ecology of phasmids - KLUEDO - Universität Kaiserslautern

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