s ubs tance and introduced into the natural environment of the fly; ins ects feeding on it would
become s terile and in the cours e of time the s terile flies would pre dominate and the ins ects
would breed the ms elves out of existence. The testing of chemicals for a sterilizing effect is
much more difficult than the tes ting of chemical pois ons. It takes 30 days to evaluate one
chemical—although, of cours e, a number of tes ts can be run concurrently. Yet between April
1958 and December 1961 s everal hundred chemicals were screened at the Orlando laboratory
for a possible sterilizing effect.
The Department of Agriculture s eems happy to have found among thes e even a handful of
chemicals that show promise. Now other laboratories of the Department are taking up the
problem, testing chemicals against stable flies, mosquitoes, boll weevils, and an assortment of
fruit flies. All this is pres ently experime ntal but in the few yea rs since work began on
chemos te rilants the project has grown enormous ly. In theory it has many attractive features.
Dr. Knipling has pointed out that effective chemical insect sterilization ‘might easily outdo some
of the best of known insecticides.’ Take an imaginary situation in which a population of a
million insects is multiplying five times in each generation. An insecticide might kill 90 per cent
of each generation, leaving 125,000 insects alive after the third generation. In contrast, a
chemical that would produce 90 per cent s terility would leave only 125 insects alive.
On the other side of the coin is the fact that some extremely potent chemicals are involved. It is
fortunate that at least during thes e early s tages mos t of the men working with che mos terilants
s eem mindful of the need to find s afe chemicals and s afe methods of application. Nonetheles s ,
s ugges tions are heard here and there that thes e s terilizing chemicals might be applied as aerial
s prays—for example, to coat the foliage chewed by gypsy moth larvae. To attempt any such
proce dure without thorough advance res earch on the hazards involved would be the height of
irresponsibility. If the potential hazards of the che mos terilants are not cons tantly borne in mind
we could eas ily find ours elves in even wors e trouble than that now created by the ins ectic i des.
The s terilants currently being tes ted fall generally into two groups , both of which are extremely
interes ting in their mode of action. The first are intimately related to the life processes, or
metabolism, of the cell; i.e., they so closely resemble a s ubs tance the cell or tis s ue needs that
the organis m ‘mis takes ’ them for the true metabolite and tries to incorporate them in its
normal building proces s es. But the fit is wrong in s ome detail and the proces s comes to a halt.
Such chemicals are called antimetabolites.
The s econd group cons is ts of chemicals that act on the chromos omes , probably affecting the
gene chemicals and causing the chromos omes to break up. The che mos terilants of this group
are alkylating agents, which are extremely reactive chemicals, capable of intense cell
des truction, damage to chromos omes , and producti on of mutations. It is the view of Dr. Peter
Alexander of the Ches ter Beatty Res earch Ins titute in London that ‘any alkylating agent which is
effective in sterilizing insects would als o be a powerful mutagen and carcinogen.’ Dr. Alexander
feels that any conceivable us e of s uch chemicals in ins ect control would be ‘ open to the mos t
s evere objections ’. It is to be hoped, the refore, that the pres ent experime nts will lead not to
actual us e of thes e particular chemicals but to the dis covery of others that will be safe and also
highly specific in their action on the target insect....
Some of the mos t inte res ting of the recent work is concerned with s till othe r ways of forging
weapons from the ins ect’s own life processes. Insects produce a variety of venoms, attractants,
repellents. What is the chemical nature of thes e secretions? Could we make use of them as,
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