Plant-associated fungi directly affect cotton aphid survival

We investigated the direct pathogenicity of different plant-associated fungal isolates towards cotton aphid, Aphis gossypii Glover. Spores’ suspensions of four presumably non-pathogenic species of fungi originally isolated as endophytes from cotton, as well as spores from the commercially-available entomopathogen, Beauveria bassiana, were diluted with sterile water to final concentrations of 1x10⁷, 10⁶,10⁵, 10⁴, 10³, and 10² spores/ml. Second instar aphids were dipped in spore suspensions for 5 seconds. Controls were dipped in sterile water only. Ten aphids per treatment were placed on cotton leaf squares (2cm²) in 100 mm diameter Petri dishes on moistened filter paper and sealed with parafilm. There were three replicates per treatment. Plates were kept in an incubator with a 14L:10D photoperiod, 25 °C ± 1 °C and 60-70% RH. The number of surviving aphids was recorded daily for 14 days. We performed Kaplan-Meier survival analysis and pairwise comparisons using Log-Rank test with Holm method p-value adjustment to compare the survival probability between the treatments. Overall, we observed lower survival in cotton aphids dipped in all fungal treatments compared to the control. Effects were present at all fungal spore treatment concentrations when we combined the replicates. Our results indicate novel insect pathogenicity of several plant-associated fungi.