Effects of endophytic fungus, nutrient level, and plant damage on performance of fall armyworm (Lepidoptera: Noctuidae)

We tested the effects of soil nutrient level, endophyte infection status, and prior herbivory. on the performance (survival, growth, and assimilation) of fall armyworm, Spodoptera frugiperda (J.E. Smith). Using a 3-factor design, we fed larvae all possible combinations of the following treatments: endophyte-infected or uninfected tall fescue, Festuca arundinacea von Schreber, fescue receiving high or low nutrient levels, and fescue that was either previously damaged or not previously damaged with a fabric tracing wheel. Low nutrient treatments showed a consistent negative effect on 8-d larval mass, pupal mass, development time, assimilation efficiency, and survival of fall armyworm larvae. Previous damage negatively affected larval mass, development time, and assimilation efficiency, but did not affect pupal mass or survival. Infection status also gave mixed results: infection negatively affected pupal mass, but accelerated development time, positively affected larval mass and did not affect survival or assimilation. In general, interactions among nutrient level, wounding damage, and infection status did not affect insect performance. However, we did find that the influence of endophyte on insects depended upon nutrient level supplied to the plants. The adverse effect of endophyte on pupal mass was most pronounced when plants received low fertilizer applications: under high fertilizer applications the effect of endophyte on pupal mass was negligible. Our results show that the interaction among endophytic fungi: their host grasses, and insect herbivores is complex and can be influenced by environmental factors, such as nutrient availability.