The population dynamics and host utilization of ... - Phthiraptera

288 R.W. Rust
parasite, the biotic parameters are in general related to or originate from
the host. The degree of adaptation of the parasite to the biotic parameters
corresponds to the host specificity of the parasite. The degree of host
specificity also indicates the adaptations of the parasite to the abiotie
parameters influencing the host. Mallophaga, biting lice, are host specific
(Hopkins, 1949; Werneck, 1950), and the restriction of all life stages to
the body of the host refines the specificity and adaptations of a louse to
its host and host's environment (see Clay, 1949; Ash, 1960; Baum, 1968;
Foster, 1969, for avian lice; Ewing, 1924; Hopkins, 1949; Waterhouse,
1953; Craufurd-Benson, 1941; Scott, 1952; Murray, 1957b-d, 1965;
Hopkins and Chamberlain, 1969, for mammalian lice). For lice, the
combination of interacting mortality factors and a species innate capacity
for increase will determine the population level on a particular host.
Evans and Smith (1952), in their classic demographic analysis of Pedi.
culus humanus Linnaeus, were the first to study the reproductive potentials
of an ectoparasite. Murray and Gordon (1969) modeled the population
dynamics of Bovicola ovis (Linnaeus), a biting louse of sheep. They
showed mathematically the development of the population from a low
summer density to a winter high density.
The genus Geomydoecus, parasites of the fossorial rodent family
Geomyidae, possesses morphological adaptations not found in other
trichodectid lice (Ewing, 1936). Degenerate adaptations as the absence
of eyes and lack of abdominal spiracles and tergites might be a response
to the altered conditions of the host's burrow environment (Kennerly,
1964; McNab, 1966; Darden, 1970), and specializations of the antennae
and well-developed hair-groove could relate to life on the gopher. Recently,
Price and Emerson (1971) studied Geomydoecus and found 45 taxa
on 29 of the 36 species of gophers. Most gophers have only one louse
species; exceptions were hosts with extensive geographical distributions.
The relative accessibility, small size, and peculiar habitat of the host
provide a system for analyzing a parasite's population dynamics. Thus,
Geomydoecus oregonus Price and Emerson, a parasite of Thomomys bottae
(Eydoux and Gervais), was selected for analysis and interpretation.
Methods and Materials
Field
A minimum of 20 pocket gophers per month as live-trapped from two irrigated
alfaHa fields located on the University of California, Davis Farm, and 2 consecutive
months of collection data were combined for analysis. The field sizes, agricultural
practices, measurement of environmental parameters, gopher collecting and laboratory
handling techniques and parasite recovery methods are treated in Rust
(1973a, b).
Three age classes were established for both sexes of gophers: juvenile, subadult
and adult. Separation was based on reproductive condition, skull features, and body