Extracts from "Agricultural production and malaria resurgence in Central America and India" by Georganne Chapin and Robert Wasserstrom published in
Nature Vol 293 17 September 1981 pages 181--185
Among the inhabitants of Asia, Latin America and tropical Africa
malaria, remains a major cause for alarm. Yet only a few years ago,
health officials in a dozen developing countries (capitalizing on the
discoveries of British parasitologist Ronald Ross half a century
earlier) pointed triumphantly at their efforts to eradicate entirely
this mosquito-borne scourge[1-5]. Following World Health Organization
(WHO) guidelines, for example, Indian authorities instituted a
programme of medical treatment and pesticide application in 1952 which
within a single decade reduced the number of cases from over 100
million to 50,000 (ref. 6). Ten years later, using the same methods,
health workers in Sri Lanka cut the annual incidence of malaria from
three million cases to fewer than 25.
By 1970, however, it had become clear that malaria eradication had run
into severe difficulties. Instead of dwindling to insignificance, the
number of infected individuals rose again to distressing
proportions. In India, which had served as a showplace for WHO
policies, five million people were soon infected; in Sri Lanka, two
million people became sick again almost overnight; and in Central
America infection rates grew to previously unknown
levels. Moreover, unlike earlier outbreaks, this new plague was
often carried by mosquitoes which had become resistant to pesticides
like DDT and dieldrin and could not be controlled by conventional
means[8-15]. The origins of this major ecological disaster must be
sought as much in the unwitting actions of international organizations
as in hapless nature.
A seeming success
It is worth noting that early programmes to contain parasitic diseases
primarily malaria and yellow fever --- achieved remarkable success
without recourse to sophisticated technologies. Efforts to
overcome malaria before the Second World War concentrated on the ways
in which mosquitoes of the Anopheles subfamily transmit Plasmodium
parasites to human beings. After reproducing in astronomical numbers,
these parasites transform their human hosts into a reservoir of
illness which may be spread to uninfected individuals.
In 1907, Dr William Gorgas, an American Army surgeon in the Panama
Canal Zone, set out to break this cycle by draining swamps, emptying,
covering or oiling pools of standing water and screening human
habitations. Although he was unable to eradicate the disease
completely, within two years the death rate from malaria among canal
company employees had fallen to 8.86 per thousand --- a decrease of 80
per cent. More or less simultaneously an Italian physician, Dr Angelo
Celli, noticed that in southern Europe the disease tended to attack
people who were either poor or landless, particularly those who worked
as seasonal labourers on certain large farms. He reasoned that
transmission depended to a considerable degree on the flow of fresh
human blood into malarious zones just as the Anopheles population
began its annual explosion. Not only sanitary measures and medical
treatment, then, but land reform and other social programmes might
play a substantial part in conquering the disease.
By the end of the Second World War, however, it seemed that a
technology had finally been devised that could eliminate malaria in
much of the non-Western world: chemical pesticides. Insecticides like
DDT and dieldrin were not only cheap and easy to use, but they also
remained active for several months after each application. For
this reason, they appeared to be ideally suited for the task of
killing Anopheles mosquitoes, which characteristically rested for a
short time on the inside walls of human houses after biting their
victims. By spraying walls with DDT, WHO officials reasoned they could
reduce the vector population to manageable levels. Simultaneously,
they proposed to treat everyone affected by the disease with
chloroquine or other anti-Plasmodium drugs so as to destroy the
reservoir of disease. If these conditions could be maintained for
three or four years, they calculated, malaria transmission might be
broken forever. Moreover, projects of this sort could be carried out
without altering political arrangements or patterns of land tenure.
Despite the simplicity of the plan, WHO officials were aware that a
worldwide campaign to eradicate malaria would face nearly
insurmountable obstacles. In many regions, control programmes were
virtually non-existent, and even those that did exist suffered from a
lack of funds, technical expertise and administrative efficiency. But
there was another obstacle which experts at WHO were more reluctant to
engage: as early as 1953, they obtained conclusive evidence that
Anopheles mosquitoes, like many insect pests, sooner or later became
resistant to DDT and other pesticides. Within a few years, in fact,
such resistance had been reported in Greece and Italy (where
insecticides were used both in public health and in agriculture) as
well as in the Lebanon, Iran, Saudi Arabia and Nigeria. In some cases
a single application was sufficient to reduce mortality (that is, in-
crease resistance) among mosquitoes by 80 per cent. Accordingly, WHO
malariologists urged their local counterparts to conduct
"time-limited" spraying operations --- to complete the "attack" phase
as quickly as possible.
