tions only about 1% of wild-caught females
mated. Changes in mating behaviour appar-
ently due to captive rearing have also been
observed in houseflies (Fye and LaBrecque,
1966). In a laboratory simulation of SIT, ster-
ile males from a 20-year-old laboratory popu-
lation competed poorly with males from a
wild-caught population, whereas sterile
males from a newly established laboratory
population were much more successful. In
another example, Fletcher et al. (1968)
showed significant differences between two
captive populations of screw-worm fly. Males
from both populations produced the male
pheromone, but only females from one of the
populations responded to the chemical. The
authors suggested that differences in the cap-
tive rearing of the two populations may have
selected for this difference.
Changes in mating behaviour are not only
a problem for SIT. In classical biological con-
trol, the aim is to establish a self-perpetuat-
ing population of the natural enemy. If the
mating system has been disrupted through
domestication, the probability of establish-
ment is inevitably reduced.
Life-history traitsCaptive-rearing conditions almost inevitably
select for faster development. This has been
observed in medfly (Rössler, 1975; Wong and
Nakahara, 1978; Vargas and Carey, 1989), ori-
ental fruit fly (Foote and Carey, 1987),
Caribbean fruit fly (Leppla et al., 1976) and
melon fly (Miyatake, 1993; Miyatake and
Yamagishi, 1999). In the melon fly, these
changes occurred during the first nine gener-
ations of captive rearing (Miyatake and
Yamagishi, 1999).
Selection for faster development generally
leads to a correlated decrease in adult size and
lifetime female fecundity (Nunney, 1996);
however, the expected correlations can break
down when a population is introduced into a
new environment (Service and Rose, 1985).
Thus, although the adult size of melon fly
decreased in response to selection for a shorter
developmental period, lifetime fecundity did
not, and captive melon-fly populations gener-
ally have a higher fecundity than wild-caught
flies (Miyatake, 1998). Similarly, in both the
Caribbean fruit fly (Leppla et al., 1976) and the
oriental fruit fly (Foote and Carey, 1987), the
shorter development time of domesticated
populations was associated with higher fecun-
dity, relative to recently wild-caught flies.
Correlated responses can affect traits that
we may not a priori expect to be influenced.
Miyatake (1998) notes that selection for faster
development in the melon fly results in indi-
viduals that have a shortened circadian
period and that mate earlier in the day. These
responses were not arbitrary; they were due
to the pleiotropic effects of a single gene
(Shimizu et al., 1997). This result is an excel-
lent illustration of how adaptation to the
rearing facility (faster development) could
have an unexpected negative effect on mat-
ing success in the field (due to flies attempt-
ing to mate at the wrong time of day).GeneralWe do not know which genetic loci are
involved in the adaptation to a captive envi-
ronment. The rapidity of adaptation is sugges-
tive that relatively few loci are responsible for
most of the change. For example, in tobacco
budworm, it took only four generations for the
oviposition pattern of a wild-caught popula-
tion to converge on that of a laboratory culture
(Raulston, 1975). More typically, significant
adaptive change seems to occur over the first
6–10 generations (Raulston, 1975; Loukas et
al., 1985; Miyatake and Yamagishi, 1999).
In the screw-worm fly, Bush and Neck
(1976) identified a candidate gene, the -
glycerophosphate dehydrogenase (-GDH)
locus. They found that one allele, rare in nat-
ural Texas populations, was very common in
each of four large ‘factory’ populations. They
argued that this was an adaptive change in
response to the novel rearing conditions
(constant high temperature, combined with
selection for rapid development and reduced
flight). Similarly, Loukas et al.(1985) found
rapid changes at several allozyme loci when
a population of the olive fly was reared in
the laboratory. In only five generations, the
commonest allele at the 6-phosphogluconate
dehydrogenase (6-PGD) and alcohol dehy-Managing Captive Populations 77