Acaricidal activity of commercialized insecticides against Haemaphysalis longicornis (Acari: Ixodidae) nymphs

• The acaricial activity of 13 commercialized insecticides in Korea against Haemaphysalis longicornis nymphs was evaluated.
• The activity of insecticides belonging to pyrethroids was high.
• Especially, deltamethrin 1.5% and lambda-cyhalothrin 5.5% exhibited 93 and 87% mortality at 7 days after treatment.
• However, their residual acaricidal activity was rapidly decreased under field conditions.

The acaricial activity of 13 commercialized insecticides in Korea against the hard tick nymphs Haemaphysalis longicornis collected in a field was tested using nymph dipping and folded filter paper methods and a spraying-residual assay. In a nymph dipping bioassay, 100% mortality at all tested doses was observed in insecticides containing active ingredients such as phthalthrin 8% + d-phenothrin 2% + piperonyl butoxide 20%, deltamethrin 1.5%, pyrethrum 0.5%, lambda-cyhalothrin 5.5%, alpha-cypermethrin 10% and teflubenzuron 50%, whereas the insecticide containing etofenprox 5% + octachlorodipropyl ether 11% at recommended dose (RD) and 0.5 times RD showed 97 and 90% activity, respectively. Other insecticides containing alpha-cypermethrin 5%, polyoxyethylene isostearylether 10%, etofenprox 5%, bistrifluron 10% and Bti did not show any significant activity. In the folded filter paper contact test with nymph H. longicornis at RD, polyoxyethylene isostearylether 10%, deltamethrin 1.5% and alpha-cypermethrin 10% showed 100% mortality at 1 day after treatment (DAT). At 7 DAT, polyoxyethylene isostearylether 10%, deltamethrin 1.5% and lambda-cyhalothrin 5.5% exhibited 100, 93 and 87% mortality. Although the selected 5 insecticides showed strong mortality under laboratory conditions, their residual effect sprayed on field grown lawn leaves significantly decreased depending on DAT. Etofenprox 5% mixture (+ octachlorodipropyl ether 11%) only showed 93 and 80% mortality at 1 and 2 DAT, respectively. Polyoxyethylene isostearylether 10% gave 0% mortality at even 1 DAT and the other insecticides also showed 60–70% mortality at 1 DAT. These results indicate that pyrethroid insecticides gave good activity against the H. longicornis nymphs but their residual effect is within 1 DAT under field conditions.

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