463 lines
26 KiB
Plaintext
463 lines
26 KiB
Plaintext
file: pestlock.doc
|
|
Derived from File: Azadirac.doc (alpha version)
|
|
<modified 20/11/1999>
|
|
|
|
|
|
Bigger IS better : why it is harder to evolve resistance against a complex
|
|
poison molecule than it is to evolve resistance against a simple one.
|
|
----------------------------------------------------------------------------
|
|
|
|
Since before the start of the 20th century, there's been an "arms race"
|
|
between pesticide manufacturers and their new killer chemicals, and the
|
|
target pests who eventually learn how to tolerate them. It always seems to be
|
|
that these synthetics are hailed as a silver bullet, but soon enough the
|
|
target organism learns to dodge it. Why might this be the case? And more
|
|
pertinently what might be the solution?
|
|
|
|
This doesn't just happen down on the farm, either. It occurs at all biological
|
|
scales. The physical size of the pest animal is irrelevant, since the war is
|
|
fought at a molecular level. The wars are being lost : there's plenty of
|
|
antivirals to which viruses are now resistant, bacteria which eat multiple
|
|
antibiotics for breakfast and survive, fungi which are not killed by
|
|
antifungal agents, insects which can happily metabolise insecticides all day
|
|
long, and plants which manage to survive despite an onslaught of herbicides.
|
|
|
|
(It is important that this happens. Some of the things we kill with our
|
|
nonspecific poisons are actually our allies, and we need every ally we
|
|
can get, but that's another issue.)
|
|
|
|
Many of the agents employed in the quest to kill various organisms are
|
|
extremely effective in their initial application, but less effective with
|
|
repeated use. All those drums of "Kill-O" in the shed which did great work
|
|
last year will underperform next year and be useless the year after that.
|
|
Why? The pests literally engineer a way out. But how do they do it? Why
|
|
can they do it? How do we stop them?
|
|
|
|
To define this problem further we will have to go down to the molecular
|
|
arena where these battles are fought out, and first gain an understanding
|
|
of what a poison actually does.
|
|
|
|
Enzymes, poisons, and the art of the evolutionary molecular locksmithing
|
|
------------------------------------------------------------------------
|
|
A useful aid to understanding the toxicological concepts without having to
|
|
drown oneself in the agonies of biochemistry is to use an analogy. Most of us
|
|
have a bit of a familiarity with locks, and although the analogy isn't exact
|
|
it can give you a good idea of what's going on.
|
|
|
|
Locks permit gates to be opened and closed by specific keys. In biochemistry
|
|
the gates have to open and close at specific times or, amongst other things,
|
|
nutrients and raw materials can't get where they need to go. As in real life
|
|
the the keys control the state of the locks, and the locks control the state
|
|
of the gates. Enzymes often combine the "lock" and "gate" in the one,
|
|
dual functional package.
|
|
|
|
As with locks, in biochemistry, you can have the locks and keys set up in
|
|
particular ways. If you have one gate and two locks in tandem, opening one
|
|
lock will open your gate even if the other lock is still locked. On the
|
|
other hand, you can have a gate with two locks in parallel, each on separate
|
|
hasps, so you need to unlock both locks at the same time to open the gate.
|
|
|
|
In nature, although you will occasionally find a setup where only one lock in
|
|
several needs to work for the gates to open and close appropriately, the
|
|
set-up is usually parallel, in the sense that all the locks must work or
|
|
the gate can't be opened and closed at the right times.
|
|
|
|
There is one significant difference in biochemistry: you CAN'T change the
|
|
keys, because the keys also happen to be very same nutrients and raw
|
|
materials that the gate will permit through it!
|
|
|
|
Locks are constructed a particular way, and will admit only certain types of
|
|
key - round keys on vending machine locks, U-shaped keys on Bi-lock locks,
|
|
your front-door lock takes a familiar brass Yale key into its keyhole.
|
|
Then, of the keys that fit, then only the one with the right wiggles on it
|
|
will open the lock.
|
|
|
|
It's a similar thing with the enzymes which run living things. They are
|
|
shaped a particular, specific way, will only let particular substances into
|
|
their gaps and crevices, and they are very choosy. Just as you can't fit a
|
|
round key into a lock with a U-shaped keyhole, you can't fit molecules into a
|
|
given enzyme unless they are shaped just right.
