Fungal endophytes, Beauvaria bassiana and Purpureocilium lilacinum, positively affect the growth of sorghum and impact the behavior and performance of the sugarcane aphid, Melanaphis sacchari

Plant-fungal endophyte associations can play an important role in plant growth and resistance against insect herbivores. We examined the potential for two fungal endophytes, Beauvaria bassiana and Purpureocilium lilacinum (formerly Paecilomyces lilacinus), to improve the development of Sorghum bicolor and to control sugarcane aphids (Melaniphis sacchari), an invasive pest on sorghum. Seed treatment with B. bassiana and P. lilacinum increased plant height and fresh biomass 7 days and 30 days after planting. Endophyte treatment also affected the performance of sugarcane aphids, but performance was conditional on both the identity of the endophyte and the part of the plant where the aphids were located. There was no effect, and sometimes a positive effect, of endophyte treatment on aphid performance when aphids avoided lower plant parts and segregated on upper parts. In a subsequent experiment when we controlled for the location of aphids on plants, fecundity was consistently negatively affected on lower plant parts than on upper plant parts, irrespective of treatment type. Interestingly, when aphids did not show preference for any part of the plant, treatment with either B. bassiana or P. lilacinum significantly reduced aphid performance. Altogether, exploiting the use of beneficial fungal endophytes for improved plant growth and resistance to stress is a promising strategy in agriculture. However, fungal endophyte-mediated defense against insect herbivores could be a variable phenomenon conditional on the behavioral response of insects on specific plants.