Location: Pest Management Research Unit
Title: Simulated aerial sprays for field cage evaluation of Beauveria bassiana and Metarhizium brunneum (Ascomycetes: Hypocreales) against Anabrus simplex (Orthoptera: Tettigoniidae) in Montana Authors
Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 31, 2011
Publication Date: November 1, 2011
Repository URL: http://handle.nal.usda.gov/10113/53799
Citation: Foster, N.R., Jaronski, S., Reuter, K.C., Harper, J.D., Schlothauer, R.J., Black, L.R. 2011. Simulated aerial sprays for field cage evaluation of Beauveria bassiana and Metarhizium brunneum (Ascomycetes: Hypocreales) against Anabrus simplex (Orthoptera: Tettigoniidae) in Montana. Biocontrol Science and Technology. 21(11): 1331-1350. Interpretive Summary: In a joint USDA APHIS and ARS field test, two commercial mycoinsecticides were evaluated for efficacy against immature Mormon crickets at their respective recommended rates, using a new, APHIS-designed apparatus that simulates aerial, ultra-low volume sprays to 0.1 m2 areas of ground. Mormon crickets were confined for 3 days to replicate areas of ground treated with either fungus or an oil carrier control. Treated insects, which were then moved into the lab and incubated at temperatures optimal for the fungi, suffered 90-100% mortality within 12 days, indicating that the rates used were highly efficacious and that via only only indirect acquisition from sprayed foliage, not direct spray. Insects left in field cages, however, suffered only 28% or 45% kill by either fungus, and that only after 28 days. Our observations indicate that high field temperatures and/or thermoregulation by the Mormon crickets, in excess of the upper thermal limits of both fungi, prevented higher mortality from being expressed in the field. Timing of mortality in field cages was consistent with temporal models developed from estimates of Mormon cricket body temperatures throughout the test. The implications of our data are that neither commercial fungus would be satisfactorily effective in operational programs without some sort of insect stressor or material to reduce the efficiency of the insects’ thermoregulation.
Technical Abstract: Field efficacy of the entomopathogenic Ascomycete Beauveria bassiana strain GHA and Metarhizium brunneum strain F52 was evaluated against nymphs of the Mormon cricket, Anabrus simplex. Fungi were applied with a new apparatus that allows simulated aerial sprays to 0.1m2 areas in the field. The Mormon crickets were individually housed in cylindrical, metal hardware cloth cages on treated grass. Both fungi demonstrated only marginal success in reducing immature Mormon cricket survival in the field cages. After 28 days, the respective field mortality of insects, corrected for control deaths, was 28% and 45% for B. bassiana and M. brunneum. Field-exposed but laboratory incubated insects, however, suffered 90-100% mortality due to mycosis within 12 days with initial deaths occurring on Day 6 (Beauveria) or Day 5 (Metarhizium), indicating a lethal rate was applied and acquired by the crickets through movement and feeding in the field. Potential body temperatures were determined on a diel basis for the entire post-treatment observation period using special thermal surrogates. High ambient temperatures and/or thermoregulation by the Mormon crickets, in excess of the upper thermal limits of both fungi, prevented higher mortality from being expressed in the field. Thermal surrogates were used to develop models for predicting onset of mortality from infections. The surrogate data indicated mortality should begin between 8 and 26 days after treatment with M. brunneum and 11 and 33 days after treatment with B. bassiana. The timing of mortality in field cages was consistent with the upper boundaries of the temporal models developed from the thermal surrogates, i.e., at or after 28 DAT.