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Daily News Blog

21
Apr

More Data Shows Failure of Crops Genetically Engineered to Incorporate Insecticide

(Beyond Pesticides, April 21, 2023) Into the annals of “entropic methods of agricultural pest control” arrives recent research showing that pests are, unsurprisingly, developing resistance to a genetically engineered (GE) biopesticide used for more than 90% of U.S. corn, cotton, and soybeans. Bt (Bacillus thuringiensis) is a naturally occurring bacterium; the versions deployed in conventional agriculture are engineered into Plant Incorporated Protectants (PIPs) — GE ingredients “inserted” into seeds for multiple kinds of crop plants. These PIPs target multiple crop-destructive insect species, including (in larval form) the corn rootworm and cotton bollworm, in particular. Beyond Pesticides continues to warn that “controls,” whether synthetic chemical pesticides or GE “biological” agents (such as GE Bt) that target living things (e.g., pests and weeds) are not sustainable over time because — in addition to the harms they cause — the issue of resistance will ultimately thwart their efficacy.

There are two basic categories of genetic engineering employed in conventional agriculture. One technology transfers genetic material into seed to make plants tolerant of specific herbicide compounds that will be applied after planting (for example, the infamous “Roundup Ready,” glyphosate-tolerant seeds and plants). The other comprises plant-incorporated protectants (PIPs), in which the genetic material introduced causes endogenous production of proteins harmful to particular insect pests. (See much more on Bt through the Beyond Pesticides Bt archive.)

As U.S. Right to Know (USRTK) explains in its coverage of a 2016 independent research study on the subject, “Crops engineered with Bt genes express specific proteins (known as Cry proteins) that make the crops toxic to specific insects — the plants effectively provide their own insecticide — [theoretically] reducing the need for chemical applications. . . . Th[is] research adds to evidence that after 20 years of use of crops engineered to tolerate herbicides and resist certain harmful insects, both technologies are losing effectiveness.”

Corn seed engineered with Bt was developed in 2003 by Monsanto and deployed to deal with the Western corn rootworm. EPA stepped in early on to require that producers using Bt products create so-called “refuge” areas — fields of specific size and proximity (to the Bt fields) that are planted without PIPs. These “refuge” areas aimed to ensure that breeding would occur between nonresistant rootworms from the untreated corn and resistant individuals that would emerge from the areas planted with Bt varieties. The theory is that such breeding would dilute the frequency of the genes that encode resistance and inhibit their inheritance in subsequent generations of rootworms.

This refuge tweak has largely failed, in part because of noncompliance. PIP manufacturers responded to that issue by creating a farmer-friendlier “refuge in a bag” system that allowed farmers to avoid setting aside some of their field areas as free of the Bt trait. How? By encouraging the spreading of uneven low doses of the Bt toxin to feeding insects throughout all their fields. Monsanto “‘touted refuge-in-a-bag’ as fast and convenient for farmers, allowing them to plant the specialized seed ‘fence row to fence row.’” In reality, the tactic catalyzed resistance in the insects over time. Progressive Farmer warned of this in 2012.

In addition, critics of EPA’s introduction of the “refuge” tactic noted that to be at all effective, the refuge areas needed to be much bigger than EPA required. In 2012, a study concluded that, “EPA should more than double the percentage of corn acres planted to mandated refuges to delay insect resistance.” (One investigator and co-author of that study was the same Bruce Tabashnik, PhD who was lead author on the subject study cited above.)

The increasing recognition of developing resistance to GE-Bt-as-PIP underscores several problems:

(1) all pesticides are ultimately doomed to fail because of the all-but-inevitable development of resistance in organisms (including weeds)

(2) the response of industry and the U.S. Environmental Protection Agency (EPA) to resistance continues to be, respectively, doubling down on chemical approaches, and/or tweaking use parameters to try to rein in problematic impacts

(3) there are many Bt strains, some of which are permitted for pest management purposes in organic agriculture (in addition to the many GE insecticide versions); the increasing use of Bt in GE-plus-chemical agriculture — and the resulting uptick in resistance — represent a real threat to this useful tool for the organic sector

EPA acknowledges the resistance issue: “Like [with] most pesticides, insects are capable of developing resistance to Bt proteins. In Bt PIPs, this risk may be heightened by the fact that: 

  • Bt proteins are expressed at high levels in most or all plant tissues
  • the proteins are produced by the plant continually during the growing season (i.e., throughout the lifespan of the plant)
  • some of the major target pests, such as European corn borer, corn rootworm, and pink bollworm, feed almost exclusively on corn or cotton

These factors can increase insect exposure to the controlling toxins (Bt protein) and hence, increase selection pressure for resistance. That means that if the toxin kills susceptible insects, those that survive and reproduce are more likely to be resistant to the toxin.”

