klaflamme's blog

A control treatment is a baseline treatment against which one or more other treatments will be compared. Depending on your question, this can be an untreated treatment, a procedural treatment, or a different treatment to that of the treatment group. Determining the appropriate control can be difficult. In an experiment done by researchers to examine how foxes and wolves affect plant communities, they set up fenced plots to exclude predators and outsiders. The hypothesis was the excluding predators in fenced plots will cause higher rodent populations, leading to greater seed predation and dispersal since rodents consume them. But, the result of this was that fenced plots had lower rodent populations because hawks would perch themselves on the fence posts and prey on the rodents. The fence posts unintentionally caused a higher predation rate inside the predator-excluded plots. A better control for this treatment would be to put posts all round the area that is being examined so that they mimic the real fence posts and all hawks don't perch solely on the posts put in for the fences.

After 14 days, 100 surviving plants were transplanted to pots and treatment fertilizer was added (Osmocote Classic 14-14-14, Scotts-Sierra Horticultural Products Company, Marysville, OH). Treatment of application of jasmonic acid and fertilizer amount was randomized, 50 plants were assigned treatment and 50 were not. The same soil used to plant the seeds was used. Half of the plants in each treatment group received one teaspoon of fertilizer, the other half received two. After application of fertilizer, plants were put onto greenhouse bench and watered. Plants were watered daily for 14 days. After 14 days, plant height was recorded on surviving plants. Non-surviving plants were discarded. Treatment of mechanical damage was done by cutting off half of some leaves and 1 spray jasmonic acid in acetone solution was applied. Control received 1 spray of acetone. Plants were placed on heat mat in greenhouse. 

Experiment begun January 19, 2019. Tomato species Lycopersicon lycopersicum, a dwarf variety to mature in 50 days, was used. Seeds used were “Tumbler Hybrid Tomato” (Lake Valley Seed, Boulder, CO). Seeds were sown into two 128-plug flats with a moist seed starter soil (Organic Starter Premium Potting Mix, Epsoma, Millville, NJ). Flats were placed on a greenhouse bench with natural light. Germination was induced by placing onto a heat mat. After 17 days in these conditions, 100 ppm N of 20-10-20 were added at every watering. The N was increased to 200 ppm after 7 days of growth.

I hypothesize that spraying jasmonic acid onto mechanically damaged plants will reduce herbivore desirability for the plants. Doing so will cause necrosis to some of the leaves of the plants which receive a normal amount of fertilizer but will not cause necrosis to the doubly fertilized plants, and the plants receiving double fertilizer will show an increased amount of defenses, such as trichomes. 

The reaction of plants to stress from their environment, be it the plant’s consumers or the environment, involves a series of pathways which induce defenses (Tian, Peiffer, et al.). These pathways involve several hormones which trigger defense responses in plants. Jasmonic acid is a hormone that plants release to control responses from stress, such as damage from weather or herbivores. It has been observed that applying jasmonic acid onto a tomato plant can be used as a pesticide by inducing defenses plants use naturally to deter herbivores from consuming them (Tian, Tooker, et al.; Tian, Peiffer, et al.). Administering jasmonic acid onto a tomato plant can cause plants to grow more trichomes (hair-like structures that grow on the leaf of the plant that make traversing them more difficult for herbivores) (Tian, Tooker, et al.). Tomato plants treated with jasmonic acid have been shown to be less preferable to consume by herbivores as a result of secondary compounds produced, and the herbivores that consume them do not grow as large (Tian, Peiffer, et al.). 

However, artificially inducing plant defenses has been shown to affect the growth of plants, the reproductive process, and may negatively affect the fruit and leaves of the plant (Redman et al.; Koussevitzky et al.)Applying jasmonic acid to tomato plants can result in larger but fewer fruits, the amount of seeds produced, and the success of germination (Redman et al.). Treating plants with jasmonic acid has been shown to enhance the amount of polyphenol oxidase in the chloroplasts of the plants (Koussevitzky et al.) Excess polyphenol oxidase could cause the fruits and/or leaves to brown faster and the fruits to consist of more pigments, which is a sign of an increased rate of cell death (Araji et al.).

The reaction of plants to stress from their environment, be it the plant’s consumers or the environment, involves a series of pathways which induce defenses (Tian, Peiffer, et al.). These pathways involve several hormones which trigger the defense responses in plants. Jasmonic acid is a hormone that plants release to control the responses from stress, such as damage from weather or herbivores. It has been observed in many studies that applying jasmonic acid onto a tomato plant can be used as a pesticide by inducing defenses plant naturally use to deter herbivores from consuming them (Tian, Tooker, et al.; Tian, Peiffer, et al.). Administering jasmonic acid onto a tomato plant can cause plants to grow more trichomes, which are hair-like structures that grow on the leaf of the plant that make traversing them more difficult for herbivores (Tian, Tooker, et al.). Tomato plants treated with jasmonic acid have been shown to be less preferable to consume by herbivores as a result of secondary compounds produced, and the herbivores that consume them do not grow as large (Tian, Peiffer, et al.). 

We will compare the damaged plants (mechanical and jasmonic acid spray) with a regular amount of fertilizer and the non-damaged plants with a regular amount of fertilizer in order to analyze the effect of spraying jasmonic acid onto plants. We will compare them by measuring how tall the plants grow, the rate they grow, the surface area of the leaves before and after, and if there are any signs of chlorosis or necrosis. By doing so, we will be able to see how mechanical and jasmonic acid damage affects new versus old growth on the plant.

120 tomato plants will be used in the study. 100 of the plants will receive a form of damage to their leaves by caterpillars eating bits of leaves off of each plant, the remaining 20 will serve as a baseline. The caterpillars will be left on the plants for enough time to do a measurable/visible amount of damage to the plant. 75 tomato plants will receive JA, there will be three groups receiving treatment and one group will receive no treatment (this will be our control). 25 will receive five sprays of JA, 25 will receive three sprays of JA, 25 will receive one spray of JA, and 25 will receive no treatment of JA (this way, we can see if too much JA hurts the plants, if any amount of JA hurts the plants, or if more JA applied to plants then the plants will repair themselves faster or better than they would have without the extra spray). The responses could be measured by weighing the plants before and after to see if there is a change in biomass. They could also be measured visually by analyzing the plants to see which ones look healthier or if their leaves grew back entirely and then some.

In the bumble bee (Bombus impatiens), the gut parasite Crithidia bombiis related to the causes of Chagas disease and Leishmaniasis in the bumble bee. The parasite is transmitted via ingestion of cells in feces of infected bees, and is present in 80 percent of the Bombus impatienspopulation in New England. In the lab, we will be infecting bumble bees with the gut parasite through a nectar feeder and randomly assign which bees get the treatment. We will then leave them alone for a week, dissect their guts, and count the amount of Crithidia bombicells.

Plant defense mediate tri-trophic interactions. A plant’s response to a threat can influence herbivore mutations and eventually predator mutations. Plant defenses directly reduce herbivore performance, but they can also indirectly benefit herbivores because they can acquire new traits from the new chemicals made by the plant they are consuming. Since pollinators are herbivores (they consume nectar and pollen from plants), they also can acquire new traits from the nectar and pollen containing new plant defenses.