Truth: GM Bt crops change the way in which insecticides are used

Myth at a glance

GM proponents claim that GM Bt crops reduce insecticide use, as farmers do not have to spray chemical insecticides.

But GM Bt crops do not reduce or eliminate insecticides. They simply change the type of insecticide and the way in which it is used – from sprayed on, to built in. The amount of Bt toxin expressed in the plant is generally far greater than the amount of chemical pesticide displaced.

The most optimistic claim for reduced pesticide use from GM crops, from an industry consultancy source, is 6.9% globally. In contrast with this small reduction, in France by 2009, herbicide use was down to 82% and insecticide use was down to 12% of 1995 levels. Similar trends were found in Germany and Switzerland. These benefits were achieved without the use of GM crops.

Far from being safe insecticides, the Bt toxins expressed in GM Bt crops harm beneficial and non-target insects. The high levels of Bt toxin expressed in stacked-trait GM crops like SmartStax maize have not been tested to see if they are safe to eat.

Pests are rapidly evolving resistance to the Bt toxins in GM Bt crops. Even when Bt toxins are effective in killing the target pest, secondary pests that are not controlled by Bt toxins are moving into the ecological niche. Both developments are forcing a return to chemical insecticides.

Attempts to delay pest resistance to Bt crops by planting refuges of non-Bt crops have not been completely successful, both because refuge recommendations have not been enforced and because refuges are not working as planned.

It is not valid to measure insecticide use only by the amount of insecticide sprayed onto the growing crop. Increasingly insecticides are applied to seeds before planting and to soil.

When evaluating the impact of GM Bt crops on insecticide use, a more useful comparator than chemically-grown non-GM crops would be non-GM crops under organic or integrated pest management, where insecticide use is reduced or eliminated.

GM proponents claim that GM Bt crops reduce insecticide use, as farmers do not have to spray chemical insecticides. But this claim does not stand up to analysis, for several reasons. The first and most important is that the GM Bt gene turns the plant itself into an insecticide. The GM insecticide is present in active form in every part of the crop, including the parts that people and animals eat. So Bt crops do not reduce or eliminate insecticides. They simply change the type of insecticide and the way in which it is used – from sprayed on, to built in.

What is more, the amount of insecticide produced by the plant is in many cases far more than the amount of chemical insecticide spray that is displaced. This is confirmed by data collected by the agronomist Dr Charles Benbrook from industry documents on Bt toxin expression levels in GM Bt plants submitted for regulatory purposes.1 Benbrook’s findings were as follows.

GM Bt maize targeting the European corn borer

Bt maize events targeting the European corn borer (ECB) produce nearly as much or more Bt toxin per hectare (ha) than the average rate of chemical insecticides applied on a hectare planted to non-Bt maize for ECB control (about 0.15 kgs insecticide per ha; 0.13 pounds/acre in 2010):

  • MON810 produces 0.2 kg/ha of Bt toxin
  • Bt11 produces 0.28 kg/ha
  • MON 89034 produces two Bt toxin proteins totalling 0.62 kg/ha
  • TC1507 produces the least amount of Bt toxin – 0.1 kg/ha.1

GM Bt maize targeting the corn rootworm

Every Bt maize hectare planted in recent years targeting the corn rootworm (CRW) expresses substantially greater volumes of Bt toxin than the approximately 0.2 kg of insecticides applied on the average hectare for corn rootworm control (0.19 pounds/acre):

  • MON88017 expresses 0.62 kg/ha of Bt toxin
  • DAS 59122–7 expresses two Bt toxin proteins totalling 2.8 kg/ha, 14-fold more than the chemical insecticides displaced.1

SmartStax maize

SmartStax GM maize synthesizes six Bt toxin proteins, three targeting the ECB, and three the CRW. Total Bt toxin protein production is estimated at 4.2 kg/ha (3.7 pounds/acre), 19 times the average conventional insecticide rate of application in 2010.1

This high level of Bt toxin expressed in GM plants has never been tested to see whether it is safe to eat over the long term in animals or humans.

Claims that GM Bt crops reduce or eliminate insecticides invariably fail to take these plant-produced pesticides into account.

Reduction in chemical insecticides from Bt crops unspectacular

Let’s ignore for a moment the fact that Bt crops generally produce more insecticides than the chemical sprays displaced and only consider the claimed reduction in chemical insecticide sprays due to Bt crops.

