Unraveling the secrets of the sawfly in MonDak region

WILLISTON, N.D. (AP) — The wheat stem sawfly, much to the farmer’s dismay, lives a mostly secret life inside – as the name would imply – the stem of wheat plants. It is a creature that has managed, by and large, to keep its secrets close and hidden for 100 years or more, but researchers at the USDA-ARS Northern Plains Agricultural Research Laboratory are working on to unravel those secrets.

Sawflies begin as eggs in the stem of the wheat plant. When the larvae hatch, they begin eating the stem, which causes some reduction in size – but that’s not the real problem of this pest. The real problem comes later when the sawfly larvae drop to the base of the stem and cut it to form overwintering chambers. At that point, the farmer will notice his wheat has fallen over in the field. It’s now unable to be harvested – a total loss due to lodging.

Sawflies have annually caused regional losses of between $100 to $350 million dollars, the Williston Herald reported. It has mostly been a problem in the MonDak and some adjacent Canadian provinces, but has of late been moving south, causing substantial economic losses in Colorado, Wyoming and Nebraska.

“There is a lot of concern the pest is spreading, so there’s a lot of interest right now in finding ways to manage the insect,” said research entomologist Tatyana Rand.

She has been working on a better understanding of the pest for the past six years and is presently examining the effects of rainfall on the pest’s lifestyle.

Historical papers going back to the 1800s and on up to the present day have noted that sawflies do very poorly in both high rainfall or severe drought years. It’s not known how or why, however, rainfall levels are so critical.

“We want to put some rigorous science behind this and figure out what is going on,” Rand said. “Many fields don’t have parasitoids, and we’re trying to figure out why they are not everywhere, so we can make them more numerous and better at attacking sawflies.”

Her study looks at three different moisture levels, both with and without parasitoid wasps, to better pinpoint the factors that play into successful management of sawflies.

For drought scenarios, water is excluded using drought frames, while drip tape adds water for the other extreme. Insect cages surround the test plants to create a controlled environment for each scenario.

In addition to improving management strategies, Rand’s data may also improve the ability to predict wheat stem sawfly outbreaks, providing growers with more guidance for management decisions. They’d have a better idea when to plant solid-stemmed wheat or alternative crops such as pulse or oilseeds.

Another avenue of research came up rather unexpectedly when research entomologist Stefan Jaronski observed that a number of wheat stem sawfly larvae had been infected with a fungus called Beauveria in the course of doing some laboratory work.

Some strains of Beauveria have been used for pest management in other plants without harm to the plants or to people consuming the plants.

In fact, two strains of the bacteria are already registered with the EPA, and thus the human and environmental safety of Beauveria is already relatively well known, making this a particularly appealing line of research.

Jaronski has since been out in the fields of North Dakota, Montana, Wyoming, Nebraska and Colorado surveying for strains of Beauveria. While distribution of the sawfly-killing kind of Beauveria appears to be restricted to a few fields, in those few fields, most of the larvae had the infection.

Jaronski believes the particular strains that work against sawfly are probably endophytic – meaning the bacteria has infected the wheat itself.

Otherwise it could not get into the stem of the wheat plant to infect the larvae and kill them.

“This opens up intriguing possibilities for helping manage the sawflies,” Jaronski says.

While an endophytic Beauvaria infection would not get the present year’s infestation, it could help control the next and keep infestations low in future years. The bacteria can be applied by spraying it on the crop, or by putting it in the soil at planting so it colonizes the plant’s root system – sort of like a probiotic, but for plants.

“It’s not a magic bullet,” Jaronski said. “We still have to figure some things out, but stay tuned.”