Infectivity of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) to female ticks of Boophilus annulatus (Arachnida: Ixodidae).

Exposing Boophilus annulatus (Say) to different concentrations of Steinernema carpocapsae (Filipjev) infective juveniles in petri dishes (50-10,000 nematodes per dish) resulted in high mortality (greater than 90%) at nematode concentrations as low as 500 nematodes per dish within 8 d. At a concentration of 10,000 nematodes per dish, 100% of the ticks died within 2 d after infestation. After exposure to 500 nematodes per dish, complete mortality was achieved with the Heterorhabditis bacteriophora strain 'HP88' within 4 d. During the same period, only 15 and 40% mortality were recorded with the 'Mexican' and 'All' strains of S. carpocapsae, respectively. In a lethal dose analysis, S. carpocapsae strain 'DT' was the most infective strain with the lowest LD50 and LD90 values (15 and 165 infective juveniles per tick, respectively). The 'All' strain of S. carpocapsae was the least infective of the four strains tested, with LD50 and LD90 values of 372 and 9,251 infective juveniles/tick, respectively. Optimal temperature for tick control by the nematodes was between 22 and 26 degrees C. Mortality rate was reduced at 18 and 30 degrees C. The susceptibility of fully engorged ticks was not influenced by the weight of the replete females. Nematode infection did not have an adverse effect on egg laying by surviving ticks.