In vitro EVALUATION OF Beauveria bassiana ISOLATES AGAINST GASTROINTESTINAL NEMATODES FROM GOATS.

Biological control has emerged as a promising alternative for the control of gastrointestinal nematodes in small ruminants. However, additional information is still needed on the nematicidal portencial of Beauveria bassiana and on the early interaction between fungal conidia and infective larvae. In this study, six B. bassiana isolates (LCMS19-LCMS24) were evaluated in vitro using a coproculture assay with fecal samples from naturally infected goats. Larval recovery was compared with that of an untreated control to estimate the percentage reduction in third-stage larvae (L3). The most effective isolate was subsequently examined by scanning electron microscopy (SEM) to characterize its interaction with L3. All isolates reduced L3 recovery compared with the control, although their efficacy differed. LCMS21 showed the greatest reduction in L3 recovery and differed significantly from the other treatments. SEM revealed extensive adhesion of LCMS21 conidia to the L3 cuticle, in the anterior and median regions. However, no clear evidence of conidial germination, germ tube formation, cuticle penetration, or hyphal development was observed after 48 or 72 h. These results indicate that B. bassiana isolates differ in their in vitro activity against gastrointestinal nematodes and identify LCMS21 as the most promising isolate among those tested. The ultrastructural observations support an early fungus-larva interaction, but they do not allow the nematicidal effect to be attributed to adhesion. Further studies are needed to clarify the mechanisms involved and to evaluate the potencial application of this isolate in integrated parasite control programs.