Conclusions
The importance of maintaining quality has
long been recognized as a problem in the
rearing of natural enemies, but there has
been little effort to consider the problem
quantitatively. Here I argue that the paradox
of captive rearing – the trade-off between
rearing quantity and field quality – should
be evaluated in terms of the parameter ‘effec-
tiveness’. Effectiveness is defined as the
product of quantity and quality, and recog-
nizing the importance of this parameter
allows us to define how much of a decline in
quality is acceptable (and necessary) to
achieve the optimal strategy.
The shape of the trade-off curve between
quantity and quality created by captive rear-
ing defines the optimal strategy (Fig. 6.1).
Unfortunately, we lack the data necessary to
draw this curve for any specific case.
Admittedly, getting these data is no easy
task; however, it is very important to encour-
age measurement of these curves. The alter-
native is either to ignore the problem of
adaptation to captive rearing or to attempt to
manage such adaptation based on guess-
work. The dollar costs of failing to maximize
effectiveness can be extremely large.
Sometimes the best solution, when it can
be employed, is to maintain natural enemies
as isofemale lines and then hybridize these
lines two or three generations prior to
release. However, this approach does not jus-
tify maintaining only a handful of isofemale
lines. In order to release a population that
has levels of genetic variability comparable
to a natural population, the minimum would
be 100 or more lines; however, maintaining
around 50 lines will perpetuate most of the
common genetic alleles.
Most of the data documenting the
genetic changes associated with captive
rearing and documenting the effect of these
changes on field performance are derived
from tephritid fruit flies used in SIT.
However, there is no reason to believe that
large-scale captive rearing of predators or
parasitoids is fundamentally different.
Indeed, many species of natural enemy are
difficult to rear, creating a high potential for
laboratory adaptation and for a large trade-
off with field performance. While none of
these tephritid studies can be considered
complete, the high-quality work carried out
on the melon fly illustrates the kinds of data
we should be gathering on commonly used
biological control agents.84 L. Nunney
References
Ahrens, E.H., Hofmann, H.C., Goodenough, J.L. and Peterson, H.D. (1976) A field comparison of two
strains of sterilized screwworm flies. Journal of Medical Entomology12, 691–694.
Aspi, J. (2000) Inbreeding and outbreeding depression in male courtship song characters in Drosophila
montana. Heredity84, 273–282.
Bartlett, A.C. (1994) Maintaining genetic diversity and laboratory colonies of parasites and predators. In:
Narang, S.K., Bartlett, A.C. and Faust, R.M. (eds) Applications of Genetics to Arthropods of Biological
Control Significance. CRC Press, Boca Raton, Florida, pp. 133–145.
Beckendorf, S.K. and Hoy, M.A. (1985) Genetic improvement of arthropods natural enemies through
selection, hybridization or genetic engineering techniques. In: Hoy, M.A. and Herzog, D.C. (eds)
Biological Control in Agricultural IPM Systems. Academic Press, Orlando, Florida, pp. 167–187.
Bijlsma, R., Bundgaard, J. and Boerema, A.C. (2000) Does inbreeding affect the extinction risk of small
populations? Predictions from Drosophila. Journal of Evolutionary Biology13, 502–514.
Boller, E. (1972) Behavioral aspects of mass-rearing of insects. Entomophaga17, 9–25.
Boller, E.F., Katsoyannos, B.I., Remund, U. and Chambers, D.L. (1981) Measuring, monitoring and
improving the quality of mass-reared Mediterranean fruit flies, Ceratatis capitataWied. 1. The
RAPID quality control system for early warning. Zeitschrift für angewandte Entomologie92, 67–83.
Burton, R.S., Rawson, P.D. and Edmands, S. (1999) Genetic architecture of physiological phenotypes:
empirical evidence for coadapted gene complexes. American Zoologist39, 451–462.
Bush, G.L. and Neck, R.W. (1976) Ecological genetics of the screwworm fly, Cochliomyia hominivorax
(Diptera: Calliphoridae) and its bearing on the quality control of mass-reared insects. Environmental
Entomology5, 821–826.