This reduction is based on the assumption that farmers who grow Bt crops do not also spray chemical insecticides. Even if that assumption were true, the resulting reduction in chemical insecticide use due to GM Bt crops is an unspectacular56 million kilograms (123 million pounds) over the first sixteen years of GM crop cultivation in the US.1

This small reduction is swamped by the massive estimated 183 million kg (404 million pounds) increase in pesticide use resulting from the adoption of GM herbicide-tolerant crops. This means that overall pesticide use has increased by 7% due to the introduction of GM crops.1

Even the modest reduction in chemical insecticides attributed to GM Bt crops has proved temporary and unsustainable, due to the emergence of pests resistant to Bt toxin (see below).

Moreover, there is a question mark over whether Bt crops can even be said to have reduced chemical insecticide use in view of the facts that most corn seed – Bt and non-Bt – is now coated in toxic neonicotinoid pesticides (see below) and farmers plagued with Bt toxin-resistant pests are returning to harmful soil-applied insecticides.2,3

Pesticide use number crunching

In his 2012 paper discussed above, Benbrook calculated that overall pesticide use (including herbicides) increased by 7% in the US due to the introduction of GM crops.1

The most optimistic claim for reduced pesticide use from GM crops, in a 2006 paper by a consultancy firm to the GM industry, P G Economics, and based on “farm-level impact data” from an unnamed source, is 6.9% globally.4

In contrast with this small (unvalidated) reduction, by 2007 France reduced both herbicide use (to 94% of 1995 levels) and chemical insecticide use (to 24% of 1995 levels). By 2009 herbicide use was down to 82% and insecticide use was down to 12% of 1995 levels. Similar trends were found in Germany and Switzerland. These benefits were achieved without the use of GM crops.5

These progressive trends do not have to mean a severe drop in yield or farmer income. A 2011 study by French government scientists found that pesticide use could be reduced by 30% through adoption of integrated agriculture techniques, with only a small reduction in production (96.3% of the current level) and without impacting farm income.6 GM crops were not part of the equation in this study.

Resistant pests are making GM Bt technology obsolete

Insect pests quickly adapt to tolerate pesticides, especially when under constant exposure to the insecticide. The Bt toxin engineered into GM Bt crops are no exception. GM Bt insecticidal crops express the Bt toxin in every cell for their entire lifetime, constantly exposing pests to the toxin. This is different from the traditional use of natural Bt as a spray, where targeted pests are only exposed for a brief period before the Bt breaks down in daylight and the toxin is only activated within the insect’s gut.

Exposing pests to a pesticide for long periods of time inevitably speeds up the emergence of resistant pests, since selective pressure eliminates all but the most resistant pests, which then reproduce and pass on their resistance genes.

For this reason, GM Bt crop technology sometimes enjoys short-term success in controlling pests but is soon undermined by the emergence of pests resistant to the toxin.7,8,9In 2011 a paper was published showing that corn rootworms in some areas of the US were already resistant to two of the three available Bt toxins that previously controlled them. Fields in the corn belt were sustaining severe damage.10,11Bt-resistant rootworm populations have been reported in Iowa10,12 and Illinois.13,14

Entomologist Elson Shields of Cornell University commented on the evolution of pests resistant to Bt toxin in GM plants, “The insect will win. Always bet on the insect if there is not a smart deployment of the trait.”11

Refuge recommendations ignored

By “smart deployment of the trait”, Shields was referring to the refuge concept. From the time GM Bt technology was introduced, scientists and even the US EPA have recommended that farmers plant “refuges” of non-Bt crops alongside the Bt crops as a resistance management strategy to delay the emergence of Bt-resistant pests.

The idea is that the non-Bt crop acts as a refuge where Bt-susceptible pests can survive, ensuring the existence of a population of Bt-susceptible pests to mate with any Bt-resistant pests that survive in the adjacent field where the Bt crop is under cultivation. It is assumed that the Bt-susceptible pest population will dilute out the Bt-resistant population that survives in the Bt crop, assuring that the predominant population is Bt-susceptible.

However, these recommendations were watered down by the EPA itself, which started out arguing for 50% refuges but ended up accepting voluntary 20% refuges. Even these, in practice, were widely ignored.11,3The result has been widespread Bt resistance in the corn rootworm.10

Refuge concept breaking down

Refuges may be less effective than believed. A study on rootworm resistance found that refuges were redundant in the case of substantial Bt-resistant rootworm populations, as the pests were able to live and reproduce in Bt maize fields. The study concluded, “Even with resistance management plans in place, sole reliance on Bt crops for management of agriculture pests will likely hasten the evolution of resistance in some cases.”10

Also, the effectiveness of refuges relies on the Bt crops expressing doses of Bt toxin that are high enough to kill pests, and the non-Bt refuges remaining free from Bt toxin-expressing genes. But cross-pollination between GM Bt and non-Bt maize has been found to cause “low to moderate” Bt toxin levels in the refuge plants,15 making refuges less effective.

