Colonization of crop plants by fungal entomopathogens and their effects on two insect pests when in planta

Fungal entomopathogens can directly regulate populations of various insects. The entomopathogen Beauveria bassiana can also endophytically colonize various plants. Endophytic colonization by entomopathogens might be more widespread than currently realized and may provide a source of indirect interactions between fungi and insects. We tested whether some common entomopathogens could colonize six crop plants. We also assessed whether the performance of two insects, Aphis gossypii and Chortoicetes terminifera, was affected by entomopathogens in plants. The entomopathogens B. bassiana, Lecanicillium lecanii and Aspergillus parasiticus individually colonized the leaves of all six crop plants when inoculated as conidia. L. lecanii also readily colonized five different cultivars of cotton. When the entomopathogens were present in the soil in which either cotton or wheat seedlings were grown, A. parasiticus was subsequently isolated from the leaves, stem and roots of both plants and B. bassiana from the leaves, stem and root of wheat only, whereas L. lecanii failed to colonize either plant through the soil. Of the three entomopathogens tested, endophytic presence of A. parasiticus reduced growth of cotton, but none reduced growth of wheat. Feeding by A. gossypii on cotton leaves colonized by either B. bassiana or L. lecanii slowed aphid reproduction, and consumption of wheat leaves colonized by either B. bassiana or A. parasiticus slowed the growth of C. terminifera nymphs. The life cycle of at least three entomopathogens potentially includes plants. The presence of entomopathogens as endophytes can influence growth and fecundity of insect herbivores, suggesting a possible role for endophytic entomopathogens in the regulation of insect populations.