Survival dynamics of stick insect and the impact of environmental factors on natural fungal infection during the rainy season.

Phasmatodea, commonly known as stick insects, are recognized as noteworthy pests globally, impacting agriculture and forest ecosystems. Among them, the outbreak of Ramulus mikado has emerged as a notable concern in East Asian forests. Recently, Metarhizium phasmatodeae has been identified as utilizing stick insects as hosts. We have observed evidence of this entomopathogenic fungus infecting stick insects. Given the increase in these occurrences during the rainy period, this study investigated the relationship between the survival of R. mikado and the M. phasmatodeae infection during the rainy seasons of 2022 and 2023. We collected stick insects in two representative forests of the Republic of Korea and examined insect survival, fungal infection, and various environmental factors. No infections were detected in specimens collected in June before the rainy season, but from July onwards, both the mortality of R. mikado and the fungal infection substantially increased. By the last sampling date of each year, 75% (2022), 71.4% (2023) of the specimens were infected, and over 90% of the total individuals succumbed as a result. Fungi isolated from deceased R. mikado were successfully identified as M. phasmatodeae using morphological and taxonomic approaches. Various statistical analyses, including principal component analysis and modeling, revealed a robust association between fungal infection and the survival of stick insects. The results highlight the correlation between mass deaths of stick insects and fungal infection, particularly during the summer rainy season. These findings offer valuable insights for forecasting R. mikado population in the upcoming year and developing effective pest control strategies.

Integrated Identification and Genetic Diversity of Potentially Invasive Clearwing Moths (Lepidoptera: Cossoidea: Sesiidae) in Korea.

The populations of clearwing moth borers in Korea have recently caused extensive and severe damage to pin oaks (Quercus palustris Munchh.). We conducted field monitoring and molecular analyses to identify them in an integrated manner. Morphological examination and molecular analyses of the COI gene, based on intra- and interspecific genetic divergences (GDs), revealed that the borers were identified as two invasive species, Sphecodoptera sheni and Paranthrenella pinoakula sp. nov. The maximum intraspecific GD was found to be 1.9%, whereas the minimum interspecific GD was confirmed as 8.1%, indicating a distinct barcoding gap. Both the MJ network and NJ tree also showed that 18 haplotypes (Hs) were detected from the 52 COI sequences. The borers revealed a total of 17 Hs: (i) H1-H7 were detected in all seven regions with S. sheni; (ii) Wonju and Goyang populations of S. sheni revealed more than three Hs; (iii) H7 was closely connected with H8 of the Chinese population of S. sheni; (iv) H9-H10 were detected in other samples from the Wonju population with P. pinoakula sp. n. and were closely located with congeneric species. A maximum likelihood tree also revealed that P. pinoacula sp. n. nested within the congeneric species, genetically separating from S. sheni.

Spatial ensemble modeling for predicting the potential distribution of Lymantria dispar asiatica (Lepidoptera: Erebidae: Lymantriinae) in South Korea.

The spongy moth, Lymantria dispar, is a pest that damages various tree species throughout North America and Eurasia, has recently emerged in South Korea, threatening local forests and landscapes. The establishment of effective countermeasures against this species' outbreak requires predicting its potential distribution with climate change. In this study, we used species distribution models (CLIMEX and MaxEnt) to predict the potential distribution of the spongy moth and identify areas at risk of exposure to a sustained occurrence of the pest by constructing an ensemble map that simultaneously projected the outcomes of the two models. The results showed that the spongy moth could be distributed over the entire country under the current climate, but the number of suitable areas would decrease under a climate change scenario. This study is expected to provide basic data that can predict areas requiring intensive control and monitoring in advance with methodologically improved modeling technique.

Can insecticide applications used to kill vector insects prevent pine wilt disease?

BACKGROUND: The aerial application of insecticides is a primary method used to prevent the spread of pine wilt disease by reducing the population density of Monochamus beetles, the vector insects of pine wood nematodes (PWNs). This study investigated the mortality of vector insects and the ratio of PWN-infected trees according to systemically remaining thiacloprid residues in Pinus densiflora. To do this, thiacloprid was sprayed on a nursery of 5-year-old P. densiflora in meshed cages. Then Monochamus alternatus adults carrying PWNs were placed into meshed cages 1 and 15 days post-treatment (T1 and T15 groups for thiacloprid spraying, and N1 and N15 groups for nonsprayed groups) and tree mortality was monitored. We also measured the thiacloprid residues in pine branches in each treatment. RESULTS: In pine trees, more thiacloprid residues were found in the T1 group than in the T15 group, but most M. alternatus adults died in the T1 and T15 groups and PWNs were detected in 51.3% of all recaptured beetles. In the 16th week after each treatment, the average tree mortalities in T1 and T15 were 0% and 16.7%, respectively, whereas mortality of ≈50-60% of all tested trees in the nonsprayed groups was observed. CONCLUSION: The current aerial application of insecticides may have a limitation in preventing PWN transmission from dying M. alternatus adults when they are exposed to low thiacloprid residues in pine trees.

A comparison of spider communities in Bt and non-Bt rice fields.

To assess the potential adverse effects of a Bt rice line (Japonica rice cultivar, Nakdong) expressing a synthetic cry1Ac1 gene, C7-1-9-1-B, which was highly active against all larval stages of Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Crambidae), we investigated the community structure of spiders in Bt and non-Bt rice fields during the rice-growing season in 2007 and 2008 in Chungcheongnam-do, Korea. Spiders were surveyed with a sweep net and suction device. Suction sampling captured more spiders, measured in terms of species level and abundance, than sweeping. Araneidae and Thomisidae were captured more by sweeping, and certain species were captured only by sweeping. These findings show that both suction and sweep sampling methods should be used because these methods are most likely complementary. In total, 29 species in 23 genera and nine families were identified from the 4,937 spiders collected, and both Bt and non-Bt rice fields showed a typical Korean spider assemblage. The temporal patterns of spider species richness and spider abundance were very similar between Bt and non-Bt rice, although significant differences in species richness were observed on a few occasions. Overall, spider community structure, including diversity, the dominant species, and abundance did not differ between Bt and non-Bt rice. The results of the study indicated that the transgenic Cry1Ac rice lines tested in this study had no adverse effects on the spider community structure of the rice fields.