Thus, anti-malaria teams were directed to treat the interior walls of
all human habitations and shelters within the target zone on a regular
schedule --- a gargantuan task under the best of circumstances.
Meanwhile, by organizing an elaborate system of regional laboratories
and clinics, public health officials were supposed to administer
chemotherapy and monitor the campaign's progress. In areas where these
tactics proved to be successful, where the number of active cases
diminished to zero, attack gave way to consolidation. And if no new
illness occurred during the following three years, consolidation was
in turn replaced by maintenance, the constant vigil against a
recurrence of infection. This strategy was adopted in 1954 by the Pan
American Health Organization (PAHO) and subsequently by the entire
Initially, at least, it seemed that WHO'S campaign enjoyed almost
unmitigated success. In India, after ten years of struggle against
malaria (1961), only 50,000 cases of the disease were uncovered by
government inspectors and a number of regions had passed from attack
to consolidation or maintenance. Similar triumphs were registered in
Pakistan, Sri Lanka, Paraguay, Venezuela, Mexico and Central America.
In ten other countries, Plasmodium infection was completely
Within a short time, however, the campaign began to falter. Between
1961 and 1966, disease rates in India increased threefold; by 1970,
half a million people caught malaria each year many in areas where
health authorities had recently scored impressive victories. Much the
same course of events took place in Sri Lanka, which in 1968
experienced an epidemic that left 1.5 million people stricken. On the
other side of the world, in El Salvador, Nicaragua and Honduras (where
anti-malaria measures began in the late 1960s), the incidence of
disease in 1975 was three times greater than a decade earlier, before
the programme had started (Table 1). As a result, eradication projects
which had reached consolidation frequently reverted to the attack
phase --- or even entered the newly defined stage of "permanent
attack". Even so, it soon became clear that there was a major
resurgence of malaria in India and Central America that existing
administrative and technological methods could do little to
prevent[19-24]. The question which malariologists in these areas then
asked themselves was quite simply, "What has gone wrong?".
In fact, as early as 1962 a number of specialists had expressed their
reservations about the WHO campaign and its chances of success. Among
other things, they pointed out that as infection rates dropped during
the attack phase, hard-pressed governments often diverted critical
resources from anti-malaria activities to other essential
projects[25,26]. As a result, many infected people were not detected
by surveillance systems, which themselves broke down under poor
management and supervision. Even more ominously, however, resistance
to DDT and dieldrin had reached alarming proportions among Anopheles
mosquitoes --- just as WHO officials had originally feared[27,28].
The case of El Salvador is illuminating. In 1958 a group of
entomologists reported that the local vector. Anopheles albimanus,
had lost its susceptibility to all major organochlorine compounds and
was proliferating rapidly along the Pacific coast[29-30]. Four years
later, researchers in southern Mexico encountered the same problem,
which forced them to admit that the disease had not been eradicated in
several areas. In India, widespread tolerance to organochlorine
was discovered among two important vectors, Anopheles culifacies and
Anopheles fluviatilis, particularly in regions which had recently
shifted to high-yielding forms of agricultural production.
In such places, effective control might be regained only by using
insecticides which cost four, five or even ten times as much as common
toxins --- a burden which few governments were willing to
bear. Yet even measures of this kind might serve at best only as
temporary expedients: vectors which became resistant to one compound
frequently enjoyed mysterious immunity to other unrelated poisons, and
in any case it was only a matter of time before natural selection
favoured those insects which could withstand a broad spectrum of
chemical agents[34-36]. Faced with these problems, in 1973 WHO
officials reluctantly transformed the Malaria Eradication Division
into the Division of Malaria and other Parasitic Disease[37,38].
Increased pesticide use
In these circumstances, it is not surprising that the death rate from
infectious and parasitic diseases in Central America has remained
extremely high and that the incidence of malaria has generally in-
creased --- despite an impressive diminution in the late 1960s and
early 1970s. The relationship between fibre production and the
recrudescence of malaria has been clearly established in a study by
the United Nations Environmental Programme and the Institute
Centro-americano de Investigacion y Tecnologia Industrial
(ICAITI). To combat cotton pests and to raise yields, planters in
Guatemala, Nicaragua and El Salvador have not only expanded their
acreage, but since 1970 they have also applied heavier concentrations
of pesticides. Whereas a decade ago, fields were sprayed only eight or
nine times each season, they must now be fumigated on as many as 50
occasions. Consequently, the amount of pesticide which enters the
local ecosystem has expanded at an increasing rate.
