Minhyung Jung

This study addresses how gut symbiont, Caballeronia insecticola, could change reproductive capacity, mating behaviors, and copulation success of host insect, Riptortus pedestris (Fabricius) (Hemiptera: Alydidae). First, we evaluated symbiotic effects on the female reproductive capacity with varying numbers of males available to a female. Overall, symbiotic females displayed on average a 1.8-fold increase in egg production compared to aposymbiotic individuals. However, eggs from symbiotic females were on average 42% less viable, compared to those from the aposymbiotic, when paired with single male. The decrease in the hatchability was alleviated to 12% when paired with 3 males. Consequently, this yielded significant increase in the number of viable offspring by symbiotic females when multiple males were available. Second, we evaluated symbiotic effects on male morphometric characteristics including hind legs used as weapon, and found significant increases in hind leg sizes associated with symbiosis. Finally, we investigated mating behaviors between a female and 2 males of different symbiotic status. Symbiotic females displayed on average a 1.4-fold increase in the number of copulations compared to the aposymbiotic. From both female types, however, no significant difference was observed in their mate choice and copulation success rate between aposymbiotic and symbiotic males. However, symbiotic females exhibited on average 17% reduction in copulation duration compared to the aposymbiotic. Copulation failure was caused more frequently by female’s rejection than by intruder male’s disruption for both female types. Our study demonstrates that symbiotic females benefit from the symbiosis increasing their reproductive capacity and copulation frequency.

Riptortus pedestris is a major agricultural pest on leguminous plants in South Korea and Japan. Recent studies have revealed that R. pedestris can form beneficial symbiosis with bacteria belonging to genus Burkholderia acquired from soil newly for every generation. Although their physiological interactions are relatively well-understood, infection rate and abundance of the Burkholderia in overwintering natural populations of R. pedestris remain unknown. Therefore, the objective of this study was to characterize Burkholderia infection ratio and clade composition of overwintering R. pedestris populations as well as prevalence and diversity of the genus Burkholderia in soil by conducting a two-year field survey. From the field survey, we found 29 overwintering R. pedestris adults in forested areas nearby soybean fields. Diagnostic PCR analysis revealed that overall infection rate of the symbiotic Burkholderia was 93.1% from overwintering adults. Among the Burkholderia-infected R. pedestris, 70.4% of individuals harbored unclassified Burkholderia clades whereas 22.2% and 7.4% of R. pedestris harbor stinkbug-associated beneficial and environmental (SBE) group and Burkholderia cepacia and complex (BCC), respectively. All R. pedestris were infected with a single clade of Burkholderia. In soil, 56.2% of soil samples were Burkholderia positive, and unlike R. pedestris, multiple Burkholderia clades were detected from 62.2% of those samples. Clade composition of the genus Burkholderia in the samples with the bacteria was 91.1%, 60.0%, 31.1% and 8.8% for plant-associated beneficial and environment (PBE), BCC, SBE and unclassified clade, respectively.

BACKGROUND: Although Haemaphysalis longicornis (Acari: Ixodidae) is an important disease vector, its small size restricts the tracking methods applicable. Recently, fluorescent marking as a conventional detection method for small arthropods has been improved by combining it with an ultraviolet laser. We examined the application potential of this new fluorescent marking system (FMS) for tracking H. longicornis by evaluating the effect of fluorescent marking on the ticks and detection efficacy.RESULTS: Under laboratory conditions, fluorescent marking did not significantly affect the survivorship, movement patterns, and CO₂ response of H. longicornis at all three developmental stages. Fluorescent‐marked individuals could be detected at distances ranging from 12 to 29 m under dark, increasing with the body size. Finally, in grassland, >90% of fluorescent‐marked individuals were retrieved at night regardless of developmental stage. However, the overall detection rate (H. longicornis at night. Nevertheless, fluorescent‐marked individuals are not as conspicuous under sunlight when they are illuminated with ultraviolet lasers, limiting the use of FMS during the day. Therefore, the development of an alternative tracking method is warranted for an effective detection of ticks during the day. © 2019 Society of Chemical Industry

BACKGROUND: Although portable harmonic radar system and fluorescent marking system are two widely used detection methods, their comparative effectiveness has not been studied. Therefore, we first tested the applicability of fluorescent marking system on Riptortus pedestris (Hemiptera: Alydidae). Then, we evaluated the efficacy of the two methods used either alone or combined in a grass field and bean field, varying with complexity, during day and night.RESULTS: Fluorescent marking did not affect the behavior or fitness of Riptortus pedestris except for vertical walking, while allowing the detection from >25 m when paired with a handheld laser. Generally, the portable harmonic radar system and both methods combined were more successful in sample detection, although the fluorescent marking system in the bean field at night was as competitive as the two. Combining both methods made sample retrieval easier at night than the portable harmonic radar system. Nevertheless, the total detection time showed a large variance across the methods.CONCLUSION: The portable harmonic radar system can be an effective detection method in either landscape during both day and night. Furthermore, the fluorescent marking system can be a reliable tool at night as well. Lastly, combining both methods can improve the night detection. © 2018 Society of Chemical Industry

Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) is a major agricultural pest on leguminous plants and tree fruit in South Korea and Japan. Only anecdotal information is currently available about its overwintering behavior and ecology. Therefore, we conducted laboratory experiments and field sampling to characterize overwintering structures and landscapes that R. pedestris use and prefer in South Korea. Under laboratory conditions, we identified the overwintering structure preference of R. pedestris adults and analyzed their spatial distributions. Among tested structures including pile of rocks, rotten wood, and leaf litter, R. pedestris was almost exclusively found in leaf litter. Spatial analysis using Spatial Analysis by Distance IndicEs (SADIE) indicated that most overwintering R. pedestris showed no spatial-aggregation behavior in the test arena. Field surveys were also conducted to characterize overwintering landscapes during the two winter seasons between 2014 and 2016. We selected two distinct landscapes: mountain areas and agricultural areas. Mountain areas were high-elevation mountains remote from agricultural practice, whereas agricultural areas were low-elevation forested landscapes adjacent to agricultural fields, including soybeans. From the 2-yr field survey, 92% (11 out of 12 individuals) of overwintering R. pedestris were found in the agricultural area without a significant aggregation pattern.