Posted: December 2014
Potential Unintended Effects of RNAi-based Insecticidal Crops
A new form of genetic engineering is being developed in which genetically
modified plants make a special kind of RNA that, when taken up by insect
pests, can induce harmful effects through silencing genes in the insect.
Two USDA scientists have written a review article discussing the manifold
potential unintended effects of this technology, especially in connection
with harming nontarget insects.
This new technique is called RNA interference (RNAi). The idea is to
genetically modify crop plants to produce a specific type of
double-stranded RNA (dsRNA), which is then taken up by insects that feed
on the plant. This dsRNA is subsequently broken down into small
interfering RNA strands (siRNA) that, in a complex process, silence the
activity of a specific gene in the pest, which in turns weakens or even
kills the pest. The technique has been tested experimentally and shown to
work in principle (with varying degrees of actual harm to the pest).
USDA research entomologists Jonathan Lundgren and Jian Duan (2013) discuss
a number of different unintended effects that the widespread planting of
RNAi genetically modified crops could have. Their focus is on potential
effects on nontarget organisms that would ingest the GM crops, including
Here are some of their concerns about unintended effects of small
interfering RNAs (siRNA). In the article they provide examples out of the
scientific literature to underscore these concerns.
Lungren and Duan point repeatedly to “knowledge gaps” in assessing the
broader impacts of this technology. It seems evident that applying great
caution in allowing commercialization of RNA-based GM crops is warranted.
siRNAs may silence the target gene in nontarget insects (or other
organisms) and thereby harm or kill them.
Although siRNAs are purported to target specific genes to silence, the
literature shows that they commonly silence unintended genes in the target
organisms, which can lead to undesired effects in the target organism.
Similarly, siRNAs could silence unintended genes in nontarget organisms.
siRNAs have been found to stimulate immune reactions in mammals. “It is
unclear how the immune systems of other organisms will react to an influx
of small RNAs. Nor is it known how this immuno-stimulation will affect the
fitness of nontarget organisms.”
Foreign siRNAs may saturate a cell’s RNA interference system and thereby
negatively impact the ability of cells to regulate their own gene
Many nontarget species will be exposed to the RNA-based GM crops.
“Knowledge gaps make it unclear how dsRNAs that target a pest will
function with the RNAi pathways of other organisms (especially
phylogenetically divergent ones).”
Since both the physiological state of an organism and the specific
environmental conditions play a large role in when genes are expressed and
how genes are expressed in a given time and place, it will be very
difficult to predict nontarget effects based on laboratory experiments or
even small field experiments.
Lundgren, J. G. and J. J. Duan (2013). “RNAi-Based Insecticidal Crops:
Potential Effects on Nontarget Insects,” BioScience vol. 63,
Note: The authors are research entomologists with the U.S. Department of
Agricultural Research Service in Washington, D.C.
Copyright 2014 The Nature