Evaluation of Commercially Available Beneficial Insect Habitat Seed Mixes on an Organic Farm

Overview:

Plantings referred to as ‘beneficial insect habitat’ have become popular over the years with both organic and conventional farmers. These plant groupings usually contain a variety of flowering plants that provide pollen and nectar that insects need for reproduction as well as a “safe” habitat free from pesticides and disturbances. The general consensus is that if you provide the beneficial insects (predators & parasitoids) with the resources they need, that they will attack and keep all of your pests under control, thus decreasing the need for pesticides. However, while these plantings do provide some of the life sustaining resources needed by the beneficial insects, there is little or no research indicating its effectiveness in increasing the “good bugs” and decreasing the “bad bugs”. 

 

Objectives:

The purpose of my masters project is to evaluate the use of beneficial insect habitats on small farms in the South. Our primary aim is be to help organic growers, but we believe data generated will be useful to conventional farmers as well. Very little data exists to aid farmers in their attempts to increase natural control of pest insects, resulting in the scarcity of guidelines. Some growers are creating their own beneficial insect habitat based on hearsay or anecdotal information, while others have turned to commercially available habitat seed mixes. While it appears that some of the commercial blends offer some of the life sustaining resources needed by beneficial insects, there is no data demonstrating growth, beneficial insect attraction or value to nearby crops in the southeastern United States. The objectives of this proposed study are to; 1) examine the purity, germination and on-farm growth characteristics of selected commercial seed blends; 2) determine what insects (beneficial or otherwise) are attracted to select cut flowers, cover crops and commercial beneficial insect habitat blends; and 3) to construct and evaluate a simple beneficial insect habitat based on existing literature.

 

Project #1: Seed germination

In general, parasitoid wasps are very small (some measuring no more that 1-2mm) and need flowers with extra floral nectaries or accessible nectar and pollen. The three seed mixes were chosen based on the flowers types they contained. One had many small umbelliferous flowers like fennel, dill and carrot, one had very large showy cut flowers such as black-eyed Susans, Shasta daisys and Coreopsis and the third seed mix fell somewhere in the middle with a mixture of both small and large flowers.

1) For each of the three seed mixes we wanted to look at the germination, purity and composition of each seed mixture. Ideally, we wanted to separate three packets of each seed mix. However, all three mixes were offered in the different sizes ranging from a 1-ounce packet to a 5-pound bag. After many months, all the seeds were separated using a variety of techniques:
Various kinds of sieves South Dakota Seed Blower – an air column seed blower that blows the lighter weight seeds up and leaves all the heavier stuff at the bottom A LOT OF HAND SEPARATION – this is my good friend and former lab technician Melinda Gibbs working on some very tedious small seeds

After all the seeds were finally separated we could start the germination tests. I tested 100 seeds of each flower species from each seed packet to (under ideal circumstances) how well they would germinate. We put the seeds on special paper (germination blotters) in petri dishes and placed them in germination chambers for several days and recorded how many germinated.

Rudbeckia hirta
(Blackeyed Susan)
This is a good example of well germinated seeds.

Angelica aropurpurea L.
(Angelica)
This is (obviously) an example of poor germination.

What the… some of the seeds (especially buckwheat) showed poor germination due to the presence of Bostrichids or seed beetles!

Project #2: Insect catalog

We took the three seed mixes, as well as some commonly grown cut flowers (Celosia “Cock’s comb” and Zinnia) and herbs (buckwheat and fennel), and planted them on an organic farm. After they became established we sampled them periodically in order to identify what kinds of insects were visiting the flowers.

