Modern Applied Statistics with S-PLUS

Abstract

Root-associated entomopathogenic fungi (R-AEF) indirectly influence herbivorous insect performance.However, host plant-R-AEF interactions and R-AEF as biological control agents have been studied independently and without much attention to the potential synergy between these functional traits.In this study, we evaluated behavioral responses of cabbage root flies [Delia radicum L. (Diptera: Anthomyiidae)] to a host plant (white cabbage cabbage Brassica oleracea var.capitata f. alba cv.Castello L.) with and without the R-AEF Metarhizium brunneum (Petch).We performed experiments on leaf reflectance, phytohormonal composition and host plant location behavior (behavioral processes that contribute to locating and selecting an adequate host plant in the environment).Compared to control host plants, R-AEF inoculation caused, on one hand, a decrease in reflectance of host plant leaves in the near-infrared portion of the radiometric spectrum and, on the other, an increase in the production of jasmonic, (+)-7-iso-jasmonoyl-l-isoleucine and salicylic acid in certain parts of the host plant.Under both greenhouse and field settings, landing and oviposition by cabbage root fly females were positively affected by R-AEF inoculation of host plants.The fungal-induced change in leaf reflectance may have altered visual cues used by the cabbage root flies in their host plant selection.This is the first study providing evidence for the hypothesis that R-AEF manipulate the suitability of their host plant to attract herbivorous insects.Biological interactions between plants and root-inhabiting fungi have been found in the fossil record 1 , implying a symbiotic success story.Furthermore, no plant species is known to grow successfully without a relationship with fungi 2 .Root-associated fungi can colonize both the internal and external parts of developing roots without damaging the host plant 3 .The presence of root inhabiting fungi is associated with enhancements in plant growth, i.e. fungal endophytes facilitate host uptake of soil nutrients and water 4 .Concurrently with functional research into complex ecological interactions between plant-associated fungi, their host plants and plant-associated insects there are also applied studies describing the use of multiple strains of Beauveria spp.and Metarhizium spp.(Hypocreales: Ascomycota) as root-associated entomopathogenic fungi (R-AEF) 5 .R-AEF can be plant endophytes and soil saprophytes, and some have been reported to reduce herbivore damage by direct insect infection and are commercially available for arthropod pest management in a wide range of cropping systems 6 .In addition, R-AEF have been shown to increase host plant resistance to arthropod herbivores by triggering plant induced systemic resistance or to produce secondary metabolites that elicit feeding deterrence and antibiosis to herbivorous insect 6 .When R-AEF are considered to act as bodyguards, host plants are believed to manipulate insect pathogens to increase their own fitness 7 .However, this concept remains purely speculative and morecomplex interactions involving R-AEF and host plants can be expected, mainly due to the inherent risks in terms of increasing herbivorous insect attack 8,9 .