ecology of phasmids - KLUEDO - Universität Kaiserslautern

Adult female feeding preference & nymph performance 50
closed with cotton batting. The vial then was attached to a wire clamp in a single feeding arena so that
leaves stood upright. When all arenas were equipped, I collected the animals from the lab colony and
started the trial by setting one adult female in each arena. A trial usually started around noon and then
lasted 24 hours. To quantify consumption, leaf area was measured again after a trial was finished.
The second half of each leaf was used for measuring water content. For assessing water content I used a
punch to get a leaf disc of 15 mm diameter, which was weighed and then freeze-dried for at least three
days. Afterwards dry mass was weighed. By that I could calculate water content for each leaf used in
feeding trials. The leaf remnants also were freeze-dried for analysis of leaf phenol and tannin contents.
Each M. diocles female was used only once per test plant species. I conducted 30 plus individual choice
tests for each of 14 test plant species (for sample size see Table 4-1). Differences in numbers of
replicates resulted from females that did not feed in trials and from females having died while the
choice-test was running. For Piper arboreum only 20 replicates could be accomplished, as no more
females were available.
4.2.3 Problems inherent with dual-choice feeding trials
To assure the accuracy of the results from choice tests I addressed two major problems inherent in the
use of feeding trials: Food choice of an animal may be based on prior feeding experience (e.g., Sandlin
& Willig 1993) and the selection of the reference test plant may affect the preference ranking (see e.g.,
Richardson & Whittaker 1982; Capinera 1985).
4.2.3.1 Conditioning due to prior feeding experience
The number of females in the lab colony generally restricted the number of replicates. As a basic
principle no individual was used twice with the same test plant species. But individuals had to be
deployed in feeding trials with different test plant species, i.e. preference data in different choice-tests
(e.g. P. grande and P. hispidum as test plant species) origin from the same female. As a consequence
prior experience and conditioning on a particular food source of these females could have influenced the
outcome of succeeding choice tests. The resulting question was whether females of M. diocles showed
such conditioning behavior or whether they acted naively in every new choice situation. Only in the
latter case data gathered in feeding trials would be independent as every female in every new choice
situation differentiated among offered food sources.
To test for female naivety I designed a sequence of two dual-choice tests with different test plant species
(P. grande and P. hispidum) and P. marginatum as reference. In both dual-choice tests identical females
were used. The procedure of the feeding trials followed the protocol as described above (Chapter 4.2.2).
In case food selection was influenced by prior experience, I assumed females to display similar
preference patterns in succeeding feeding trials. In contrast to this expectation food preference of
females differed significantly (Figure 4-1). The preference shift from P. hispidum in test 1 towards
P. marginatum in test 2 clearly demonstrated that in the following choice-test females decided in a naïve