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FIGURE 13.2 Model simulations examining (A) applied population replacement and (B) applied suppression
strategies by cytoplasmically incompatible Wolbachia infections. (A) Following the introduction of Wolbachia -
infected hosts into an uninfected population at generations one to three (one release/generation). The size of
each release is equivalent to 5% of K U (i.e., the carrying capacity of the uninfected host population) and
consists of 50% females. The Wolbachia infection spreads into the host population in the subsequent gener-
ations, replacing the uninfected cytotype with the infected cytotype. The total population size decreases 33%
to a minimum ( N min ) during population replacement due primarily to the reduced hatching rates caused by CI.
As the infection invades, the frequency of incompatible crosses decreases, and the total host population size
recovers. However, the new carrying capacity of the infected population ( K I ) is reduced relative to K U due to
CI and fecundity costs associated with Wolbachia infection. (B) This simulation is identical to that shown in
(A), except that the host population size is further reduced by initiating releases of an additional, bidirectionally
incompatible infection (Y). The additional releases of the Y infection are begun at generation six and repeated
for a total of three generations (release size equivalent to 5% K U per generation; 50% female). In this simulation,
the host population is reduced by more than 83%. Host population size is shown as percent carrying capacity,
which is calculated using the following formula: N t / K U , where N t is the host population size at time t . For (A)
and (B), the initial uninfected population is at carrying capacity; b = 0.00002; H Z = 0.05; F Z = 0.95; and n Z
= 0.03. For (A), R = 2.0 and h = 1.
public-health concerns associated with insecticide use and problems related to insecticide resistance.
As discussed above, shortly after the description of CI in C. pipiens (common house mosquito), its
potential applied use in insect-control strategies was recognized (Laven, 1967a). The early strategies
were based on the release of cytoplasmically incompatible males, which would cause sterility when
mated with Ýeld females. This research included Ýeld tests that successfully suppressed populations
of C. pipiens by releasing cytoplasmically incompatible males (Laven, 1967a).
Despite the successful suppression of C. pipiens populations in Ýeld tests, work with this
strategy was not continued due to political problems and scientiÝc criticism. ScientiÝc critics argued
that the strategy was impractical due to the requirement that only incompatible males be released
(Pal, 1974). With conventional SIT strategies, releases were designed to consist primarily of males
 
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