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

296 R.W. Rust
Table 1. Recovery of Geomydoecus oregonus from gophers, each artificially infested
with newly hatched first instar nymphs. Gophers maintained in artificial burrows
Days Inoc- I~umber and stage of development Total %
after ulum Mortality
infesta- Immatures Adults
tion 1st 2nd 3rd ~
6 36 18 . . . . 18 50.0
10 58 1 16 -- -- -- 17 70.3
15 49 -- 8 1 -- -- 9 81.7
20 32 -- 2 2 -- -- 4 87.5
25 31 -- -- 2 -- -- 2 93.5
30 40 -- -- -- 2 1 3 90.0
the lice and a delay (12 h) before they could feed or assume a correct
posture on the gopher. The results (Table 2) obtained from cohorts
starting with the egg stage, indicate a Type II survivorship curve for the
louse population. Thus, age frequency mortalities can be calculated as
0.02 for eggs, 0.18, 0.24, and 0.06 for the nymphal instars, and 0.50 for
adult lice. Due to the 10 day age difference of eggs used to initiate these
tests, females and new eggs were already present on the gophers in the
30 day samples, and at 40 days, new first instar lice appeared in the
samples. Using the pivotal frequency for reproductives, it is possible to
estimate the net reproductive rate, Ro=Zlxm x. Thus, R o for G. oregonus
is 1.272 (0.53 X 2.4= 1.272). This assumes a 1:1.2 sex ratio, equal survival
of sexes and an average of 4 eggs per female louse. The intrinsic rate of
increase (r) can be calculated from Ro=e% Thus, r is equal to 0.24 per
generation or 0.006 per day, and the population doubles in 2.8 genera-
tions.
Duration
days
Table 2. Recovery of Geomydoecu8 oregonus from gophers, each naturally infested
with eggs. Gophers maintained in artificial burrow systems
Num- Inoc- Number and stage of development Mortality
ber
of
ulum
eggs Immatures Adults Eggs % %
gophers eggs total
1st 2nd 3rd ~ !~ Unhatched new
%a
age
interval
20
30
40
2 295 65 127 34 7 -- 2.3 20.0
4 551 -- 7 187 42 43 11 21 1.9 49.4
5 914 13 b -- 30 150 180 ? 157 ? 60.7
a Determined initially from 2 % egg mortality and rounded to nearest whole number.
b First instars of second generation.
18.0
30.0
ll.0