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Adult female feeding preference & nymph performance 52 4.2.4 Long term feeding trials with M. diocles nymphs To document growth and mortality of M. diocles nymphs I conducted long term feeding trials on single host plant species. At least 30 nymphs were raised on each of 13 food plant species. All performance trials lasted 6 weeks (performance sensu survival and growth). The selection of food plant species resulted from diet assessment from field records and no-choice feeding trials of M. diocles (see Chapter 2). Because Piper spp. were the main potential food sources in the field I tested 10 Piper species to evaluate interspecific differences in diet suitability of congeners. I included three species of Araceae: two Philodendron species were also recorded as potential food in the field whereas no M. diocles individual was found on Dieffenbacchia longispatha (but D. longispatha was accepted in no-choice feeding trials). Due to partial lack of nymphs and to restrictions in labor potential I could not include all Piper species tested in adult female preference tests. Newly hatched nymphs were weighed and then separately kept in plastic food containers (10cm wide, 5cm deep, 5cm high). Adult leaves were harvested in the forest, placed in a sealed plastic zip log bag and brought back to the laboratory. Within 2 hours of being collected leaf discs (punch of 13 mm diameter) were cut and presented to nymphs. Leaf discs were stuck into a piece of cardboard to assure free access for the nymph. A piece of humid paper towel helped minimizing desiccation. If multiple nymphs hatched on the same day they were allocated to different food plant species. Nymphs then were provided with new food daily and controlled for survival. To document growth, nymphs were weighed in weekly periods. 4.2.5 Dual-choice feeding trials with M. diocles nymphs This experiment was conducted at the Technical University of Kaiserslautern, Germany. P. hispidum plants were grown in greenhouses from cuttings I imported from Panamá. M. diocles nymphs had hatched from eggs I previously had collected from a lab population at Barro Colorado Island, Panamá. As defensive or deterring effects of phenolic or tannic compounds may be dose-dependent (Feeny 1970; Rhoades 1977; Coley 1986), I designed a test series of dual-choice feeding trials where nymphs were offered leaf discs with artificially increased natural phenol and tannin contents by use of a method described by Beyschlag & Pfanz (1990) and modified by Herz (unpublished). Beyschlag & Pfanz (1990) used pressure infiltraton of water into a leaf via the stomatal pores to determine stomatal aperture. Herz (unpublished) used this method to infiltrate sugar solutions in leaves and offered these to leaf cutting ants. I modified the method as I used leaf discs (15 mm punch) of Piper hispidum and infiltrated aqueous solutions of tannic acid and of total phenol extract from P. hispidum leaves. Phenolic compounds were extracted with 70 % aqueous aceton from P. hispidum leaves following the same procedure as described by Waterman & Mole (1994). Aceton and water of the phenolic solution evaporated within 48 hours under room temperature and the remaining phenolic aliquot was resolved in
Adult female feeding preference & nymph performance 53 distilled water. The phenolic content of the resulting solution was assessed by the Price and Butler method (1977) as described above. In preliminary infiltration trials I assessed the amount of water that could be infiltrated into leaves (27.4 ± 4.3 % fresh weight). In combination with dry weight and natural total phenol contents of P. hispidum leaves I could then calculate the concentration of solution needed to yield particular increases of % TAE in leaf discs. Infiltration was carried out with a 50 ml syringe filled with approximately 25 ml of aqueous phenol or tannin solution (or water for the control). Immediately after punching the disc was weighed and put in the syringe. All remaining air was removed through the outlet. Then the outlet was closed and the piston was forcefully pulled outward the depression leading to an evacuation of the internal air and the intercellular space. Simultaneously the syringe was shaken to remove gas bubbles from the leaf surface and prevent them from entering the leaf disk during the following infiltration process. By slowly pushing the piston back into the syringe the solution (or water) column was set under pressure and entered the leaf via open stomatal pores and via intercellular space at the cutting edges. After infiltritation the leaf disc surface was dried carefully with a peace of paper towel and weighed again. Weight gain was considered as infiltrated amount of solution (water). In combination with natural total phenol contents of leaves and their dry weight infiltrated percent TAE in the leaf disc was calculated. Until the start of the feeding trials leaf discs were kept on ice. First instar nymphs of M. diocles were presented with two leaf discs: 1) infiltrated with water (control) and 2) infiltrated with the according solution (treatment). Nymphs were set in plastic food containers (10 cm wide, 5 cm deep, 5 cm high). Leaf discs were stuck into a piece of cardboard to assure free access for the nymph. A piece of humid paper towel helped minimizing desiccation. Climate chambers allowed for conditions similar to the tropics (27 o C average temperature, 70 to 90 % relative humidity). Dual-choice feeding trials lasted 24 hours. This was a sufficient time span to assess preference because a preliminary test on dual-choice feeding trials over three days showed no differences in preference among days (Friedmans ANOVA χ 2 (N=38, FG=2) = 1.28, P < 0.53). After finishing the trial consumed leaf area was measured with a transparent grid. Preference was then calculated on the base of consumed dry weight (see Chapter 4.3.2). To assure that infiltration did not alter feeding behavior I tested normal leaf discs against water infiltrated leaf discs. Both, control and treatment were fed equally resulting in a relative preference of 0.5 indicating that infiltration did not affect feeding behavior (compare to control in Figure 4-12 & Figure 4-13). 4.3 Data analysis Multiple groups where compared in Analysis of Variance. ANOVA assumes normality of data and homogeneity of variances. If not stated differently data transformation resulted in normally distributed data and allowed minimizing differences in variances whereas homogeneity of variances could not be
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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
Page 16 and 17: Introduction 2 Regardless whether s
Page 18 and 19: Introduction 4 Description of phasm
Page 20 and 21: Introduction 6 Solanum and Piper (T
Page 22 and 23: Introduction 8 1.3.4 Data analysis
Page 24 and 25: Community structure & host range 10
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
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Literature cited 102 Hagerman, A. E
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Literature cited 104 Kearsley, M. J
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Literature cited 106 McNeill, S., T
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Literature cited 108 Reich, P. B.,
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Literature cited 110 Strong, D. R.,
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Appendix 113 9 Appendix Please cont
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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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