Survival of entomopathogenic nematodes in oil emulsions and control effectiveness on adult engorged ticks (Acari: Ixodida)

Abstract

Although their control is based on chemical products, the infestations by ticks <i>(Ixodes scapularis</i> Say) are causing great losses and damages in the livestock production worldwide. In this study, the survival of the entomopathogenic nematodes <i>Heterorhabditis bacteriophora, Steinernema carpocapsae</i> and <i>Steinernema websteri</i> in vegetal oil suspension at concentrations of 13% and 33% and their effectiveness to control ticks at concentrations of 50 ± 5 and 100 ± 10 nematodes in oil suspensions of <i>Cymbopogon citratus, Pelargonium</i> sp<i>, Juniperus virginiana, Rosa</i> sp, and <i>Mentha piperita</i> were evaluated in lab conditions. In field conditions, the Lethal Concentration (LC₉₀) of <i>S. websteri</i> in oil suspensions of <i>J. virginiana</i> and <i>C. citratus</i> in dogs infested with ticks was evaluated. In the laboratory, it was found that an oil emulsion of <i>C. citratus</i> and <i>J. virginiana</i> at 13% maintained the survival of <i>S. carpocapsae, H. bacteriophora</i> and <i>S. websteri</i> from 55% to 60% for a period of 96 hr. The combination of the <i>S. websteri</i> nematode with 50 or 100 nematodes in oil emulsions of <i>J. virginiana</i> at 33% presented a control effectiveness of 80–100% in adult ticks 24 hr post-application. In field, the LC90 of 119 juveniles of <i>S. websteri</i> in oil emulsions of <i>J. virginiana</i> at 33% on domestic dogs presented an accumulated a control effectiveness of 89% after 96 hr post-application. The combined application of <i>J. virginiana</i> and <i>S. websteri</i> could be a good alternative for the control of ticks. It was observed that the time of contact and the type of vegetable oil were crucial factors to increase the effectiveness of control.