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 73<br />
amalgo 31 amides have been isolated while P. reticulatum seems not to have any amides (Dodson,<br />
unpublished in Dyer et al. 2003). Supposedly the lack <strong>of</strong> amides in P. reticulatum may explain its high<br />
preference by M. diocles adult females. Likewise some Pipers have very diverse herbivore faunas (95<br />
species in P. arieianum; Marquis 1990) indicating that these species may be poor in defensive<br />
compounds.<br />
Secondary plant compounds need not necessarily act as deterrents to herbivores, they also can stimulate<br />
feeding (Bernays & Chapman1994). Particularly interesting examples <strong>of</strong> such phagostimulants are<br />
phenolics and other compounds such as alkaloids, terpenes and flavonoids that can be taxon specific<br />
(listed in Bernays & Chapman 1994, p. 133) and that are thought to play a major role in defining host-<br />
ranges <strong>of</strong> associated insects. Nevertheless, phagostimulatory effects are only observed when the<br />
compounds are present in low concentrations and loose their stimulating effect when deterrent<br />
chemicals increase (Bernays & Chapman 1978). The presence <strong>of</strong> particular secondary phenolic<br />
compounds in Piper possibly acting as phagostimulants to M. diocles may explain the positive trend<br />
between leaf phenol content and nymph performance. When phenol content then increases, for example<br />
by induction, then deterrence outweighs stimulation.<br />
Above that some insects use secondary compounds for pheromone production or for defensive<br />
sequestration (i.e. pharmacophagy, e.g., Boppré et al. 1984; Bernays & Chapman 1994). For example,<br />
highly polyphagous Zonocerus grasshoppers feed preferentially on plants or flowers containing<br />
pyrrolizidine alkaloids and sequester the chemicals for defense against predators (Boppré et al. 1984).<br />
Most <strong>phasmids</strong> dispose <strong>of</strong> defensive glands at their prothorax (Bedford 1978). Their secretions have<br />
been shown to deter predators can be already functional in nymphs (Eisner 1968; Eisner et al. 1997).<br />
Likewise, M. diocles uses these glands and when threatened the smell <strong>of</strong> its spray becomes apparent<br />
(pers. obs.). Probably, this secretion is the result <strong>of</strong> sequestration <strong>of</strong> secondary compounds from<br />
M. diocles host plants. Thereby M. diocles would turn the potentially defensive biochemical diversity in<br />
its host range into its own protection against natural enemies. This would be <strong>of</strong> particular importance for<br />
nymphs as they are supposed to be most vulnerable to predation (Cornell & Hawkins 1995; Cornell et<br />
al. 1998).<br />
Yet, the principle phagostimulants are nutrients. Many authors previously showed positive effects <strong>of</strong><br />
nutritious plant quality (e.g. Nitrogen and carbohydrates) on survivorship and growth <strong>of</strong> insect<br />
herbivores (e.g., Joern & Gaines 1990; Joern & Behmer 1997). And insect herbivores are known to<br />
discriminate among food sources <strong>of</strong> different nutritional quality (Behmer & Joern 1993, 1994; Simpson<br />
& Simpson 1990). For example, growth and survival <strong>of</strong> grasshopper nymphs is <strong>of</strong>ten protein dependent<br />
(Behmer & Joern 1993, 1994) and host plant and tissue selection <strong>of</strong> grasshoppers has repeatedly been<br />
related to N-content reflecting protein (Behmer & Joern 1993, 1994). Nymphs <strong>of</strong> Locusta migratoria<br />
can regulate food intake based on protein (Abisgold & Simpson 1987). Other studies supported the