Biology Reference
In-Depth Information
This approach to genetic control has been called the
Sterile Insect Release
Method
(
SIRM
) or the
Sterile Insect Technique
(SIT)
. Male insects are mass reared
and sterilized, usually by irradiation, and released. By releasing approximately
100 sterile males for each wild male, wild females should mate most often with
sterile males (assuming equal fitness), resulting in reduced numbers of prog-
eny. [Why does the program manager need to have a good estimate of the
population size of the wild species in order to release the appropriate number
of sterile males?] The SIRM program is most effective when females mate only
once, but can be successful with species that mate more than once if sufficient
numbers are released over a sufficiently long time. Serious pests, including the
Mediterranean and Caribbean fruit flies, mosquitoes, and the New World screw-
worm,
Cochliomyia hominivorax
, have been controlled or eradicated in these
genetic-control programs (
Tan 2000
).
A significant example of the SIRM is the eradication of the New World screw-
worm from the United States (see Chapter 10, Box 10.1). Later the program was
expanded to eliminate
C. hominivorax
from Central America to provide a buffer
zone to preclude its reintroduction into the United States. Benefits of the SIRM
program in 1996 to U.S., Mexican, and Central American cattle producers were
estimated to be US$796 million, US$292 million, and US$77.9 million, respectively
(
Wyss 2000
). The benefit-to-cost ratios for the eradication programs ranged from
an average of 12.2 to 1 for Central America to 18 to 1 for the U.S. and Mexican
programs (
Wyss 2000
). In addition, screwworm eradication has a significant
human and wildlife health component not included in these calculations.
14.4 Why Use Molecular-Genetic Methods?
Traditional genetic methods have limitations and molecular-genetic methods
offer new opportunities for improving pest-management programs. Such poten-
tial benefits were perceived by many shortly after the seminal publication on
P
-element transformation of
Drosophila
by Rubin and Spradling in 1982. For
example, significant benefits could accrue if molecular-genetic methods allowed
sterile insects to be produced without incurring the negative effects of irradia-
tion. During the sterilization process, the insect's whole body is irradiated, which
produces damage in all tissues. As a result, the SIRM requires that large num-
bers of insects be reared for release. Often, pest populations first are reduced by
pesticide applications or through natural seasonal (winter) mortality so that the
number of insects that have to be reared can be reduced. Rearing huge numbers
of sterile insects requires effective mass-rearing methods and costly facilities.
Another issue is whether females should be reared and released; eliminating
females using genetic methods is another desirable goal.