|
|
|
|
Nature would prefer that she could open and close her molecular locks and
|
|
biochemical gates as she sees fit. If she can't do it, certain gates are shut
|
|
or open when they shouldn't be, so valuable things escape, or nutrients can't
|
|
come in. Things die, simple as that.
|
|
|
|
It is useful to think of poisons as a kind of a dud key. Whereas normal keys
|
|
enable you to open or close a door by unlocking or locking a lock, the poison
|
|
key still fits the lock, but has to gum up the lock's working somehow so the
|
|
gate can't be opened ever again, or is locked open when it should be shut,
|
|
or whatever.
|
|
|
|
Poisons look similar to the usual stuff a protein interacts with, but are
|
|
different in some critical way which happens to ruin the protein. There are
|
|
many different interactions. To continue with our lock and key analogy,
|
|
it's as if a key has been filed in such a way that it jams against the pins
|
|
and won't come out, kind of like a dynabolt: it changes once it is inserted
|
|
so you can't pull it out again. This consequently means you lose control of
|
|
your gate - it is open or closed at inappropriate moments.
|
|
|
|
This sort of stuff happens when poisons interact with biochemical systems,
|
|
but nature can't change the keys!
|
|
|
|
It's worth noting that historically some locks were made with detector levers
|
|
in them... enabling them to be easily `poisoned' or made unopenable. If you
|
|
tried the wrong key, relockers were engaged and then NO key would open the
|
|
lock, including the correct one.
|
|
|
|
It seems now that a lot of our dud keys are in fact no longer jamming the
|
|
targetted locks. How do bugs get resistant to our dud chemical keys?
|
|
|
|
Nature changes the locks.
|
|
-------------------------
|
|
Nature isn't conscious in the conventional sense. It doesn't say, "Hmmm,
|
|
yeah, if I rip off a chlorine atom here I can neutralise this poison."
|
|
|
|
Instead, routinely, nature's organisms make hundreds of slightly different
|
|
versions of their locks - in this case, many versions of target enzymes in a
|
|
pest's biochemistry. All of these will still perform their usual biochemical
|
|
job, and most of these versions are messed-up by poison. However, because
|
|
organisms have twenty different types of amino acids to play with, in each of
|
|
several hundred positions in the target protein, they have an amazing range of
|
|
lock versions to potentially construct, and chances are that they can come up
|
|
with one which will still work with the original key, but which now won't
|
|
admit the dud key (poison) which jams up the lock.
|
|
|
|
The rate at which an organism comes up with a solution is related to a couple
|
|
of things, mainly how flexible the organism's improvisational locksmithing is,
|
|
and also how often the organism reproduces. Each member of the target
|
|
species has a slightly different plan for their own personal locks, which
|
|
still use the original key but varies in some other way, which might happen
|
|
to make it un-poisonable. Each new member gets a crack at accidentally
|
|
inheriting the lucky new lock variety, which still uses the original key
|
|
but which won't be wrecked by the dud one. What this means is that the more
|
|
often the bug species reproduces, the more bugs there are trying to figure
|
|
out what the work-around lock version should be, with each generation of
|
|
surviving bugs.
|
|
|
|
When this biochemical locksmithing problem is solved, the bug that solves it
|
|
reaps an enormous benefit. It not only is it now immune to the poison key but
|
|
almost all of its progeny have the design for the new locks encoded in their
|
|
DNA - resistance is hereditary - so they are immune too.
|
|
|
|
It all sounds wonderful, but there is a caveat.
|
|
|
|
If the dud key is complex, and very subtly made to simultaneously interact
|
|
with many parts of the lock, or worse still, interacts with many different
|
|
kinds of locks at the same time, nature has a much harder time of it and has
|
|
to devote serious, often unaffordable resources to build the new locks so it
|
|
can run its biochemistry again. It is then that other approaches tend to be
|
|
tried, such as systems which recognise dud keys and chop'em up, or which
|
|
pump the dud keys out of the organism.
|
|
|
|
It is here that the lock analogy breaks down a bit and we have to return
|
|
into the real world for a little while. There is another analogy which will
|
|
be useful, but I'll get to that when I come to it.
|
|
|
|
Humans make simple poisons, nature makes complex ones.
