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Factors affecting structure of the pinworm (oxyurida: nematoda) community of the American cockroach, periplaneta americana (Linnaeus) Connor, Stephen J.


Thelastoma bulhoesi (Magalhaes, 1900), Leidynema appendiculatum (Leidy, 1850), and Hammerschmidtiella diesingi (Hammerschmidt, 1838), (Order Oxyurida), parasitize the colon of the American cockroach, Periplaneta americana (Linnaeus). Individual hosts may harbour 1, 2, or all three species simultaneously. These helminths inhabit the same region of the host gut, are transmitted the same way, and have similar feeding behaviours. Such similar life histories lead to the expectation that communities within hosts will be interactive, with such interactions being mainly competitive. Using 3 replicate cockroach colonies containing all species of parasite, as well as single colonies of hosts infected with either!, appendiculatum alone, or T. bulhoesi alone, I have looked for evidence of interspecific interactions in the distributions of females of each species among hosts. I examined 72 hosts from each colony, and found evidence of negative interaction between T. bulhoesi andZ,. appendiculatum, and positive interactions between these two species and H. diesingi. The first two species were found together less often than expected under an assumption of independent distribution, while H. diesingi was found with both of these species more often than expected. L. appendiculatum was more prevalent among small, immature hosts than either T. bulhoesi or H. diesingi, indicating possible niche segregation based on host size.. Examination of effects of number of females of each species in an inffacommunity on female fecundity provided further evidence for both negative and positive interactions among the species. Fecundity of both L. appendiculatum and T. bulhoesi females was reduced in the presence of H. diesingi, while that of H. diesingi was enhanced in the presence of either of these species. Analysis of dietary preference based on size of food item revealed complete overlap among the three species, though L. appendiculatum and T. bulhoesi consumed substantially more of the model food items than did H. diesingi, indicating that differences in interactions among the species may be based upon differences in diet. Lastly, larval resistance to expulsion from the host gut during host moult for T. bulhoesi and L. appendiculatum indicated that L. appendiculatum''s apparently greater ability to exploit young hosts is not based on greater resistance to expulsion from these hosts. I conclude that the three pinworm species form interactive infracommunities, but that there is evidence of both positive and negative interactions.

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