Field–scale evaluation of irrigation–applied entomopathogens against the truffle pest Leiodes cinnamomea in commercial black truffle orchards

Leiodes cinnamomea is a major pest of black truffle ( Tuber melanosporum ) orchards, where management is constrained by the need to preserve soil biota and ectomycorrhizal symbioses. Field-scale evaluation is complicated by spatial heterogeneity, adult mobility, and reliance on indirect indicators. We evaluated irrigation-applied entomopathogenic agents against L. cinnamomea in a commercial orchard, using trap captures as an activity proxy. Field trials were conducted over two seasons in a 4.5-ha orchard with nine irrigation sectors. Beauveria bassiana (strain GHA) and Steinernema carpocapsae were applied through drip irrigation, with weekly trap monitoring. Laboratory bioassays assessed adult susceptibility to B. bassiana at field-relevant temperatures (12°C ± 2 °C). Delivery and viability were verified at dripper outlets. Treatment effects were evaluated using before-after-control-impact analysis and complementary approaches focused on the autumn emergence peak. Adult activity showed pronounced spatial structure, with captures differing by up to an order of magnitude among sectors. Sectors treated with B. bassiana consistently exhibited 25%–26% lower captures during peak emergence compared to controls in both seasons, although permutation-based tests provided limited statistical support due to spatial heterogeneity and restricted replication. S. carpocapsae showed only a weaker first-season reduction in adult captures and was not evaluated in the second season, whereas halloysite supplementation did not improve the capture response despite higher conidial concentrations at dripper outlets. Irrigation-applied B. bassiana was associated with reproducibly lower adult captures during the peak-emergence window, supported by laboratory evidence of susceptibility. While capture responses were moderate and confined to peak emergence, results highlight both the potential and the limitations of soil-applied entomopathogenic fungi as timing-dependent candidates for integrated pest management in truffle orchards.