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William Snyder

Oct 14, 2014
Dr. William Snyder

Dr. William Snyder

A lot of your research focuses on increasing biodiversity in agricultural systems. Why do you think biodiversity on farms is so important?

We know that modern farming practices, which often involve huge monocultures of just a single crop species, have been associated with explosive pest outbreaks. In contrast, it is relatively rare to see any single

species suddenly become very common in more diverse, natural environments. This suggests that the ecological simplification that we see on many farms might be the underlying cause of many pest problems. If we can figure out specifically how and why greater biodiversity is beneficial, and how to practically restore biodiversity to farms, we might be able to capture biodiversity’s benefits.

My lab group works mostly with the predators, parasitoids, and pathogens that attack plant-feeding (herbivorous) pest insects. We have consistently found that greater biodiversity among these “natural enemies” leaves pests with no place to hide in space or time. So, biodiversity is good for biological control.


What exactly does bio-control mean and how does it work?

Biological control, what we sometimes call natural pest suppression, is the combined effect of the many different predators and pathogens that attack pest insects, weeds, and other “unwanted biodiversity” on farms. Beneficial predators and pathogens are naturally present on most farms, but can be disrupted by tillage, pesticide applications, or other disturbances.

salad greens

‘Diversity’ can mean different things. How do you define diversity, and what aspects of diversity are most important to consider in healthy farm ecosystems?

Ecologists generally split biodiversity into two components—richness and evenness. Richness is the number of species that is present, while evenness is the balance in species’ abundances. In our research, we have found that natural pest control is strongest when (1) there are many predator, parasitoid and pathogen species attacking the pest all at once, and (2) when the natural enemy species are similarly abundant. That is, you need both many species and a balance among those species.

Natural enemy biodiversity provides at least two things of value. First, having many species makes it more likely that you will have a natural enemy that is particularly good at killing each of the different pests that may arrive on your farm. Second, when you have many different enemy species that do many different things, this provides a “blanket attack” such that pests have nowhere to hide in space or time. For example, many predatory insects and spiders hunt pests in the plant foliage, while many insect-killing pathogens live in the soil. When both predators and pathogens are present, pests face attack whether they are climbing on the plant or moving from one plant to another across the ground.


What are some projects that your lab is currently working on?

A syrphid eating aphids

A syrphid eating aphids

We always have a lot of different things going on, but there are two new projects that we are particularly excited about. The first is our “Biodiversity and Natural Pest Suppression (BAN-PestS)” project. This was inspired by an interesting observation: long-time organic farmers reported to us that aphids and caterpillars no longer seemed to be a problem in their brassica (broccoli, cauliflower) crops. This is surprising because these are some of the most troublesome pests for beginning organic farmers. The long-time growers suspect that pest-killing natural enemies have become more abundant and diverse on their farms through time. Another possibility is that improved soil quality is leading to “healthier” plants, better able to defend themselves against pests. On both “old” and “new” organic farms, we are tracking predation by looking for the DNA of pest insects within the stomachs of their predators – sort of a “CSI” approach to measuring natural pest control. To search for links between soil quality and plant health, we are carefully characterizing soil quality on each farm, while also looking at the activity of plant genes active in plants’ defense against pests. Our goal is to provide growers with practical information for how to encourage naturally pest-resistant farms.

The other research that we are really excited about is our “A natural approach to human-pathogen suppression: Can biodiversity fill the GAPs?” project, which I talk more about below. Both of these projects are funded by USDA’s Organic Transitions granting program, which is part of USDA’s increasing investment in research useful to organic farmers. Thank you to all the organic growers that have fought for more attention from USDA through the years.


Can bio-control on farms replace pesticides?

Most of the plant-eating herbivores in agricultural crops never become abundant enough to cause noticeable damage. At least in part, this is because most herbivores face attack by many natural enemies that keep the would-be pests in check. So, we know that biological control works to prevent pest outbreaks much of the time. The trick is to find ways to make your farm more welcoming to natural enemies, so that their densities (and benefits) can grow. Avoiding, where possible, the use of broad-acting insecticides is one straightforward way to encourage biological control. Other strategies include planting flowering plants between rows or at field perimeters—many beneficial predatory insects also eat pollen and nectar, and so can benefit from access to these non-pest foods.

Animal feces on a farm

Animal feces on a farm

 Some of your research focuses on increasing food safety by reducing E.coli contamination in crops through increased biodiversity. Aren’t animals sometimes responsible for contaminating produce?  How can further increasing biodiversity on farms help solve the problem?

Wildlife such as deer and birds can indeed contaminate produce when they defecate in or near cropping fields. To try to reduce this risk, some growers (often under pressure from processors or government regulators) are removing all natural habitats such as hedgerows and ponds, to try to discourage wildlife from visiting their farms. But nature also provides us with an army of “natural pooper scoopers” – the dung beetles, flies, and microbes that look at feces and say “yummy dinner!”  These unglamorous and largely unnoticed beneficial insects keep the world from being buried in poop, and probably remove most feces before they have the chance to contaminate produce. Our worry is that growers who reduce biodiversity on their farms to repel wildlife are also removing habitat for dung beetles and other poop eaters – inadvertently making the risk of E. coli contamination worse rather than better. The goal of our “Natural approach to human pathogen suppression” project is to learn more about nature’s pooper scoopers, and what farmers can do to encourage these under-appreciated creatures and the valuable clean-up work that they do.


Many of your studies take place in organic farming systems. Why?

A big challenge in farm ecology work—maybe the biggest challenge—is to do experiments at a scale that is relevant to farmers. However, the very different approaches used by organic versus conventional farmers provides a “natural experiment” on a grand scale. By looking at ecological differences between organic and conventional farms, we can learn more about how species interact more generally. Beyond this, the greater biodiversity typical of organic farms provides just the type of complexity that is likely to keep many ecologists busy for many years to come, trying to figure out what’s going on in these interesting ecosystems. Hopefully what we find will be useful to farmers, and help them manage pest insects without the need for many insecticide applications.

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