Defensive chemistry of Papilio polytes caterpillar

May 24, 2017 | Autor: Arkajyoti Shome | Categoria: Chemical Ecology, Ecology, Lepidoptera, Volatile Organic Compounds, Butterfly, Defensive mechanisms
Share Embed


Descrição do Produto

RESEARCH OUTLINE Chemical defense are one of the primary defense used by the insects against predators(Malcolm 1994; Agrawal et al. 2012). Defense chemicals are usually synthesized or sequestered from the food (Brower et al. 1984; Honda 1983; Seligman & Doy 1973; Greeney et al. 2012; Nishida 1995). Chemically defended organisms advertise their unpalatability via bright colors which helps predators identify and avoid them. This phenomenon is known as aposematism (Malcolm 1994). An interesting example of use of chemical defenses against natural enemies is exhibited by Lepidopteran caterpillar (Honda 1980; Eisner 1965; Boppré 1990). While some species are aposematic, some species are cryptic and evade predators by using camouflage(Greenery et al. 2012; Malcolm 1994). Being cryptic may help avoid predators that hunt using visual cues, it is not particularly helpful to avoid natural enemies that use the caterpillars’ chemical signature to track and attack them. Thus, in response many species have evolved counter chemical defenses. One such example is Papilio polytes. They have a defense organ called osmeterium which resembles like the bifurcated tongue, this is characteristic feature of Papilio caterpillars(Ômura et al. 2012; Waterhouse 2006; Heart 1986). When the caterpillars are disturbed by both invertebrate and vertebrate predators the immediate response is they get into a characteristic “threat posture” in which they uplift the front part of their body (Eisner 1965; M. R. Berenbaum, B. Moreno 1992) but after that point they will inevitably extrude the osmeterium if the stimulus goes on. After extruding the osmeterium they will try to wipe it against that offending agent(Eisner et al. 1970). The osmeterium is protruded by the help of blood pressure and is retracted by special retractor muscles(Eisner 1965). It is highly successful against arthropods and ants and also helpful against parasitoids. This osmeterial secretion have very offensive odor and also toxic which makes predators to avoid those caterpillar(Eisner et al. 1970; Honda 1983; Honda 1980; Ômura et al. 2012).The quality and quantity of chemicals in the osmeterial secretions do not depend on the host plant(Eisner 1965). The interesting aspect of this osmeterial secretion is that the chemical composition may or may not vary with the different instar. As in case of

species belonging to genera of

Atrophaneura , Graphium , Luehdorfia, Pachiolopta, sericinius, and Parnassius it has been seen

the chemical composition remains similar in the different instar(Honda 1980; HAYASHI 1995) , whereas in case of Papilio chemical composition remains almost similar in the third and fourth instar. The variation of osmeterial chemistry has been observed in Papilio species between the fourth and fifth instar larvae(Honda 1980; Ômura et al. 2012). Earlier work done by Eisner 1965, 1970; Honda 1980; Ômura et.al 2012 has shown the presence of various terpenoids and aliphatic acids in 7 Papilionidae species in both 4th instar and 5th instar. The observation showed in 4th instar the compounds being mostly terpenoids whereas in 5th instar they are mostly aliphatic acids or their esters. The heterogeneous composition of osmeterial secretion was hypothesized to be associated with the change in body coloration of the larvae in between those 4th and 5th instar , but it was later seen in Chilasa species that they resemble same body coloration though having different osmeterial mixture(Ômura et al. 2012). The chemicals emitted from the osmeterium are aliphatic acids, esters , monoterpene hydrocarbons and sesquiterpenes(Eisner et al. 1970; Honda 1980; Honda 1983; Ômura et al. 2012). The compounds are mostly volatile and have offensive smell which deter predators such as spiders, ants, mantids, soldier bugs(Ômura et al. 2012). In an experiment by Honda et al., (1983) showed that aliphatic acids such as iso-butyric acid, 2-methylbutyric acid, isovaleric acid proved to be fatal for two ant species Lasius niger and Crematogaster matsumurai used as predators in the experiment. Monoterpene compounds also found to be toxic whereas sesquiterpenes found to slightly toxic(Honda 1983). I tried to look into the chemical composition of the osmeterial secretion of 3rd and 5th instar larvae. We tried to look into the osmeterial secretions of Papilio polytes larvae belonging to 5th instar. We checked for the chemical composition and concentration of the osmeterial secretions of these two different groups to see whether the chemical composition and concentration between the instars groups remains same or varies accordingly.

Lihat lebih banyak...

Comentários

Copyright © 2017 DADOSPDF Inc.