ecology of phasmids - KLUEDO - Universität Kaiserslautern

Adult female feeding preference & nymph performance 67
To account for taxonomically related biochemical leaf properties correlation analysis was repeated
among Piper congeners under exclusion of the two species of the Araceae. Within Piper host plants
performance of nymphs did not relate to phenol content, but exclusion of Araceae host plants led to
marked increases in correlation coefficients (Product Moment Correlation, df = 8: survival to phenol
content r = 0.58, relative growth rate to phenol content r = 0.61, both P > 0.05). In contrast to the
expectation of a defensive function of phenolic compounds correlation coefficients demonstrated a
positive trend in the relationship of performance and phenol contents.
Particular biochemical properties of Araceae leaves could also have influenced performance of nymphs,
thereby covering relationships between physical leaf traits and nymph performance considering Piper
congeners. Exclusion of Araceae from correlation analysis did not reveal any significant relationship
between any of these leaf traits and nymph performance (Product Moment Correlation, df = 8, relative
growth rate to: leaf toughness r = -0.40, water content r = 0.30, specific leaf weight r = 0.31; survival to:
leaf toughness r = -0.41, water content r = -0.03, specific leaf weight r = -0.04; all P > 0.05). The
exclusion of Araceae host plants had no effect on the resulting correlation coefficients except for the
relation of survival and leaf toughness that decreased from r = -0.03 (cf. Figure 4-11) to r = -0.41.
Performance of nymphs seemed not to relate to female adult preference, indicating that prior feeding
experience did not affect preference of females. In correlation analysis on MAI of females to survival
and relative growth rates of nymphs no significant relation was detected (Product Moment Correlation,
df = 9, MAI to: survival r = 0.50, relative growth rate r = 0.25, all P > 0.05). However, low mortality of
nymphs on Phil. inaequilaterum corresponded with significant preference of adult females (compare to
Figure 4-6), but growth of nymphs was intermediate on this food source. Opposed to that, 69 % of
nymphs had died on P. reticulatum, a highly preferred food of adult females.
4.4.4 Preference of M. diocles nymphs under varying total phenol and
tannin contents
The results of an infiltration experiment indicated that increased total phenolic contents as well as
increased tannin levels in leaves might act against herbivory by phasmid nymphs. Both the increase of
total phenol contents with phenol extract and tannin solution resulted in significantly reduced feeding
preference (i.e., water infiltrated control discs were preferred; Figure 4-12 & Figure 4-13). Yet, tannins
may play a minor role in defense against M. diocles herbivory compared to other phenolic compounds.
Increased contents of total phenols (by infiltration of phenol extract) proofed to be more effective than
an increase of phenols by tannin solution alone. A rise of 0.5 % of total phenols by leaf phenol solution
showed a significant effect in preference shift (Figure 4-12) whereas infiltration of 1.2% tannin was not
different from the control (Figure 4-13). An increase of tannin concentrations up to 11.7 % above
natural total phenol contents resulted in total rejection of tannin infiltrated leaf disks. Natural phenolic
content in P. hispidum leaves from greenhouse plants was 2.86 ± 0.1 % TAE (similar to natural phenol
content from field samples with 2.45 ± 0.6 % TAE).