Evidence for population self-regulation, reproductive competition and arrhenotoky in a thelastomatid nematode of cockroaches

Abstract

SummaryExperimental infection of adultDrymaplaneta variegataShelford, 1909 (Blattodea) with known numbers of eggs ofProtrellus dixoniZervos, 1987 (Nematoda: Thelastomatidae) showed that each infrapopulation was 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, 1–8 (usually 1–3) adult females and 0–28 juvenile females. In structure, these laboratory-produced infrapopulations resembled those in field-collected hosts. Parasite-mediated chemical interference competition is suggested as the cause of infrapopulation regulation.Per capitaegg production was greater in uncrowded worms which suggests that self-regulation benefits those nematodes that survive competition. Unmated females produced male offspring only (probably by arrhenotokous parthenogenesis). Only females that occurred with a male produced females although some also produced males; such females may avoid insemination or prevent fertilization of some or all eggs. Female offspring probably result from amphimixis.