Endophyte infection in perennial ryegrass reduces the susceptibility of black cutworm to an entomopathogenic nematode

Abstract

The perennial ryegrass, Lolium perenne , forms a symbiotic relationship with Neotyphodium lolii , a fungus that produces alkaloids. This relationship provides a competitive advantage to the host plant in grassland communities by increasing drought tolerance, and disease and herbivore resistance. Black cutworm, Agrotis ipsilon , is among the few insect species that are able to feed and develop on endophytic perennial ryegrass. Some insects can use plant secondary compounds to defend themselves against predators, therefore we hypothesized that the cutworms fed on endophytic grasses would exhibit greater defense against a lethal endoparasitic nematode, Steinernema carpocapsae . Laboratory experiments involving 4 -5th instars support the hypothesis that A . ipsilon feeding on grass clippings from field plots with high (> 90%) incidence of endophyte infected perennial ryegrass are less susceptible to entomopathogenic nematodes than larvae fed grass clippings from plants with little or no incidence of endophyte. Laboratory studies resulted in similar overall mortality after 48 h. Field studies, however, show decreased susceptibility to S . carpocapsae when larvae were confined to areas of endophytic grass (> 75% infected). Early instars (2-3rd) fed on endophyte free grass suffered greater overall mortality at all nematode concentrations than 4 -5th instars fed similarly. Early (2-3rd) instars were equally susceptible to nematode attack regardless of food source. Our results indicate that the fungal endosymbionts of grasses can influence the biology of natural enemies of an herbivorous insect.

Insect pathology and fungal endophytes

“…Cascading effects of endophytes could also be possible. For example, in addition to the direct negative effects of grass fungal endophytes on nematodes (West et al, 1988;Kimmons et al, 1990), it has been found that in some instances, they protect herbivores against entomopathogenic nematodes (Kunkel and Grewal, 2003;Kunkel et al, 2004).…”

Entomopathogenic Nematodes in the Soil Environment: Distributions, Interactions and the Influence of Biotic and Abiotic Factors

“…The presence, density and architecture of plant roots influence dispersal and host finding by EPNs (Bal, Michael & Grewal, 2014;Choo & Kaya, 1991;Demarta, Hibbard, Bohn, & Hiltpold, 2014); and insect damaged maize and citrus roots have been shown to release HIPVs (herbivore-induced plant volatiles) that attract EPNs that subsequently attack the insect pests (Ali, Alborn, & Stelinski, 2010;Rasmann et al, 2005). Moreover, potential host insects feeding on certain plants must contend with endophytes and plant secondary chemicals, which can influence the insects' growth and resistance to EPN attack, and subsequently impact reproduction of the EPNs in complex multitrophic interactions (Barbercheck, 1993;Barbercheck et al, 1995;Gassmann, Stock, Tabashnik, & Singer, 2010;Grewal, Grewal, & Gaugler, 1995;Kunkel & Grewal, 2003;Kunkel, Grewal, & Quigley, 2004;Rasmann et al, 2005;Richmond, Kunkel, Somasekhar, & Grewal, 2004).…”

“…Root density and architecture can affect the ability of EPNs to find a host insect (Choo & Kaya, 1991;Demarta et al, 2014) and hydraulic lift associated with plant roots can create favorable conditions for EPNs and their insect hosts in otherwise dry surface soils (Duncan & McCoy, 2001). The efficacy of natural enemies of herbivorous insects can often be related to plant secondary chemistry, and this has been demonstrated for several pathogen groups, including EPNs (Barbercheck, 1993;Barbercheck et al, 1995;Epsky & Capinera, 1994;Grewal et al, 1995;Kunkel & Grewal, 2003;Kunkel et al, 2004;Richmond et al, 2004).…”

Defensive mutualism between plants and endophytic fungi?

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