Efficacy and Phytotoxicity Assessment of Successive Application of Methyl Bromide and Cold Treatment on Export Strawberry Fruits.

Recently, spotted wing Drosophila, Drosophila suzukii, is globally prevalent and causes agricultural losses to many fruits. To export Korean strawberry, methyl bromide fumigation is required to remove D. suzukii infestations, but Korean strawberry farmers are worried about fruit damage because methyl bromide can cause phytotoxicity on fresh commodities. In this report, we assessed the efficacy and phytotoxicity of single and successive application of methyl bromide and cold treatment on an export variety of strawberry to reduce fruit damage. The currently recommended dosage of methyl bromide, 40 g/m3 for 3 h at 18 °C, was enough to control all stages of D. suzukii without phytotoxicity. A dosage of 20 g/m3 of methyl bromide treatment for 3 h, followed by 1 d of cold (0 °C) treatment, showed 100% mortality in all growth stages of D. suzukii without fruit damage. Successive application of methyl bromide and cold treatment shows potential as a method of decreasing phytotoxicity and reducing the use of methyl bromide for environmental considerations.

Population Genetics for Inferring Introduction Sources of the Oriental Fruit Fly, Bactrocera dorsalis: A Test for Quarantine Use in Korea.

To infer the introduction sources of the oriental fruit fly, Bactrocera dorsalis, we used a mitochondrial marker to reconstruct the haplotype network and 15 microsatellite loci to reveal genetic structure and relationships between the geographically or temporally different collections from Asia. We performed Approximate Bayesian computations to infer a global origin and a source of the quarantine collections found in Korea. As a result, the 40 populations were divided into three groups, of which genetic similarity is not related to the geographic vicinity. Korean samples had a similar genetic structure to Taiwan and Thailand ones. Our results suggest that the place of origin of the B. dorsalis specimens found in Korea's border quarantine is likely to be Taiwan or Thailand. As the global origin of B. dorsalis, we estimated that Taiwan and Thailand were most likely the global origins of Southeast Asian populations by testing hypothetical scenarios by the approximate Bayesian computation analyses. Our results will allow easier identification of the source region of the forthcoming invasion of quarantined B. dorsalis specimens.

Comparison of gene expression in the red imported fire ant (Solenopsis invicta) under different temperature conditions.

The red imported fire ant (RIFA), Solenopsis invicta Buren is native to South America and is known as a global problematic invasive species. This study focused on the molecular response of RIFA by comparing gene expression profiles after exposing ants to low (10 °C) and high (40 °C) temperature stress and comparing them to untreated controls (30 °C). A total of 99,085 unigenes (the clustered non-redundant transcripts that are filtered from the longest assembled contigs) were obtained, of which 19,154 were annotated with gene descriptions, gene ontology terms, and metabolic pathways. 86 gene ontology (GO) functional sub-groups and 23 EggNOG terms resulted. Differentially expressed genes (DEGs) with log2FC ≥ 10 were screened and were compared at different temperatures. We found 203, 48, and 66 specific DEGs co-regulated at 10, 20, and 40 °C. Comparing transcriptome profiles for differential gene expression resulted in various DE genes, including cytochrome P450, NADH dehydrogenase subunit 1, cuticle protein and heat shock protein (HSP), which have previously been reported to be involved in cold and high temperature resistance. GO analysis revealed that antioxidant activity is up-regulated under high temperature stress. We verified the RNA-seq data by qPCR on 20 up- and down-regulated DEGs. These findings provide a basis for future understanding of the adaptation mechanisms of RIFA and the molecular mechanisms underlying the response to low and high temperatures.

Arthropods as potential vectors of African swine fever virus outbreaks in pig farms in the Republic of Korea.

The seasonality of African swine fever (ASF) in the summers and outbreaks in farms with high biosecurity levels suggest that the ASF virus (ASFV) may be transmitted by arthropod vectors. Arthropods were collected in this study from 14 pig farms with ASF outbreaks in Korea in 2019 to explore the role of arthropods as potential ASFV vectors. A total of 28,729 arthropods, including 28,508 (99.2%) Diptera, were collected using blacklight traps, insect nets and yellow sticky strips. All arthropod samples were negative for ASFV genomic DNA according to laboratory tests using real-time polymerase chain reaction. This result may reflect the effects of immediate control measures following the detection of farms with ASF outbreaks in the early phase of infection in Korea.