|
|
-------------------------------------------------------
|
|
So back to the molecular machinery of resistance in insects. Insects have
|
|
been under attack from many organisms for millennia, the most recent being
|
|
h.sapiens, which fancies itself a bit of an organic chemist, but we're nowhere
|
|
near as clever as Nature at this molecular art. Humans have synthesised and
|
|
sprayed all sorts of stuff around to kill insects, and other things.
|
|
|
|
Maybe some of the names will be familiar... alachlor, aldicarb, aldrin,
|
|
atrazine, benomyl, amitrole, 2,4-D, chlordimethiform, carbaryl, carbofuran,
|
|
chlordane, chlordimethiform, chlorvenifos, chlorpyrifos, chlorotoluron,
|
|
cyclodiene, DBCP, DDT, dicamba, dieldrin, dicrotophos, dimethoate, disulfoton,
|
|
endothall, fenthion, glyphos, heptachlor, hexazinone, lindane, malathion,
|
|
mancozeb, monocrotophos, oxychlordane, paraquat, permethrin, primicarb,
|
|
simazine, thiocarb, trifluralin, zineb.
|
|
|
|
You might notice a few sounds repeated. For example, chlor- means there
|
|
is one or more chlorine atoms in the stuff. It is interesting that halogens
|
|
don't show up very often in plant toxins. Phos- and fos- suggest a phosphorus
|
|
which is another atom which doesn't tend to show up in natural poisons either.
|
|
|
|
You might notice a few sounds are repeated frequently. For example,
|
|
chlor- appears several times. So does -phos, -azi, -thio/sulf. Thio and sulf
|
|
imply a sulfur, which is another uncommon atom in plant poisons, unless you
|
|
look at relatives of the onion and garlic familes which tend to use
|
|
non-protein sulfur compounds a lot. Pyr- suggests one of several rings with
|
|
nitrogen and carbon in them. Carb- suggests a member of a family of the
|
|
carbamate family.
|
|
|
|
A lot of these chemical "Leggo-blocks" show up time and again in humanity's
|
|
artificial synthetic pesticides.
|
|
|
|
There are others, but it doesn't matter that I omit them. I'm using the
|
|
phonetic similarity in the names to illustrate a structural similarity in the
|
|
pesticide molecules. If you looked at structural drawings of them, or even
|
|
had to wrestle with their special chemical names, you'd see similarities
|
|
there too.
|
|
|
|
The "dud" keys we use to jam nature's molecular locks have some commonalities.
|
|
|
|
They're simple, small and structurally fairly similar. Firstly, they
|
|
generally aren't very big, as far as molecules go. Also, since they are made
|
|
of heavy atoms, weight for weight, they aren't very complex compared to
|
|
equivalently heavy molecules made of lighter atoms. Look at something like
|
|
heptachlor - it's basically a loop of carbon atoms where molecular weight
|
|
is gained by bolting on a few fat chlorine atoms. The molecule has a lot
|
|
of similar and simple branches on it. Which raises a third point: synthetics
|
|
often they tend to have similar and simple structural backbones. Our
|
|
synthetic pesticides are all simple variations on the same themes, childish
|
|
molecular Leggo structures compared with the amazingly complex pesticidal
|
|
sculptures nature comes up with.
|
|
|
|
Complexity is determined by how much stuff you have to build with, and
|
|
also how configurable all the bits are. You can only build so much with five
|
|
bits of leggo, but nature dictates that by doubling the pieces of leggo, you
|
|
get far far more than double the number of ways of putting them all together.
|
|
You can, weight for weight, get many more permutations and combinations out
|
|
of a given mass of "light" C, O, H and N atoms than you can out of the same
|
|
mass of atoms like S, P, Cl and related "heavies". The total mass of the
|
|
leggo is not the issue - it is the complexity of its configuration.
|
|
|
|
Some of the reasons for this are that humans simply haven't been doing
|
|
chemistry for several million years and simply cannot cheaply make these
|
|
complex backbones which nature seems to do so easily and cheaply. So our
|
|
approach is, yeah, let's synth this, then drown it in nitriles or halogens or
|
|
something else amenable to synthesis by the bulk chemical synthetic methods
|
|
we humans tend to use.
|
|
|
|
In contrast, poisons plants make and use against bug attack are made naturally
|
|
and most of them are made out entirely of carbon, hydrogen, oxygen and
|
|
to a lesser extent nitrogen. These elements are also the main ingredients in
|
|
plant toxins with other atoms in them, like sulfur or bromine.
