Frequently Asked Questions

Questions Frequently Asked by Farmers

What midge tolerant wheat varieties are commercially available?

AAC Camerson VB, AAC Foray VB, AAC Jatharia VB, AAC Marchwell VB, AAC Prevail VB, AAC Tenacious VB, AC® Conquer VB, AC® Enchant VB, AC® Fieldstar VB, AC® Glencross VB, AC® Goodeve VB,  AC® Shaw VB, AC® Unity VB, AC® Vesper VB, CDC Carbide VB, CDC Titanium VB, CDC Utmost VB, KWS Sparrow VB and SY479VB are all commercially available. 

Who funded the development of these varieties?

These varieties were developed using funds from the Western Grains Research Foundation check-off program, AAFC, CDC and variety distributors. AAC Camerson VB, AAC Foray VB, AAC Jatharia VB, AAC Marchwell VB, AAC Prevail VB, AAC Tenacious VB, AC® Conquer VB, AC® Enchant VB, AC® Fieldstar VB, AC® Glencross VB, AC® Goodeve VB,  AC® Shaw VB, AC® Unity VB and AC® Vesper VB were developed through the work of Agriculture & Agri-Food Canada wheat breeders at Winnipeg and Swift Current. CDC Carbide VB, CDC Titanium VB and CDC Utmost VB were developed at the Crop Development Centre at the University of Saskatchewan. KWS Sparrow VB was developed by KWS and SY479VB by Syngenta.

Do all midge tolerant wheat varieties use the same form of tolerance?

Yes, all varieties contain the Sm1 gene which provides midge tolerance.

How does the Sm1 gene work?

When the insect begins to feed on the seed, the Sm1 gene causes the level of phenolic compounds (naturally occurring organic acids in wheat kernels) to elevate more rapidly than in wheat kernels without the Sm1 gene. The higher levels of phenolic acids cause the midge larvae to stop feeding and the larvae starve to death.

The mechanism that triggers the production of phenolic acids does not operate if midge larvae are not feeding on the seed, and in addition, these acids are reduced to normal levels by the time wheat reaches maturity — thus not affecting the quality or food value of the harvested grain.

Is this a GMO?

No. The Sm1 gene is a naturally occurring gene in wheat. Sm1 was incorporated into CWRS through crossing with a winter wheat variety from the U.S. This used traditional plant breeding techniques, not biotechnology.

Why is the Sm1 gene likely to break down?

The Sm1 gene does not change or “break down”. However, the Sm1 gene is single gene insect resistance, which has a history of becoming ineffective over time as insect populations change. Since a small number of midge carry a mutation allowing them to attack varieties carrying the Sm1 gene and survive (referred to as virulent midge), these can mate with other virulent midge and quickly build up a large population that can feed on wheat varieties with the Sm1 gene. The objective of the interspersed refuge is to slow down the potential shift in the midge population towards the virulent biotype.

What is the difference between virulent and non-virulent midge?

Virulent wheat midge are those resistant to the effects of the Sm1 gene. They carry a mutation that allows them to attack wheat plants with the Sm1 gene and survive. A very low level of virulent midge exists within the natural midge population.

Non-virulent wheat midge cannot survive the Sm1 gene contained in midge tolerant wheat. If non-virulent midge mate with virulent midge, the progeny of this cross will be non-virulent since this is usually the dominant gene.

What is a refuge?

Refuge refers to the 10% susceptible variety in the varietal blend (VB). The blend is 90% tolerant and 10% susceptible.

What is an interspersed refuge system?

An interspersed refuge system means that the refuge variety is evenly distributed (inter-seeded) throughout the field. This is different to the Bt corn refuge management system where the refuge is grown as a block beside or within the same field.

How does the interspersed refuge system work?

In an interspersed refuge system, non-virulent midge survive on the 10% susceptible plants interspersed throughout the wheat field. The non-virulent midge would inter-mate with virulent (resistant) midge. The progeny of this cross would be non-virulent. This prevents a build up of virulent midge, and could extend the life of midge tolerance to 90 years or longer.

What happens if midge tolerant wheat is grown in a pure stand?

If midge tolerant wheat is grown in a pure stand, only virulent (resistant) midge will survive. The virulent midge would mate only with other virulent midge. A large virulent population quickly builds and feeds on tolerant varieties. Without an interspersed refuge system, midge tolerance could break down within 10 years.

Could 10 percent of the crop (the refuge variety) be really damaged by the pest?

Yes, it is possible that the refuge variety will suffer severe damage under a heavy midge infestation.

Has this midge tolerant system proven to be as effective as spraying Lorsban?

We have very little experience comparing field scale use of insecticides versus field scale production of varieties carrying the Sm1 gene. However, it appears that the Sm1 gene is effective in protecting the crop from large scale losses in yield due to wheat midge. There may be some down-grading in varieties carrying the Sm1 gene since the midge larvae need to nibble on the wheat kernels before they die.

Why is it necessary to limit the use of farm-saved seed to one generation past Certified Seed?

This condition is critical because wheat midge may attack the refuge variety and the level of the refuge in farm-saved seed may change substantially over multiple generations. For example, under an extremely heavy midge infestation, the susceptible refuge variety could sustain up to 50 percent yield loss. To keep the refuge at the desired level of 10 percent of the plant population, it is necessary to limit the use of farm-saved seed to one generation past Certified Seed.

Why is it necessary to sign a stewardship agreement?

The stewardship agreement is necessary to make sure that the importance of the refuge is communicated to farmers and that the refuge is followed. We need to preserve midge tolerance so farmers can continue to benefit from this technology. The agreement ensures that all farmers will maintain the interspersed refuge system in midge tolerant wheat. This is necessary to preserve midge tolerance because:

  • The tolerance is based on a single gene, which has a history of becoming ineffective over time. An interspersed refuge system could extend the life of midge tolerance from as little as 10 years to 90 years or longer.
  • It took researchers more than 15 years to move this single gene into spring wheat varieties.
  • No other known source of midge tolerance has been identified so we all need to work together to maintain this valuable trait for today and for generations to come.