Date of Award

5-1980

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Entomology

First Advisor

G. R. Carmer

Second Advisor

Lither W. Baxter Jr.

Third Advisor

Farrell B. Brown

Abstract

Cadavers of Heliothis larvae infected with the three species of Beauveria were used to field treat mounds of the red imported fire ant, Solenopsis invicta Buren. The Beauveria spp. tested in 1978 caused mound mortality of 21.7-47.1% with no difference in pathogenicity noted between species. In 1979, mortality ranged from 37.3-71.8% with B. bassiana causing higher mortaliy than B. globulifera or B. tenella. Laboratory studies to determine pathogenicity of several strains of Beauveria and Metarrhizium to the fire ant revealed differences between genera, species and strains. Beauveria bassiana, B. globulifera and B. tenella caused the highest mortality (ca. 90%). Relative humidity (RH) was more critical than temperature in determining levels of Beauveria infection. Only B. globulifera caused high mortality > 85% at relative humidity lower than 94%. The entomophilic nematodes, DD-136 (Neoaplectana carpocapsae) and NC-19 (Heterorhabditis heliothidis) caused fire ant mound mortality of 22.4 - 96.8%. The highest concentration (2 x 10^6 nematodes/mound) of DD-136 caused mortaliy of 88.2-96.8%. The highest concentration of NC-19 caused mortality of 75-86.3%. Mortality of fire ants removed from treated mounds ranged from 10.4-51.6%. A dosage response was noted with higher concentrations of nematodes causing higher mortality. In field evaluation of insecticides and DD-136 alone and in combination the highest mound mortality was achieved with combinations of DD-136 and insecticides. Sevin® and Knox-out®(Pennwalt) were more effective than Orthene® as fire ant insecticides. Laboratory studies revealed that minor workers were more susceptible to insecticides than major workers. Major workers were more susceptible to DD-136 infections than minor workers.

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