Bt crops are the opposite of integrated pest management

Integrated pest management (IPM) is a successful and respected approach to minimizing pesticide use. It is widely practised by farmers who are not prepared to give up pesticides entirely.

A central principle of IPM is avoiding the evolution of pest resistance to insecticides. Resistance is caused by continuous exposure to the pesticide. Only those pests that survive the exposure end up reproducing and passing on their genes, leading to the rapid emergence of a resistant pest population. IPM requires that insecticides are only sprayed when needed – when pest infestation has reached a critical point of damage to the plant. That way, the pests do not get a chance to become resistant and the pesticide’s effectiveness is preserved.

GM Bt crops, with their permanently active pesticides built into every cell, are incompatible with the IPM approach.

Bt crops harm natural enemies of pests

Indiscriminate use of insecticides does not only kill pests, but also the natural enemies of the pests, the beneficial predators. Pests are generally far more resilient than their predators and recover from insecticide spraying more quickly. Therefore spraying insecticides, while effective in the short term, soon leads to rapid surges in pest populations, which are no longer kept in check by their natural enemies.

This process is well documented by Professor Robert van den Bosch of the University of California, one of the developers of integrated pest management, in his book, The Pesticide Conspiracy.16 Van den Bosch concluded that pesticides do not control pests, but create them.

Bt crops are no exception to this rule. Contrary to claims by GMO promoters, the pesticides built into Bt crops are not restricted to insect pests but also affect beneficial predators (see Myth 5.4). For example, the rootworms that are killed by the Bt toxins in GM crops are beetles, and are related to many beneficial insects, such as ladybirds, which can then become collateral damage.3,17 In 2012, scientists at Cornell University found that rootworm Bt toxin is likely to be harming several important species of beneficial beetles in GMO corn.18 It has been established that Bt toxins harm ladybirds.17

Destruction of beneficial pest predators, combined with rising resistance to Bt toxins in the pests themselves, will result in pest proliferation. This in turn enables GMO seed developer companies to sell more and different pesticidal GMOs and accompanying chemical sprays.

Secondary pests move in on GM Bt crops

Nature abhors a vacuum. So even when Bt toxin succeeds in controlling the target pest, secondary pests move into the ecological niche. For instance, in the US, the Western bean cutworm has increased significantly in GM Bt maize fields.19 In China and India, Bt cotton was initially effective in suppressing the target pest, the bollworm. But secondary pests that are resistant to Bt toxin, especially mirids and mealy bugs, soon took its place.20,21,22,23,24,25

Two studies from China show that GM Bt cotton is already failing under the onslaught of secondary pests:

  • A study of 1,000 farm households in five provinces found that farmers noticed a substantial increase in secondary pests after the introduction of Bt cotton. The researchers found that the initial reduction in pesticide use in Bt cotton cultivars was “significantly lower than that reported in research elsewhere” and that “more pesticide sprayings are needed over time to control emerging secondary pests” such as aphids, spider mites, and lygus bugs. In addition, a quarter of the farmers thought Bt cotton yielded less than non-GM varieties. Close to 60% said that overall production costs had not decreased, due to the higher price of Bt cotton seed.26
  • Field trials conducted over ten years in northern China show that mirid bugshave increased incotton and multiple other crops, in proportion to a regional increase in Bt cotton adoption. The researchers’ analyses show that “Bt cotton has become a source of mirid bugs and that their population increases are related to drops in [chemical] insecticide use in this crop.” Mirid bug infestation of other food crops (Chinese dates, grapes, apples, peaches, and pears) also increased in proportion to the regional planting area of Bt cotton.27

Do GM Bt crops have lowered defence against non-target pests?

GM plants’ vulnerability to secondary pests may be explained by the findings of a study examining aphid attacks on Bt cotton. The study found increased numbers of aphid pests on Bt cotton compared with non-Bt cotton. The authors suggested that this may have been due to the Bt cotton plants’ reduced levels of certain protective substances that non-Bt cotton plants produce to defend themselves against a variety of pests. This would have left the Bt cotton plants vulnerable to secondary pests such as aphids, which are not killed by the Bt toxin in the crop.28

GM Bt cotton farmers don’t always give up insecticides

GM proponents often assume that farmers who adopt Bt crops give up chemical insecticides – but this is not necessarily the case. Tabashnik (2008) reported that while bollworms have evolved resistance to a type of Bt toxin in GM cotton, this has not caused widespread crop failure because “insecticides have been used from the outset” to control the pest.9 So claims of reductions in insecticide use from Bt crop adoption are unreliable unless there is evidence that the farmer does not use chemical insecticides.

