius species, with the lowest rate of adult emergence and the shortest adult longevity at 5 kHz. The potential of using Nysius bug susceptibilities to radiofrequency as an alternative to chemical treatment is discussed.

The soybean pod borer, Maruca vitrata is one of the key insect pests of tropical legumes. It damages tender leaf axils, flower buds, flowers and pods by webbing and boring clusters of flowers and pods. In this study, we investigated the survival and life table parameters of M. vitrata on several leguminous crops; soybean (cvs. Daewon, Poongsannamool and Socheongja), azuki bean (cv. Hongeon), mung bean (cv. Sanpo), and cowpea (cv. Jangchae), compared to artificial diet to assess the antibiosis resistance to M. vitrata. The life‐variables of M. vitrata were significantly affected by the tested legume cultivars. None of the larvae fed cowpea cultivar Jangchae survived. The azuki bean cultivar Hongeon and mung bean cultivar Sanpo were found susceptible to M. vitrata, whereas cowpea cultivar Jangchae and soybean cultivar Daewon showed antibiosis resistance to M. vitrata. Further studies should examine the chemicals associated with leguminous crop cultivars and its mechanism to develop a control method against M. vitrata.

Callosobruchus chinensis (L.) (Coleoptera: Chrysomelidae) is a common insect pest of stored legume seeds around the world. Since chemical insecticides and fumigation can have adverse effects on human health and environment, the development of a non-chemical method to replace chemical insecticides is urgently needed for the control of stored products pests. In this study, we investigated the oviposition preference, development, and adult performances of C. chinensis at five radiofrequency levels of 0 (control without frequency), 5, 10, 20, and 30 kHz on three leguminous seeds: azuki bean, cowpea, and mung bean. In addition, the effects were also studied in three successive generations (parent, F1- and F2-generations) of C. chinensis. We found that radiofrequency application had significant effects on the life history variables of C. chinensis. Radiofrequency exposures on C. chinensis not only affected developmental period, adult longevity and adult weight, but also negatively affected the fecundity of subsequent generations. The total developmental period from egg to adult emergence was longer and adult longevity was shorter in the radiofrequency treatments than in the untreated control. Reduced radiofrequency levels coincided with increased sexual development of adults. The lowest rate of adult emergence and the shortest adult longevity both occurred at 5 kHz. The outcomes of this study are discussed in terms of targeting susceptibilities to radiofrequency in storage and semi-field conditions as an alternative to chemical treatments.

The stink bugs, Halyomorpha halys and Riptortus pedestris, are two of the most economically important pests of leguminous crops and fruits in Korea. Here we present the results from a field monitoring test that evaluated the effect of variation in rocket trap type and color on stink bugs captures. We tested various types of rocket traps, along with wing combinations and landing boards of various colors. The test was run in soybean fields in Miryang, Korea. We developed a modified rocket trap intended to enhance the capture efficacy of stink bugs. We evaluated traps including (1) yellow rocket trap with a solar fan and blue LED lamp, (2) a yellow trap with solar fan but no light, (3) rocket traps with black, green, yellow, white, red, brown, and blue color stimuli, (4) different color combinations of trap wings, and (5) traps with a landing board were evaluated. Our results showed that yellow winged rocket traps with solar fans and blue LED lamps attracted significantly more stink bug species than other traps, in both soybean fields. Use of these improved traps such as a yellow trap with a solar fan and blue LED lamp, and a yellow trap with a solar fan would therefore enhance the monitoring and capture of stink bugs in diversified agro-ecological landscapes. The potential use of traps with a specific hue, combination of features, and modifications to monitor stink bugs accurately is discussed. Continuing improvements to traps to meet the demands of a changing pest landscape and agricultural mechanization are needed.

