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制剂——Metarril® SP有机制剂（干分生孢子型）与Metarril® SC有机制剂（以植物油为基质的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防控效果。针对两种制剂，分别配置了10⁸、10⁷、10⁶ 个分生孢子·mL⁻¹三种浓度的悬浮液，溶剂为添加0.1%（体积比）吐温®80的水溶液；随后，采用浸渍法分别对微小牛蜱的各虫态开展生物测定，其中Metarril® SP采用其悬浮液，Metarril® SC则采用其成品制剂。Metarril® SP悬浮液的防治效果较低，且对处理后的饱血雌蜱的生物学参数无显著影响；仅在卵和幼虫阶段观察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，但其整体防控效果更优：针对饱血雌蜱，可显著降低其卵块重量（Egg Mass Weight，简称EMW）与产卵指数（Egg Production Index，简称EPI）；针对卵期，10⁸ 个分生孢子·mL⁻¹浓度可延长孵化期（Incubation Period，简称IP）、缩短出壳期（Hatching Period，简称HP），并将孵化率最高降低61%；针对幼虫阶段，在真菌暴露10天后，10⁷和10⁸ 个分生孢子·mL⁻¹浓度的幼虫死亡率分别可达99.6%与100%。综上，后续需开展更多针对油基制剂（如Metarril® SC）的相关研究，以实现对蜱虫的有效防控，尤其是针对其最易感的虫态——卵与幼虫。