Sex and death in the cornfields, Part II- Why rootworms?

Written by Stephanie Gorski

Hi, I started this series to explain a little more background behind the news and opinion articles you may have seen about Bt-resistant corn rootworms, with scary titles like Voracious worm evolves to eat biotech corn engineered to kill it and Evolution one-ups genetic modification. I started out talking about the system as it was originally developed for moths, but I wanted to come back to talk about why rootworms are so good at developing resistance to Bt crops. Part I of this article talked about refuges and how they are used to slow insect resistance, so I’m assuming you know how a refuge works. If you don’t, check out Sex and death in the cornfields: What is a refuge?

Diabrotica virgifera virgifera — Western corn rootworm. Image by S Gorski.

There are several different pestiferous species of rootworms, but they are often lumped together because their larvae are difficult to tell apart. The Western corn rootworm (Diabrotica virgifera virgifera) is the most damaging and most studied.
As you may recall, transgenic Bt-expressing corn targeting rootworms has only been around since 2003, and there are already reports of resistance. Resistance has been confirmed in Iowa. Reduced susceptibility has been reported in Colorado, Minnesota, Nebraska, and South Dakota. (Reduced susceptibility is basically the same idea as resistance, but is defined more loosely; there is a lower standard of evidence to meet.) So it looks like there will be more resistance occurring in the near future.
It looks like we haven’t been as effective in slowing resistance development with rootworm-active transgenics as with moth-active transgenics. Why? There are lots of things about the rootworm system that make it less simple and less elegant than the moth system. Continue reading →

Sex and death in the cornfields: What is a refuge?

Written by Stephanie Gorski

A lot of people have sent me news articles about the spread of Bt-resistant corn rootworm because they know I am interested in transgenic Bt. These articles have alarming titles like Voracious worm evolves to eat biotech corn engineered to kill it and Evolution one-ups genetic modification. Yes, unfotunately, corn rootworm that are resistant to transgenic Bt corn are real (Cullen 2013, EPA 2014a). But the story is more complex than you’d think from these headlines. To explain, I’d like to talk about IRM (insect resistance management), specifically, the IRM for Bt corn targeting pest caterpillars (Lepidoptera). Please note that corn rootworms are not Lepidopterans, but Lepidopterans are a good model for understanding how IRM works. Continue reading “Sex and death in the cornfields: What is a refuge?” →

Pest Control Part 2: How Pesticides are Used in Integrated Pest Management

Doesn't this corn earworm larva look delicious? Image courtesy of Cyanocorax from Wikipedia Commons.

In Part 1 of Pest Control, I discussed what a pest was and how they were divided into categories as well as how those categories overlap. Identifying pests and how they cause damage is only one part of the puzzle. There’s another part of the puzzle that comes along when you start treating the crops and when talking about pesticides, it’s one that’s the most frequently overlooked. Economics need to be taken into account when treating crops because, believe it or not, going easy on the pesticides can actually be beneficial to farmers.
The latest paradigm for pest control in agricultural situations is called ‘integrated pest management’, which I’ll refer to as IPM from here on out. It takes an economical approach to pest management by sampling pests, looking at how they damage crops and what numbers of a pest are sufficient to damage a set of crops. This is much better than randomly spraying pesticides at anything which looks like it might be eating your crops because it takes into account how much money you’ll spend and save on treatments. It also encourages a conservative use of pesticides which not only lessens a pest’s exposure to pesticides and selection pressure for pesticide resistance but also lowers the amount of pesticides sprayed in the field. Although not all farmers use IPM (although most figures I see are well over 50%), it’s the best way to deal with pests because you know roughly how much money you’re saving by treating versus spraying randomly and you limit the amount of pesticides you spray on your fields.
Continue reading →