In 1971, for example, farmers in El Salvador sprayed 58.4 kilos on
each hectare of cotton; three years later, applications had reached
70.0 kg per hectare. As a result, DDT consumption in El Salvador
increased threefold between 1970 and 1977 --- from 555,200 kg to 1.6
million kg. Similar circumstances prevailed in Nicaragua, where DDT
imports rose from 29,000 kg in 1974 to 521,600 kg in 1976.
Naturally, the importation of pesticides on this scale could be
accomplished only as long as cotton revenues offset the rising cost of
toxins. Fearful that unstable prices and soaring expenses might soon
cut their earnings and anxious to maximize the returns on their
investments, many growers have attempted to achieve total control of
insect parasites --- an obsession which has only enhanced their
reliance on expensive. chemicals. Correlating the use of DDT in El
Salvador with renewed malaria transmission, it can be estimated that
at current rates each kilo of insecticide added to the environment
will generate 105 new cases of malaria[47-49].
Ironically, Anopheles resistance in India has developed even in areas
where cotton is grown on relatively small plots of land or where food
grains --- primarily rice --- still predominate. In Tamil Nadu, for
example, most farmers (77.5 per cent) own less than one hectare; few
possess more than two50. Even so, these men (and their counterparts
in Maharashtra and Gujarat) produce nearly one-third of the country's
cotton and an impressive share of its rice[51,52]. By 1968, too, the
incidence of malaria in this region had decreased to insignificance
--- indeed, in Tamil Nadu, the disease was largely confined to urban
areas such as Madras[53-56]. Within a few years, however, public
health officials throughout southern India reported that mosquitoes of
both the Anopheles and Aedes subfamilies (the latter transmit
yellow fever) had become resistant to a wide variety of chemicals
including DDT, BHC, malathion (an organophosphate) and propoxur (a
Resistance to pesticides
Indisputable evidence is not yet available but it appears that
resistance began to occur with the introduction of green revolution
technology --- particularly of high-yielding varieties (HYV) of rice
(Fig.l). According to entomologists at the Vector Control Research
Centre in Pondicherry, "the major changes that have been taking place
in the area are in the tremendous increase of acreage under
cultivation, the near total replacement of organic manure by chemical
fertilizers and the extensive use of insecticides for paddy and other
crops". It should be noted that the new strains of rice have been
adopted primarily by wealthy landowners and have proved to be
especially susceptible to insect infestation[63-66].
Recent studies in Tamil Nadu indicate that families which own two
hectares or more (7.2 per cent of the total number) alone possess the
means to purchase HYV seeds, fertilizers and pesticides[67-69]. As
Figs 2 and 3 suggest, such farmers have responded to increased
infestation by applying heavy doses of DDT, BHC and dieldrin --- a
procedure which is closely related to the recent explosion of malaria
in the region. Significantly, as these growers have switched from DDT
to more sophisticated chemicals, traditional vectors have been
replaced by rarer species which in turn show a diminished sensitivity
to such poisons. Little wonder, therefore, that as early as 1972 the
Indian Journal of Public Health warned that "the most serious threat
to public health ... is the uncontrolled use of pesticides for
There seems to be a three-stage relationship between the evolution of
cotton agroecosystems and the spread of malaria. During the first
stage, eradication programmes are more or less effective and often
permit farmers to exploit previously infected areas. An example is to
be found in eastern Paraguay, where landless peasants from so-called
overpopulated regions have been encouraged to clear and colonize
"uninhabited" jungle in which malaria is endemic. The Paraguayan
government has made great efforts to eliminate the Plasmodium parasite
--- as a stimulus to both immigration and productivity. Among its
primary objectives, the production of cotton and tobacco (also a heavy
user of pesticides) for export occupies a pre-eminent position. By
1978, these two crops provided over 27 per cent of the country's
foreign exchange. Having prepared vast expanses of virgin forest for
commercial exploitation, however, peasants in many areas have begun to
abandon their farms and to look for wage labour elsewhere. As their
lands are consolidated into larger holdings, such areas will
inevitably be treated with intensive applications of DDT or dieldrin.
