• The Korean Journal of Ecology
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• v.24 no.6
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• pp.377-380
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• 2001

Herbivory is an important selective forces on plants by reducing the ability of the plant to compete with its neighbors and to produce offspring. Oak nut weevil(Mechoris ursulus Roelofs) females lay eggs in unmatured acorns and cut off the branch of oviposited acorns. To investigate the influences of branch-cutting behavior of oak nut weevils on oak production, we surveyed the horizontal and vertical distribution ranges of damaged oaks and depth of sites of overwintering larvae and quantified the amounts of biomass and acorn removed by the weevils on deciduous oak species. All of the endemic oak species in Korea were damaged by oak nut weevils in all of the study sites including Mt. Halla and Mt. Seorak. The upper limit of vertical distribution of damaged oaks by the weevils raried from 700 m to 900 m. Mostly their larvae were found in soil from 8.1 cm to 10.0 cm depth in winter. Percentage of annual net primary productivity($720g{\cdot}m^{-2}{\cdot}day^{-1}$) of oak species removed by the weevils was about 7%, which is higher than the percentage removed by all the herbivores in typical temperate forest(5%) and equivalent to that by all the herbivores in tropical forest. The predation percentage of annual acorn production by oak nut weevil was 27% in Q. mongolica and 33% in Q. acutissima. This results indicate that the branch-cutting behavior of oak nut weevil may be the most important factor regulating oak population and affecting other predators dependent on acorns.

• Korean Journal of Environmental Biology
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• v.35 no.4
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• pp.515-520
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• 2017

Sexual dimorphism of the mouthpart, antenna and mandible of the Cyllorhynchites ursulus in South Korea was studied with linear measurements. The mouthpart and antenna measurements were conducted with a stereoscopic microscope using 122 specimens (72 males and 50 females). Microscopic observation of the mandible were conducted with a Field Emission Scanning Electron Microscope (FE-SEM) using 103 specimens (73 males and 30 females). Results showed that the size difference between males and females was significant in the size of the mouthpart and antenna. On the other hand, we could not detect sexual size dimorphism in the microstructure of the mandible. The bivariate plots made by the result of Principal Component Analysis (PCA) and Discriminant Analysis (DA) showed a size dimorphism in the size of the mouthpart and the antenna between males and females. Based on our study, sexual dimorphism in the mouthpart and antenna exists in C. ursulus from the South Korean population, and this difference seems to be related to the behavioral differences between males and females.

• Korean Journal of Environmental Biology
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• v.37 no.3
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• pp.343-350
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• 2019

Cyllorhynchites ursulus drills holes in acorn and cuts branches with mandibles. To understand this special behavior, we observed the mouthpart of this species using several microscope methods. The stereoscopic microscope used in this study shows that the adductor tendon is thicker than the abductor tendon which confirms that mandibles exert more force pulling inwards than pushing outwards. Also, the shape and position differences were observed using an optical microscope. We found differences of the shape, position, and movement of mandibles among C. ursulus, Curculio sikkimensis and Paracycnotrachelus longiceps by way of observation using SEM. The width of the adductor tendon and the abductor tendon of males of the C. ursulus species was 32.87 ㎛, and 53.83 ㎛, respectively. And, the width of females was 40.81 ㎛ and 75.55 ㎛, respectively. Based on a variety of observations and analyses, we found that the unusual behavior of C. ursulus is deeply related to the morphological features, and these features could be applied to biomimicry.