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The planthopper Peregrinus maidis (Ashmead) (Hemiptera: Delphacidae) is an important vector of maize viruses in tropical and subtropical areas. Planthoppers are biologically controlled with several species of entomopathogenic fungi that have been isolated from these insect pests of rice in Asia. Beauveria bassiana (Balsamo-Crivelli) Vuillemin and Metarhizium anisopliae (Metschnikoff) Sorokin (Hypocreales: Clavicipitaceae) appear to be the most useful against planthoppers because of their ease of mass production, storage, virulence, and application. In the present study, adults of P. maidis infected with B. bassiana and M. anisopliae were observed under light and scanning electron microscopy to characterize morphologically the process of infection and the development of these fungi, prior to and after the death of the host. The hydrophobic conidia of both fungal species were able to attach to all body regions, with a preference for surfaces containing hairs. Few germinated conidia were observed on the insect's body surface at 24, 48, and 72 hr post-inoculation. On the cuticular surface of P. maidis treated with B. bassiana and M. anisopliae, bacillus-like bacteria were observed. These microorganisms could be interacting with fungal conidia, playing a role of antibiosis that will not allow the fungal pathogens to germinate and penetrate. In the colonization events observed in this study, the formation and multiplication of hyphal bodies by both fungal species inside the host's body was noted. The host's whole body was invaded by hyphae between five and six days post-inoculation, and body fat was the most affected tissue.

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Preliminary screening assays were carried out on 17 isolates from five fungal species Beauveria bassiana, Lecanicillium muscarium, Metarhizium anisopliae, Isaria farinosa, and I. fumosorosea. The three most effective isolates against Peregrinus maidis (Hemiptera: Delphacidae) were B. bassiana CEP 147, CEP 150, and CEP 189. There were no consistent differences found in males and females regarding fungal susceptibility. However, more females than males were proportionally infected. There was not a correlation between the percentage of conidial germination and the percentage of mortality caused by fungal infection in any of the treatments. Only B. bassiana CEP 147, which caused a cumulative mortality of 69.8 +/- 6.4% after 7 days post-inoculation, was selected to be assayed against adults of P. maidis, Delphacodes kuscheli (Hemiptera: Delphacidae), and Dalbulus maidis (Hemiptera: Cicadellidae). In pathogenicity tests significant differences were observed among treatments. After 2 weeks post-inoculation, both D. kuscheli (cumulative mortality of 73.3 +/- 9.0%) and P. maidis (cumulative mortality of 68.6 +/- 6.7%) were significantly more susceptible than D. maidis (cumulative mortality of 49.9 +/- 9.7%) to the selected isolate.