How rootworms can adapt and become resistant to the practice of crop rotation.
You know it’s not only you and me who are constantly evolving by adjusting to our living environment; There are millions of others too who are doing this job as efficiently as it could be. Researchers from University of Illinois have discovered that gut bacteria facilitate the adaptation of the western corn rootworm, which is basically a beetle, to crop rotation.
Crop rotation is a practice of growing two different types of crop in the same field in sequential seasons. Corn and Soybean are two important crops in the Midwest Corn Belt. They are grown alternately, meaning that after a season of farming corn crop, farmers usually plant soy in the same field. This practice should wipe out corn rootworms (Diabrotica virgifera virgifera) which feed on corn during summer and lay eggs in the fall. The larva feeds essentially on corn roots during spring, which causes severe root injury and yield loss. In order to avoid this, soybean is grown in the subsequent season, so that when larvae emerge, it feeds on potentially toxic soy and dies. This way crop rotation had been effective for several decades until recently.Things have changed, however, and farmers began to find rootworms even in the rotated fields.
A research team led by Chia-Ching Chu now analyzed the microbiota of resistant and non-resistant beetles. They dissected almost 4000 insects and found significant differences in the two types of microbe’s community in their gut. The specialized microbe community helped the resistant rootworms to physiologically adapt to consuming soybeans.
The scientists also found that resistant rootworms had elevated levels of cysteine protease inhibitors when being the soy field. Cystein proteases are group of enzymes that are present in Soybean leaves/foliage. When rootworms feed on them, the proteases degrade important proteins of rootworms and therefore, the worms die. Due to evolution, resistant rootworms produces Cysteine protease inhibitors, which means they degrade those enzymes and hence, the rootworms can now feed on soybean without getting affected.
This is perhaps why resistant rootworms are able to survive in soybean fields after hatching eggs and crop rotation was unsuccessful.
The study published in PNAS Early edition paves way for the need of much deeper understanding of the host-microbe relationship from an evolutionary perspective that may have significant importance in sustainable management.
Reference:Chu CC, Spencer JL, Curzi MJ, Zavala JA, & Seufferheld MJ (2013). Gut bacteria facilitate adaptation to crop rotation in the western corn rootworm. Proceedings of the National Academy of Sciences of the United States of AmericaPMID: 23798396
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