Location: Biological Control of Pests ResearchTitle: Mortality of Solenopsis invicta workers (Hymenoptera: Formicidae) after indirect exposure to spores of three entomopathogenic fungi
Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2018
Publication Date: 6/13/2018
Citation: Rojas, M.G., Elliott, R.B., Morales Ramos, J.A. 2018. Mortality of Solenopsis invicta workers (Hymenoptera: Formicidae) after indirect exposure to unformulated spores of three entomopathogenic fungi. Journal of Insect Science. 18(3):1-8.
Interpretive Summary: The red imported fire ant is a tremendous pest in lots of countries. Strategies to control them in sensitive areas like around schools, hospitals, parks, etc. requires the use of benign methods. Here we report the efficacy of 3 different fungi which produced mortality when indirectly exposed to fire ant workers in a laboratory test. From the 3 fungi tested, Beauveria bassiana (NI8 strain) produced the highest mortality more than 50% after a week of being exposed. This result is important because it opens the possibilities to create new formulations to control this obnoxious pest.
Technical Abstract: Mortality caused by indirect exposure to Metarhizium (M.) brunneum and Beauveria (B.) bassiana (GHA and NI8) to the red imported fire ant (Solenopsis invicta) workers was evaluated under laboratory conditions. A dual square arena was used to run the bioassays. 50 workers were place in one side of the arena and filter paper squares previously sprayed with unformulated purified spores (106 spores/ml) suspended in 0.2% Ethal TDA 3, HLB 8 of the three fungal strains, or clean papers as the control, were aseptically placed in the empty arena. Daily observations were done to determine mortality for a week. Dead ants were separately collected by treatment and control, surface cleaned, and placed in PDA media and incubated at 27°C and 60% RH for 7 days to detect fungal growth. Fungal spores infected workers while walking on treated paper due to the presence of fungal growth in the dead ants. M. anisopliae and B. bassiana GHA killed workers sooner, 51.35 and 56.68%, respectively, occurring during days 1 and 2. However only 9.47 and 35.96% of the mortality could be explained by fungal infection by M. anisopliae and B. bassiana GHA, respectively. Most of mortality observed in the B. bassiana NI8 treatment (84.48%) occurred later (between days 4-6) and most of this mortality occurring on during day 4 (89.06%) could be explained by B. bassiana infection. Overall mortality was significantly higher in the B. bassiana NI8 treatment than the other two tested fungi and control. Implications for potential application of these fungal strains for fire ant control are discussed.