In vitro evaluation of the effect of entomopathogenic nematodes on different developmental stages of the brown dog tick Rhipicephalus sanguineus (Acari: Ixodidae)

Abstract

The brown dog tick, Rhipicephalus sanguineus (R. sanguineus) is a worldwide ectoparasite of veterinary and medical concern. Entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis are occasionally used as bio-control agents for external parasites such as ticks and flies. This study aimed to evaluate the effect of five different concentrations of the EPNs Heterorhabditis bacteriophora HP88 and Steinernema sp. SII [4000, 2000, 1000, 500, and 250 infective juveniles per milliliter (IJs/ml)] on different developmental stages of R. sanguineus ticks. The EPN application caused mortality in both engorged larvae and newly molted nymphs [H. bacteriophora HP88 (10% - 40%) and Steinernema sp. SII (10% - 18%)]. However, mortality was much higher in both engorged nymphs and newly molted adults (54% - 82% with H. bacteriophora HP88 and 84% - 96% with Steinernema sp. SII). Both EPNs were 100% effective on engorged females 9 days post-exposure. As this life stage was the most susceptible, it was used to calculate the LC (lethal concentration) values in order to determine which EPN was most virulent. The LC<sub>50</sub> and LC<sub>95</sub> at 5 days post-exposure were 76 and 5421 IJs/ml for H. bacteriophora HP88 and 885 and 5700 IJs/ml for Steinernema sp. SII, respectively. In conclusion, although the efficacy of the two EPN species differed among tick life stages, both nematode species can induce mortality and could be used as an alternative option for the biological control of non-parasitic (off-host) tick stages.