Mutualisms, Commensalisms, and Predation: The Direct and Indirect Effects of Fire Ants on Arthropods and Plants
Type of DegreeThesis
DepartmentEntomology and Plant Pathology
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The red imported fire ant, Solenopsis invicta, is a voracious generalist predator that has dramatically affected the native arthropod community since its introduction approximately 75 years ago. Most research suggests S. invicta negatively affects most native arthropods by consumption or displacement. However several studies have found that S. invicta forms mutualisms (positive species interactions) with honeydew-producing insects such as aphids. In field and greenhouse experiments we found evidence that S. invicta also forms a positive interaction with spittlebug nymphs. The presence of S. invicta has a significant negative effect on spittlebug predators such as spiders which in turn increases spittlebug nymph abundance. Therefore spittlebug nymphs indirectly benefit from the presence of S. invicta and thus fire ants and spittlebug nymphs form a comensalistic relationship. We hypothesize that the impact of red imported fire ants on arthropod communities varies due to the formation of these positive species interactions. Additionally we quantify the direct benefits that the cotton aphid, Aphis gossipii, and the red imported fire ant, Solenopsis invicta, receive from their mutualistic relationship in a series of greenhouse experiments. We compared the growth of aphid populations, alate production, and the composition of honeydew of ant attended and unattended colonies in the absence of natural enemies. In addition, we examined worker and brood survival among ant colonies with and without access to aphid colonies. We found strong evidence that both aphids and ants receive direct benefits from the mutualism. Aphid population growth was significantly higher in the presence of fire ants. The presence of fire ants also decreased the proportion of aphids that developed wings (alates) and increased honeydew production by aphids. Survival of fire ant workers and larvae (brood) was significantly higher when fire ant colonies had access to aphids than when they did not. This suggests that honeydew is a high quality food source for fire ants and honeydew consumption directly affects colony survival and growth.