Meet Corn Earworm

We thought you might like to get acquainted with the creature that helped itself to some of your peaches-and-cream sweet corn this summer: corn earworm.

Your dining companion, the adolescent corn earworm.

Your dining companion, the adolescent corn earworm.

According to the Cooperative Extension at North Carolina State University, corn earworm is pervasive in the Western Hemishpere. It feeds on more than 100 different species, but its favorite food is corn. The guys who stole our kernels this summer were earworm larvae, which emerged from tiny eggs laid by the adult version of this creature, the corn earworm moth.  In our neck of the woods, “corn earworms overwinter as ‘resting’ (diapausing) pupae in soil at a depth of more than 5 cm,” NC State reports. “Adults emerge in early May, mate, and seek suitable oviposition (egg-laying) sites. A high percentage of first generation eggs are laid on the leaves of seedling corn when it is available.”

Not a little wormie anymore.

Not a little wormie anymore.

Each female moth lays up to 3,000 eggs, one at a time, and each egg becomes a little wormie fellow. Despite those numbers, you probably never saw more than one green caterpillar on any of your ears of corn because the biggest of the nasty buggers eat their little brothers and sisters before they settle into veganism, which they practice for two or three weeks before digging into the dirt to pupate themselves. They grow wings underground, then they emerge, lay eggs, and the cycle starts again. In a Virginia growing season, that cycle repeats itself at least three times.

Earworms aren’t the primary target of the genetic modification that causes most American corn to produce the bacterium B. thuringiensis subsp. kurstaki, also known as Bt; that technology is aimed at rootworms, which eat from below, not from above; but the protein Bt makes is bad for all lepidopteran caterpillars, so a lot of earworms do succumb to its charms. However, most conventional sweetcorn growers control earworm with applications of Mustang Max, Warrior, or Capture/Brigade, all of which are toxins belonging to the pyrethroid group.

“For many years the pyrethroids have provided exceptional levels of control of earworms,” Purdue images-1University says. However, “in recent years, there have been scattered reports of pyrethroid failures in small plot trials and in commercial fields. Recent research has shown that populations of earworms collected in Indiana and Illinois have low to moderate levels of resistance.”

And there’s the rub: when every female lays thousands of eggs, and three or four generations of females lay their thousands of eggs every summer, it doesn’t take long for the gene pool to change.

The corn we grow doesn’t produce Bt, because the seed hasn’t been genetically modified to do so, and we don’t spray the ears with Mustang Max or Warrior or any other pyrethoid because

“While pyrethroids may be amongst the least toxic of insecticides, they are an excitatory nerve poison, acting upon the sodium ion channels in nerve cell membranes:

  • by sending a train of impulses rather than a single one, they overload the pathways, blocking the passage of sodium ions across cell membranes; similar in action to organophosphates (which include the now banned DDT); inhibits ATPase, which affects the release of acetylcholine, monoamine oxidase-A and acetylcholine;
  • inhibits GABAa receptors, resulting in convulsions and excitability (and more ‘minor’ problems such as sleep disorders);
  • known to be carcinogenic;
  • liver damage
  • thyroid function
  • cause chromosomal abnormalities in mice and hamsters;
  • are highly toxic to insects, fish, and birds;
  • mimic estrogen, leading to estrogen dominant health problems in females and feminizing effects in males, including lowered sperm counts and abnormal breast development;
  • sublethal doses have produced a wide array of abnormal behaviors, including aggression, and disruption in learning and learned behaviors”

It seems better in the long run to share a little of our corn with worms.

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