In vitro efficacy of two commercial products of Metarhizium anisopliae s.l. for controlling the cattle tick Rhipicephalus microplus

Abstract The effects of two different products - Metarril® SP Organic (dry conidia) and Metarril® SC Organic (emulsifiable concentrated conidia in vegetable oil) - on eggs, larvae and Rhipicephalus microplus engorged females were here explored. Three concentrations (108, 107, and 106 conidia mL-1) for both products were prepared in water + 0.1% Tween® 80 (v/v); afterward, bioassays were carried out for all R. microplus stages by immersion in suspensions (Metarril® SP) or formulations (Metarril® SC). Metarril® SP suspensions showed low efficacy and did not affect biological parameters of treated engorged females; for eggs and larvae, only slight decreases in hatchability and larvae population were observed. Despite a delay in germination, Metarril® SC presented better results; for females, reductions in Egg Mass Weight (EMW) and Egg Production Index (EPI) were reported. On eggs, 108 conidia mL-1 increased Incubation Period (IP), shortened Hatching Period (HP) and decreased hatchability by up to 61%; for larvae, 107 and 108 conidia mL-1 reached 99.6 and 100% larval mortality respectively, 10 days after fungal exposure. Thus, further studies involving the use of oil-based formulations for ticks such as Metarril® SC need to be performed, especially to control the most susceptible stages (eggs and larvae).

摘要 本研究探究了两种不同产品——Metarril® SP有机型（干分生孢子制剂）与Metarril® SC有机型（植物油基可乳化浓缩分生孢子制剂）对微小牛蜱（Rhipicephalus microplus）的卵、幼虫以及饱血雌蜱的作用效果。研究人员为两种产品分别配制了3种浓度（10^8、10^7、10^6 分生孢子·mL^-1），溶剂为添加0.1%（体积比）吐温®80（Tween®80）的水溶液；随后，通过将各阶段微小牛蜱浸渍于Metarril® SP的悬浮液或Metarril® SC的制剂中，完成了针对该蜱虫各发育阶段的生物测定。Metarril® SP悬浮液的防治效果欠佳，且未对处理后的饱血雌蜱的生物学参数产生显著影响；仅在卵与幼虫阶段观测到孵化率与幼虫种群数量的小幅下降。尽管Metarril® SC存在分生孢子萌发延迟的问题，但其整体防治效果更优：对于饱血雌蜱，可显著降低其卵块重量（Egg Mass Weight, EMW）与产卵指数（Egg Production Index, EPI）；在卵阶段，10^8 分生孢子·mL^-1浓度可延长孵化期（Incubation Period, IP）、缩短孵化周期（Hatching Period, HP），并将卵孵化率最高降低61%；对于幼虫，在真菌制剂暴露10天后，10^7与10^8 分生孢子·mL^-1浓度的幼虫死亡率分别可达99.6%与100%。综上，未来仍需开展针对以Metarril® SC为代表的油基蜱虫防治制剂的相关研究，尤其应聚焦于对该类药剂最为敏感的蜱虫发育阶段——卵与幼虫。