The half-inch-long corn rootworm larva packs a surprising punch. It
feasts on the root system of corn before pupating into a black and
yellow beetle that does further damage to the plant�??s leaves. Before the
advent of genetically modified (GM) crops that produce insecticidal
proteins to fight rootworm, these insects cost US farmers an estimated
$1 billion annually in damage and control measures.

But as insects such as the corn rootworm evolve resistance to the suite
of traits baked into commodity crops, scientists are queuing up a new
application for a biotech tool that targets the protein-making machinery
of insects. First identified in 1990, RNA interference (RNAi) entails
using double-stranded RNA (dsRNA) to block messenger RNA from its usual
function (i.e., sending out instructions to make proteins). With
impressive specificity, RNAi can potentially block nucleotide sequences
that are only found in a target pest and not in friendly insects or
humans. As a result, some scientists are keen on making RNAi the next
big tool in agricultural science.

The EPA first approved an RNAi pesticide in 2017. That product, called
SmartStax Pro, is a GM corn seed that will deploy both transgenic
insecticidal proteins and RNAi to fight western and northern corn
rootworm. It�??s expected to be released in the United States in the next
few years, according to its maker, Bayer AG, which is headquartered in
Leverkusen, Germany.

But GM crops are just one of many agriculture-related applications for
RNAi. As the cost of producing dsRNA has dropped precipitously, biotech
companies are developing dsRNA formulations that could also serve as
spray pesticides, making the technology more affordable to smaller farms.

�??RNAi is really different from everything that�??s come before because you
can pick your target,�?� says Bruce Tabashnik, professor of entomology at
University of Arizona. But he cautions that this new tool should not be
considered a silver bullet against invertebrate pests. �??Insects are the
champions of adaptation,�?� he adds. �??They will adapt to any challenge we
can throw at them but if we do a combination of challenges
simultaneously, we have a much greater expected durability of our strategy.�?�

Inner Workings: RNA-based pesticides aim to get around resistance
problems | PNAS [www.pnas.org]