What is RNAi?

• RNAi is a biological process that interrupts the function of messenger RNA(mRNA), which carries DNA's instructions for making new critical proteins.  

• These small pieces of RNA bind the messenger RNAs required to code the critical proteins required by the insect.

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How does RNAi work on rootworm?

• When rootworm larvae ingest root tissue containing the RNAi toxin, the small pieces of RNA exit the insect gut and enter into the body cavity where these small pieces of RNA begin binding with critical messenger RNA.  

• Messenger RNA’s function is to regulate the production of critical insect protein required for insect growth and development.  After ingesting the toxin, rootworm death follows in about 7 days, depending on the actual amount of toxin ingested.

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Why does root feeding/damage by rootworm continue until death after consumption?

• Death from RNAi ingestion is a slow process, requiring about 7 days.  It takes time for the small pieces of RNAi to bind and disrupt the messenger RNA, sufficiently prevent critical protein production and cause death.  

• During this time, the rootworm continues to feed, causing more root damage before death.

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How does RNAi toxin mode of action differ from Bt-RW?

• Bt susceptible rootworm (back in the beginning), stopped feeding after ingesting a small amount of Bt toxin.  Although death requires about 7 days, susceptible rootworm do not continue to feed.

• As rootworm larvae became more resistant to Bt-RW, the level of feeding increased until the larvae ingested a large enough amount of the toxin to die.  

• Highly resistant rootworm larvae continue to feed and complete development, causing the high level of root damage currently occurring in many continuous corn fields.

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How quickly will rootworm develop resistance to RNAi?

• In laboratory studies, field collected rootworm developed resistance in 2 generations which is equivalent to two growing seasons.  Click here to download the full 2018 Monsanto paper.

• The source of these rootworm were the surviving beetles from a 40 ac field with a record of Bt-RW failure and planted to corn containing RNAi.  

• Clearly, this new toxin is susceptible to rapid rootworm resistance development without careful management.  Commercially, SmartStax Pro™ and Vorceed™ are the corn seed containing this new RW toxin.

• As a result of this high rootworm potential resistance, growers and consultants should seriously consider incorporating an integrated rootworm management approach to help preserve the effectiveness of this new toxin.