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Adult female feeding preference & nymph performance 68 mean mean acceptability acceptability index 1.0 0.8 0.6 0.4 0.2 0.0 Median 25%-75% Min-Max a a control Phenol +0.5% Phenol +0.9% Figure 4-12: Feeding preference of M. diocles nymphs under varying levels of leaf total phenol content (expressed as increase of percent TAE compared to natural total phenol content of P. hispidum; total phenol content was increased by infiltration of leaf phenol extract solution). An increase of 0.9% TAE of total phenols resulted in a significant preference shift (Mann-Whitney U = 579, P < 0.05, control vs. Phenol+0.9%, Ncontrol=37, NPhenol+0.9%=43). mean acceptability index 1.0 0.8 0.6 0.4 0.2 0.0 Median 25%-75% Min-Max a a control Tannin +1.2% Tannin +11.7% Figure 4 -13: Feeding preference of M. diocles nymphs under varying levels of leaf tannin content (expressed as increase of % TAE compared to natural total phenol content of P. hispidum; tannin content was increased by infiltration of tannin solution). An increase of 1.2 % TAE tannin had no effect on feeding preference whereas nymphs refused to feed on leaf discs with 11.7 % TAE more tannin (Mann-Whitney U = 401, P < 0.01, control vs. Tannin+11.7%, Ncontrol=37, NTannin+11.7%=24).
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
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ECOLOGY OF PHASMIDS (PHASMATODEA) I
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ECOLOGY OF PHASMIDS (PHASMATODEA) I
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Acknowledgements I Acknowledgements
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Table of Contents III 3 Life cycle,
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List of Figures V List of Figures F
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List of Abbreviations VII List of A
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Introduction 2 Regardless whether s
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Introduction 4 Description of phasm
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Introduction 6 Solanum and Piper (T
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Introduction 8 1.3.4 Data analysis
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Community structure & host range 10
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Page 32 and 33: Community structure & host range 18
Page 46 and 47: Life history & potential population
Page 58 and 59: Adult female feeding preference & n
Page 92 and 93: Predation mediated mortality & migr
Page 105 and 106: Concluding remarks 91 6 Concluding
Page 107: Abstract 93 7 Abstract Herbivory is
Page 110 and 111: Literature cited 96 Basset, Y. 1997
Page 112 and 113: Literature cited 98 Brown, B. J., M
Page 114 and 115: Literature cited 100 Croat, T. B. 1
Page 116 and 117: Literature cited 102 Hagerman, A. E
Page 118 and 119: Literature cited 104 Kearsley, M. J
Page 120 and 121: Literature cited 106 McNeill, S., T
Page 122 and 123: Literature cited 108 Reich, P. B.,
Page 124 and 125: Literature cited 110 Strong, D. R.,
Page 127: Appendix 113 9 Appendix Please cont
Page 130 and 131: Appendix 1: Phasmid species previou
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Tabellarischer Lebenslauf Angaben z
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Berger J., Schaefer, M., 1997. Wild
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