The Biology of Solenopsis krockowi:
A Potential Predator of the Red Imported Fire Ant
Fire Ant Laboratory, Department of Biological Sciences,
The University of Texas at El Paso, TX 79968
The objectives of this project was to delineate and to find the density of Solenopsis krockowi colonies within a designated area of the Chamizal National Memorial called S. krockowi Corner and to examine predation of Solenopsis invicta queens by S. krockowi. The specimens were collected from six grid frames that were randomly selected locations within S. krockowi Corner. Aggressions between samples would indicate delineation. The density of S. krockowi Corner indicated that there are approximately 2.08 colonies per square meter in this area. Results of this study show that S. krockowi is not an effective predator of S. invicta queens.
Solenopsis krockowi is one of at least nine species of Solenopsis spp. also known as thief ants that are found in the state of Texas. There is very little known about these ants because of their minute size and difficulty to locate since they are mostly subterranean. Based on the information by Blum, M. S. and Jones, T. H. (1980) these thief ants build a complex of subterranean tunnels to brood chambers of other species and spread a chemical trail back to their own nests. They also recruit other ants to raid the neighboring species with a pheromone that comes from the Dufour’s gland. Thief ants have also been discovered to be predators of founding S. invicta queens (Lammers, 1987). Solenopsis krockowi sting includes powerful venom which enables them to overcome larger ant hosts (Blum, 1985). Solenopsis krockowi is a complex derived of three to five species but not enough information is known about these small cryptic ants.
The purpose of this study is to delineate and to find the density of S. krockowi colonies. It was hypothesized that S. krockowi is an effective predator of S. invicta queens. The null hypothesis for this project states that S. krockowi is not an effective predator of S. invicta queens.
Methods and Materials
The experimental site for this project was at the Chamizal National Memorial in a designated area known as S. krockowi Corner. This area is located in the northeastern corner of the Chamizal near the corner of Paisano Dr. and the entrance to the Bridge of the Americas. Solenopsis krockowi Corner is covered by a nice fertile lawn that is watered five days a week. It has a variety of trees and pine trees including a large Cottonwood almost in the center of this area. This experimental site was designated after several collections in the area showed that there are dense populations of S. krockowi. Other species of ants present at the study site were Pogonomyrmex, Dorymyrmex and a native species of fire ants named Solenopsis xyloni.
The materials that were used for this experiment were a 200cm by 200cm PVC pipe frame, orange string, 2mL Cryogenic vials, live meal worms, small picks, scintillation vials and Fluon lined plastic containers. The Fluon was used so that the ants could not climb out of the containers because it is a Teflon covering that is very slippery. A grid frame was built that was 200cm by 200cm with PVC pipe frame and it was strung with orange string with 50cm partitions. The rows on the frame were lettered A through E and the columns were numbered 1 through 5. (See Figure 1). Six random areas of S. krockowi Corner were selected to conduct this study. Twenty-five Cryogenic vials with live meal worms buried 15cm underground at each 50cm partition within the grid. The Cryogenic vials were extracted from the ground and were placed in the scintillation vials when S. krockowi was present. The samples were brought back to the laboratory and using the Fluon lined plastic containers the S. krockowi specimens were interacted together in order to determine their aggressiveness towards each other. The aggressions of the ants were noted in order to delineate colony size and to calculate the nest density of S. krockowi Corner. The specimens from S. krockowi Corner were also interacted with S. invicta queens to determine the predation of S. invicta queens by S. krockowi.
The results from the interactions showed that S. krockowi were aggressive towards each other regardless of colony size or location. There were six frames used to collect specimens from S. krockowi Corner. The frames consisted of: frame 1 had 15 colonies, frame 2 had 15 colonies, frame 3 had 3 colonies, frame 4 had 4 colonies, frame 5 had 2 colonies and frame 6 had 11 colonies after all S. krockowi samples were interacted for aggressions. In order to find the nest density results from S. krockowi Corner the number of nests in each frame were divided by 4m2. The mean was calculated by adding the results of the division which was 12.5 and divided by six frames which totaled an approximate 2.08 colonies per square meter within S. krockowi Corner.
The final results show that the null hypothesis must be accepted because S. krockowi was not an effective predator of S. invicta queens. The project believed that S. krockowi would be an effective predator of S. invicta queens in the laboratory setting. This may be due to a number of possible factors. The first factor that was run across was since S. krockowi is subterranean there were not enough specimens to work with. The second factor is that virgin queens were used and not founding queens and maybe virgin queens aren’t that much of a threat since they still have their wings. The third factor is that the ants aren’t in their natural surroundings and in the laboratory the S. invicta queens had more freedom to run around and not let S. krockowi workers attack. The fourth factor maybe to control their diet because S. krockowi samples that had not eaten in several days were more aggressive. The final factor could possibly be that since S. krockowi comes from a complex of three to five species maybe this project dealt with a less aggressive species. This project should be continued in order to see if these factors can be eliminated and research if the conclusions change in any way.
I would like to thank Dr. William P. Mackay, Dr. Raphael Cabeza, Dr. Jerry Johnson, Nic Lannutti, Matthew McMillan, Veronica Treviso, Cindy Morales, Isidra Moreno, Hilda Taylor, Cynthia Altamirano, Daniel I. Padilla, Jerome T. Flood, Jesus (Chuy) Bravo, Gus Enger my little buddy for all his help in the laboratory and all the students from the Desert Ecology Laboratory, The Chamizal National Memorial staff and all the students in the Bridges to the Future Program for all of their help and support.
Blum, M. S. 1985. Alkaloidal Ant Venoms: Chemistry and Biological Activities. American Chemical Society. Symposium series 286. Bioregulators for Pest Control; sp. Conference II.
Blum, M. S. and, T. H. Jones. 1980. Alkaloidal Venom Mace: Offensive Use by a Thief Ant. Naturwissenschaften 67: 144-145.
Jones, T. H., M. S. Blum, H. M. Fales, and C. R. Thompson. 1980. (5Z, 8E)-3-Heptyl- 5-methylpyrrolizidine from a Thief Ant. Journal of Organic Chemistry 45: 4778- 4780.
Lammers, J. M. 1987. Mortality Factors Associated with the Founding Queen of Solenopsis invicta Buren, the Red Imported Fire Ant: a Study of the Native Ant Community in Central Texas. MS Thesis, Texas A&M University 206p.
This figure shows the grid that I used for the sampling of S. krockowi Corner at the Chamizal National Memorial. The specimens were numbered A1 through A5, B1 through B5, C1 through C5, D1 through D5 and E1 through E5.?