Entomopathogenic nematodes in insect cadaver formulations for the control of Rhipicephalus microplus (Acari: Ixodidae)

This study evaluated the efficacy of four entomopathogenic nematode (EPN) strains in insect cadaver formulations against Rhipicephalus microplus and compared the efficacy of the most virulent EPNs applied in cadavers of Galleria mellonella and Tenebrio molitor. In the first experiment, infected G. mellonela larvae were used as the source of EPNs. Engorged females of R. microplus were placed in pots filled with soil and different numbers of G. mellonella larvae infected with one of four species of nematodes. All treatments with EPNs of the genus Heterorhabditis caused significant reduction (p < 0.05) in the egg mass weight and hatching percentage of larvae. The EPNs of the genus Steinernema, except for the group exposed to Steinernema carpocapsae ALL, whose source nematodes included six larvae of G. mellonella, caused a significant reduction (p < 0.05) in the egg mass weight produced per female. Steinernema feltiae SN applied with two, four, and six cadavers and S. carpocapsae ALL with two cadavers caused a reduction in hatching percentage of larvae of R. microplus (p < 0.05). The percentage of control was above 95% in all groups treated with Heterorhabditis bacteriophora HP88 and Heterorhabditis indica LPP1 and in the treatment with four larvae infected with S. feltiae SN. The second experiment followed the same methodology, using G. mellonella and T. molitor larvae infected by the two most virulent EPNs. H. bacteriophora HP88 and H. indica LPP1 in different formulations caused reduction in the egg mass weight and hatching percentage of larvae. The percentage of control were 82.4 and 84.9% for H. bacteriophora HP88 and H. indica LPP1, respectively, formulated in T. molitor, and reaching 99.9% in groups formulated with G. mellonella. The EPNs tested in insect cadaver formulation showed pathogenicity to engorged females of R. microplus and EPNs of the genus Heterorhabditis formulated in G. mellonella larvae were more effective.