Structure of the pinworm (Oxyurida: Nematoda) guild in the hindgut of the american cockroach, Periplaneta americana

Abstract

The pinworm (Oxyurida: Nematoda) guild in a laboratory colony of Periplaneta americana was investigated to answer the following questions. (1) Is guild structure stable with time? (2) Is there evidence of interaction among the species? (3) Is there evidence for niche diversification with respect to spatial distribution or developmental stage of host? Four species were found: Thelastoma periplaneticola, Thelastoma bulhoesi, Hammerschmidtiella diesingi and Leidynema appendiculatum; females of the first two could not be distinguished and they were lumped and referred to as Thelastoma sp.; 328 mid-instar hosts were dissected between September 1987 and February 1990, and the number of adult females of each pinworm species was recorded to investigate changes in guild structure through time. Seventy-five percent of hosts had Thelastoma sp., 62% had H. diesingi and 40% had L. appendiculatum; mean intensities were 6.5 (Thelastoma), 2.9 (H. diesingi) and 1.9 (L. appendiculatum). Relative numbers were stable with time and intensities of the species were similar whether they occurred alone in the host or in conjunction with other species. Thelastoma sp. and L. appendiculatum occurred together less often than expected and their numbers in individual hosts were negatively correlated. Both species occurred alone more often than expected. Surprisingly, H. diesingi and L. appendiculatum occurred together more often than expected. Intestines of 44 roaches were frozen in liquid nitrogen and divided into 5 equal sections to study longitudinal distributions of the species in the gut. Most L. appendiculatum and H. diesingi were found in the first, whereas most Thelastoma sp. occurred in the second segment. However, Thelastoma sp. dominated all segments of the gut. Worms were counted in 192 hosts belonging to 4 categories (early instar, late instar, adult male and adult female). Single species infections were more common in early instar hosts but there was no evidence that different species preferred different host stages. Modal distributions in male L. appendiculatum and T. bulhoesi suggest that these species may exhibit intraspecific interference competition similar to that observed in other pinworms. Such effects may be more important than interspecific effects in maintaining guild stability.