The issue of resistance to Bt began to be noticed in 2008 in cotton bollworms — a mere five years after initial deployment of Bt products. The industry claim that genetic manipulation of plants would result in reduced pesticide use began to be exposed as false a decade ago. In 2013, The Wall Street Journal noted that, as resistance to Bt products began to ratchet up and corn rootworm damage surged, farmers returned with a vengeance to chemical insecticides — unraveling a central argument for the GE Bt strategy. (Beyond Pesticides wrote about typical industry response to resistance in 2019: “Manufacturer response is often either to find a new chemical, or to “double down” with combined-ingredient products that may be effective until the next wave of resistance develops.”)

A 2013 study published in PNAS (the Proceedings of the National Academy of Sciences) concluded that, “The widespread planting of crops genetically engineered to produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) places intense selective pressure on pest populations to evolve resistance. . . . These [early] cases of resistance by western corn rootworm highlight the vulnerability of Bt maize to further evolution of resistance from this pest and, more broadly, point to the potential of insects to develop resistance rapidly.”

In 2020, EPA issued a draft proposal for ways to “improve” the problem of pest resistance for Bt PIPs in corn and cotton crops. The agency’s goal was to “prolong the durability of Bt PIPs from pests.” Zeroing in on the lack of meaningful changes in the proposal, Beyond Pesticides, led a group of nine other advocate organizations, commented on it: “The agency is proposing changes to three aspects of . . . insect resistance management that consist of new resistance definitions, increased resistance monitoring and mitigation efforts, and modified annual reporting to the agency. These changes do not address or impact the biology of pest populations developing resistance, but only the recognition and identification of such resistance [emphasis by Beyond Pesticides]. In addition to the above proposed framework changes, the agency is considering options to . . . increase percent of refuge in seed blend products, and change . . . refuge compliance measures. These options at best will only delay the development of more prevalent pest resistance to Bt toxins. . . . [W]e find that the proposed new resistance management framework . . . will do little to curb the trajectory in the increasing resistance.” (See draft comment here.)

In that same year, EPA also began considering a proposal to reduce, gradually, the use of some Bt corn and cotton products in an attempt to combat pest resistance. One tactic was a three-year “phasedown” to some unspecified “minimal acreage cap” of Bt products for corn. The agency also considered (again) increasing the ratio of non-Bt corn seeds in blends used in “refuge” areas, the aim being to slow resistance by allowing nonresistant insects to mate with resistant insects. The proposal received significant pushback from grower groups and the crop protection industry. The former is very accustomed to use of Bt PIPs and considers them still useful despite evidence that efficacy is time limited, given galloping resistance. The latter is looking to Hoover up profits from this technology for as long as it can.

The very human, and very unwise, tendency to think short term is on full display throughout the agrochemical and agro-biotech sectors, as well as at EPA. In 2020, Beyond Pesticides wrote: “Resistance to pesticides is nearly inevitable. Development of resistance is an entirely normal, adaptive phenomenon: organisms evolve, ‘exploiting’ beneficial genetic mutations that give them survival advantage. For nearly a century, human response to this has been primarily a chemical ‘chasing’ of such evolutionary changes — developing a compound that kills the offending organism (whether pest or weed or bacterium or fungus) for a while. Organisms nearly inevitably change to become resistant to that particular chemical assault, whereupon people — the chemical industry, researchers, applicators, farmers, public health workers, clinicians, et al. — have typically moved on to the next chemical ‘solution.’” To the “chemical” critique, “biotechnical” approaches can now readily be added.

Last year, Beyond Pesticides coverage of a study on emerging Crispr technology quoted Ethan Bier, PhD on that new technology. His comment is equally relevant in this Bt context, and underscores Beyond Pesticides’ perspective: “This is no silver bullet. You never win when you try to play the evolutionary game with insects.” We would add, “or with other living organisms.” Industry focus on, and EPA collusion with, the search for “silver bullets” without precautionary forethought to the issue of resistance is the Achilles heel of pesticide — and now biotech — dependence in conventional agriculture. These are eventually doomed to failure, and meanwhile, EPA continues to power the pesticide and GE treadmills.

Beyond Pesticides believes that consideration of (1) the incorporation into food crops of genes from a natural bacterium, such as Bt, (2) the development of herbicide-tolerant crops and their paired use with herbicides, such as Roundup Ready soybeans and glyphosate, and (3) the ongoing planetary assault by thousands of synthetic pesticide compounds leads to the conclusion that these GE and chemical approaches to agriculture and pest management are short sighted and dangerous, and as noted above, entropic by their very nature. At broad scale, they generate adverse environmental, human health, biodiversity, climate, and economic consequences; they also are undermining the use of Bt as a biological pest management tool in organic production. Regenerative organic approaches are the only genuinely sustainable practices, and are the linchpin of a thoughtful, future-conscious route forward for humankind.

Source: https://entomologytoday.org/2023/04/18/insect-resistance-transgenic-bt-crops-bacillus-thuringiensis/

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

 

 

 

 

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