The proposed research centers on the red imported fire ant (Solenopsis invicta) and the Argentine ant (Linepithema humile), the two most widespread, abundant and ecologically damaging invasive ants in North America. Both of these ants commonly develop mutualistic relationships with honeydew-producing true bugs (Hemiptera), including a wide variety of aphids, scales, and mealybugs. These associations lead to immense damage in agricultural systems. The goal of this research is to understand how these associations between invasive ants and honeydew producing insects enhance the dominance of invasive ants and their impacts in the United States. This will be accomplished through a combination of greenhouse experiments, field manipulations, and stable-isotope analysis.
Ants and their associated Hemiptera provide unique educational opportunities. The familiarity of fire ants and Argentine ants as urban pests and their prominence as invasive species make them ideal instructional tools for students interested in ecology, behavior, and conservation. Moreover, interactions between ants and honeydew-producing Hemiptera provide ubiquitous and easily observed examples of mutualisms. The experimental tractability of this research has the potential to generate numerous opportunities for student involvement. The PIs are committed to fostering diversity and will continue to involve and to mentor under-represented groups in science. The findings of the proposed research will also figure prominently in a web-based educational tool.
I Intellectual merits Reciprocally beneficial species interactions (mutualisms) encourage the establishment, spread, and impacts of introduced species to a degree that is currently underappreciated and that may alter how ecologists view the relationship between biotic interactions and invasion success. The aim of this award was to examine how commonly formed associations between invasive ants and honeydew-producing Hemiptera (aphids, scales, and mealybugs) enhance the abundance and behavior of invasive ants in ways that contribute to ecological success. Our research broadly supports the hypothesis that access to carbohydrate-rich honeydew underlies the ability of invasive ants to achieve ecological dominance. Our field research suggests that native populations (from Argentina) of invasive ants are less likely to engage in mutualistic relationships that supply honeydew compared to introduced populations (from the US). Moreover, the ability to monopolize honeydew in introduced populations appears to be key to their success as invaders. Our field and laboratory experiments, for example, demonstrate that access to these honeydew enhances colony growth. Our results not only support our proposal’s core hypotheses, they suggest a mechanism for the success of invasive species in introduced populations and provide a framework for control strategies that can reduce access to essential resources for invasive ants. This body of work provides one of the most detailed assessments to date of how mutually positive species interactions influence the success of terrestrial animal invasions. Broader impacts Support from this proposal has directly trained six graduate students and one post-graduate researcher. Between the three partnering institutions (Texas A&M University, University of Illinois, and UC San Diego), over 20 undergraduates participated in research supported by this grant. Undergraduates were trained in a variety of field and lab based methods, ant identification, and experimental design. PI Suarez has given over 10 invited seminars where research from this proposal was discussed. PI Suarez has also trained over 90 students on ant taxonomy and identification at the ant course over the last three years (co-sponsored by the California Academy of Sciences and Harvard University). PI Eubanks has presented 10 invited seminars at universities that included data from this project and his lab has presented over a dozen related presentations at scientific meetings. PI Holway has presented four invited seminars at universities and three presentations at scientific meetings that included data from this project. Lastly, key ideas developed during this research formed the intellectual basis for a symposium ("The nutritional ecology of social insects") organized by the three PIs that convened at the annual meeting of the Entomological Society of America in December 2010. This symposium united researchers from a variety of fields with the goal of generating novel insights related to a rapidly developing field. At the University of Illinois, outreach activities related to this proposal include the development of web-based resources, ant displays for the annual Insect Fear Film Festival, research highlights in a number of newspapers and magazines, including the New York Times Science section, and lab tours for 5th -8th graders from local grade schools to educate them on the importance of science, invasive species, and the roles that ants play in ecological communities. Outreach at Texas A&M University has included presentations to the general public and to pest control operators as part of the Texas Imported Fire Ant program as well as the production of a web-based video on invasive fire ants. Outreach activities at UC San Diego include 10 outreach presentations over the past three years; one of which is available for public viewing at the website of UCSD TV (www.ucsd.tv). Publications directly related to funded research (this list is incomplete; numerous manuscripts describing results of this research are in preparation) Cook SC, MD Eubanks, RE Gold & ST Behmer (2010) Colony-level macronutrient regulation in ants: mechanisms, hoarding and associated costs. Animal Behavior 79:429-437. Kay AD, T Zumbusch, JL Heinen, TC Marsh & DA Holway (2010) Nutrition and interference competition have interactive effects on the behavior and performance of Argentine ants. Ecology 91:57-64. Menke SB, AV Suarez, CV Tillberg, CT Chou & DA Holway (2010) Trophic ecology of the invasive Argentine ant: spatio-temporal variation in resource assimilation and isotopic enrichment. Oecologia 164:763-771. Styrsky JD & MD Eubanks (2010) A facultative mutualism between aphids and an invasive ant increases plant reproduction. Ecological Entomology 35:190-199. Wilder SM & MD Eubanks (2010) Extrafloral nectar content alters foraging preferences of a predatory ant. Biology Letters 6:177-179. Wilder SM & MD Eubanks (2010) Might nitrogen limitation promote omnivory among carnivorous arthropods: comment. Ecology 91:3114-3117. Wilder SM, DA Holway, AV Suarez & MD Eubanks (2011) Carbohydrate-Limited Growth in a Carnivorous Arthropod. Ecology, In press. Wilder SM, AV Suarez & MD Eubanks (2010) The use of simulation modeling to evaluate the mechanisms responsible for the nutritional benefits of food-for-protection mutualisms. Ecological Modeling 221:1505-1511.
