Abstract
Phenethyl isothiocyanate isolated from Armoracia rusticana root oil and its derivatives were tested at different doses in a bioassay designed to evaluate repellency against individual Haemaphysalis longicornis nymphs. Among the tested compounds, benzyl isothiocyanate exhibited repellency against H. longicornis nymphs at the lowest dose of 0.00625 mg/cm2, followed by phenethyl isothiocyanate (0.0125 mg/cm2) and phenyl isothiocyanate (0.025 mg/cm2). The behavioral responses of H. longicornis nymphs exposed to benzyl isothiocyanate and phenethyl isothiocyanate indicated that the mode of action of these compounds can be mainly attributed to the vapor phase. Encapsulated benzyl isothiocyanate showed repellency up to 120 min post-application at 0.1 mg/cm2, whereas pure benzyl isothiocyanate showed repellency up to 60 min post-application at 0.1 mg/cm2. The present study suggests that benzyl isothiocyanate is a potential repellent for protection against H. longicornis nymphs, and encapsulation in yeast cells may enhance the repellency effect.
Highlights
The Asian longhorned tick, Haemaphysalis longicornis (Ixodida: Ixodidae), is an important livestock pest transmitting various tick-borne infectious diseases including severe fever with thrombocytopenia syndrome (SFTS)
The median difference between A. rusticana root oil and the negative control was highly significant (p < 0.01) for doses greater than 0.025 mg/cm2. This indicates that repellent compounds exist in A. rusticana root oil
Similar results were obtained in an experiment on Ixodes ricinus that used a Y-tube olfactometer bioassay with DEET-treated filter paper. These findings indicated that olfaction was involved in the observed repellency of benzyl isothiocyanate and phenethyl isothiocyanate
Summary
The Asian longhorned tick, Haemaphysalis longicornis (Ixodida: Ixodidae), is an important livestock pest transmitting various tick-borne infectious diseases including severe fever with thrombocytopenia syndrome (SFTS). SFTS is an emerging infectious disease caused by the SFTS virus (SFTSV), a member of the genus Phlebovirus [1]. As there are no specific medications or vaccines available for SFTS, control is mostly focused on targeting its primary vector, H. longicornis. H. longicornis is native to Eastern Asia (China, Japan, and South Korea) but has become common as an invasive tick in New Zealand and Australia [2]. H. longicornis was discovered in New Jersey and is rapidly spreading throughout the United States of America [3]. The rapid spread of H. longicornis and H. longicornis-borne diseases, including SFTS, presents a potential worldwide threat
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