ecology of phasmids - KLUEDO - Universität Kaiserslautern

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Adult female feeding preference & nymph performance 76 forest (Croat 1978). Considering it’s high acceptance by M. diocles this plant species may account for the presence of M. diocles in the understory (cf. Chapter 2). In addition, while many phasmids flick and drop their eggs (Bedford 1978), M. diocles attaches them to a substrate and indicating a selective oviposition behavior. 4.5.3 Conclusions The study presented here, demonstrated that particularly M. diocles nymphs may be exposed to severe selection pressure depending on its food source. Differential mortality of nymphs depending on the host plant may directly (survival) or indirectly (slow-growth high-mortality) contribute to population control of M. diocles. Further studies on M. diocles should particularly focus on oviposition behavior for one striking reason: If an evolved life history trait, such as female choice of oviposition, is strongly linked to offspring performance then the reproductive response of females to host plant quality is the critical factor regulating population densities (Craig et al. 1989). Now, does the fact that M. diocles seemed not to be affected by physical plant defenses contradict its specialization? I tend to say no. M. diocles was not affected by natural contents of leaf tannins or phenols of its host plants indicating that this phasmid can handle the large variability in secondary compounds in its host range. This supports the consideration of M. diocles as herbivore specialist, simply because host range is ultimately defined by the occurrence of deterrent compounds in non-hosts (Bernays & Chapman 1994).
Predation mediated mortality & migratory behavior of nymphs 77 5 Predation pressure and its effects on survival and off-plant migration of M. diocles nymphs 5.1 Introduction Predation is considered an important determinant of the abundance and distribution of prey organisms (Sih et al. 1985; Begon et al. 1996). To date, numerous studies have confirmed that predators and parasitoids can have significant impact on insect herbivore populations (e.g. Chang 1991; Gomez & Zamora 1994; Floyd 1996; Moran & Hurd 1998). Extensive analyses of life table data found natural enemies as the most important source of mortality for holometabolous herbivorous insects (Cornell & Hawkins 1995; Cornell et al. 1998; Walker & Jones 2001). Cornell et al. (1998) concluded that this applies in particular for insects feeding externally on plants, starting out that the importance of natural enemies of holometabolous herbivores increases from the early larval stage to the pupal stage. These results emphasize the role of predation as a key factor in determining herbivore survival (Hairston et al. 1960; Walker and Jones 2001). Data on predation pressure on exophytic feeding hemimetabolous herbivores mainly concentrate on Orthopterans. In general, natural enemies exert a significant impact on populations of grasshoppers and population dynamics are most affected by nymphal mortality (Joern & Gaines 1990 and references therein). Oedekoven and Joern (1998) showed that the youngest instars experience the greatest losses and that predation from wandering spiders contributed significantly to nymphal mortality. The majority of larval mortality however reflected other undefined sources. According to Belovsky and Slade (1995) grasshopper nymphs may be more likely to suffer death from starvation, while adults may be at greater risk from other factors such as avian predation. Thus specific mortality causes of different stages remain uncertain and to my knowledge there is no data available that assess the impact of predation on early life stages of phasmids. Herbivorous insects face predation from a variety of natural enemies (Abrahamson & Weis 1997). These undoubtedly influence how and where an herbivore feeds (Hawkins & Lawton 1987). In response, prey organisms have developed a variety of mechanisms to escape from top-down pressure, for example morphological mimicry, or behavioral and phenological escape (Sillen-Tullberg et al. 1982, Kinsmann & Platt 1984, Damman 1987, Witz 1990). Migration patterns often reflect such predation avoidance, either in prey moving within (Hopkins and Dixon 1997, Magalhães et al. 2002) or off (Roitberg & Myers 1979) their host plants. Such behavior usually involves costs such as reduced fecundity (Roitberg & Myers 1979) or larval growth (Heads 1986, Gotthard 2000). The latter may lead to prolonged development times, increasing exposure to natural enemies during vulnerable immature stages (Feeny 1976, Benrey & Denno 1997). In consideration of these costs, predator avoidance via
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ECOLOGY OF PHASMIDS (PHASMATODEA) I
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ECOLOGY OF PHASMIDS (PHASMATODEA) I
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Acknowledgements I Acknowledgements
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Table of Contents III 3 Life cycle,
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List of Figures V List of Figures F
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List of Abbreviations VII List of A
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Introduction 2 Regardless whether s
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Introduction 4 Description of phasm
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Introduction 6 Solanum and Piper (T
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Introduction 8 1.3.4 Data analysis
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Community structure & host range 10
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