WOW!!! This was REALLY challenging. I had to grow adequate numbers of transplants of each kind of plant, plus all the plants for the third part of my project. All in all, I think that at any given point that spring I have well over 10,000 plants going in our greenhouse at the lab.
I never knew I had such a green thumb! Actually most of them lived and thrived.
The next step was to transplant them onto the Center for Environmental Farming Systems Student Organic Farm in Goldsboro, North Carolina. The seed mixes were transplanted based (approximately) on the seed composition of each packet. To do this and get the spacing just right, we devised these planting boards where in each hole we planted a different plant and repeated the pattern over the entire 20 foot strip. We repeated each flower strip 3 times over the farm. Here my first summer helper Shawn demonstrating how we planted.
After the flower strips were transplanted, we needed to mulch the plants because the soil is very sandy and water conservation is really important. Here I am using a “Bale Chopper”. It was really cool, you put a bale of hay or straw into the back of the tractor attachment and it gets chopped up and actually sprays out nice little manageable bits of mulch. What would have been REALLY great was if I had worn some long sleeves because the straw we used was infested with follicle mites, which burrow in the skin, last for a week or two and are about 1,000 times more miserable than chiggers. What fun!
  This is what the “flower strips” looked like after they were up and growing. You can see (from left to right) one of the seed mixes, fennel and Celosia.
Now for the real part of the project. We wanted to get an idea about the different insects that were using each of the 7 different planting on the flower strips. So, using aerial nets, soil pitfall traps and a machine called a “D-vac” (which is actually like a big bug vacuum cleaner) we sampled each one of the seven flower components in all three flower strips for 7 dates in the summer of 2003. In this photo, David Orr, my major advisor, is wearing the D-vac, Shawn is collecting some of the quick strong flying insects like dragonflies and wasps with an aerial net and Maritsa is using the long hose of the D-vac to collect the rest of the bugs.
“What happens with all the bugs you collected?” you ask. Well, I will spend the next 6 months identifying them down to the family level and place them in categories based on what they eat. Predator, parasitoid, hyperparasitoid, herbivore, etc. Once we got into the samples and saw the tens-of thousands of insects we were dealing with, we decided that I would identify all the big stuff (anything over approximately 2-3mm and would take some subsamples of al the little stuff. Here is a photo of a subsample. For the record, I have identified over 20,000 insects and am not quite half way done!  

Project #3: Field Trial

This is the project that pulls everything together. We wanted to take a commonly grown crop (tomatoes) and plant what we determined to be an ideal beneficial insect habitat mix around the plot and see if the presence of this habitat actually increases the beneficial insects (good bugs) and decreases pests (bad bugs). However, this is really difficult to measure directly. So we used indirect measures of predator and parasitoid activity. Using moth eggs we could measure predator and parasitoid activity and by monitoring field populations of hornworms we could measure parasitoid populations.

We used small plots (4 rows of 14-15 plants) surrounded on all sides by our ideal beneficial insect habitat mix. We also needed a control plot that we decided to surround with foxtail millet (a grass-like plant) which has few pests.
Like I mentioned before many of the parasitoids we are looking for are incredible tiny. Trichogramma spp. are usually no more that 1mm in total body length, so it is incredibly difficult to monitor them in a field situation. Instead, we used tomato fruitworm and hornworm moth eggs. Trichogramma lay their eggs inside the moth eggs and as the tiny wasps develop they turn the egg, which is naturally a greenish-yellow, to dark gray. Here are some nonparasitized hornworm eggs, which are roughly 2-4 times bigger than fruitworm eggs, so think how small a parasitoid wasp must be to lay about 15 eggs inside one of these eggs!
We also recorded how many hornworms were found in each plot and whether or not they had been parasitized. The parasitized ones were really easy to pick out.  The parasitoid wasp inserts its eggs into the live caterpillar and the wasp larvae develop in the caterpillars hemolymph (or bug blood). When the wasps are ready to pupate just before becoming adults, they break through the caterpillar skin and form white cocoons on the caterpillars back, like these.
So… That is what I have been up to for the last 2 years. I am not able to publish any results at this time because I am still working on my thesis. I am hoping that I will be done by Christmas 2004 or very early January 2005. I still have a long way to go but will try to update this as soon as I have some free time.
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