Perilla seed bugs (Nysius sp.) are considered to be the emerging pests causing nutritional and yield losses in perilla and cereal crops. A survey of perilla seed bugs on weeds and perilla crops was conducted over the course of 2 yr in Korea to determine the species composition, abundance, and seasonal dynamics of perilla seed bugs. Three species of Heteroptera (Nysius plebeius, Nysius hidakai, and Nysius inconspicuus), nymphs of Nysius species, and several parasitoid species were collected from weeds and perilla crops. Nysius hidakai was the most abundant perilla seed bugs. In 2019, adult perilla seed bugs, nymphs of perilla seed bugs, and parasitoid species were more abundant in weed species than in perilla crops. An early peak with a greater number of adult perilla seed bug (N. hidakai) was observed in weeds in 2020. However, an identical peak with a similar number of perilla seed bug (N. hidakai) was found in perilla crops in both years. Peak perilla seed bugs densities were observed in the 4th week of June, 2020 in weeds. Parasitoid species from Aphidiidae (1), Braconidae (11), Eulophidae (7), Figitidae (5), Ichneumonidae (7), Platygastridae (1), and Pteromalidae (5) subfamilies were collected. Perilla seed bugs seem to be a serious and increasingly important pest in several field crop species including perilla crops grown on the southern Korean peninsula. Monitoring and early detection of insect species are vital to predicting seasonal colonization and population build-up of perilla seed bugs on perilla crops from a climate change perspective, and essential for developing appropriate management techniques. Thus, continuous monitoring of perilla seed bugs in alternative weed hosts is needed to protect perilla crops from perilla seed bug infestation.

Fusarium wilt samples were collected in 2017 and 2019 from two soybean (Glycine max) fields, Yesan (36°73'N, 126°81'E) and Gimje (35°76'N, 126°80'E), in Korea. The disease incidence rate in each field was approximately 1%. For fungal isolation, root lesion fragments were surface-sterilized in 1% sodium hypochlorite for 2 min, rinsed thrice with sterile distilled water, and then incubated on water agar (WA) plates at 28 °C in an incubator for 5 days. Two isolates (YS37231 and GJ3050) were obtained using the hyphal tip method. Colonies of the isolates on potato dextrose agar (PDA) produced white aerial mycelia, which later turned pinkish yellow. The isolates on PDA formed abundant chlamydospores and macroconidia, but microconidia were absent. Macroconidia were 3-5 septate and prominently curved, measuring 12.4 to 41.2 × 3.3 to 4.3 µm (Leslie and Summerell, 2006). For the identification of the isolates, translation elongation factor 1 alpha (EF-1α) and RNA polymerase second largest subunit (RPB2) regions were amplified and sequenced using EF1, EF2, RPB2-5f2, and RPB2-7cr primers, respectively (O'Donnell et al. 2010). EF-1α sequences of YS37231 (MT445439) and GJ3050 (MT445440) showed 99.01 and 99.67% identity with F. armeniacum (FD_01843 and FD_01305; FUSARIUM-ID database), respectively. The RPB sequences of YS37231 (MT445442) and GJ3050 (MT445441) showed 100 and 98.48% identity with that of F. armeniacum (FD_01869; FUSARIUM-ID database), respectively. The sequences MT445439, MT445440, MT445441, and MT445442 were deposited in NCBI GenBank. The pathogenicity of the two isolates on the soybean cultivar Daewonkong was determined using two inoculation methods. In the first method, a pathogenicity assay was performed on seedlings using WA plates (Cruz Jimenez et al. 2018). Eight surface-sterilized seeds were transferred to WA plates, with or without actively growing cultures, for 3 days; and then incubated at 25 °C in a growth chamber (12 h photoperiod) for 7 days. After 7 days, brown lesions were observed on the roots in inoculated plates; however, no symptoms were observed in the control. -In the second method, 10-day old soybean seedlings were inoculated by cutting and soaking the roots in the spore suspension (1 × 106 conidia/mL) for 2 h. The inoculum was prepared by incubating isolates on PDA for 10 days, then adding sterile distilled water, scraping the growth medium, and filtering the suspension. The seedlings were then transplanted into 18 cm plastic pots (20 cm height) and grown under greenhouse conditions (26 °C ± 3 °C, 13 h photoperiod) for 2 weeks. After 7 days, the inoculated plants showed wilting symptoms, developed brown lesions in the roots, and eventually died within 2 weeks after inoculation. No such symptoms were observed in the control (inoculated with sterile distilled water). The isolates were re-isolated from the inoculated seedlings for confirmation. Although the fungus and associated mycotoxins have been reported in the rice produced in Korea (Hong et al. 2015), to the best of our knowledge, this is the first report of F. armeniacum causing Fusarium wilt on soybean in Korea. In the US, it was first reported by Ellis et al. (2012). Fusarium wilt is a soilborne disease of growing concern in soybean cultivation worldwide. Our findings will help increase awareness about the global spread of this disease.