These lands will therefore probably come to resemble many parts of
Central America (stage two), in which the high price of cotton appears
to justify augmented doses of pesticides. Malaria transmission will be
stimulated most markedly among migrant workers and impoverished
peasants. Perhaps in anticipation, PAHO has already commissioned a
study in Paraguay, The Impact of Malaria on Economic Development,
according to which seasonal increases in Plasmodium infection do not
interfere with cotton or tobacco cultivation --- although they may
wreak havoc on food production. Finally, in places like India,
Pakistan and Bangladesh (stage three), more and more DDT must be
sprayed simply to maintain a fixed yield (Fig. 4). In this case,
pesticide addiction and a full-fledged epidemic of malaria have
entered their most destructive phase.
So must countries such as India and El Salvador cease to grow cotton
and high-yielding food grains? Can foreign currency be obtained only
at the expense of widespread malnutrition and disease? It is
instructive to examine how such crops are produced in the United
States. American farmers who started raising cotton with only small
quantities of insecticides found that insect pests reappeared in their
fields almost as soon as the fumigators departed[74-78]. Most often,
they responded by applying stronger poisons with greater frequency
until they were spraying every two or three days for five
months. The side effects had by then become apparent: cattle
fodder had to be destroyed because it contained pesticide residues too
high to be fed to animals while crops that had never suffered severe
infestations were suddenly devastated by previously innocuous
Integrated pest management
In response, entomologists developed what they call integrated pest
management systems[85-86], the key to which lies in timing insecticide
applications so that the crop is protected from predators only at the
most vulnerable stages of its growth cycle. As it turns out, cotton
buds destroyed by pests regrow throughout the plant's life, so that
producers can afford to sustain a high level of insect damage before
there is a need to apply pesticides. Simple precautionary measures may
also lower their chemical costs: up to 75 per cent of the hibernating
boll weevil population may be eliminated by the ploughing under of
crop debris after harvest. Thus many growers west of the Mississippi
now spray their fields only seven or eight times each season instead
of 25 or 30; similar measures have been developed for raising corn,
rice and many kinds of fruit.
So why did WHO not urge cotton producing countries to employ
integrated management systems that would not interfere with malaria
eradication programmes? A possible answer may perhaps be found in the
activities of another international agency, the Food and Agricultural
Organization (FAO). Like WHO, FAO was established to provide
technical advice and assistance to members of the United Nations. In
the case of pesticides, which are manufactured and distributed by a
few multinational corporations, FAO's advice might have played a
critical role in reducing environmental contamination. Both farmers
and extension agents in developing nations must normally rely on
pesticide company salesmen for information about how to use
agricultural chemicals --- much as physicians in Western countries
rely upon pharmaceutical companies for information about new
drugs. Beginning in 1967, therefore, FAO put together a small working
group of experts on integrated pest management which published
technical manuals and disseminated other information[88-94].
Three years later, it commissioned an American entomologist, Dr Louis
Falcon, to develop an integrated system in Nicaragua, a system which
achieved remarkable success within a few seasons. Similar programmes
were subsequently undertaken in Mexico, Peru and Pakistan. Then, in
1975, FAO delegates met in Rome to consider the question of pesticides
in agriculture and public health. Although they recognized that
integrated pest management offered a potential solution to many health
problems, they recommended that FAO place its emphasis on teaching
growers in developing nations how to make more "safe and efficient"
use of pesticides[96,97].
Whys and wherefores
Why did FAO choose this course of action, which in retrospect does not
appear to have been guided by an accurate appreciation of the perils
of pesticide addiction? It is important to examine how pesticide
manufacturers have influenced the policies of international
agencies. As public concern about the effects of toxins like DDT began
to grow in the 1960s, these corporations formed a trade association
called GIFAP (Groupement International des Associations Nationales de
Pesticides) which in turn worked directly with UN technicians through
a FAO bureau known as the Industry Cooperative Programme (ICP). By the
early 1970s joint FAO-ICP regional seminars had been organized in many
parts of the world to promote new and better ways of distributing
agricultural, pesticides. More important, high-level officials in WHO
and FAO, who share the industry's views on many major issues, invited
GIFAP to play an active part in agency "consultations" and other
internal meetings[98,99]. In this way, for example, no fewer than 25
corporate representatives lent their expertise to the meeting in Rome
on pesticides in agriculture and public health and served on
subcommittees responsible for formulating UN policy. Not
surprisingly, these subcommittees stressed the need to apply more
pesticides in a more effective manner rather than to limit their use
or replace them with alternative forms of pest control. And what is
more curious, none of these deliberations included representatives
of other international constituencies such as environmental groups,
labour unions or farmers' organizations. Perhaps for these reasons, in
June 1978, the current director general of FAO, Eduard Saoumi, finally
expelled ICP from his agency.
