ecology of phasmids - KLUEDO - Universität Kaiserslautern
ecology of phasmids - KLUEDO - Universität Kaiserslautern
ecology of phasmids - KLUEDO - Universität Kaiserslautern
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Adult female feeding preference & nymph performance 69<br />
4.5 Discussion<br />
The initially formulated hypothesis that M. diocles preference and performance would be particularly<br />
influenced by physical leaf properties <strong>of</strong> host plant species could not be supported in this study. Food<br />
plant species <strong>of</strong> M. diocles differed markedly in quality considering leaf toughness, water content,<br />
specific leaf weight, total phenol and tannin contents. Adult females clearly differentiated among host<br />
plant species and nymph performance differed significantly depending on their food source. However,<br />
nor adult female preference neither differential performance <strong>of</strong> nymphs (sensu survival and growth) did<br />
relate to any <strong>of</strong> the assessed leaf traits over the whole host range (Araceae and Piperaceae) and among<br />
Piper congeners. These results indicate that the measured leaf characters may be <strong>of</strong> minor importance<br />
for M. diocles feeding behavior. However, an intraspecific increase <strong>of</strong> total phenols via infiltration <strong>of</strong><br />
phenol extract in leaves negatively influenced preference <strong>of</strong> nymphs while increased tannin contents<br />
were effective only in substantially higher concentrations. The deterring effect <strong>of</strong> increased total phenol<br />
on nymphs suggests that phenolic compounds may play an important role as qualitative defenses<br />
especially considering induced increases and intraspecific variation in total phenol contents <strong>of</strong> leaves.<br />
Adult preference for plant species did not consistently reflect best nymph performance suggesting that<br />
adult preference does not relate to experience in early life stages. Survival and growth <strong>of</strong> nymphs on a<br />
particular diet corresponded significantly, albeit highest survival was not linked to highest growth rate.<br />
Consequently host plant choice in early life stages <strong>of</strong> M. diocles may crucially determine survival and<br />
growth and hence could have a substantial impact on population density.<br />
(In the following discussion I will use the term preference-performance describing adult female<br />
preference and nymph performance. In another context preference-performance describes oviposition<br />
preference and larval performance.)<br />
4.5.1 The pattern <strong>of</strong> feeding preference and performance: an attempt <strong>of</strong> an<br />
explanation<br />
Adult M. diocles females displayed significant feeding preferences and diet source differentially<br />
influenced survival and growth <strong>of</strong> early life stages <strong>of</strong> M. diocles. However, in the presented study<br />
interspecific differences in physical and chemical leaf characters seemed not to relate to nymph<br />
performance or adult preference. These results do not support the initially stated hypotheses that in<br />
particular physical leaf traits should affect preference and performance <strong>of</strong> a specialist herbivore.<br />
Both, high leaf toughness (Cherret 1968; Coley 1983; Lowman & Box 1983; Reich et al. 1991; but see<br />
Landa & Rabinowitz 1983) and low water contents (e.g., Moran & Hamilton 1980; Coley 1983;<br />
Schädler et al. 2003) have been shown to negatively affect insect herbivores. Coley (1983)<br />
demonstrated that toughness and water contents had the highest negative correlations (among a