Soybean (Glycine max L.) is one of the most important crop plants in the Republic of Korea. Here, we conducted a soybean virome study. We harvested a total of 172 soybean leaf samples showing disease symptoms from major soybean-growing regions in the Republic of Korea. Individual samples were examined for virus infection by RT-PCR. Moreover, we generated eight libraries representing eight provinces by pooling samples and four libraries from single samples. RNA-seq followed by bioinformatics analyses revealed 10 different RNA viruses infecting soybean. The proportion of viral reads in each transcriptome ranged from 0.2 to 31.7%. Coinfection of different viruses in soybean plants was very common. There was a single dominant virus in each province, and this geographical difference might be related to the soybean seeds that transmit viruses. In this study, 32 viral genome sequences were assembled and successfully used to analyze the phylogenetic relationships and quasispecies nature of the identified RNA viruses. Moreover, RT-PCR with newly developed primers confirmed infection of the identified viruses in each library. Taken together, our soybean virome study provides a comprehensive overview of viruses infecting soybean in eight geographical regions in the Republic of Korea and four single soybean plants in detail.

The Azuki bean weevil, Callosobruchus chinensis (L.), is a destructive pest of stored mung bean [Vigna radiata (L.) Wilczek] as well as other leguminous seeds. The development of resistant seeds to manage this pest is of current great interest to plant breeders. In this study, we investigated the oviposition preference and development of C. chinensis on two susceptible mung bean cultivars (Seonhwa and Gyeongseon) and one previously reported resistant cultivar (Jangan), compared to the susceptible cowpea (Vigna unguiculata L.), cultivar (Yeonbun) using both multiple-choice and no-choice tests. In addition, the development of C. chinensis was also examined at four constant temperatures (20, 25, 30, and 35 °C). Both tests found cowpea to be the most suitable seed for oviposition. Total developmental time from oviposition to adult emergence ranged from 27.01 to 38.2 days, being shortest on cowpea and longest on the mung bean, cv. Jangan. However, no successful development of C. chinensis larvae on mung bean, cv. Jangan, occurred at any temperature. The highest rate of adult emergence and the longest adult longevity both occurred on cowpea and certain mung bean cultivars (Seonhwa and Gyeongseon), with the dramatic exception of cv. Jangan. These results suggest that the higher preference and performance of C. chinensis on cowpea (3.3 egg/seed) and least on mung bean, cv. Jangan (0.4 egg/seed). This information may facilitate the exploration of resistant genetic materials and chemicals associated with seeds for successful breeding. Further studies should examine the chemicals associated with mung bean cultivars and its resistant mechanism to develop a control method against bruchines.

Azuki bean weevil, Callosobruchus chinensis L. is a cosmopolitan pest of stored grain legumes. Larvae cause huge losses of energy and seeds in the storage. This study assessed the effects of short-term exposure to low-temperatures (4, 0, and − 4 °C) under seven durations of storage (1, 5, 10, 15, 20, 25, and 30 days) on the survival, development, and adult performance of C. chinensis in laboratory. The effects were studied on three life stages (egg, larva [2–3 instar], and pupa) of C. chinensis. The results showed that low-temperature treatments have significant effects on the life variables of C. chinensis. Among the stages, egg and pupa stages were most sensitive to low-temperature. The very low survival rates of eggs at − 4 °C, no pupa stages of C. chinensis survived after 10 days storage. Cold exposure at − 4 °C for

Alydids and pentatomids are economic pests of leguminous crops and fruits in Korea. Direct impacts given by these phytophagous adult and nymphal by sucking on the pods, seeds and fruits can reduce germination potential of leguminous seeds, and yield poor nutritional quality. For monitoring of these bugs, various types of traps housing species-specific baiting with pheromones are widely practiced. However, a trap developed for one species has not been found to capture other species. Here, we developed a multi-species trapping device with some modification for enhancing capture efficacy of sympatric hemipteran bugs, called ‘rocket trap with solar fan’ pertaining to its shape. The trap with and without solar fan, and yellow, black, and white color stimuli were examined for the attractiveness of sympatric hemipteran bugs against conventional traps such as pyramid and fish-net traps. In addition, the attractiveness of single or mixed baits combination to sympatric hemipteran was also tested. Among the tested traps, yellow rocket trap with solar fan was found to attract significantly higher number of stink bug species. Major stink bugs, Riptortus pedestris , Halyomorpha halys , and Piezodorus hybneri were attracted to yellow rocket trap with solar fan baited with aggregation pheromone of H. halys in the fields. The yellow rocket trap baited with aggregation pheromones along with food and synergist was found more attractive to stink bugs. Results designate that yellow rocket trap with solar fan, and yellow rocket trap baited with mixed form of baits would have enhanced the monitoring and capturing sympatric hemipteran bugs in diversified agricultural landscapes.

