In vitro versus in planta: Comparing the compatibility of Akanthomyces lecanii with pesticides against Trialeurodes vaporariorum

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Abstract Lecabiol® is a registered biopesticide based on the entomopathogenic fungus Akanthomyces lecanii (Hypocreales: Cordycipitaceae) for the control of the greenhouse whitefly Trialeurodes vaporariorum (Hemiptera: Aleyrodidae) in tomato crops. This product is commonly applied with several pesticides and fungicides in integrated pest management programs, and a reduction in efficacy is expected. The present work aimed to evaluate the compatibility of A. lecanii with pesticides used in tomato. Three insecticides (bifenthrin, chlorfenapyr and spinetoram) and six fungicides (dimethomorph, kasugamycin, metalaxyl:mancozeb, difenoconazole, pyrimethanil and propineb: cymoxanil) were tested in vitro and in planta. The compatibility was determined by using the biological index (BI). For in vitro test, germination, mycelial growth and conidial production were evaluated, and for in planta, the mixture of pesticide + fungus and alternating applications was carried out to assess the efficacy to control the pest. The insecticide chlorfenapyr was compatible in vitro (BI = 78) but moderately toxic (BI = 52) when the product was applied as a mixture with the fungus to control T. vaporariorum in planta; in contrast, bifenthrin was initially classified as moderately toxic (BI = 57) but was compatible in planta (BI = 71). The fungicides dimethomorph and kasugamycin were compatible (BI = 81–97); propineb: cymoxanil was moderately toxic (BI = 51), and metalaxyl:mancozeb and difenoconazole were toxic (BI = 0–37) in vitro, whereas most fungicides were moderately toxic or toxic when evaluated in planta. The pesticides spinetoram and pyrimethanil remained compatible in both assays (BI = 85–90). For the alternating application, the fungicides dimethomorph and pyrimethanil significantly diminished the efficacy of the fungi below 40% to control T. vaporariorum. The findings demonstrate that compatibility of the fungus with insecticides and fungicides varied among in vitro and in planta assessments (combined or via alternation).

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