ecology of phasmids - KLUEDO - Universität Kaiserslautern

Adult female feeding preference & nymph performance 75
where nymphs suffer littlest mortality resulting from food quality or from predation, mediated via
extended larval development. However, a single food type of poor or even toxic quality rarely will
provide all essential nutrients for survival. As a consequence herbivores may have to leave a host to feed
on a mixture of plants (Joern 1979; Cates 1980; Bernays et al. 1994).
From the plants perspective it is most favorable to motivate the herbivore to leave as soon as possible.
Early instars cause little damage but food consumption increases with development (e.g., van Dam et al.
2001) and thereby may increase a plants fitness loss. To cite an example, Marquis (1992) showed that a
leaf loss of 10 % on single reproductive branches in Piper arieianum caused a local seed loss of 80 %.
However, in a competitive environment the production of lethal herbivore defenses may also involve
high fitness costs (e.g., Baldwin 1998). Thus many plants may use defenses on less cost-intense
sublethal levels (Price et al. 1980) that already affect early larval instars and may motivate them to
change hosts (van Dam et al. 2001). In this hypothetical framework M. diocles nymph performance then
would reflect variation in sublethal reduction of leaf quality, and the observed mortality patterns would
rather result from the experimental setup ‘forcing’ nymphs to stay on such low quality food. The
positive relation of nymph survival and growth gives support to this thought.
As demonstrated, selection pressure on early lifestages of M. diocles may be high depending on food
source. This pressure could be reduced if adult female oviposition was related to best nymph
performance. Feeding habits of adult herbivores often reflect previous feeding experience throughout an
individual’s lifetime (Cassidy 1978; Papaj & Prokopy 1988; Redfearn & Pimm 1988; Karowe 1989;
Sandlin & Willig 1993). For example, adult feeding behavior of the neotropical phasmid Lamponius
portoricensis depended on sex and prior experience and persistence of feeding preference (as proportion
of a species in its diet) was stronger in females than in males (Sandlin & Willig 1993). Concluding from
this, one could hypothesize that if adult feeding preference reflected prior feeding experience as
nymphs, selection would favor evolution of oviposition on preferred host plants of females and nymphs
would perform best on this food. In the many examples of insect females that lay their eggs on plants for
larval development, the observed relationship between oviposition preference and offspring
performance ranges from good to poor correspondance (for review see Thompson & Pellmyr 1991).
Clearly, a preferential oviposition on high quality foods would involve immediate consequences for
plant herbivore interactions and for herbivore population dynamics (Price et al. 1995). In the
‘Phylogenetic Constraints Hypothesis’, Price et al. 1990 predicted that larvae of such species would
exhibit higher survival, that females would recognize and compete for rare high quality resources, and
that they would disperse large distance to spread spacing of eggs preventing larval competition and
overexploitation. In contrast to my expectations performance of nymphs seemed not to relate to female
adult preference, indicating that prior feeding experience did not affect preference of females. Albeit,
adult preference tended to relate modestly with nymph survival (r = 0.50; P > 0.05) and low mortality of
nymphs corresponded with significant preference of adult females on Phil. inaequilaterum (compare to
Figure 4-6 and Table 4-3). This Araceae is a typical and abundant plant in the understory of the BCI