Fungal Formulations to Control Rhipicephalus sanguineus Engorged Females

Abstract

Entomopathogenic fungi are promising alternatives to chemical acaricides in controlling tick populations; however, biological formulations are required to improve conidial performance of these pathogens in the field. This study evaluated the effect of in vitro treatment of Rhipicephalus sanguineus with conidial formulations of Beauveria bassiana (Bb) or Metarhizium anisopliae (Ma). Conidia were formulated (at 10(8) conidia mL(-1)) in (1) emulsifiable concentrate (EC), (2) polymerized cellulose gel (PCG), or both (3) emulsifiable concentrate and polymerized cellulose gel combined (EC+PCG). Engorged females were weighed and exposed to one of six treatment groups: EC+Bb, EC+Ma, PCG+Bb, PCG+Ma, EC+PCG+Bb, EC+PCG+Ma; or to control groups: C1 (untreated) or (C2) treated with Tween 80 aqueous solution, EC or PCG. After exposure, ticks were placed in petri plates and kept at 27 +/- 1 degrees C and 80% relative humidity (RH). Ticks treated with formulated conidia of entomopathogenic fungi showed significantly higher control percentage in comparison to that of control groups. The formulation of B. bassiana with EC and PCG combined (EC+PCG+Bb) caused the highest control percentage (86.79%) of R. sanguineus. This study concludes that entomopathogenic fungus conidial formulations are important to ensure effective tick control.

Auto‐dissemination of commercially available fungal pathogens in a laboratory assay for management of the brown dog tick Rhipicephalus sanguineus

“…However, the results of the present study are consistent with other studies that treated ticks with entomopathogenic fungus; ticks die much more slowly than insects, varying from 1 week to 1 month when directly exposed (Weeks et al ., ). Previous studies with R. sanguineus have reported substantial mortality between 7 and 28 days post‐exposure (Samish et al ., ; Gindin et al ., ; Garcia et al ., ; Reis et al ., ; Cafarchia et al ., ). Mortality as a result of infection with B. bassiana or M. anisopliae takes time because a conidium that lands on a tick must germinate and penetrate the cuticle.…”

“…Management of ticks with entomopathogenic fungi is typically restrained by environmental limitations of the fungi with relation to high temperatures, low humidity and ultraviolet exposure (Morley‐Davis et al ., ; Reis et al ., ; Weeks et al ., ). Furthermore, the non‐target effects of these fungi, which are often not species‐ or even order‐specific, need to be considered.…”

“…However, previous research testing R. sanguineus sensitivity to entomopathogenic fungi has focused on dipping ticks, an unnatural exposure method, or using laboratory fungal strains for inoculation. Because efficacy varies greatly by exposure method and subsequent to formulation of the fungus into a commercial product (Reis et al ., ; Nchu et al ., ; Camargo et al ., ; Rot et al ., ), the present study aimed to determine the efficacy of commercial fungal formulations for reducing the longevity of ticks when directly exposed to fungi by walking on a fungi‐treated surface and indirectly exposed to fungi‐treated conspecifics.…”

“…An appropriate formulation is needed to maintain pathogenicity at the same time as ensuring an even spread of hydrophobic conidia and enhancing the persistence of conidia subsequent to exposure to the environment (e.g. ultraviolet light and high temperatures) (Morley‐Davis et al ., ; Reis et al ., ). However, the use of such fungi for indoor tick control may avoid such problems as high temperatures, low humidity and ultraviolet exposure, which typically reduce the efficacy of entomopathogenic fungi in the field.…”

“…Reis et al . () tested three formulations of B. bassiana and M. anisopliae and found that a formulation consisting of an emulsifiable concentrate with polymerized cellulose gel resulted in the highest mortality in exposed R. sanguineus .…”