In 1976, WHO published a technical report entitled Resistance of
Vectors and Reservoirs of Disease to Pesticides. In this report,
WHO'S Expert Committee on Insecticides declared that "resistance is
probably the biggest single obstacle in the struggle against
vector-borne diseases and is mainly responsible for preventing
successful malaria eradication in many countries .... Evidence has
also accumulated to show conclusively that resistance in many vectors
has been caused as a side-effect of agricultural pesticide
usage". Accepting this unhappy fate, the report concluded that "vector
control was likely to depend on substantial, continued use of
pesticides for at least a decade". In these circumstances, it foresaw
no alternative but to "encourage commercial firms to continue the
search for pest control, especially compounds with a novel mode of
action". And yet, as many specialists have pointed out, such compounds
are unlikely to resolve this dilemma or to undo the damage which
in-bred tolerance has already caused: detoxification appears to rely
on physiological processes which are both irreversible and difficult
to disrupt. In effect, throughout southern India, the recrudescence of
malaria now represents a social cost of growing high-yielding rice ---
just as elsewhere in India and Central America it represents a social
cost of producing cotton.
See also correspondence on this paper.
Recent developments in cotton pest management
Biotech cotton 8: Bugs 0
October 19, 2005
University of Arizona
Biotech cotton has beaten back pink bollworm eight years running, reports a team of scientists from The University of Arizona in Tucson.
The surprising finding is good news for the environment. Arizona farmers who plant the biotech cotton known as Bt cotton use substantially less chemical insecticides than in the past.
Insect pests sometimes evolve resistance to such chemicals in just a few years, a fate that was predicted for biotech crops genetically altered to produce Bt toxin, a naturally occurring insecticide.
"This is the most complete study to date for monitoring resistance to Bt crops," said team leader Bruce E. Tabashnik, the head of UA's department of entomology, a member of UA's BIO5 Institute and an expert in insect resistance to insecticides.
"We found no net increase in insect resistance to Bt. If anything, resistance decreased. This is the opposite of what experts predicted when these crops were first commercialized." He added, "I'm definitely surprised."
Cotton fields in Parker Valley, Ariz. Bt cotton is the greener field in the foreground. The whiter swath of cotton in the background is a refuge field of non-Bt cotton. Photo credit: Timothy Dennehy.
Tabashnik, Timothy J. Dennehy, a UA Distinguished University Outreach Professor of Entomology and extension specialist and a member of BIO5, and Yves Carriere, UA associate professor of entomology, will publish their research in an upcoming issue of the Proceedings of the National Academy of Sciences.
Bt cotton has been planted in Arizona since 1996. Now more than half of the state's 256,000 acres of cotton fields are planted with the biotech plants. Without the protection provided by Bt cotton, some fields can have 100 percent of plants infested with pink bollworm caterpillars, which live inside the cotton boll, destroying the crop.
Dennehy said, "In an extreme infestation, you can have every single boll in the field infected." The caterpillars eat the seeds and damage the developing cotton fibers.
In contrast, when the caterpillars eat Bt cotton, they die.
Before the use of Bt cotton became widespread, pink bollworm was one of the top three insect pests of cotton in the Southwest. In 1995, losses from pink bollworm in Arizona cotton were estimated to be $8.48 per acre, totaling $3.4 million statewide. Cotton is grown in eight Arizona counties: Cochise, Graham, La Paz, Maricopa, Mohave, Pima, Pinal and Yuma.
"Moreover, the harsh insecticides used to control pink bollworm resulted in a host of other insect pests becoming more serious problems," Dennehy said.
Everything changed in 1996, he said, when Bt cotton and two other "soft" insect control tactics replaced a large amount of the harsh pesticides used on cotton crops. Spraying less chemical insecticides means more beneficial insects survive, further reducing the need for spraying.
