The giant water bug, Lethocerus deyrollei which is the largest aquatic insect in Korea, has been designated as an endangered species by the Ministry of Environment of Korea since 1997 and is also recorded as “Vulnerable” on red Data Book of Japan (Japan Environment Agency, 2000). The populations of L. deyrollei have decreased dramatically in Korea because of loss of wetland habitats, road kill and artificial lighting. Since 2007 Holoce Ecosystem Conservation Research Institution (HECRI) has been reared L. deyrollei through breeding in captivity and 90 pairs individuals were released from 2012 to 2013. On the basis of previous field monitoring which was considered sufficient food such as fish, tadpoles and frogs and emergent plants such as Phragmites communis, Phragmites japonica, Typha angustifolia and Acorus calamus, Hyeon-cheon(E128°09’38“, N37°30’23“, 556m) was selected as a release site. After release on July 16, 2013 and carried out monitoring twice. We observed several egg clusters on July 25 and 1st larvae on July 30 respectively. Hyeon-cheon seems to be appropriate and expected to be as a major natural wet habitats for L. deyrollei.

This study was carried out to investigate whether giant water bug, designated as an endangered species by the Ministry of Environment of Korea since 1997, can control American bull frog tadpole which has been designated as an Invasive Alien Species(IAS) by the Ministry of Environment of Korea since 1998. The experiment was conducted through food preference between fish (Crucian carp, Carassius auratus) and American bull frog tadpole(Rana catesbeiana) in laboratory condition (25±1°C) in HECRI. Potential food such as fish(weight: 8.2±0.6, length: 87.4± 1.6mm) and American bull frog tadpole(weight: 6.8±0.4g, length: 92.3±1.6mm) were inserted 5 individuals respectively in the nineteen acrylate cages with one pair of L. deyrollei simultaneously. Twice(10:00, 18:00) per a day was monitored. Once we confirmed prey was consumed by L. deyrollei, removed and replaced with same species to maintain same number immediately. Preference for American bull frog tadpole was significantly higher(93.6%) than fish(6.4%) (F=30.65, df=1, 18, P<0.0001).

The toxicity of methanol extract from 28 plants toward four agricultural insect pests were examined using contact toxicity bioassay with spray methods. At a concentration of 1,000 ppm Achyranthes japonica whole body was observed strong activity against Myzus persicae. Paeonia lactiflora root and Corydalis turtschaninovii rhizome methanol extract were observed strong activity toward Tetranychus urticae. Catalpa ovata leaf and Ginkgo biloba leaf and stem methanol extracts were revealed high activity toward Nilaparvata lugens. Actium lap root methanol extract was observed moderate activity against Plutella xylostella. High or moderate insecticidal activity of plant extracts were listed in Fig.1. These plant resource, particularly plant methanol extract or insecticidal constituents, merit further as potential insect pest control agents or leads because of their great activity as a insecticide.