Phytosanitary Cold Treatment of Spotted-Wing Drosophila, Drosophila suzukii (Diptera: Drosophilidae) in 'Campbell Early' Grape.

The effects of cold storage temperature and exposure duration on different developmental stages of spotted-wing drosophila (SWD) Drosophila suzukii (Diptera: Drosophilidae) on 'Campbell Early' grapes were examined to establish a phytosanitary control method. The immature stages (eggs, larvae and pupae) of SWD were all dead after a 6-d cold treatment at 1°C and 8-d cold treatment at 1.5 and 2°C. Probit-9 estimated a fourfold increase in cold treatment duration to achieve 99.9968% mortality, compared with the observed mortality. Efficacy tests using pupae, which were the most cold-tolerant stage, confirmed the validity of the selected temperature and exposure durations. Based on these results, 1°C, which requires a shorter exposure for complete mortality, was selected for the test in conditions that mimic those of grape exportation. Six-day cold treatments at 1°C produced 99.57%, mortality in different replicates, although the surviving pupae died later. Conversely, the 8- and 10-d treatments at 1°C showed 100% mortality, suggesting that these treatments can provide quarantine security against infestations of SWD on exported Campbell Early grapes, although an additional experiment with an increased sample size is required for further reliable conclusion.

Geographic variation in the spotted-wing drosophila, Drosophila suzukii (Diptera: Drosophilidae), based on mitochondrial DNA sequences.

The spotted-wing drosophila (SWD), Drosophila suzukii (Diptera: Drosophilidae), is an economically damaging pest that feeds on most thin-skinned fruits. It was originally native to a few Asian countries, including Korea, but is now found in North America and Europe. In this study, we sequenced portions of the mitochondrial (mt) COI and ND4 genes from a total of 195 individuals collected mainly from Korea. We then combined GenBank-registered COI sequences from all ancestral-range and introduced-range populations with our own COI data to assess the worldwide diversity, divergence, and relatedness of SWD haplotypes. A total of 139 haplotypes were obtained from the concatenated COI and ND4 sequences. Most haplotypes were confined to single localities, but 12 of them were found in more than two localities, and one haplotype (SWDCN61) was found from Korea to Canada. A dataset combining GenBank sequences with our own data identified a total of 94 worldwide COI haplotypes with a maximum sequence divergence (MSD) of 5.433% (32 bp). Although most haplotypes were found in only a single country, a few haplotypes were found commonly in China, Korea, and Japan; these occurred at a higher frequency and were often involved in introductions. A rough estimate of genetic diversity in each country showed higher diversity in ancestral distributional ranges, but the invasion over Asian countries seems to have been substantial because haplotype diversity was only 2.35 to 3.97-fold lower in the U.S.A, Canada, and Italy than that in the populations' ancestral ranges.

Complete mitochondrial genome of the spotted-wing drosophila, Drosophila suzukii (Diptera: Drosophilidae).

The spotted-wing drosophila, Drosophila suzukii (Diptera: Drosophilidae) is an Asian species introduced into North America and Europe. It damages a wide variety of thin-skinned fruits. We sequenced the complete mitochondrial genome (mitogenome) to better understand the mitogenomic characteristics of this species. The 16 230-bp complete mitogenome of the species consists of a typical set of genes, including 13 protein-coding genes (PCGs), two rRNA genes and 22 tRNA genes, and one major non-coding A + T-rich region, with an arrangement typical of insects. Twelve PCGs began with the typical ATN codon, whereas the COI began with TCG, which has been designated as the start codon for other Drosophila species. The 1525-bp A + T-rich region is the second longest in Drosophila species for which the whole mitogenome has been sequenced, after D. melanogaster. Phylogenetic analysis using the 13 PCGs of the Drosophila species indicated that D. suzukii is placed, with a strong support, in the basal lineage of the previously defined Melanogaster group.