ecology of phasmids - KLUEDO - Universität Kaiserslautern

Predation mediated mortality & migratory behavior of nymphs 84
Table 5-2: Potential predators of M. diocles nymphs observed on 119 control plants. Each plant was surveyed 29
times in runs 1 to 3 and 15 times in run 4 (including one night check per run).
Predator group No. of observations
Ants (Formicidae); Ectatomma spp.
Army ants (Eciton spp.)
Others
Spiders (Araneae) 44
Reduvid bugs (Hemiptera) 3
Frogs (Anura) 2
Katydids * (Orthoptera); adults 35
* Katydids are often omnivorous
5.3.2 Predation and off-plant migration
The initially stated hypothesis that migration may be a response to predation pressure (i.e., a mechanism
for predator avoidance) was not supported by the observed pattern of migratory activity in the field
experiment, because proportions of migrating nymphs between treatments were similar (25 % in
exclosures, 31 % in controls; Table 5-1). Nevertheless, migratory activity in the field was markedly
increased compared to the greenhouse experiment (15 %), and the proportion of migrating nymphs in
the control plots was significantly higher than in the greenhouse plots (X 2 = 4.07, df = 1, P < 0.05).
In contrast nymph migration was related to the number of healthy leaves per host plant (as measure of
resource availability). Plants from where nymphs emigrated (i.e. nymphs from both treatments that
never returned to their host) had significantly fewer healthy leaves than plants from sessile nymphs (i.e.
nymphs from both treatments that never left their host) (Figure 5-3). In contrast, there was no difference
between leaf numbers of plants from remigrating and sessile nymphs.
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