orangeSome interactions the Papilio xuthus has with other species is with its food source. The swallowtail butterfly feeds on plants from the Rutaceae family, an example of an organsim from this family is the Citrus limon, you can click here to read more about this organism. Most species of Papilio use citrus as its host plants and the Papilio xuthus feeds on Poncirus trifoliota also known as the trifoliate orange (Miller et al. 2004). An organism related to the trifoliate orange is the Citrus sinensis. Other speicies of Papilio (sometimes the xuthus) feed on plants from the Umbelliferae (Scott 1986). Types of plants in this family are the celeries, carrots, and parsleys. It is most common that the larvae of these butterflys feed on this family of plants.
     An interesting interaction the Papilio butterfly's larvae has is with birds and snakes. The larvae will mimic these organisms as a defense system. The larvae sometimes resemble bird droppings so they are not eaten by other organisms. Sometimes these larvae also resemble small snakes. The larvae will have an osmeterium, which is an organ on the prothoracic part of the larvae, that lookes like an orange snake tounge and eyes (Scott 1986). Some Papilio also look like the butterfly Troidini so they have a less chance of being eaten by birds. The Troidini butterflys are poisonous (Scott 1986). Birds know that the Troidini are dangerous to eat so they stay away from them. 
     Another interesting interaction the P. xuthus has is with the Pteromalus puparum also known as the Pteromalid Wasp. These two species have a parasitic interaction (Zhu et al. 2009). Researchers did experiments to determine how the P. xuthus reacts to a parasitic attack of the P. puparum at a molecular level. These wasps use other organisms to lay their eggs and reproduce. The way this waspwasp does this is by injecting its host with a venom. This venom inhibits the immune response of the host organism so it cannot defend itself from a molecular level. The venom disrupts metabolic activities and development leading to the host organism’s death (Zhu et al. 2009). Researchers looked at how the P. xuthus responds to this type of attack. It was found that there was changes to 16 proteins in the P. xuthus. Some of these changes were to proteins important in immune response, cell structure, signal transduction, and detoxification. Researchers used an SDS-PAGE to see what proteins were expressed. They concluded that some of these proteins were under-expressed which could mean the proteins were not functioning properly. They also saw that some proteins were not expressed at all which could mean the function was lost completely (Zhu et al. 2009). Ultimately this change in protein function leads to the death of the P. xuthus.
    The P. xuthus has many interactions with organisms including its food source, parasitic interactions, and defense system interactions. The P. xuthus not only use mimicry as a defense system but it also uses chemicals. The next page (facts) goes more in depth into what their chemical defense system is.


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