Suhas Vyavhare and David Kerns
We have had a few inquiries around ThryvOn technology
in cotton which has recently been fully commercialized in the US.
What is ThryvOn?
ThryvOn is a genetically engineered cotton expressing Bacillus
thuringiensis (Bt), toxin mCry51a2. This protein has insecticidal activity
(mostly deterrence/repellency) against thrips and plant bugs. Cry51 has an
excellent activity on thrips. Field research indicates that ThryvOn cotton will
not need insecticidal seed treatment (e.g., imidacloprid) or a foliar insecticide
application for thrips in cotton. We do find adult and immature thrips in
ThryvOn cotton but significantly fewer than the non-ThryvOn and with little or
no injury to seedlings.
What would be the recommendation for
thrips control in ThryvOn cotton?
We do not recommend insecticide treatment for thrips
in ThryvOn cotton. Seed treatment (imidacloprid) will be optional when
purchasing seed in West Texas but not in the East region where ThryvOn is
packaged with insecticidal seed treatment. Contact your seed rep for more info
on seed availability and seed treatment options.
How good is it on Lygus bug?
Not as dramatic as it is on thrips. There seems to be little
or no activity on adults, but overall, there would be fewer and relatively smaller
nymphs in ThryvOn cotton compared to the non-ThryvOn. Plant bug populations
develop relatively slower in ThryvOn cotton which will provide some flexibility
in terms of crop management (e.g., product choice, application timing) but will
not necessarily eliminate the need for foliar application. Until we have a
better understanding on ThryvOn on plant bugs, we are recommending following the
current action
threshold for plant bugs in both ThryvOn and non-ThryvOn cotton.
Plant bug thresholds are based on combination of insect numbers and the level
of fruit retention.
Does it have any activity on cotton
fleahopper?
Cotton fleahopper will not be included on the ThryvOn
label as a target pest. However, bioassays conducted by Bayer suggest mCry51Aa2
has activity on cotton fleahopper. Research conducted by Dr. David Kerns at
Texas A&M indicates that ThryvOn cotton exhibits some activity on cotton
fleahopper under field conditions and in cage studies, and slightly reduces the
number of large nymph survival. However, these effects will most likely not
prevent the need for foliar insecticide applications. Although cotton
fleahopper numbers may not vary much between ThryvOn and non-ThryvOn cotton, ThryvOn
cotton has consistently shown better square retention than non-ThryvOn at
varying levels of cotton fleahopper infestation. Similar to Lygus bugs,
we are recommending treating cotton fleahoppers in ThryvOn cotton using our
current action
threshold.
Does this technology have any impact on beneficial
insect populations?
Considering the relatively broad-spectrum activity of mCry51Aa2
compared to the older Bt proteins in cotton, this is a concern among several.
We have not noticed any negative impact on the beneficial populations that will
affect the natural control at field level. Research conducted by Bayer
indicated that mCry51Aa2 is unlikely to pose much risk to a number of beneficial
insects in cotton including lady beetles, lacewings, minute pirate bugs,
big-eyed bugs, damsel bugs and assassin bugs. Thus, we anticipate any impact on
beneficial insects will be little to none.
In summary, ThryvOn is yet another tool in the toolbox
that will further improve insect pest management in cotton. It will reduce the
insecticide applications targeted at thrips and maybe to some extent against
plant bugs. Regular field scouting, however, still remains critical to monitor
plant bugs and other insects to make timely management decisions.
