Abstract
Wind is an important abiotic factor that influences an array of biological processes, but it is rarely considered in studies on plant-herbivore interactions. Here, we tested whether wind exposure could directly or indirectly affect the performance of two insect herbivores, Plutella xylostella and Pieris brassicae, feeding on Brassica nigra plants. In a greenhouse study using a factorial design, B.nigra plants were exposed to different wind regimes generated by fans before and after caterpillars were introduced on plants in an attempt to separate the effects of direct and indirect wind exposure on herbivores. Wind exposure delayed flowering, decreased plant height and increased leaf concentrations of amino acids and glucosinolates. Plant-mediated effects of wind on herbivores, that is effects of exposure of plants to wind prior to herbivore feeding, were generally small. However, development time of both herbivores was extended and adult body mass of P.xylostella was reduced when they were directly exposed to wind. By contrast, wind-exposed adult P.brassicae butterflies were significantly larger, revealing a trade-off between development time and adult size. Based on these results, we conducted a behavioural experiment to study preference by an avian predator, the great tit (Parus major) for last instar P.brassicae caterpillars on plants that were exposed to either control (no wind) or wind (fan-exposed) treatments. Tits captured significantly more caterpillars on still than on wind-exposed plants. Our results suggest that P.brassicae caterpillars are able to perceive the abiotic environment and to trade off the costs of extended development time against the benefits of increased size depending on the perceived risk of predation mediated by wind exposure. Such adaptive phenotypic plasticity in insects has not yet been described in response to wind exposure.
Highlights
Plants and insect herbivores make up nearly half of all described organisms on Earth (Strong, Lawton, & Southwood, 1984), and they clearly have a profound influence on community structure and ecosystem functioning
The composition of leaf sugars did change in response to wind exposure (Fig. 4d): wind exposure prior to herbivory significantly increased the ratio of monosaccharides to total sugars (F1, 40 = 12.37, P < 0.01), this effect was annihilated in the presence of herbivores (interaction wind x herbivory (F2, 40 = 6.41, P < 0.01)
We found that wind had strong differential effects on the development of P. xylostella and P. brassicae
Summary
Plants and insect herbivores make up nearly half of all described organisms on Earth (Strong, Lawton, & Southwood, 1984), and they clearly have a profound influence on community structure and ecosystem functioning. Plants produce a range of toxic secondary metabolites and exhibit a range of morphological adaptions that act as defense against attackers (Schoonhoven, van Loon, & Dicke, 2005) Biotic factors, such as herbivory or pathogen infection, can affect plant quality (Karban & Baldwin, 2007), abiotic factors, such as wind, rainfall and temperature, may affect plants and insects in ways that influence community structure and function (Kingsolver, 1989; Ritchie, 2000). In both of these studies insect development was studied in the context of changes in plant quality, mediated by wind exposure, and not by any effects of direct wind exposure on the insects themselves
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