Today, we split up into two groups. While John, Louie, and Marshal spent most a majority of class calculating engineering metrics for our field LED scheme, the rest of us hammered out how to make an appropriate field apparatus. Our plan is to start our experiment by the start of April. That means having 90 complete apparatuses in the field. Not only do we have to make these apparatuses, we also have to figure out how to orient them in the field so that each replicate is independent. Their orientation is also limited by the electrical engineering!
Making the perfect apparatus
Imagine a fancy tomato cage. Surrounding three plant species, our tomato cage will house LED lights and be able to sample flying and ground insect communities. We’ve previously talked about a design, but many specific aspects remained undecided.
Chicken wire: First off, we’ve decided to partially surround our tomato cage with chicken wire. The chicken wire will function to keep out mammals (rabbits), and we’re hoping it will also provide a suitable web-building substrate and encourage spider colonization of our plants.
LEDs: 60 of 90 total apparatuses will contain a set of LEDs. Artificial light at night (ALAN) is the basis of our experiment, so this part of the tomato cage is super important. Last class, we ordered a role of LEDs, which we messed around with today. Disappointingly, these lights were dimmer than expected. We played around with ways to make these lights brighter. First, it was clear that we needed to move them closer to the plants. We originally decided to mount them atop the tomato cage, about 2 feet from the ground. Now, we would have to move our lights significantly lower to the ground in order to obtain a certain brightness. We also played around with creating a sort of ‘lamp shade’ that would surround and direct the light source downward. This worked well, and we ultimately decided on using a Styrofoam bowl. This bowl functioned to direct and concentrate light downward.
As it happens, we have actually decided to order new, brighter LEDs. After many calculations by John, Louie, and Marshal, it is more feasible to use brighter (significantly more expensive) LEDs. This solves our tomato cage problem. We’re still going to use the styrofoam bowl shade, but will attach the lights to the top of the tomato cage. To increase attractiveness to insects, we are going to hang some sort of reflective material (paper or screen) from the styrofoam cup. As the LEDs shine light downward on our plants, this material will also brighten to help attract insects.
Sticky and Pitfalls: We will use a non-reflective, clear surface as a sticky trap to sample flying insects. Each tomato cage will have a single sticky card fastened on all 4 sides. Tentatively, we plan on creating our own sticky cards with acetate sheets and tanglefoot (though, I vote for buying some if possible). Each tomato cage will also contain one (or two?) pitfall trap(s). Pitfalls function for ground insect sampling, but can also function as a predator removal treatment. For 30 replicates, we may include a non-lethal pitfall in order to remove cursorial spider predators from the system.
Mylar Tape: We seem to be worried about birds using our cage as a perch and possibly eating our sampled insects. Mylar tape will function to deter birds.
Things we still need to buy:
- Propylene glycol or ethanol for pitfall traps
- Sticky cards?
- Window screen or Write In the Rain paper
Setting up 90 apparatuses in the field is tricky. Each apparatus has to be a certain distance away (about 3 meters) to create independence. This makes it difficult to power each LED. If replicates are 3 meters apart, we soon run into a problem of voltage drop. However, John, Louie, and Marshal have solved this problem. They suggest using three 12V car batteries, each responsible for powering a third (60 of 90) of lit replicates. Each battery will contain 3 parallel circuits.
Also, we’re going to invest in more expensive, brighter LEDs. These lights will be more cost effective (surprisingly), because we can get much more power over a shorter segment of LEDs.
Ultimately, we have decided on a grid scheme to set up apparatuses in the field. Our experiment will consist of 3 grids. A grid will be 5 by 6 apparatuses, and will be powered by a single 12V battery. The battery will power 20 LED units in 3 parallel circuits. This scheme is necessary to avoid voltage drops across many lit cages.
However, Asia brought up a good point: we need to have equal numbers of LEDs attached to each battery source, in order to obtain equal brightnesses. In this way, we might have to change the number of each lit treatment in a grid (more on this next class).
We made a lot of progress today! There is still a ton of work to do in order to start the experiment by April!
On a semi-side note: we’ve planted about 200 Brassica nigra seeds! They’re germinating in conetainers at the greenhouse!
- Price window screen
- Find and price mylar strips
- Price Propylene glycol or ethanol
- Get more styrofoam
- Buy new lights
- Update on field permission?
(1:40 – 2:30) Group discussion on things we need still need to buy and any new ideas/concerns people have.
(2:30 – 3:50) Split into two groups again. One group will attempt to streamline a process for creating tomato cage materials (chicken wire, sticky cards, pitfall traps, etc.). The other group will solidify and precisely diagram how to set up field apparatuses.
(3:50 – 4:15) Group discussion. Mainly, what have engineering group determined? As a group, let’s decide where we want to have each block at the Experimental Field.
(4:15 – 4:30) Discussion of finals schedule and spring break schedule.