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Hormonally mediated insect-plant relationships: Arthropod populations associated with ecdysteroid-containing plant, Leuzea carthamoides (Asteraceae)

2013; Institute of Entomology; Volume: 94; Issue: 2 Linguagem: Inglês

1802-8829

Jiří Zelený, Jan Havelka, K. Sláma,

Plant Toxicity and Pharmacological Properties

An extensive zoocenotic study of arthropod populations was performed on a Siberian plant Leuzea carthamoides, which was recently introduced to Central Europe as a medicinal crop. Because it contains a very high concentration of insect hormones (ecdysteroids) (300-1,000 ppm of 20-hydroxyecdysone equivalents in the leaves), the plant was thought to be resistant to attack by non-adapted arthropod herbivores (effective concentrations 25-100 ppm in insect diet). Two consecutive seasons of analysis revealed that, in spite of the high ecdysteroid content, the crops of L. carthamoides contained a well-established and consolidated arthropod fauna. 126 species of arthropods were observed on these plants during 1993 and 1994. Of this number, 74 were feeding on the leaves, and 33 of these could complete their adult development on the plants without apparent difficulties. There were also 52 parasitoid and predatory arthropod species of secondary importance.The results revealed the following four observations that are relevant to the possible resistance of L. carthamoides to phytophagous arthropods: (a) the plant is by no means universally resistant to all phytophagous arthropods; (b) the most abundant and, perhaps, most resistant herbivores that can complete their life cycle on the plant are from groups in which ecdysteroid action is little known or unknown, e.g., spider mites, collembolans, thysanopterans, psocopterans or Exopterygota with sucking mouthparts; (c) Endopterygote insect pests, which are the most sensitive to ecdysteroid-containing diet, were represented by only a few species and relatively low abundances; and, (d) all arthropods colonizing this plant belonged to polyphagous or oligophagous species with a relatively wide range of different host plants. Composition of arthropod fauna within plantations of L. carthamoides was similar to that observed in studies of the sugar beet (Beta vulgaris), which is also an introduced plant. Physiological conditions associated with possible resistance of insects to dietary ecdysteroids are discussed in terms of the following two points of virtual insensitivity: (a) use of molecules other than the plant-contained ecdysteroid as the endogenous hormone, and (b) elimination of the exogenous dietary ecdysteroid by excretion during feeding period.