|
|
|
|
The reason for this is that probably N, P and S are environmentally scarce
|
|
and metabolically not worth the price of manufacture for defense purposes.
|
|
Phosphorus is so rare and presumably so precious to the organism's energy
|
|
(ATP) and information (DNA) metabolism, that it will not be allocated to
|
|
other tasks, because these energy and information metabolism functions are
|
|
so critical to the system that there would be a selection pressure against
|
|
an organism that didn't allocate P only to these critical tasks. Same for
|
|
sulfur, which is a critical component of many proteins but which is
|
|
relatively rare in the environment. From a plant's point of view, compared
|
|
to N, P and halogens, there's a stack of "cheap" carbon and oxygen around
|
|
with which to build complex stuff, so the plant making a toxin to defend
|
|
against attack is less pressured not to deplete these elements by using them
|
|
to make defensive chemicals.
|
|
|
|
On the other hand nature might just be better at complex carbon oxygen and
|
|
hydrogen chemistry than she is at complex sulfur phosphorus and nitrogen
|
|
chemistry. But that's not really central to the issue. The central issue is
|
|
the complexity.
|
|
|
|
Nature seems to rely more on taking whatever is lying around and building a
|
|
really complicated pest-repellent molecule, instead of building heavy, but
|
|
simple, molecule. The molecules which nature uses as pest repellents, if they
|
|
are heavy, get this way by being complicated artworks of light atoms, rather
|
|
than being structurally simple molecules with heavy atoms attached to them.
|
|
|
|
Simple vs Complex Dud Keys
|
|
--------------------------
|
|
So what? Why should the complexity of a poison matter? It's the interactions.
|
|
|
|
A large, complex poison molecule will necessarily interact with many parts
|
|
of its target enzyme at once. The ultimate poison key is something which
|
|
interacts with a lot of the lock components and renders them useless, e.g. a
|
|
squirt of adhesive from a hot glue gun, all the way up the inside of the lock,
|
|
will jam up that lock in a much more irreparable way, than will a wad of
|
|
chewing gum stuck shallowly in the keyhole.
|
|
|
|
Putting a bubble-gum shield on keyhole is easy: add-on a strip of teflon, and
|
|
the gum can't stick to the lock, but you can still use the original keys.
|
|
|
|
Compare this simple bubble-gum-repulsion problem, to the problem of
|
|
redesigning a lock to keep liquid epoxy out of the keyhole, the broach, all
|
|
the little pins and springs, and out of the surface where the lock barrel
|
|
turns inside the lock body- it's a screaming nightmare if you need to
|
|
continue to use the existing keys, which demands that there remains a open
|
|
hole in the lock through which the existing key (or the deadly hot glue) can
|
|
be inserted.
|
|
|
|
Hot glue is a hell of a poison for locks, because it gets intimate with so
|
|
much of the guts of just about any mechanical lock you can build. Once inside
|
|
it forms a complex shape which happens to match all the inner surfaces of the
|
|
lock guts. To get around this, the design of the locks must be radically
|
|
changed to keep the glue out. This change is so radical, it means you also
|
|
need a kind of key which you don't have to actually insert into the lock.
|
|
|
|
There are locks immune to hot glue. They lack keyholes and their key is a
|
|
specially constructed blade of plastic, which contains embedded magnets.
|
|
The magnetic field passes through the wall of the lock directly, and needs no
|
|
keyhole. You can drown the magnetic lock in as much glue as you want but it
|
|
will still work. Magnetic locks are immune to destruction by hot glue guns.
|
|
|
|
The price we paid for locks immune to a hot-glue poisons, was thet we had to
|
|
change not only the lock, but also change all the keys too, because all the
|
|
old brass keys don't work in the new locks. When locksmiths first made
|
|
magnetic locks they had to start using unfamiliar materials like plastics
|
|
(they used to work with metals and ceramics) and they had to learn about
|
|
magnetism, which was a considerable lot of new stuff to learn. The magnetic
|
|
locks were expensive to construct because the tools needed to make them were
|
|
very different to the tools via which the usual metal locks were made.
|
|
Of course, the new magnetic locks didn't work with all the old brass keys so
|
|
they keys all had to be changed too.
|
|
|
|
But nature can't change keys, she is constrained to continue to build
|
|
locks which are susceptible to ruin by complex poisons. The very nature of
|
|
the existing keys render the locks vulnerable to a complex attack.
