Plant Galls Lab Report

Introduction

A gall is an abnormal growth that occurs on plant tissues. A plant growth is similar to a tumor or a wart that would occur on an animal; plant galls, however, are typically caused by various parasites and insects. In order for a gall to form, a female insect needs to implant an egg into a plant. It is important that the insect does so when the plant is maturing, this ensures the plants meristem is extremely active and prepared to grow a gall suitable for the insect’s young. The larvae and possibly the adult insect as well release chemicals into the plants that causes the growth of the plant. Multiple studies have been done in attempt to find the exact cause for the growth of plant galls, but studies have not reached a similar

conclusion just yet.
According to Abrahamson et al. there are multiple pressures put upon the Solidago gall size. Relatively small galls tend to be preyed on by ova positing parasitic organisms. Large galls, on the other hand, tend to be more frequently preyed on by avian predators. Nonetheless, survival depends on gall size, some of the gall maker’s natural enemies differentially attack galls based on their various sizes. This study puts Abrahamson et al.’s study to the test and attempts to look at a series of data collected during the fall of 2016 from three different locations in Massachusetts. Is it true that the size of a Solidago gall affects predation? If true, I believe that larger gall will be more likely predated. If Abrahamson et al. are correct then avian predators will easily spot the larger galls and thus largely increasing the amount of galls preyed on.
Methods
Study Site(s):
The first study site that data were collected from was Reservoir Road. Reservoir road appeared to have large open spaces. Tree density increased the further away one moved from the street. Poison ivy as well as many grasses covered the floor. Trees present were typically in close proximity to one another. There also seemed to be birds present, although they could not be seen they were easily heard.
The second site was Hatfield Post Office. Hatfield Post Office was a large flat piece of land that was mostly open except for a few trees that were far away from one another. Stalks covered the ground as well as other organic debris.
Data
Data Collection:
Using measuring tape, a group of students cut across an assigned patch of Solidago galls making the tape measure parallel to the street and then placed the tape measure on the ground. Any one of the stalks touching the measuring tape were then examined but only the ones which have galls are to be used as part of the sample. Distance to the nearest tree, distance to the next stalk, and distance to the next gall were measured.
Once all galls were collected, students proceeded to measure gall height from bottom of stem with meter tape. The stems were cut and gall diameter was measured using circle templates. The smallest hole in which the gall fit was selected. Presence of holes was noted. The galls were then cut open using pruning shears. Using pictures as well as the internet the larvae within the gall was identified and if the larvae was missing or dead, cause of death was noted. Other information collected includes the presence of an exit tunnel or whether more than one gall was present on a single stem. All data were inputted into a spreadsheet for further use.
The following list display notation used to determine information discussed above:
1. Note presence of holes
a. No hole present = N
b. Woodpecker hole (clean single conical hole) = WP
c. Chickadee hole (messy, dispersed pecking around hole) = CD
d. Giant wasp emergence hole (not likely at this time of year) = GW
e. Unknown cause of hole = U
2. Note whether the larvae were alive or dead
a. Gallfly larva alive = A
b. Gallfly larva dead = D
c. Gall empty with no evidence of predation = E
d. Gall empty with evidence of predation or parasitism = P
3. Identify the cause of death if possible:
a. None: gallfly larva alive = N/A
b. Bird hole in the gall and no gallfly larva present = WP or CD
c. Pupa present or gallfly not present but obtuse wasp larva present = OW
d. Gallfly not present but tumbling flower beetle present = TFB
e. Unknown = U
Data Analysis:
In order to determine whether larger galls are more likely predated than smaller sized galls. Data from all sites were analyzed. All diameters were categorized into two sections, the first pertaining to galls that were predated (notated with the letter P) and the second pertaining to the rest of the galls not listed as predated (all others). A Two Sample T-Test of Means was used to compare mean diameters of Predated and Non-Predated galls.
Results
Data Analysis:
The test yielded a significant result with a p-value of 5.74x10^-5. The mean of predation was 21.3 and non-predation 19.7. Since the p-value was below 0.05 it was understood that there was a significant difference between the two means. In other words, those that showed evidence of predation had a significantly larger mean diameter than those who showed no evidence of predation. We could then have concluded that there was convincing evidence that supported our alternative hypothesis which stated that larger gulls were more likely to experience predation.
Data Presentation:

Discussion
Overall, the results yielded reflected Abrahamson et al.’s study.

Since data were collected during November in Massachusetts when the weather was beginning to get colder, I think it’s fair to assume that more birds began to prey on galls making them easy target. Subsequently since birds tend to prey on largely more visible things, it would only make sense that larger galls would experience more predation. However, after looking back at the data it seems that not all galls that were predated were included in the data set. This alone is sufficient to make any claim stated within this report invalid.

Assuming data were well collected and results were justified, the results could have been more reliable if more places had been taken into account. The locations previously used as sites might have a larger avian population thus creating the illusion that larger galls are more largely predated. To prevent from these factors limiting results, future test might look at multiple predators and what size gall they are more likely to prey on. Abrahamson et al.’s article discusses the likely that smaller galls are more likely to experience parasite oviposition and larger galls avian

predation.