Discipline: Biological Sciences
Subcategory: Plant Research
Room: Marriott Balcony A
Roberto G. Diaz-Gonzalez - University of Puerto Rico at Bayamon
Water is important in the growth of Lepidopteran larvae; less dietary water can result in reduced growth. Low water content of plant tissues has also been shown to have reduced preference by insects in general as this reduces their performance. Pseudosphinx tetrio is a member of the Sphingidae family of Lepidopterans and is a common moth in the Greater Antilles. Plumeria alba is a perennial plant, a member of the Apocynaceae family of plants. It is native to Puerto Rico and the preferred host-plant of Pseudosphinx tetrio. The adult moth can deposit up to 150 eggs on branches or the leaves of Plumeria alba. These trees are predominantly attacked by the Pseudosphinx tetrio larvae from August to November, the wet season. A previous study determined that Pseudosphinx tetrio preferred Plumeria alba trees that had been watered monthly compared to un-watered trees and that moths preferentially oviposited on large trees. The study did not identify if the leaves of the watered trees had a greater water content. Here, it is hypothesizing that Pseudosphinx tetrio selects Plumeria alba trees based on the water content of their leaves. As such, it was expected that the leaves of large Plumeria alba trees with Pseudosphinx tetrio (eggs or larvae) would have greater leaf water content than those of large, neighboring Plumeria alba trees without Pseudosphinx tetrio. It was also expected that larger Plumeria alba trees would have proportionally more water in their leaves than smaller trees.
Three undamaged leaves were removed from Plumeria alba trees that had Pseudosphinx tetrio; three leaves were also taken from similar sized, neighboring Plumeria alba trees and smaller trees as well. Once removed, all leaves were placed in separate, labelled, air-tight bags. The sampled leaves were weighed the same day they were collected to the nearest hundredth of a gram. They were then placed in a drying oven at 30°C for a period of two weeks and re-weighed. Proportional leaf water content was determined by subtracting the dry weight of the leaves from the wet weight and dividing the difference by the wet weight to remove variation due to leaf size. No difference was observed in the water content in any of the categories of the study. However, some interesting trends were observed in the data. There was a tendency for small trees to have a greater leaf water content than larger trees and trees with Pseudosphinx tetrio tended to have a higher leaf water content than neighboring trees without Pseudosphinx tetrio. In the design of this study, it was assumed that the large, neighboring Plumeria alba trees that did not have the presence of Pseudosphinx tetrio had been evaluated by the adult moth. Yet, even though they were chosen for the study, it does not mean that they had been evaluated by the moth. As a result, the neighboring trees may have been suitable, and their leaves could have a higher water content like the chosen host trees. The small trees, on the other hand, may tend to have a greater leaf water content but may not be selected by the moth because they are not as apparent to moths as the larger trees. Pseudosphinx tetrio may use other cues to determine which host plants are suitable, such as leaf quantity or the chemical content of the leaves. Future research should focus on the chemical analysis of leaves to see if other elements, such as nitrogen, play a role in host selection.
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Funder Acknowledgement(s): Funding was provided by the Puerto Rico Louis Strokes Alliance for Minority Participation (PR-LSAMP).
Faculty Advisor: Steven A. Sloan, firstname.lastname@example.org
Role: Travel to the field and collecting samples from the three categories of trees: Plumeria alba trees with Pseodosphinx tetrio presence, large neighboring Plumeria alba trees and small Plumeria alba trees. Additionally, I weighed the wet leaves and reweighed them once they were dried to obtain the leaf water content. Lastly, I also took part in the data analysis.