Effect of oil-based formulations of acaripathogenic fungi to control Rhipicephalus microplus ticks under laboratory conditions

Abstract

The formulations of acaripathogenic fungi to control ticks have been widely studied. The present study evaluated the efficacy of oil-based formulations of Metarhizium anisopliae sensu lato (s.l.), isolate Ma 959, and Beauveria bassiana, isolate Bb 986, on different Rhipicephalus microplus stages, comparing the efficacy between aqueous suspensions and 10, 15 and 20% mineral oil formulations. Twelve groups were formed: one aqueous control group; three mineral oil control groups, at 10, 15 or 20%; two aqueous fungal suspensions of M. anisopliae s.l. or B. bassiana; and three formulations of M. anisopliae (s.l.) or B. bassiana containing 10, 15, and 20% mineral oil. To prepare aqueous suspensions and oily formulations, fungal isolates were cultivated on rice grains in polypropylene bags. The conidial suspensions and formulations had a concentration of 10(8)conidia/mL. Bioassays were repeated twice. After treatment, the following biological parameters of engorged females were evaluated: hatching percentage, egg production index, nutritional index, and percentage of tick control. The following parameters were evaluated in the bioassays with eggs: period of incubation, period of hatch, and hatching percentage. Mortality was evaluated in bioassays with larvae. M. anisopliae s.l. and B. bassiana oil-based formulations were more effective than aqueous suspensions against R. microplus eggs, larvae and engorged females, however, there was no significant difference between the three oil concentrations used. M. anisopliae s.l. and B. bassiana formulated in mineral oil reached 93.69% and 21.67% efficacy, respectively, while M. anisopliae s.l. and B. bassiana aqueous suspensions attained 18.70% and 1.72% efficacy, respectively. M. anisopliae s.l. oil-based formulations caused significant effects in all biological parameters of engorged females while B. bassiana oil-based formulations modified significantly the nutritional index only. Eggs treated with M. anisopliae s.l. and B. bassiana oil-based formulations showed hatching rates that decreased 102.5 and 3.65 times, respectively. In the bioassay with larvae, M. anisopliae s.l. oil-based formulations caused nearly 100% mortality five days after treatment, while larva treated with B. bassiana oil-based formulations reached 100% mortality at day 20 after treatment. Larva from oil-based control groups showed mortality at day 15 after treatment, which indicated a possible toxic effect of the oil for this R. microplus stage. The results showed that the fungal mineral oil formulations tested were more effective than the aqueous suspension. Oil-based formulations at 10, 15 and 20% enhanced the activity of M. anisopliae s.l. Ma 959, and B. bassiana Bb 986, isolates against R. microplus eggs, larvae, and engorged females tick. Mineral oil was effective as an adjuvant in formulations of M. anisopliae s.l., Ma 959, and B. bassiana, Bb 986, for the control of R. microplus under laboratory conditions.

Evaluation of alternativePlutella xylostellacontrol by twoIsaria fumosoroseaconidial formulations - oil-based formulation and wettable powder - combined withBacillus thuringiensis

“…Mineral and vegetable oils are used in formulations as adjuvants to protect conidia and to maximise fungal performance . Extensive research showed that oil formulations are more efficacious than aqueous formulations or wettable powders under various temperature and moisture conditions . In our experiment, compared with wettable powders, oil‐based formulations of I. fumosorosea were more effective against P. xylostella at the same conidial concentrations.…”

“…78 Extensive research showed that oil formulations are more efficacious than aqueous formulations or wettable powders under various temperature and moisture conditions. 79,80 In our experiment, compared with wettable powders, oil-based formulations of I. fumosorosea were more effective against P. xylostella at the same conidial concentrations. Although the reason for the higher mortality induced by oil formulations is not known, it can be explained by the increased adherence of conidia on the cuticle.…”

Effect of heat stress and oil formulation on conidial germination of Metarhizium anisopliae s.s. on tick cuticle and artificial medium

“…Most studies on microbial control of ticks available report the performance of fungal formulations in bioassays held in optimal conditions of temperature and RH (Kaaya and Hassan, 2000;Maranga et al, 2005;Lopes et al, 2007;Fernandes and Bittencourt, 2008;Angelo et al, 2010;Camargo et al, 2012). The current study, however, reports the performance against the tick R. sanguineus of M. anisopliae formulated in oil or water, and exposed or not exposed to heat stress.…”

“…In addition, oil extends the viability of conidia held at ambient conditions or under refrigeration (Prior et al, 1988). The positive effects of formulating entomopathogenic fungi in oil have been reported as, (a) increased fungus-induced mortality against cocoa weevil (Prior et al, 1988), triatomine bugs (Luz and Batagin, 2005), grasshoppers (Lomer et al, 2001) and whiteflies (Malsam et al, 2002); (b) increased ovicidal activity against Aedes aegypti mosquito (Albernaz et al, 2009) and Rhipicephalus annulatus tick (Samish et al, 2014), and (c) increased virulence against different life stages of the tick R. microplus (Angelo et al, 2010;Camargo et al, 2012).…”

Advantageous Fungi against Parasites Transmitted through Soil

“…Trials consisted of the topical administration of oil solutions, targeted against immature or adult stages [44]. The aim is to reduce the indiscriminate use of chemical acaricides, for avoiding contamination of food and environment, as well as the appearance of chemical resistance among tick populations [45].…”