Adult beetle grazing induces willow trichome defence against subsequent larval feeding

Abstract

Induced increases in trichome density to grazing by herbivores have been suggested to increase plant resistance to future herbivore attack. In this paper we present results which show that plants of Salix cinerea L. respond to adult leaf beetle (Phratora vulgatissima L.) grazing by developing new leaves with an increased trichome density. The same plants are usually attacked again later in the season when the next generation of larvae hatches on the plants. The effect of the induced response was studied by comparing larval growth and feeding on newly developed leaves of plants exposed to different defoliation treatments. Larvae on plants previously exposed to adult grazing consumed less total leaf area and showed more dispersed feeding than larvae on plants protected from previous grazing. Larvae on plants exposed to mechanical defoliation responded intermediately. These results corresponded to the increased trichome density of defoliated plants. However, we found this larval response only in whole plant tests--when reared on single, excised leaves in petri dishes, larvae in all treatments behaved similarly. This discrepancy between the on-plant experiment and that in petri dishes highlights how experimental design may alter the conclusion of a study. We suggest that the induced response to adult grazing may act as a defence against subsequent larval feeding.

The effects of foliar pubescence and nutrient enrichment on arthropod communities ofMetrosideros polymorpha(Myrtaceae)

“…This independence of morphological and physiological features has been documented in other plant species (Roy et al, 1999;Forkner & Hare, 2000). However, increased trichome density may be induced by heavy herbivore defoliation or by intense disturbance events, such as hurricanes (Pullin & Gilbert, 1989;Dalin & Bjo¨rkman, 2003;Spiller & Agrawal, 2003) -this alternative has not been tested in the present system.…”

Mechanisms of plant defense against insect herbivores

“…22 This increase in trichome density in response to damage can only be observed in leaves developing during or subsequent to insect attack, since the density of trichomes of existing leaves does not change. 16 Dalin and Bjorkman 23 reported that damage by adult leaf beetles, Phratora vulgatissima L. in Salix cinerea L. induced higher trichome density in the new leaves developing thereafter. Likewise, increase in trichome density in S. cinera in response to coleopteran damage has also been reported.…”

“…Changes in trichome density occur within days or weeks after insect damage. [22][23][24] Furthermore, change in relative proportion of glandular and non-glandular trichomes is also induced by herbivory. 22 A positive correlation has been observed between natural enemies' abundance and trichome density.…”

Root growth ofNicotiana attenuatais decreased immediately after simulated leaf herbivore attack

“…3,4,5 Acclimation occurs both on the biochemical and morphological level, e.g., by increasing defence compounds, 6 by synthesizing defence related proteins, by emitting volatiles to attract predators and parasites of herbivores 7 and by altering plant morphology via increased formation of trichomes, thorns or scleromorphy. 8,9 Many studies demonstrated resource based trade-offs between growth and defence on a large time scale (e.g. refs.…”