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