期刊
BIOLOGICAL CONTROL
卷 29, 期 1, 页码 100-108出版社
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/S1049-9644(03)00119-1
关键词
entomopathogenic nematodes; Steinernema carpocapsae; Agrotis ipsilon; multitrophic interactions; Neotyphodium lolii; perennial ryegrass; ergot alkaloids; black cutworm; Lolium perenne
Perennial ryegrass forms a symbiotic relationship with the fungus Neotyphodium lolii, which provides many benefits including resistance to herbivory through the production of alkaloids. The impact of endophytic grass on the third trophic level has received little attention. The black cutworm, Agrotis ipsilon, is less susceptible to the entomopathogenic nematode, Steinernema carpocapsae, when it consumes the endophytic grass. We examined the potential mechanisms of the resistance exhibited by A. ipsilon against S. carpocapsae. Although A. ipsilon larvae fed on endophytic grass had similar numbers of nematodes attached and that successfully developed into adults, they had significantly lower mortality than larvae fed on endophyte-free grass when exposed to nematodes for 1.5 h. We examined the effects of N. lolii produced ergot alkaloids, ergotamine tartrate, ergonovine maleate, ergocryptine, and erogcristine on nematode viability and infectivity. Ergonovine malate increased and ergocristine decreased the rates of nematode infectivity, whereas other treatments had no significant effect. We also investigated the effects of ergocristine on Xenorhabdus nematophila, the symbiotic bacterium of S. carpocapsae. Bacterial growth and pathogenicity were significantly reduced when the bacterium was grown in nutrient broth containing 200 mug/ml concentration of ergocristine. We conclude that herbivores capable of developing on endophytic grasses may acquire some level of resistance against S. carpocapsae due to the toxic effects of ergocristine on the bacterium, X. nematophila. Our results underscore the ability of N. lolii to affect trophic interactions through the production of alkaloids. (C) 2003 Elsevier Science (USA). All rights reserved.
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