Date of Award

5-2007

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Entomology

Advisor

Eleanor Groden

Second Committee Member

Francis A. Drummond

Third Committee Member

Andrei Alyokhi

Abstract

The European red ant, Myrmica rubra L., is an invasive pest in the Northeastern United States. The fungal entomopathogen Beauveria bassiana (Bals.) Vuill. is being considered as a potential biological control agent. However, it has been shown that ants are able to reduce the effectiveness of pathogens through hygienic behaviors, which vary among ant and pathogen species. The objective of these experiments was to determine if M. rubra can reduce the impact of disease by behavioral responses to B. bassiana infection and necrophoric behavior. M. rubra workers were inoculated with B. bassiana conidia and kept in petri dishes either alone, with nestmates or with nestmates and brood. There was no significant effect of exposure to nestmates or brood on the mortality of these workers (P=0.321). To observe worker behavior, paint-marked workers were immersed in a B. bassiana conidia suspension, released into laboratory arenas and observed. Behaviors including self-grooming, allogrooming, aggression and necrophoresis, as well as position within the nest arena, were recorded. Overall, workers that had been exposed to the fungus exhibited significantly more aggression from nestmates, self- and allogrooming events than the controls (P<0.001 for all behaviors). Workers that had been returned to the nest immediately after inoculation with B. bassiana spent more time in midden areas during the peak of infection than their control counterparts (P=0.001). The midden site preferences of M. rubra were evaluated in laboratory and field experiments. In the laboratory, choice tests were designed to independently determine the ants' preferences for three different environmental factors: surface color, temperature and light level. Nest fragments were established in laboratory arenas, each of which had two contrasting surfaces on which the workers could deposit freeze-killed cadavers. The three different treatments evaluated the ants' preference for black versus white surfaces, heated versus not heated surfaces, or shaded versus directly illuminated surfaces as midden sites. Workers deposited significantly more cadavers on surfaces that were white (P=0.002), heated (P=0.004) and receiving direct light (P=0.016). In the field, cadaver deposition in paired open and shaded midden plots was recorded. M. rubra workers placed significantly more cadavers in the open plots than in shaded plots (F=0.002). An additional laboratory study was designed to determine whether ants that deposit cadavers in middens also forage for food and return to the brood nest. Workers were taken from the nest, foraging and midden areas of laboratory arenas, marked with paint and returned. Their location was observed and noted for one week. Worker origin was a significant factor in explaining location (P=0.017), although workers originating from midden areas were observed in both foraging areas and inside the brood nest.

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