Moreover, most Bt crops currently commercialized or in the pipeline have added herbicide tolerance traits and so are likely to be grown with the application of herbicides.29 It is with good reason that one independent scientist has called GM crops “pesticide plants”.30

Hidden chemical insecticides in GM Bt maize

Studies claiming reductions in insecticide use due to Bt crops have previously focused on insecticides that are applied to the soil or sprayed onto the plant after it has begun to grow. They may neglect to mention a different, potentially environmentally destructive type of pesticide: those that are applied to the seed before it sprouts.

According to a study by US entomologists, all commercially available rootworm-directed GM Bt maize seed is now treated before it is planted with the controversial chemical insecticides known as neonicotinoids.31

In this case, GM Bt crops have not reduced or eliminated chemical insecticide sprays. Instead there has been a shift in the type of insecticides used. Where insecticides used to be applied to the plant while it is growing, now they are applied to the seed before planting.

Dr Doug Gurian-Sherman, senior scientist at the Union of Concerned Scientists, commented that neonicotinoid treatments on Bt maize seed aim to kill the insect pests that are not well controlled by Bt toxins. Ironically, prior to the introduction of Bt maize, Gurian-Sherman says a substantial amount of maize was grown without the use of insecticides. For example, maize rotated with soybeans from year to year usually needed little or no insecticide treatment, and only 5–10% of maize was sprayed for corn borers.32

Neonicotinoids are systemic insecticides, meaning that they spread throughout all tissues of the crop plant as it grows and are even present in the pollen and nectar. Like the Bt toxin engineered into GM plants, neonicotinoids differ from sprayed insecticides in that they are persistently present in the growing plant and always active. Because of this long exposure period, pests are more likely to develop resistance to them, and non-target and beneficial insects are more likely to be exposed, too.

Neonicotinoids are toxic to a wide variety of beneficial creatures, including some that help protect crops.33,34 They have highly toxic effects even at very low doses when the exposure time is prolonged.35 The rise in the use of neonicotinoid seed treatments has been implicated in bee die-off and colony collapse.36,37 Bees living near agricultural fields have been found to be exposed by multiple routes, including contaminated wild flowers growing near fields, and neonicotinoids have been found in dead bees.37

In addition to the use of insecticidal seed treatments, some seed and pesticide companies are now recommending a return to the use of soil-applied insecticides in an attempt to combat the spread of Bt toxin-resistant pests in Bt maize.1

The chief – seemingly the only – concern of defenders of GM Bt crop technology is the volume of insecticide applied as sprays after planting. If that volume decreases, they consider that Bt crops reduce insecticide use. But they are not reporting the whole story. The case of neonicotinoid seed treatments shows that it is necessary to consider other types of insecticide applications, how toxic the insecticides are (based on peer-reviewed research, not industry data), how they behave and persist in the environment, and the acreage over which they are applied.32

Given the extreme toxicity of neonicotinoids to bees and other beneficial organisms, their high degree of persistence and spread,37 and the vast acreage over which they are applied, it is questionable whether Bt crop technology has had a beneficial effect on insecticide use.

Conclusion

Claims that GM Bt crops reduce insecticide use fail to take into account the fact that the GM Bt crop is itself an insecticide. The amount of Bt toxin expressed in the plant is generally far greater than the amount of chemical pesticide displaced.

Far from being safe insecticides, the Bt toxins expressed in GM Bt crops harm beneficial and non-target insects. The high levels of Bt toxin expressed in stacked-trait GM crops like SmartStax maize have not been tested to see if they are safe to eat.

Pests are rapidly evolving resistance to the Bt toxins in GM Bt crops. Even when Bt toxins are effective in killing the target pest, secondary pests that are not controlled by Bt toxins are moving into the ecological niche. Both developments are forcing a return to chemical insecticide sprays.

Attempts to delay pest resistance to GM Bt crops by planting refuges of non-Bt crops have not been completely successful, both because refuge recommendations have not been enforced and because refuges are not working as planned.

It is not valid to measure insecticide use only by the amount of insecticide sprayed onto the growing crop. Increasingly insecticides are applied to seeds before planting and to soil.

When evaluating the impact of GM Bt crops on insecticide use, a more useful comparator than chemically-grown non-GM crops would be non-GM crops under organic or integrated pest management, where insecticide use is reduced or eliminated. This would quickly make clear which farming methods can best reduce insecticide use while maximizing yield and farmer incomes.

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