Two major pests attack pearl millet, the most important food crop in Niger in West Africa, and some scientists and policymakers believed that only one of them could be controlled.
But Virginia Tech entomologist and IPM Innovation Lab Director Muni Muniappan had a hunch.
He was determined to find out whether researchers in Niger could successfully battle both insects. So he applied for a grant from the Sorghum and Millet Innovation Lab at Kansas State University, seeking to tackle both pests using nonchemical means.
However, the reviewers were skeptical.
They were willing to underwrite his campaign against the pearl millet headminer, but not the pearl millet stem borer.
“Probably if I had been on the review team, I would have been skeptical too,” Muniappan said.
Muniappan sought to use an egg parasitoid, a small wasp that attacks an insect’s eggs, to combat both the stem borer and the headminer. But the wasp, Trichogramma, had two strikes against it. It had not been found on the stem borer in the field, and it also had not been proven to attack the headminer eggs.
So reviewers authorized Muniappan’s work to combat the documented natural enemy while demanding proof that the second half of his proposed campaign had a chance of succeeding.
Muniappan set to work on the headminer using a tiny wasp called Habrobracon hebetor, a larval parasitoid that lives on juvenile headminers and eventually kills them.
Muniappan and his international collaborators from ICRISAT-Niger and INRAN-Maradi, a national agronomic research institute in Niger’s third-largest city, began their work by breeding more of these wasps in the lab.
The wasps are parasitic, meaning they live and reproduce on other organisms, so the team bred them on the Indian meal moth insect. They then released the wasps into the field to control the pearl millet headminer.
But Muniappan refused to stop thinking about his Trichogramma theory. He and the team took what steps they could to work on Trichogramma along with the larval parasitoid work.
Because they couldn’t find Trichogramma on the stem borer in the field, Muniappan and his collaborators worked in reverse: They multiplied the Trichogramma wasps on Indian meal moth eggs and then infected the eggs of the pearl millet stem borer along with the pearl millet headminer with the wasp in the lab.
Muniappan’s hunch proved correct, leading to the first report of an egg parasitoid controlling these millet pests.
Niger is one of the world’s poorest countries, frequently experiencing drought and famine, so destructive pests on the country’s most important food crop are a deadly problem.
The discovery that Trichogramma kills the eggs of the millet headminer could halve the amount of headminers attacking pearl millet in Niger. And the additional finding that this wasp will also attack the eggs of the stem borer ensures that there will be more millet for the people of Niger to eat, Muniappan said.
Now, Malick Ba of ICRISAT-Niger and the team in Niger are mass-multiplying both the egg and larval parasitizing wasps in the lab for release in the pearl millet fields for the next growing season, which starts in June.
“I knew that if correct, my hunch about Trichogramma would be very beneficial for the millet crop in Niger, so I was determined to see it through,” Muniappan said. “Using Trichogramma to attack the eggs of both the headminer and stem borer will allow us to further ensure the health of Niger’s millet crop and overall food security.”