Dr. Suhas Vyavhare and I are conducting a very detailed experiment this year on some aspects of Bt corn. Part of the experiment involves putting 120 emergence cages on the ground under corn after corn earworm larvae (cotton bollworms) have left the corn ears and entered the soil for pupation. This lets us determine the number of moths being produced per square foot or acre under actual field conditions.
After they emerge as moths, these insects will then fly to other crops, and their eggs become the late season bollworm infestations in cotton and headworm infestations in sorghum.
2020 was a fairly light year for corn earworm infestation in corn; only 54% of the ears were infested with larvae at our Olton trial. In most years this would have been nearly 100%.
Here is the math:
This year we had 3,398 moths emerging per acre from irrigated non-Bt corn, or 407,760 moths per 120 acre field.
In a “normal” year when almost every ear had a corn earworm, this would have been 6,292 moths per acre, or 755,040 moths per 120 acres of irrigated corn.
My work with the older Bts like Cry1Ab, Cry2Ab2, Cry1F and Cry 1A.105 suggest these Bts are no longer killing as many earworms as they once did, so one could expect them to produce a significant number of moths. Vip3a corn is highly effective at killing corn earworm, so it will not contribute significantly to a moth flight (until we get resistance).
This is the first chance we have had to estimate the number of cotton bollworm moths coming off of corn on the High Plains, and the numbers are impressive, at least in their contribution to localized bollworm populations in nearby cotton. The lower number of bollworms this year in cotton seem to be directly linked to the lower number of bollworm moths that laid eggs in corn.