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Doctoral thesis, 2002

Plant volatiles mediate tritrophic interactions : barley, aphids and ladybirds

Ninkovic, Velemir

Abstract

The effects of plant-plant interactions via volatiles (aerial allelopathy) on herbivores and their natural enemies were investigated. The model system consisted of four barley varieties, an aphid pest, Rhopalosiphum padi (L.), and a common aphid predator, ladybird, Coccinella septempunctata (L). Aerial allelopathy significantly affected plant leaf temperature and biomass allocation, favouring root growth during the vegetative period, the main period for development of R. padi populations in Swedish barley fields. There was no effect of aerial allelopathy on relative growth rate and total biomass. A decrease in biomass allocation to the leaves was compensated for by an increase in specific leaf area. Significant changes in leaf temperature and biomass allocation of responding plants showed that the allelopathic effect was systemic. The effects were strictly dependent on which genotypes were combined, and the capacity of a plant to cause allelopathic induction was not necessarily linked to its capacity to respond. The four barley cultivars used did not differ in aphid attractivity and acceptance when tested separately. In specific cultivar combinations aerial allelopathy caused significant changes in both laboratory and field experiments. The results from field and laboratory conditions were not immediately congruent. There were differences between those cultivar combinations that caused changes in leaf temperature and those that affected aphid acceptance, indicating that the aphid response was not merely an effect of temperature preference. There were no differences in olfactory attraction of aphids to different cultivars, but significant changes were induced by aerial allelopathy. Olfactometer experiments with ladybird showed that aphid-attacked plants and previously attacked plants with the aphids removed were more attractive than undisturbed aphids or undamaged plants. Olfactory cues contributed to aggregation of ladybird adults in weed-infested plots in a barley field. Adults of ladybird responded positively to a mixture of barley-weed volatiles but a more complex mechanism possibly involving aerial allelopathy cannot be excluded. It is concluded that plant/plant interaction in the barley-weed-aphid-ladybird system has a significant effect on each trophic level i.e. plant physiology and development, aphid host plant relations and the searching behaviour of a common predator.

Keywords

Coccinella septempunctata; Rhopalosiphum padi; Hordeum vulgare; aerial allelopathy; plant-plant interaction; biomass allocation; aphid acceptance; olfactory response

Published in

Acta Universitatis Agriculturae Sueciae. Agraria
2002, number: 321
ISBN: 91-576-6152-9
Publisher: Swedish University of Agricultural Sciences

Authors' information

Swedish University of Agricultural Sciences, Department of Entomology

UKÄ Subject classification

Ecology
Zoology

URI (permanent link to this page)

https://res.slu.se/id/publ/107622