Susceptibility of Dalbulus maidis to insect-pathogenic fungi: unveiling the protective role of brochosomes and self-cleaning behavior

The corn leafhopper, Dalbulus maidis (Hemiptera, Cicadellidae), is an important pest of maize in Latin America, transmitting plant pathogens that impact grain production. Recently, mycopesticides have been considered as an alternative for the biological control of D. maidis populations, but there is controversy surrounding the efficacy of these products. We assessed the susceptibility of D. maidis to invertebrate-pathogenic fungi and, for the first time, investigated the protective role of the protein-lipid coat of brochosomes on the insect integument as a barrier against infections. Adult mortality was lower than 35% seven days after exposure to maize plants sprayed with water + surfactant-based conidia suspensions of 31 fungal strains from three different genera (Beauveria, Cordyceps and Metarhizium). Direct application of conidia suspensions on adults did not increase significantly the mortality rates when compared to adults exposed to contaminated surfaces. Conidia in water + surfactant readily adhered and germinated on detached forewings of D. maidis from which brochosomes were removed, but wings coated with this protein-lipid layer repelled droplets. Dry conidia easily adhered to brochosome-coated wings and their germination was not affected, although the methodical self-cleaning behavior of the adults effectively dislodged most conidia (either in suspensions or as a dry powder) from insect’s body after treatment. In conclusion, brochosomes and self-cleaning together efficiently prevent adhesion of conidia to D. maidis cuticle, serving as important barriers against fungal invasion and decreasing insect mortality. Our study highlights the importance of combining mycopesticides with effective adjuvants in spray applications to enhance infection rates and successfully control D. maidis populations.