Influence of genetic variation in fungal endophyte in the third trophic level

Abstract

Neotyphodium coenophialum (Ascomycota: Clavicipitaceae) is an endophytic fungus of grasses that produces alkaloids which can have detrimental effects on some insect herbivores, like fall armyworm caterpillars (Spodoptera frugiperda). Alkaloid production can be influenced by fungal genotype. We investigated if endophyte-produced alkaloids might also have effects at the next trophic level. We tested if variation in fungal isolate (three isolates: CS, AR502, AR542; plus a control lacking fungal infection) affected the growth and survival of Euplectrus comstockii (Eulophidae) parasitoids of S. frugiperda. Euplectrus comstockii is an ectoparasitoid of caterpillars of many noctuid species. Parasitoid pupal mass was not influenced by fungal isolate (F3,241=0.61, P=0.61, and F3,190=0.74, P=0.53 for female and male pupae, respectively). In contrast, fungal isolate influenced parasitoid survival (X2=58.3, df=3, P<0.0001). Survival was higher than expected for parasitoids reared from hosts fed plants lacking fungal infection, but was lower than expected for those reared from hosts fed plants infected with AR542 and CS fungal isolates. In contrast, parasitoids reared from hosts fed plants infected with fungal isolate AR502 did not experience higher mortality than expected by chance. Parasitoid mortality mainly occurred during the egg stage. Our results suggest N. coenophialum can influence the tritrophic interaction in ways that could be detrimental to the host plant and that this effect is influenced by fungal genotype. Keywords: fall armyworm, Euplectrus, Neotyphodium, novel endophytes, tall fescue