Cornell University

Our final trial was finished on October 2^nd. We had been collecting data for about four months, amassing a pile of data sheets. You can see some of them above. I spent a few days inputting all the data into excel a few weeks ago. Connor just sent me the preliminary graph as seen below that shows the preference of the different species we looked at. It is difficult to see the insect species names and plant species names in the picture so I will try to describe a bit of what it says. Gryllus is on the top right, Pterostichus is on the bottom right, Harpalus is on the bottom left, and Allonemobius is on the top left. As predicted in my previous post, Gryllus ate the majority of most species except velvetleaf and hairy vetch. Radish was also one of the least preferred (it also has a harder seed coat). One of most significant findings we found overall was Gryllus’ preference for red clover. They ate every red clover seed! The others they preferred most were pearl millet, triticale, giant foxtail, ragweed, winter barley and annual ryegrass.

The graph shows clearly that Pterostichus preferred pearl millet seeds to all others. If I had to guess based on all the counting I did I would’ve said Pterostichus preferred triticale and radish more than they apparently did in contrast to the millet. Millet was always their first choice though.

Harpalus seemed to favor the Giant Foxtail. This is important because, as I spoke of before, Giant Foxtail is a weed, it isn’t used as a cover. Perhaps Harpalus is ultimately beneficial (at least from an economic perspective) in an agro-ecosystem because of the suppression of that weed it offers. On the other hand it also has a particular taste for annual ryegrass, pearl millet, red clover, and white mustard. These are all commonly used cover crops that can have huge benefits on production over time. Harpalus’ potential benefit (or potential for harm) would depend on the agricultural system.

I haven’t spoken much about Allonemobius allardi. Maybe this is because until recently Connor was still debating which species of cricket this was. They are a smaller cricket than the Gryllus species we tested. We would spend hours sweeping nets across the tall grasses out behind the processing center looking for them. We caught hundreds. Interestingly they were the only species to prefer Ragweed more than the others. Ragweed is another one of the three plants that we tested that aren’t used as cover crops. They also preferred pearl millet, giant foxtail, and winter barley to the others.

These are preliminary results. Connor plans to do quite a bit more work with these numbers before they can be applied.

The final tasks have been cleaning petri dishes and recovering the traps from the field.

Thank You Connor, Matt, and the entire Sustainable Cropping Systems Lab!

Of the 13 plants we are testing in SPOC, 10 of them are often used as cover crops.

Cereal Rye is thought to be the best cool season cereal cover for absorbing unused soil nitrogen that would otherwise wash out of the system. It is a dynamic crop that has been used in many different cover crop systems, offering benefits including erosion control, additions of organic matter and weed suppression.

Winter Barley is often used to protect soil from erosion, provide weed suppression and act as an input of green manure and organic matter in the cool season when cultivation of a grower’s cash crop isn’t possible.

Radish is a plant that has been growing in its appeal as a cover crop in recent years because of its ability to protect from erosion, scavenge nutrients, suppress weeds, and alleviate compaction while creating far fewer of the challenges associated with residue in many other covers.

White Mustard is preferable as a fall seeded cover crop that winter kills. So, while mustard offers benefits such as addition of organic matter, the breaking up of hard pans, weed suppression, etc., plants won’t survive the winter and fields will be better prepared for spring planting.

Crimson Clover is a legume that is often used to provide spring nitrogen for full season crops.

Red Clover is a very common cover crop that is known for fixing nitrogen, protecting soil from erosion, suppressing weeds, helping improve soil tilth, as well as providing forage.

Triticale is known for its excellent value as forage for grazing livestock. The plants also leave a heavy residue on the soil offering good weed suppression and protection from erosion.

Pearl Millet is a warm season annual grass that is often used as forage. These plants are known for having less of a demand for nutrients than other cover crops, making them potentially useable on lands unsuitable for other covers. It is primarily used as a weed and nematode suppressor, as well as for protection from erosion.

Hairy Vetch is a legume that fixes a greater amount of nitrogen in contrast to other cover crops. As plants grow they are known for spreading out and become very dense. They offer very good weed suppression and protection of soil erosion. Vetch can also be harvested and used as forage.

Annual Ryegrass is usually used a ‘catch crop’ because it is known for having a dense shallow root system that can tolerate compacted soils. ‘Catch’ crops are crops that have a particular capability of absorbing nitrogen that would have otherwise washed out of the soil and been lost from the system. Annual Ryegrass also has other benefits including erosion control, improvement of aggregate stability and compaction prevention.

September has been consumed by trials that test the preference of Harpalus, as well as two species of crickets (Gryllus pensylvanicus and Allonemobius allardi). From August 20^th until September 27^th we ran 260 Harpalus trials which come out to 20 replications of the experiment (20 trials of each of the 13 plant species), 105 Allonemobius trials which come out to about 8 replications, and 72 Gryllus trials which come out to about 5 and a half replications.

You can see some of the physical differences between these two species of cricket in the pictures above. The first picture is of a Gryllus Pensylvanicus, the second is Allonemobius allardi. The third picture shows a Gryllus cricket molting. When I went to check that dish I actually thought this cricket was dead. Then it starting jumping, trying to shed its shell.

