Shapiro-Ilan David I, Gardner Wayne A, Wells Lenny, Wood Bruce W
USDA-ARS, Southeastern Fruit and Tree Nut Research Laboratory, Byron, GA 31008, USA.
Environ Entomol. 2012 Apr;41(2):298-307. doi: 10.1603/EN11229.
The pecan weevil, Curculio caryae (Horn), is a key pest of pecan. Endemic levels of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin can occur in pecan orchards and contribute to natural control of C. caryae. Commercial formulations of the fungus can also be applied for suppression of C. caryae. We hypothesized that a clover cover crop enhances B. bassiana efficacy and persistence (e.g., by protecting the fungus against abiotic environmental stresses). The hypothesis was tested by conducting field trials in a pecan orchard in Byron, GA, in 2009 and 2010. The study included four treatments arranged in a factorial with two levels of fungus (endemic fungus only, and application of a commercial B. bassiana product), and two levels of clover (white clover, Trifolium repens L., and no clover). Fungal persistence was measured by determining the number of CFUs per gram of soil over time (during 42 d postapplication of B. bassiana in 2009 and 29 d in 2010). Efficacy was measured by capturing naturally emerging C. caryae and subsequently determining mortality and mycosis (over 24 d in 2009 and 17 d in 2010). In 2009, greater prevalence of B. bassiana conidia was detected in plots receiving fungal applications compared with no fungus applications, and no clear effect of clover was observed in plots receiving B. bassiana applications in either year. In 2010, B. bassiana prevalence in the endemic fungus plus clover treatment was higher than fungus without clover, and was similar to plots receiving additional B. bassiana applications. Given that we observed enhanced persistence of endemic B. bassiana in 2010 but not 2009, the impact of clover appears to be a cumulative effect. Mortality of C. caryae (averaged over the sampling periods) ranged between 68-74% in plots receiving B. bassiana applications and 51-56% in plots with endemic fungus only. C. caryae mortality and mycosis data also provided evidence that endemic B. bassiana efficacy was enhanced by clover relative to plots without clover (with no clear clover effect on plots receiving fungus applications). Thus, we conclude that natural control of C. caryae can increase when clover is grown in pecan orchards with endemic populations of B. bassiana.
山核桃象甲，Curculio caryae (Horn)，是山核桃的一种主要害虫。昆虫病原真菌球孢白僵菌（Beauveria bassiana (Balsamo) Vuillemin）在山核桃果园中可呈现地方流行性水平，并有助于对山核桃象甲进行自然控制。该真菌的商业制剂也可用于抑制山核桃象甲。我们假设三叶草覆盖作物能提高球孢白僵菌的功效和持久性（例如，通过保护真菌免受非生物环境胁迫）。2009年和2010年在佐治亚州拜伦的一个山核桃果园进行田间试验对这一假设进行了验证。该研究包括四种处理，按析因设计安排，有两个真菌水平（仅地方流行性真菌，以及施用球孢白僵菌商业产品）和两个三叶草水平（白三叶草，Trifolium repens L.，和无三叶草）。通过测定施用球孢白僵菌后不同时间（2009年施用后42天内，2010年施用后29天内）每克土壤中的菌落形成单位数量来衡量真菌的持久性。通过捕获自然羽化的山核桃象甲并随后确定死亡率和真菌病感染率（2009年为24天，2010年为17天）来衡量功效。2009年，与未施用真菌的地块相比，在施用真菌的地块中检测到球孢白僵菌分生孢子的发生率更高，并且在这两年中，在施用球孢白僵菌的地块中均未观察到三叶草有明显影响。2010年，地方流行性真菌加三叶草处理中的球孢白僵菌发生率高于无三叶草的真菌处理，且与额外施用球孢白僵菌的地块相似。鉴于我们在2010年观察到地方流行性球孢白僵菌的持久性增强而在2009年未观察到，三叶草的影响似乎是一种累积效应。在施用球孢白僵菌的地块中，山核桃象甲的死亡率（在采样期内平均）在68% - 74%之间，而仅地方流行性真菌的地块中为51% - 56%。山核桃象甲的死亡率和真菌病感染率数据也提供了证据，表明相对于无三叶草的地块，三叶草增强了地方流行性球孢白僵菌的功效（对于施用真菌的地块，三叶草没有明显影响）。因此，我们得出结论，当在有地方流行性球孢白僵菌种群的山核桃果园中种植三叶草时，对山核桃象甲的自然控制作用会增强。
