Authors: Alisa Benjamin, Mary Giambruno, Mark Lyke, Anna Belle Pyle, Roger Warner

Resource Person: Jim Wetterer

Introduction

Azteca is a genus from Dolichoderinae, a sub-family of ants common in the Neotropics. Azteca and the Cecropia tree demonstrate a mutualistic relationship.  The ant protects the plant from foraging herbivores, while the Cecropia provides Azteca with food and shelter. Extrafloral nectaries called mullarian bodies, provides sugars needed for sustenance.  Another example of mutualism occurs between the Azteca and the homopteran. The ant protects the homopteran from predators, while the homopteran provides food for the ant from its excrement. This liquid sugary excrement is known as honeydew.  During field observations J. Wetterer noticed that large, successful colonies almost always have these homopterans present, whereas smaller colonies did not.  We hypothesize that mealybugs are essential for colony establishment in the Azteca ant.

Material and Methods

The study area is located about 100 meters off of the Sendero Tres Rio (STR) at the 1100 meter mark. The site was within an abandoned field of balsa trees. We selected and cut the cecropia trees from those that were of a manageable size, that is less than 3 meters. For each tree, we measured the height, base diameter, diameter of the segment second from the top, the number of leaves, and counted the mullerian bodies. We then removed the leaves and placed the tree on the ground and used a knife to split the tree open beginning with the top section. As each segment was cut open team members took turns collecting queens, broods, mealybugs, larvae, and pupae using insect aspirators (pooters). We labeled the vials for each tree that specimens were found and collected. After returning to the lab we placed our specimens in vials with alcohol for later study.

The following materials were used during this project:
Insect aspirators with vials, knife, meter tape, alcohol, forceps, labels, and notebook.

Data:
Table 1

Tree	# Colonies	#Broods	Mealybugs	Height(M)	Top Diameter (cm)
1	10	2	-	1.18	2.5
2	1	1	+	1.91	1.8
3	5	1	+	2.93	4.6
4	2	2	-	1.36	1.7
5	1	0	-	0.85	1.1
6	5	1	+	1.90	2.0
7	7	1	-	1.47	1.9
8	0	0	-	1.02	1.1
9	8	2	-*	1.97	5.6

* outside on apex

Results:
Table 2

Category	#Trees	% w/ Mealybugs	Height(M)	Top Diameter (cm)
Trees w/o ants	1	0	1.02	1.1
Trees w/ 1 founder	1	0	0.85	1.1
Trees w/ multiple colonies	3	0	1.18,1.36,1.47	2.5,1.7,1.9
Trees w/ multiple species	1	0	1.97	5.6
Trees w/ 1 dominate colony	3	100	1.91,2.93,1.90	1.8,4.6,2.0

Analysis:

 As we analyzed our data, we decided to break our data into five categories. The categories included: Tree without any ants, Tree with one founder, Tree with multiple colonies, Tree with multiple species, and Tree with one dominant colony. The Tree without ants group included one of our nine tree samples. The tree with one founder also included only one  sample. Whereas the  Tree with multiple colonies group included three of our sample trees. Our Tree with multiple species category had one sample and our last grouping of Tree with at least one established dominate colony included three of our sample group.  The height of our sampling ranged from 0.85 meters to 2.93 meters. The diameter of our samples ranged from 1.1 to 5.6 centimeters. The last category listed the percentage of trees with mealybugs. The only trees that included mealybugs were the trees that contained one dominant colony. (Although there were dead colonies present.) This sounds like our hypothesis is in great shape until we realized that the tree with multiple species had mealybugs on the outside apex of the tree. This discovery nullified our hypothesis.

Discussion:

The initial hypothesis that homopterans are essential to the success of the colony was not established from our  data. When looking at small trees, which are in the range of .85 to 1.02m, we found no or one queen. Since we refer to the queen as a colony, the lack of homopterans shows that the cecropia tree is enough to sustain the queen without the mealybugs. When we looked at the medium range of trees in the range of 1.18- 1.47m we find that there are multiple colonies, with one queen establishing a brood but still no homopterans found inside the tree. This would lead us to the fact that the homopterans are not necessary for the establishment of the colony. When the larger range of trees in the range of 1.47-2.93 was examined only then did we find the presence of the homopterans in the colony.  That would suggest that once the colony is firmly established, then the mealybugs are brought in to feed the colony. The Azteca, an aggressive ant should extra energy for colony growth (Carroll). This would explain why the medium range of trees with multiple queens is less successful than the larger with only one queen and a much larger brood population.

When examining a tree in the large range we noticed that there were multiple species present in the tree and no homopterans found inside the tree. This would indicate that the mealybugs arrive (and are not collected by the queens) on the cecropia tree prior to being used in the nest of a successful colony. Without more data concerning the second species of  Azteca ants and there use of the homopterans we can only speculate that the more aggressive species, which we observed earlier in the other trees, was close to the point of incorporating the homopterans at the top of the tree. In conclusion the homopteran is not required for the establishment of the colony.

The Essential Question La Selva Ants and Cecropia:

Our team submits following suggestions, which may be useful for applying
the information and techniques learned in our investigation to your teaching program.

Methods of data collection used in our field work included use of a “pooter” which is also
Called an aspirator. It is a tool that is easily transported in a plastic bag and used to pick up
items that are too small to directly handle without affecting the specimen. Using the pooter an
investigator can even collect ants without being stung. You may find Ecological Census
Techniques edited by William J. Sutherland helpful with construction and use instructions.

Another tool, which could be used in invertebrate work, is the flexible, fine point forceps. It allows
the investigator to collect and/or handle the delicate specimen without damaging it. A practical and
quite simple idea is to tie a piece of surveyor’s tape to the handle. When it is dropped in the field
it is easily spotted and retrieved.

In order to work with further investigation after field collection the investigator could use small
vials with screw-top lids and alcohol. The insects can be stored and later brought out for work
with dichotomous keys while using magnifiers.

The questioning techniques employed by the scientists at La Selva would work very well in the
presentations of simple investigations as well as the long-term project, such as science fair projects.
The secret to questioning technique is to allow curiosity to govern thought. Most investigations
and analyses should lead to further questions and not necessarily to some final statement.