Gryllus pensylvanicus is one of the most common species of cricket over the majority of the U.S. and much of Canada. The Gryllus are the larger of the two species we have been testing. We’ve found them to be anywhere from a third of an inch to probably a full inch. It depends how old they are. They are known to be major predators of both seeds and other invertebrates. Similar to the beetles their population is known to max out in the fall because that it when seeds are most prevalent, after they have been shed (the crickets are commonly known as the ‘fall field cricket’). These bugs really differ from the beetles and the cricket species in terms of their life cycle because of their range in diet. It is generally accepted that years with greater seed abundance produce greater populations but the variety in available prey that the species has gives it really good flexibility. But, their ability to prey on invertebrates has been proven to give them an important advantage in years with worse seed abundance. It is actually debated how significant the effect of seed abundance is at all with these species because of this range. I found an interesting study talking about how certain genotypes in these types of insects can be preferable in years of greater seed abundance, and others can be preferable in years of worse seed abundance.

 It has been easy to notice from these Gryllus trials that they aren’t exactly picky when they are hungry. We have seen one bug eat all 26 seeds in one 24-hour interval. We have seen one bug eat all 26 seeds and a good amount of the paper towel that lines the dish. They are much more rambunctious than they other species we’ve looked at. The only two plant species that they noticeably stay away from are velvetleaf and hairy vetch because of their hard seed coats.

We’ve been collecting a lot more Harpalus pensylvanicus these past few weeks. We’ve been finding about 15-30 a day, which is a very sharp change from the beginning of August. Harpalus is a genus of ground beetle with different species commonly found throughout the contiguous United States and Canada. Harpalus pensylvanicus is known as a species prevalent in croplands. You can see they are pretty easily ID-able by their tan/orange legs along with a more shiny body in contrast to other similar looking species. As seeds make up the primary portion of their diet, they have been found to be most active in the fall after weeds and the like have shed their seeds. This is why we didn’t see too many throughout the summer. Different studies have worked at trying to pinpoint the species’ eating habits and preference. (As I said in the previous post, few if any of these studies refer to cover crops). They are an important predator of many weeds. One study told of how the trials they ran resulted in this species eating up to 90% of weed seeds. It’s important to consider that not all weeds are considered cover crops. There are weeds that are accepted as generally harmful to agricultural systems from both an economic and ecological perspective. The purpose of SPOC is to test the preference of these definitive weeds against other species of plants that can are often be thought of as weeds but can be used as cover crops, and to help re-contextualize the discussion surrounding seed predation to include cover crops.

One study (co-authored by Matt Ryan!) looked at Harpalus pensylvanicus preference of Giant Foxtail. Giant Foxtail is an example of a plant that isn’t considered useful as a cover crop, it is generally considered to be undesired in agricultural fields. The study was run through two seasons and found that not only did the beetles prefer newly shed foxtail seeds to older aged ones, but also the population density of beetles was found to hit its maximum at the same time foxtail seed shed began.

The pictures above show the seed counter I spent time using in August to separate Giant Foxtail seeds from small debris and count them. I had never seen a machine like this before so it was fun to spend a few hours working with it. You set it so it rotates and vibrates with a certain amount of power depending on how heavy the seeds are you hope to count. The seeds travel around the cylinder while other debris stays behind. Eventually the seeds make their way to the top and pass across a laser as they are deposited out of the spout. They are counted one by one digitally.

In March I was delighted to be hired by Matt Ryan’s Sustainable Cropping Systems Laboratory as a research assistant full time for the summer. Work is made to be so much easier when you’re not only surrounded by very smart and honest people but also have the opportunity to be challenged to understand the complexity of your discipline in greater depth. This happens to be just the experience I’ve had the pleasure of enjoying this summer.

As the summer has progressed I’ve been working more and more with one member of the SCS Lab in particular, the great Connor Youngerman. Connor has three experiments ongoing at the moment. In June my two fellow RAs and I helped begin one of them, S.P.O.C. SPOC is an experiment that was designed earlier this year to test the seed preference of two of the most common local predators in this region of New York State, Harpalus pensylvanicus and Gryllus pensylvanicus.

Seed predation is an interesting subject from the perspective of the SCS lab. Researchers often consider these bugs beneficial because they eat weed seeds that would otherwise compete with agronomic crops for sunlight and water. What those researchers can sometimes overlook, however, is the fact that many of those species that they consider weeds can also be used as cover crops. Cover crops are seeded purposefully and are meant to provide a variety of different ecosystem services for a variety of different reasons. The appeal of cover crops is that their use can provide a way to stimulate ecological health while reducing input (in terms of cost) and maintaining yield consistently over time. By understanding the preference of these insect predators on different plant species within this cover-crop context, one can understand how to direct the use of such covers more efficiently.

For the past couple of months we have been testing 13 different species of weeds and/or cover crops, depending on whom you ask. They include: cereal rye, winter barley, velvet leaf, ragweed, radish, white mustard, crimson clover, red clover, triticale, pearl millet, giant foxtail, hairy vetch, and annual ryegrass.

You can see in these few snapshots some of the protocol upkeep that’s involved with the experiment. About 80 pitfall traps have been ‘installed’ in the field surrounding the Leland Processing Center, where most of the Lab’s experiments are maintained. Every day each trap is inspected and insects of interest are collected and taken back to Leland. Up to this point neither of the species of interest has been found in any significant quantity. We’ve been testing another common seed predator in the area, Pterostichus melanarius. Connor has said that he expects us to begin find more Harpalus in the coming weeks. We usually find anywhere from 15-50 beetles a day. Once beetles are collected they need to be starved for a certain fixed amount of time to control for their desire to eat. They spend four days in the walk-in cooler, in containers like those shown above, along with a wet paper towel as a source of moisture. Once four days passes they are taken out and placed in a petri dish along with 26 seeds of one species of plant and a moist cotton ball. These trials are termed ‘no choice’ because the bug has no choice of what they can eat. For five days at 24-hour intervals after the bugs are placed in their dishes, we record how many seeds each insect has eaten.