Author

Shicai Yan

Date of Award

5-2005

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Entomology

Advisor

Eleanor Groden

Second Committee Member

Francis Drummond

Third Committee Member

Andrei Alyokhin

Abstract

Abstract: The European fire ant, Myrmica rzibra, is an exotic species in the USA and is potentially damaging to local ecosystems. No research has been conducted on control of this species, especially with biological agents. Cadavers of M. rubra were collected during the 2002 - 2003 field seasons at Mount Desert Island (MDI), Maine. Both entornopathogenic fungi, Beauveria bassiana and Metarhizium anisopliae, were widely distributed throughout sample sites on the island, with 9.5% and 1.2% of the field collected cadavers spol-ulating with these fungi, respectively. Five isolates of B. bassiarza and one isolate of M. anisopliae were successfully mass-cultivated on SDA media, and their virulence on rM. rubra workers were compared with GHA, a commercial strain of B. bassiana. Two isolates were significantly less virulent than GHA, in terms of median lethal concentration (LCso) and median lethal time (LTso). Three isolates caused higher mortality and there was no virulence difference compared with GHA. The LCso values of these three isolates ranged from 5.75 x lo' to 6.46 x 10' conidia/ml, 10 days post infection. At a concentration of 1.0 x 1 o6 conidialml, their LTso values ranged between 9.84 to 9.93 days. However, no difference was observed among the five isolates, as well as GHA, in the proportion of cadavers that sporulated. Higher conidia concentration caused greater sporulation. At a concentration of 1.0 x lo6 conidialml, approximately 65% of the cadavers sporulated for all isolates. The effects of boric acid and sucrose concentrations on consumption and subsequent mortality of M. rubra workers were assessed under laboratory conditions. The higher boric-acid concentration led to less consumption, indicating avoidance behavior or repellency with higher boric-acid concentrated baits. There was no difference in mortality between ants fed the control and 0.1 % boric-acid baits, while at 1 .O% and 5.0% boric acid, mortality was significantly higher from the first day after application. The median lethal time (LTSo) increased with decreasing boric acid concentration from 1.8 days at 5% boric acid to 11 8.8 days at 0.1%. The most effective boric acid concentration ranged from 0.25 to 0.5% with the LT50 ranging from 14.5 to 42.3 days. Bait consumption was significantly lower with 20% and 30% sucrose concentration, compared with 10% concentration. No significant interaction in consumption was observed between boric acid and sucrose, but an interaction effect was observed for mortality. There was no mortality difference for three sucrose concentrations at control and the low rate of boric acid bait (0.1%). However, with an increasing rate of boric acid concentration (20.25%), lower sucrose-concentrated bait (1 0%) caused higher mortality. Potential synergism between boric acid and M. anisopliae for M, rzibra worlters was also investigated under laboratory conditions. There was no synergism between boric acid and M. anisopliae on consumption of bait or subsequent mortality. However, there was a synergistic effect on M. anisopliae sporulation of cadavers. Sporulation increased with M. anisopliae concentration (lo5 conidialml and lo6 conidialml) for ants exposed to 0.5% boric acid bait, but not for ants exposed to 0.25% or no boric acid.

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