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  • 1
    ISSN: 1573-1561
    Keywords: Wheat ; hydroxamic acids ; DIMBOA ; plant resistance ; cereal aphids ; Homoptera ; Aphididae ; aphid predators ; Eriopis connexa ; Coleoptera ; Coccinellidae ; tritrophic interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one), a secondary metabolite found in cereal extracts, confers resistance in wheat to aphids. Its effect on beneficial organisms was tested on larvae of the aphid predatorEriopis connexa Germar. Larvae were fed until pupation on artificial diets to which different concentrations of DIMBOA (2–200μg/g diet) were added, as well as on aphids that had been feeding on wheat seedlings with different DIMBOA levels (140–440 μg/g fresh tissue). In diets, the effect of DIMBOA was greatest on survival of third-instar larvae and on the duration of the second and fourth instars. When aphids were provided as food, those that had fed on a wheat cultivar with an intermediate DIMBOA level led to a significantly longer larval duration in the predator than did those that fed on either low or high DIMBOA cultivars. Shortest predator development times were obtained with aphid prey that had fed on high DIMBOA seedlings. Higher DIMBOA levels in the plant appear to reduce aphid feeding rates (and rates of DIMBOA ingestion), decreasing aphid survival and minimizing the effect of the toxin on the predator.
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  • 2
    ISSN: 1573-1561
    Keywords: Aphids ; Sitobion avenae ; feeding deterrents ; antibiotics ; DIMBOA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract A total of 25 compounds including benzoxazinones, benzoxazolinones, and N-glyoxylamide derivatives were tested as antifeedants and antibiotics towards the aphid Sitobion avenae in diet bioassays. The antifeedant and mortality indexes increased with the presence of electron-donating groups in the 7 position of the benzoxazinone moiety, the replacement of the oxygen atom by sulfur in the heterocyclic ring, the presence of a hemiacetal instead of an acetal at C-2 of the benzoxazine moiety (and hence the possibility of ring opening), and the presence of a hydroxyl group at C-4 of the benzoxazine moiety (hydroxamic acid) instead of a hydrogen atom (lactam). The results support earlier hypotheses on the chemical bases for the mode of action of these compounds.
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  • 3
    ISSN: 1573-1561
    Keywords: Sitobion avenae ; aphids ; hydroxamic acids ; DIMBOA ; detoxification ; cytochrome P-450 monooxygenases ; NADPH cytochrome c reductase ; glutathione S-transferases ; esterases ; catalase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Hydroxamic acids (Hx) are wheat secondary metabolites conferring resistance for cereals against aphids. The activity of five enzymatic systems were evaluated in the aphid Sitobion avenae reared on the high-Hx wheat cultivar Chagual and the low-Hx wheat cultivar Huayún for 10 generations. Enzyme solutions were prepared from aphid homogenates and assayed for mixed function oxidases (including cytochrome P-450 monooxygenases and NADPH cytochrome c reductase), glutathione S-transferases, esterases, and catalase. Specific activities per aphid individual of cytochrome P-450 monooxygenases, NADPH cytochrome c reductase, glutathione S-transferases, and esterases were significantly increased in wheat cultivars relative to oat (only marginal increase of esterases in Chagual). Aphids fed on cv. Huayún showed an overall higher induction of enzymatic systems than those fed on cv. Chagual. Comparison of these results with reported effects of Hx on detoxifying enzymes in other insects, including aphids, support the hypothesis that these enzymatic pathways play an important role in the detoxification of toxic host-plant secondary metabolites.
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  • 4
    ISSN: 1570-7458
    Keywords: wheat ; aphids ; hydroxamic acids ; DIMBOA ; DIMBOA-glucoside ; EPG ; electrical penetration graph ; feeding deterrents ; antixenosis ; plant resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Feeding behaviour of five species of cereal aphids in wheat seedlings differing in hydroxamic acid (Hx) levels, was monitored via electrical penetration graphs (EPG). Aphid species could be grouped as sensitive to the feeding deterrent effect of Hx in the seedlings (Rhopalosiphum padi, Schizaphis graminum, Sitobion avenae, andMetopolophium dirhodum) or insensitive to them (Rhopalosiphum maidis). However, when feeding behaviour was studied in artificial diets containing Hx, all species were equally sensitive to Hx. The behavour ofR. maidis was further compared with that ofR. padi through detailed EPG analysis. It was found that the insensitivity ofR. maidis to Hx in seedlings may be due to a feeding strategy avoiding contact with the compounds by decreasing the number of cellular punctures in live tissues other than sieve elements during its way to the phloem.
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