By 2004, pink bollworm losses had fallen to nearly half of earlier levels, $4.34 per acre.
Tabashnik said, "Some of the other pests are not so much of a problem because we're not killing their natural enemies with insecticides."
Dennehy added, "These soft toxins plus the good bugs acting together have driven pesticide use to historic low levels ... this is a wonderful success of integrated pest management."
Since widespread adoption of Bt cotton in 1997, insecticide use on Arizona's cotton crops is down 60 percent, said Tabashnik. The reduction in chemical pesticide use saves growers about $80 per acre. According to the Arizona Agricultural Statistics Bulletin, the value of Arizona's cotton crops for 2004 was estimated at $207 million.
The key to Bt cotton's continued efficacy is the use of refuges - patches of traditional cotton intermingled with the fields of Bt cotton.
The refuges ensure that the few pink bollworm moths that are resistant to Bt are most likely to mate with Bt-susceptible pink bollworm moths that grew up in the refuges. The offspring from such matings die when they eat Bt cotton.
In contrast, if all of Arizona's cotton was Bt cotton, only pink bollworm caterpillars that were resistant to the Bt toxin would survive. If resistant pink bollworm moths mated with each other, their offspring would be resistant and could feed on Bt cotton. Bt cotton would then become useless against pink bollworm.
The UA team used a combination of field surveys, laboratory testing and mathematical modeling to determine if pink bollworm had become resistant to Bt cotton.
The team did find Bt-resistant pink bollworm caterpillars in the field, but they were rare.
Tabashnik said that doesn't mean the insects won't bite back in the future. "It's not that pink bollworm can't beat Bt toxin, but that it hasn't beaten Bt toxin so far."
There's a new variety Bt cotton now available that has two different Bt toxins, he said. The team's next step will be to determine how to best use that combination of toxins to stay one step ahead of the pink bollworms.
Does that uncited, unlinked article discuss what happens to the organic agriculture market when bugs become resistant to the inundating of Bt into the ecosystem by industrial agriculture?
Some more relevant reading:
New research shows that Bt crops pose little threat to non-target organisms
October 19, 2005
Lanham, Md.—Environmental Entomology, an Entomological Society of America journal has just published the results of 11 field studies of the impact of Bt crops on non-target organisms. These field studies, published in 13 research papers in the October issue of the journal, represent the most comprehensive, long-term scientific assessment of this issue to date.
The effect of Bt technology on non-target organisms has been one aspect of the wide-ranging debate over transgenic crops. These crops, which have been in commercial production since 1996, are protected from specific insect pests with insecticidal proteins derived from the bacterium Bacillus thuringiensis (Bt).
The results of the new studies provide extensive data to support the conclusion reached by regulators when these crops were first commercialized—that Bt cotton and Bt corn pose little, if any, threat to organisms not targeted by the Bt proteins. These studies also bear out one of the environmental benefits of Bt crops—the reduction in the use of insecticides with broad-spectrum activity. These commonly used insecticides not only affect a wide range of pests but also have been shown to be more damaging to non-target organisms.
The field studies, conducted in the United States and Australia, focused on the longer-term assessment of potential non-target effects of transgenic Bt cotton and corn. The research encompassed two varieties of crops (upland cotton and hybrid corn) which collectively produce five insecticidal proteins, and involved the evaluation of a wide breadth of non-target arthropods. With one exception, studies were conducted over a minimum of three site-years in either controlled, moderate-sized research plots or in commercial fields subject to typical grower production practices. The majority of studies were conducted for three years or more.
Publication of these papers inaugurates a new subject area in Environmental Entomology entitled "Transgenic Plants and Insects."
"This new subject area allows us to explore issues in agricultural biotechnology," said Dr. E. Alan Cameron, the journal's editor-in-chief. "In this inaugural section, we present a unique body of research that shows that Bt crops have little effect on non-target organisms, especially compared to the alternative use of insecticides with broad-spectrum activity, which can be many times more damaging to the non-target arthropod community."
"Future topics in this subject area will include all aspects of the development, application, and assessment of transgenic technology in pest management and its environmental impact," Cameron added.
Environmental Entomology, one of four scientific, peer-reviewed journals published by the Entomological Society of America, covers a wide variety of subjects within the area of insects' interaction with the biological, chemical, and physical aspects of their environment. Published bimonthly, the current issue (October 2005, Vol. 34, No. 5) is available at http://www.entsoc.org/pubs/periodicals/ee/.