|
|
|
|
This means, from an evolutionary point of view, that to get around a complex
|
|
poison, MANY changes need to be made to the target enzyme, all at once. On
|
|
top of this is the need to maintain the ability to use the existing key. This
|
|
is a much bigger ask, just like the design of a lock immune to hot glue.
|
|
|
|
Each interaction adds itself to the list of problems which need to be solved
|
|
to enable the lock to work again, and they *ALL* need to be solved together.
|
|
|
|
It can take the target insects or plants (or whatever) decades, even
|
|
centuries to solve such a problem - sometimes they don't ever solve the
|
|
problem (basically they run out of time) and slide into extiction.
|
|
|
|
[An alternative strategy is the messing-up of more than one lock at the same
|
|
time. Sure enough, you find multiple toxins in the same plants. This is an
|
|
even bigger ask, because the pest has to evolve several new locks all at
|
|
once. Look at plants like barley, onions, horseradish, carrots, tomatos.
|
|
They have at least four phytotoxins in them. Look at the common spud, got
|
|
about 9 of them too. We usually get around them by cooking the food or
|
|
otherwise destroying the toxicity. Most pests don't do this.]
|
|
|
|
Well if nature is so smart, it probably knows that complex poisons are more
|
|
useful and give a better return on the biological resources used in their
|
|
development. Does nature tend to use simple or complex poisons? What sort of
|
|
pesticides do plants use against the bugs which suck their sap and eat their
|
|
leaves?
|
|
|
|
Nature makes complex poisons
|
|
-----------------------------
|
|
The hypothesis that the pesticide companies would need be unable to falsify,
|
|
in order to prove that their stuff is as difficult to get resistant
|
|
to as the sort of complex agents nature has taken millions of years to
|
|
patiently evolve, is that
|
|
|
|
"natural complex pesticides exhibit the same resistance problems as our
|
|
simple synthetic ones."
|
|
|
|
I think the hypothesis has already been falsified anyway, however, in the
|
|
course of Nature's ordinary problem-solving. Nature presumably knows about
|
|
resistance, after all, various organisms have been fighting chemical wars
|
|
against each other long before we ever came down from the trees. The bacteria
|
|
and fungi have, particularly, been fighting for aeons - we use the weapons
|
|
that the fungi provide in our wars against bacteria, most of our antibiotics
|
|
are derived from moulds and other organisms in the fungal realm.
|
|
|
|
If nature "thinks" big molecules are harder to get resistance too, then they
|
|
should be more common in her armament of poisons, than small and simple
|
|
molecules. The payoff for designing a poison is then greater, because it
|
|
defends the designer for a longer period in evolutionary time. The payoff is
|
|
greater than the cost of developing it.
|
|
|
|
Nature also knows that it takes considerable effort to evolve these things,
|
|
and tends to not go over the top by simply bolting on more complexity than
|
|
is absolutely warranted in keeping the pests guessing.
|
|
|
|
So what to expect? Well, few simple poisons, many complex poisons, and a few
|
|
really complex nightmares. Such a profile will reflect two things ...
|
|
|
|
1) nature CAN synthesise complex poisons against pests, when it is worth the
|
|
effort to prevent resistance over evolutionary time, and
|
|
2) will reach a plateau of complexity when the chemistry becomes too
|
|
metabolically expensive or synthetically intractable.
|
|
|
|
It also has to be remembered that it does the defending organism no good to
|
|
get poisoned by its own defensive chemicals, which further constrains its
|
|
scope for engineering poisons against pests.
|
|
|
|
A rough guide, a fingerprint to look for, is the preponderance of carbon in
|
|
the sorts of molecules which plants tend to use as poisons against various
|
|
pests.
|
|
|
|
I happened to pick up an expensive book at a half price sale some years ago,
|
|
called the Dictionary of Plant Toxins. It happens to list in the back the
|
|
molecular formulas of the molecules in the whole dictionary, in increasing
|
|
numerical order, starting with the number of carbon atoms in the poison.
|
|
|
|
Some of the molecules in this count are not toxic to things against which the
|
|
plant has had to compete - for example, there are plant toxins here which
|
|
kill tumor cells in mice, and plants don't have to compete against mouse
|
|
tumor cells. But most of these are toxins made to help the plant survive
|
|
attacks by insects, fungi, parasites, plant viruses, bacteria, grazing
|
|
animals, and even nearby competing plants.
