Soon Il Kim

Toxicity of Plant Essential Oils to Acaricide-Susceptible and -Resistant Tetranychus urticae (Acari: Tetranychidae) and Neoseiulus californicus (Acari: Phytoseiidae)

ABSTRACT The toxicity of 10 plant essential oils to adults of acaricide-susceptible, chlorfenapyrresistant (CRT-53), fenpropathrin-resistant (FRT-53), pyridaben-resistant (PRT-53), and abamectinresistant (ART-53) strains of Tetranychus urticae Koch (Acari: Tetranychidae) and to female Neoseiulus californicus McGregor (Acari: Phytoseiidae) was examined using spray or vapor-phase mortality bioassays. In bioassay with the susceptible adults, lemon eucalyptus (19.3 µg/cm3) was the most toxic oil, followed by peppermint, citronella Java, thyme red, caraway seed, clove leaf, and pennyroyal oils (LC50, 20.6–23.7 µg/cm3). The toxicity of these oils was almost identical against adults from either of the susceptible and resistant strains, even though CRT-53, FRT-53, PRT-53, and ART-53 adults exhibited high levels of resistance to chlorfenapyr (resistance ratio [RR], >9,140), fenpropathrin (RR, 94), pyridaben (RR, >390), and abamectin (RR, 85), respectively, Against female N. californicus, lemon eucalyptus (LC50, 21.4 µg/cm3) was the most toxic oil, whereas the LC50 values of the other nine oils ranged from 23.2 to 72.6 µg/cm3. N. californicus was 1–2 times more tolerant than T. urticae to the test essential oils. Thus, these essential oils merit further study as potential acaricides for the control of acaricide-resistant T. urticae populations as fumigants.

Effectiveness of carvacrol derived from Thujopsis dolabrata var. hondai sawdust against Thecodiplosis japonensis (Diptera: Cecidomyiidae).

The larvicidal component from sawdust of Thujopsis dolabrata var. hondai (Family Cupressaceae) against the pine needle gall midge (Thecodiplosis japonensis) was isolated by chromatographic techniques and characterized by spectral analysis as carvacrol. In a laboratory study using the impregnated filter paper method, carvacrol was more toxic to T. japonensis larvae than β-thujaplicine, cedrol, α-terpinol, thujone or thymol. In field studies with soil injections of carvacrol, this compound exhibited potent larvicidal activity, suggesting that this activity might be attributable to fumigant action. In a test with trunk implantation, a mixture of carvacrol and phosphamidon (0.15 + 0.15 ml cm -1 diameter at breast height) revealed much more potent larvicidal activity than phosphamidon alone (0.3 ml cm -1 DBH) in spite of little or no larvicidal activity of carvacrol alone (0.3 ml cm -1 DBH), indicating a possible synergistic effect. As a naturally occurring insecticide, carvacrol could be useful as a new preventive agent against damage caused by T. japonensis.

Fumigant toxicity of basil oil compounds and related compounds to Thrips palmi and Orius strigicollis

BACKGROUND This study was aimed at assessing the fumigant toxicity to adult Thrips palmi (a serious insect pest) and Orius strigicollis (a beneficial predator insect) of basil (Ocimum basilicum) essential oil compounds and structurally related compounds using vapour-phase toxicity bioassays. RESULTS Against adult T. palmi, linalool (LD50 0.0055 mg cm(-3) ) was the most toxic fumigant and was 15.2-fold more effective than dichlorvos (0.0837 mg cm(-3) ). Strong fumigant toxicity was also observed in pulegone (0.0095 mg cm(-3) ), (±)-camphor (0.0097 mg cm(-3) ) and 1,8-cineole (0.0167 mg cm(-3) ). Moderate toxicity was produced by camphene, 3-carene, (-)-menthone, (+)-α-pinene, (+)-β-pinene, α-terpineol and (-)-α-thujone (0.0215-0.0388 mg cm(-3) ). Against adult O. strigicollis, dichlorvos (LD50 9.0 × 10(-10) mg cm(-3) ) was the most toxic fumigant, whereas the LD50 values of these compounds ranged from 0.0127 to >0.23 mg cm(-3) . Based upon the selective toxicity ratio, the compounds described are more selective than dichlorvos. CONCLUSION The basil oil compounds described merit further study as potential insecticides for control of T. palmi in greenhouses because of their generally lower toxicity to O. strigicollis and their greater activity as a fumigant than dichlorvos.