In vitro and in vivo compatibility of isocycloseram-based insecticides with entomopathogenic fungi used for corn leafhopper management

Abstract

Recently registered, isocycloseram-based insecticides have the corn leafhopper (Dalbulus maidis) as a main target in Brazil. Nevertheless, the management of this vector is complex and requires the integration of strategies, including chemical and fungal agents. Here, we investigated the compatibility of mycoinsecticides based on isolate Esalq-1296 of Cordyceps javanica and Simbi BB15 of Beauveria bassiana with isocycloseram-based insecticides and their mixtures. In vitro, the biological index adopted indicated that the insecticide based on isocycloseram + lambda-cyhalothrin (at 125- and 250-mL ha⁻¹) was classified as moderately compatible with the Esalq-1296 isolate of C. javanica and Simbi BB15 of B. bassiana. The isocycloseram-based formulation was classified as compatible with the Simbi BB15 isolate of B. bassiana, at both doses tested, and moderate compatible and compatible with the Esalq-1296 isolate of C. javanica at 100 and 50 mL ha⁻¹, respectively. Further analysis revealed that the majority of insecticide-mycoinsecticides mixtures exhibited physicochemical compatibility, with the exception of the mixture comprising these insecticides and the mycoinsecticide-based on B. bassiana (FlyControl®), which demonstrated an absence of homogeneity. The in vivo bioassays demonstrated an additive effect on leafhopper mortality and an increase in the velocity of lethal toxicity when these insecticides (at LC₃₀) were combined with the tested mycoinsecticides. However, the insecticides reduced the extrusion rate and sporulation from dead leafhoppers. As these parameters are crucial for fungal persistence by establishing a secondary cycle of epizootics in cornfields, caution is advised when combining these chemical and fungal agents for the management of D. maidis.