|
|
|
|
I counted 'em up. What do we see?
|
|
|
|
# of Carbons : 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
|
|
Listed toxins: 2 5 2 9 6 16 14 25 15 51 51 36 34 51 169 80 78 52 66 114
|
|
|
|
# of Carbons : 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
|
|
Listed toxins: 75 68 28 21 17 16 35 10 34 32 17 25 8 13 19 21 10 12 5 9
|
|
|
|
# of Carbons : 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
|
|
Listed toxins: 19 7 4 1 8 10 9 7 3 3 2 0 1 1 3 1 1 1 1 2
|
|
|
|
Summary: a number moderately simple toxins (less than 10 carbon atoms)
|
|
A hell of a lot of complex toxins (Between ten and forty carbon atoms)
|
|
Very few extremely complex toxins (more than forty carbon atoms)
|
|
|
|
Pretty much what you might expect. It's a trade-off between effectiveness and
|
|
the molecular engineering difficulty associated with making a really complex
|
|
poison. Hey, YOU try and synthesise a complex molecule with 40 carbon atoms
|
|
in it, starting with sunlight, water and carbon dioxide! There is a bit of
|
|
bias in the low end, you just can't make much complex stuff with three carbon
|
|
atoms. You can make plenty of things with five, and more with oxygen and
|
|
nitrogen
|
|
thrown in.
|
|
|
|
The data has been available for years for anyone to look. It probably has
|
|
some sample biases (like, protein poisons are very complex but not hard to
|
|
make) but I don't think this matters : it was just a bunch of plant poisons
|
|
listed in a toxicological dictionary. It happens to fit what we might have
|
|
expected if the evolutionary economics of natural synthesis of plant
|
|
pesticides were subject to the sorts of trade-offs 1) and 2) outlined a few
|
|
paragraphs above.
|
|
|
|
Ag-pesticide companies tell us they know their chemistry, we know they have
|
|
business acumen. You might want accuse the pesticide companies of knowing
|
|
this trend and deliberately only designing simple poisons so you have to go
|
|
and buy another one when the last simple one you got became worthless due to
|
|
the appearance of resistance.
|
|
|
|
It's a kind of inbuilt obsolescence at the molecular level. It happens to
|
|
benefit the chem companies that this is the case. But I never attribute to
|
|
malice what can adequately be attributed to stupidity. In this case, it's
|
|
stupidity. We just don't yet know how to cheaply make really complex
|
|
pesticides to which it is hard for the target organisms to get resistant.
|
|
|
|
Nature has, incidentally, solved the complexity-of-synthesis issue in a
|
|
novel way : modularity. It knows how to synthesise twenty or so amino acids;
|
|
but since these amino acids can be daisy-chained by a single, uniform
|
|
mechanism, it can make an unlimted number of possible proteins simply by
|
|
bolting the amino acids together in different sequences. There is no need to
|
|
come up with new chemistry for each new protein, it is simply a matter of
|
|
changing the order in which the well-known reactions occur. Like a Rubik's
|
|
Cube, you only have six colours to choose from, but depending on the way
|
|
you configure the cube you can have billions of combinations of colours, and
|
|
getting them is a simple matter of twisting the faces - any child can do it.
|
|
Protein synthesis still remains a fairly tricky feat of peptide biochemistry,
|
|
we generally employ recombinant bacteria to do it for us because it's
|
|
something we humans just can't very easily or successfully do in a test tube.
|
|
|
|
I'm a synthetic organic chemist, and I know it is terribly, terribly hard
|
|
to synthesise complex molecules. Its possible, but the cost in unwanted
|
|
byproducts is just too much to make the final pesticide affordable. There is
|
|
another advantage. Biological poisons generally biodegrade, and don't
|
|
become long term stable environmental contaminants like most of the
|
|
organochlorines and organophosphates used in the last five decades. Throw in
|
|
the requirement for biodegradeability and we're synthetically and
|
|
economically pretty well sunk. By comparison, all of nature's poisons are
|
|
ultimately biodegradeable.
|
|
|
|
So what to do? Use nature's chemicals against pests
|
|
----------------------------------------------------
|
|
|
|
I think the way of the future is clear - stop using simple synthetics and
|
|
instead, extract complex pesticides from natural sources. Nature is a much
|
|
better pesticide chemist than humanity, after all.
|
|
|
|
-Mike Carlton
|