The efficacy of propylene glycol alginate (PGA), a food additive, in controlling Haemaphysalis longicornis ticks

Ticks and tick-borne pathogens threaten the health of both domestic animals and humans, and are associated with a high economic burden in many countries. Tick control can be achieved with chemical acaricides, but issues remain regarding their safety as well as emerging tick resistance. Propylene glycol alginate (PGA) is a food additive commonly used in China. It has been used to kill whiteflies in agriculture as an environmentally friendly insecticide. The aims of this study were to (i) explore the efficacy of PGA to kill Haemaphysalis longicornis ticks and (ii) assess the potential to develop a new tick control acaricide containing PGA and a reduced amount of synthetic pyrethroid. Beta-cypermethrin was chosen as the reference pyrethroid in this study. PGA, beta-cypermethrin and mixes (PGA and beta-cypermethrin formulated in proportions of A = 2:1, B = 1:1, and C = 1:2) were compared for efficacy to kill larval and adult H. longicornis ticks. Overall, we found no statistically significant differences in the killing efficacy of PGA as compared to beta-cypermethrin across examined time-points post-tick exposure. At 24 h post-tick exposure, similar killing efficacy for H. longicornis larvae was recorded for beta-cypermethrin alone, PGA alone, and mixed formulations B and C. Mixed formulation C had the strongest killing effect when compared to PGA alone or mixed formulation B. Similar outcomes were observed in experiments with adult H. longicornis ticks. Based on these findings, we propose that PGA can be useful as a tick control acaricide, either as a single active ingredient or formulated together with a pyrethroid.