Population regulation of thelastomatid nematodes (Nematoda: Thelastomatidae) of cockroaches
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy (PhD)
Populations of thelastomatid nematodes in cockroach hosts were investigated. The population biology, life history, habits. distribution, and gross morphology of cockroaches involved are discussed. New species of thelastomatid nematodes from cockroaches are described and keys to species of Protrellus and Blatticola are given. Evidence for population regulation in six species of thelastomatids in eight species of cockroaches collected from the field is presented. No host contained two adult males, infrapopulations with two juvenile males were very rare, the number of adult females per host was small. and monogamy was common. Juvenile males were rare while juvenile females were relatively common, indicating that, compared to females, males develop and are eliminated rapidly from hosts (leaving one), or that males are less common to start with. Infection prevalence varied markedly between the cockroach species. Reproductive competition due to crowding, and cyclical egg production were found in two species. these phenomena are discussed. Mechanisms which may control The effects of density-independent climatic factors on seasonal variation in incidence and infrapopulation structure of one thelastomatid population were transient. Evidence for population self-regulation in Protrellus dixoni was obtained from laboratory studies. Infrapopulations were regulated by a density-dependent and sex-dependent reduction in infection intensity with infrapopulation age. This reduction was not equal in initial speed or intensity between the sexes (reduction in number of males was faster) and led to infrapopulations with never more than a single adult male. and few adult females. In structure. these laboratory-produced infrapopulations resembled those in field collected hosts. Unmated females produced male progeny only (probably by arrhenotokous parthenogenesis). Female offspring probably result from amphimixis. Possible methods of thelastomatid infrapopulation regulation are discussed. It is concluded that regulation is parasite-mediated and due to chemical interference competition. Regulation benefits the surviving nematodes because per capita fecundity is greater in uncrowded infrapopulations. Self-regulation may be common among thelastomatids and other parasites.