The azuki bean weevil, Callosobruchus chinensis L., is one of the most serious stored product pests in the world. The temperature driven stage-specific development of C. chinensis was examined at eight constant temperatures of 15.97, 18.31, 22.09, 26.15, 30.50, 34.39, 38.00, and 40.00 °C on azuki bean ( Vigna angularis [Wild.] Ohwi & Ohashi) and cowpea ( Vigna unguiculata L.) seeds. Parameters for stage-specific development such as threshold temperatures and thermal constants were determined by linear and nonlinear models. The total developmental time (egg - adult) decreased with increasing temperature from 14 to 38 °C on both seeds. However, total developmental time varied from 127.93 to 122.25 days at 15.97 °C to 19.31 and 19.17 days at 38.00 °C on azuki bean and cowpea seeds, respectively. The nonlinear Logan-6 and Performance models estimated optimal temperatures as 37.3, 37.0, 36.5 and 37.1 °C on azuki bean, and as 36.7, 36.4, 34.5 and 36.6 °C on cowpea for egg, larva, pupa and egg to adult, respectively. The linear model estimated the lower temperature thresholds (T min ) of egg, larva, pupa and egg to adult as 16.97, 10.47, 1.36, and 10.28 °C on azuki bean, respectively, and 16.84, 10.33, 10.92, and 9.83 °C on cowpea, respectively. The thermal constants ( K ) for each stage completion was 35.13, 255.21, 233.11, and 503.41° days (DD) for egg, larva, pupa, and egg to adult on azuki bean, respectively and 32.45, 246.50, 107.04, and 490.02 DD for egg, larva, pupa, and egg to adult on cowpea, respectively. Temperature also influenced the adult longevity. These findings on thermal requirements and temperature thresholds can be used to predict the occurrence, number of generations and population dynamics of C. chinensis .

Maize yellow mosaic virus (MaYMV) is a novel putative polerovirus recently found in maize (Zea mays) in China and has been detected not only in Asia but also in Africa and South America (Chen et al. 2016; Goncalves et al. 2017; Palanga et al. 2017). In addition, MaYMV infection has also been reported in sugarcane (Saccharum spp.) and itch grass (Rottboellia cochinchinensis) (Yahaya et al. 2017). Recently, the first occurrence of MaYMV in South Korea has been reported from Panicum miliaceum and Sorghum bicolor using high-throughput RNA sequencing (Lim et al. 2018). Therefore, to confirm whether MaYMV exists in maize in South Korea, a total of 26 maize samples with yellowing, yellow stripe, and chlorosis symptoms were collected from three provinces (Chungcheongbuk-do, Gangwon-do, and Gyeongsangnam-do) in August and September 2017. Total RNA was extracted from all samples using the easy-spin Total RNA Extraction Kit (iNtRON Biotechnology, Seongnam, Korea). Reverse transcription polymerase chain reaction (RT-PCR) was conducted using SuPrimeScript RT-PCR Premix (GeNet Bio, Daejeon, Korea) and MaYMV-specific primers (Chen et al. 2016), producing an amplicon with expected size of 753 bp, using protocols described previously (Lim et al. 2018). Five out of six samples collected from Chungcheongbuk-do, five out of 10 samples collected from Gangwon-do, and one out of 10 samples collected from Gyeongsangnam-do were confirmed to be infected with MaYMV. One RT-PCR fragment of MaYMV from each region (Gangwon-do, Chungcheongbuk-do, and Gyeongsangnam-do) was directly sequenced (Macrogen, Daejeon, Korea), and the sequences were deposited in GenBank under accession numbers MG020517, MG020518, and MG020519, respectively. The partial nucleotide sequences of MaYMV determined in each sample collected from Chungcheongbuk-do and Gyeongsangnam-do were identical, and these nucleotide sequences differed by one nucleotide from that identified in the sample collected from Gangwon-do. The NCBI BLAST search showed that the three MaYMV isolates shared high nucleotide sequence homology (99 to 100%) with isolates Yunnan3 (KU291099) and Yunnan4 (KU291100) from maize in China. The MaYMV-infected samples showed yellow stripe and chlorosis symptoms, which tend to first appear on the tip and edge of the leaves and become worse. However, further studies are needed, because it is uncertain whether the symptoms were caused by a single infection with MaYMV. To the best of our knowledge, this is the first report of MaYMV on Z. mays in South Korea.