Research Affiliate

The Evolution of Cooperative Breeding Among Ant Queens

The ant Messor pergandei of the desert southwest provides a unique system to study the evolution of cooperation, conflict, and cooperative breeding. In one region of the species' range, queens are intolerant of others and always start new colonies alone, while in another, new colonies are initiated by groups of unrelated queens. Within the cooperative region, there is geographic variation in the duration and degree of cooperation. We exploit this variation and use a variety of field and laboratory studies to test hypotheses predicting the evolution of cooperative breeding from a non-cooperative state. This research is a group effort with my collaborator Sara Helms Cahan and graduate student Nate Newman. It is currently supported by the National Science Foundation.

Invasive Species

Our research on invasive species focuses on an important invader of the southeastern United States, the red imported fire ant, Solenopsis invicta. Honeydew produced by a species of invasive mealybug can be exceptionally important to the nutrition of this ant, and our research suggests that the success of the fire ant may be facilitated by the mealybug, and thus indirectly by the availability of the mealybug's host plants (grasses). The most important of these grasses are themselves introduced species which are encouraged by agriculture and widespread throughout the southeastern United States. Our research aims to determine the specific nature of interactions among the ants, mealybugs, an grasses, and to determine how those interactions influence the size of fire ant populations. This research has been supported by the National Research Initiative of the USDA. A story on this research was aired on National Public Radio's Morning Edition. Click here to listen.

Evolution of Sex Allocation

One of the most striking observations on sex allocation in ants is the common occurrence of colony sex ratio specialization, where the reproductive broods of some colonies consist of primarily or exclusively males, while the reproductive broods of others consist of primarily or exclusively females. My research on sex allocation is mostly concerned with understanding why such specialization occurs, particularly in cases where it is not predicted by existing theory. Empirical research has ranged from studies on ants in the genus Pheidole in the southwestern United States, to studies on ants in the genus Formica in Switzerland, the latter in collaboration with Laurent Keller and Rolf K├╝mmerli (University of Lausanne). In collaboration with Max Reuter (University College London) and Laurent Keller, we have developed mathematical models of queen-worker conflict that may provide new insight into the causes of sex ratio specialization in the social Hymenoptera.


Helms, K.R. & S.B. Vinson. 2008. Plant resources and colony growth in an invasive ant: The importance of honeydew-producing hemiptera in carbohydrate transfer across trophic levels. Environmental Entomology 379: 487-493. (Full text PDF icon pdf)

Helms, K. R., M. Reuter & L. Keller. 2005. Sex-ratio conflict between queens and workers in eusocial Hymenoptera: mechanisms, costs, and the evolution of split colony sex ratios. Evolution 59: 2626-2638. (Full text PDF icon pdf)

Kummerli, R., K. R. Helms & L. Keller. 2005. Experimental manupulation of queen number affects colony sex ratio investment in the highly polygynous ant Formica exsecta. Proceedings of the Royal Society of London, B: Biological Sciences 272: 1789-1794. (Full text PDF icon pdf)

Reuter, M, K. R. Helms, L. Lehmann & L. Keller. 2004. Effects of brood manipulation costs on optimal sex allocation in social Hymenoptera. American Naturalist 164: E73-E82. (Full text PDF icon pdf)

Helms, K. R., D. Fournier, L. Keller, L. Passera & S. Aron. 2004. Colony sex ratios in the facultatively polygynous ant Pheidole pallidula: A reanalysis with new data. Evolution 58: 1141-1142. (Full text PDF icon pdf)

Helms, K. R. & S. B. Vinson. 2003. Apparent facilitation of an invasive mealybug by an invasive ant. Insectes Sociaux 50: 403-404.(Full text PDF icon pdf)

Helms, K. R. & S. B. Vinson. 2002. Widespread association of the invasive ant, Solenopsis invicta, with an invasive mealybug. Ecology 83: 2425-2438. (Full text PDF icon pdf)

Helms, K. R., J. H. Fewell & S. W. Rissing. 2000. Sex ratio determination by queens and workers in the ant Pheidole desertorum. Animal Behaviour 59:523-527. (Full text PDF icon pdf)

Helms, K.R. 1999. Colony sex ratios, conflict between queens and workers, and apparent queen control in the ant Pheidole desertorum. Evolution 53:1470-1478. (Full text PDF icon pdf)

Cahan, S., K. R. Helms & S. W. Rissing. 1998. An abrupt transition in colony founding behaviour in the ant Messor pergandei. Animal Behaviour 55:1583-1594. (Full text PDF icon pdf)

Helms, K.R. 1994. Sexual size dimorphism and sex ratios in bees and wasps. American Naturalist 143:418-434. (Full text PDF icon pdf)


  • Postdoctoral: Arizona State University (1995-1996), Texas A&M University 1998-2000, University of Lausanne 2000-2002
  • Ph.D.: (1994) Arizona State University, Zoology


  • 802-656-9012
Office Location:

Marsh Life Science, Room 308