ecology of phasmids - KLUEDO - Universität Kaiserslautern

Adult female feeding preference & nymph performance 71
P. cordulatum ranged on third and fifth position considering survival of nymphs and shared highest
relative growth rates with two other species.
Tannin containing leaf tissue was not discriminated against other foods by adults or by nymphs.
Detectable tannins by the RDM assay (Hagermann 1987) were absent in the two Araceae detected (and
thus tannins seem not to be characteristic for Araceae as was suggested by Grayum, 1990). Similarly,
tannins were rare in tested Pipers (four out of 13 species contained tannins) and ranged on similar levels
from 1.49 to 1.79 % TAE. For example, P. marginatum leaves contained 1.58 % TAE but adult females
displayed no significant preference when tested against five tannin free plant species (as compared to
the MAI of P. peltatum, that was closest to 0.5; cf. Figure 4-6). Above that P. marginatum was clearly
preferred to three plant species missing tannins (P. aequale, P. grande, P. perlascense; cf. Figure 4-6 &
Table 4-2). These results suggest that natural levels of tannins and phenols in M. diocles host plants do
not affect its feeding behavior.
Biochemical differences between the two host plant families of M. diocles seemed not to cover
defensive functions of leaf traits within Piper congeners. According to the theory of biochemical
coevolutiondifferences in plant biochemistry will increase with increasing taxonomic distance of plants
(Ehrlich & Raven 1964). Araceae and Piperaceae are not closely related (Judd et al. 2002) and both
families are rich in secondary compounds (Sengupta & Ray 1987; Baldwin & Schultz 1988; Parmar et
al. 1997; Judd et al. 2002; Dyer et al. in press). At least for Pipers it is known that many species contain
exclusive and highly variable compounds (Dyer et al. 2003). However, an exclusion from correlation
analysis did not reveal any significant relation between defensive leaf traits and preference-performance
of M. diocles. Albeit, within Piper host plants physical leaf traits may involve a minor defensive
function: the exclusion of Araceae strengthened all relationships to nymph performance markedly. In
contrast, nymph performance tended to positively correlate with total phenols. This again may indicate
that natural levels of secondary phenolic leaf compounds do not negatively affect this phasmid.
Nevertheless, a negative effect of phenolic and tannic leaf compounds on M. diocles nymphs must not
be neglected. At least considering intraspecifically varying levels of these compounds. As noted above,
both phenolic and tannic contents may negatively affect herbivores and many authors showed that
phenolic compounds may be induced in response to insect damage (e.g., Niemelä et al. 1979; Rossiter et
al. 1988; Haukioja 1990; Kogan & Fischer 1991; Baldwin 1994; Tscharntke et al. 2001; but see Lempa
et al. 2004). M. diocles nymphs reacted with a significant preference shift when phenol contents of
P. hispidum leaf discs were increased above natural phenol levels and preferred the according control.
Likewise, but in much higher concentrations increased tannin contents deterred nymphs. Hence
M. diocles nymphs may be negatively affected at least by intraspecific variation of phenolic compounds
in a particular host plant. This may apply to all host plant species presented in this study as all species
contained notable phenolic concentrations. The deterring effect by a comparably small increase of
phenolic content denotes the qualitative character of this defensive pathway. In contrast, tannin may