Your comments suggest that you are unaware that recent scientific discussion is about the strange fact that resistance to Bt hasn't emerged in many years of "industrial" agriculture as you call it. There are in fact considered resistance management strategies in place to hopefully continue this situation.
Also the fact remains the the insect resistance to Bt that has emerged in the past as a real farming problem (eg in Hawaii) was caused by over use of Bt bacteria by organic type farmers, so the risks cut both ways.
The link is
The abstract is
Proc Natl Acad Sci U S A. 2005 Oct 14; [Epub ahead of print] Related Articles, Links
Delayed resistance to transgenic cotton in pink bollworm.
Tabashnik BE, Dennehy TJ, Carriere Y.
Department of Entomology, University of Arizona, Tucson, AZ 85721.
Transgenic crops producing Bacillus thuringiensis (Bt) toxins kill some key insect pests and thus can reduce reliance on insecticides. Widespread planting of such Bt crops increased concerns that their usefulness would be cut short by rapid evolution of resistance to Bt toxins by pests. Pink bollworm (Pectinophora gossypiella) is a major pest that has experienced intense selection for resistance to Bt cotton in Arizona since 1997. We monitored pink bollworm resistance to Bt toxin for 8 years with laboratory bioassays of strains derived annually from 10-17 cotton fields statewide. Bioassay results show no net increase from 1997 to 2004 in the mean frequency of pink bollworm resistance to Bt toxin. A synthesis of experimental and modeling results suggests that this delay in resistance can be explained by refuges of cotton without Bt toxin, recessive inheritance of resistance, incomplete resistance, and fitness costs associated with resistance.
It sure would be nice if you learned how to cite the things you quote. That's a clue. Anyway,
Dano, Your comments suggest that you are unaware that recent scientific discussion is about the strange fact that resistance to Bt hasn't emerged in many years of "industrial" agriculture as you call it.
Many people call it industrial agriculture, but thanks for the clue you provide me by putting it in quotes.
And I'm quite aware of the discussion, as I have to be if I wish to maintain my IPM certificate. But anyway,
1. Can you explain how the Env Ent articles address resistance to Bt? As I read the abstracts and introduction, I see no papers on resistance.
If you could point out which paper pooh-poohs the notion of Bt resistance, that would be great.
2. The PNAS paper is great, thanks, but the paper [and any paper you choose to read] does not say that Bt resistance will not happen. In fact, the existence of refugia and other such strategies is an indicator of a resistance danger and active management strategies will need to be maintained in order to continue resistance.
Hence the wording of my original question.
Thanks Dano. You also provide clues by your nicely ironical comments that my original guesses about your knowledge were wrong. Perhaps you also could be more explicit and direct first up next time you pose a question.
(The reason that I first didn't post the link is that it had moved down the page after I had first grabbed the pdf, due to additional items being published over the next days in PNAS, and I didn't realise that I needed to "scroll" at the PNAS website to find it off the page.)
As you know from recent scientist talks in the entomology area, the essentials of the the Arizona work just published in PNAS have been circulating for quite a while, but its nice to see them get good attention now on the internet.
As far as Bt resistance and organic agriculture, the factual remarks you make are pretty on the ball, and I can hardly do any good by trying to teach you to suck eggs. May the pessimists about Bt never shut up (because they are needed), and hopefully never be proved right!
The best recent comments I've seen recently are:
and anything by Rick Roush or Anthony Shelton is usually good.
My opinions are pretty much the same as theirs.Obviously to manage further problems we must be active to ensure that good IPM gets strongly encouraged, especially in India and China, and that further stacked Bt crops and Bt crops with other stacked traits continue to come down the research pipeline and be deployed promptly as with Bollgard II in Australia. The remarks and appropriate cautions about future resistance emergence in the discussion section PNAS paper I cited are fairly relevant too.
It may well be that some of the "industrial" scenarios provide greater security against emerging insect resistance than direct use of conventional Bt bacteria does, because they may give stronger assurance of high levels of Bt in the crops themselves plus the provision another insecticidal agent at the same site, which is a good route to preventing emergence of resistance. Refuges of course are very important.
It would be nice to hear from you about similar scientific reports in the proper management of conventional Bt bacterial powder in "non-industrial " agriculture.