Entomopathogenicity of Ascomycete Fungus <i>Cordyceps militaris</i> on the Cotton Bollworm, <i>Helicoverpa zea</i> (Boddie) (Lepidoptera: Noctuidae)
James P. Glover | Marissa I. Nufer | Omaththage P. Perera | Maribel Portilla | Justin George
This study investigated the exposure of the cotton bollworm, <i>Helicoverpa zea</i> (Boddie) (Lepidoptera: Noctuidae) to a novel pathogenic fungal agent historically associated with human medicinal value, a commercial strain of <i>Cordyceps militaris</i> ((L.) Fr.) Vuill. (Hypocreales). A series of comparative studies were conducted to evaluate the efficacy of two different exposure methods using four concentrations (<i>n</i> × 10<sup>9</sup>, <i>n</i> × 10<sup>8</sup>, <i>n</i> × 10<sup>7</sup>, <i>n</i> × 10<sup>6</sup>) of <i>C. militaris</i>, where <i>n</i> × 10<sup>9</sup> provided a concentration of approximately 420 ± 37 spores per mm<sup>2</sup> with 398 ± 28 viable spores. Survival of cotton bollworms of all stages was not affected by <i>C. militaris</i> at any concentration 1 d post-exposure. The greatest reduction in survival and highest sporulation rates were observed primarily on or after 7 d post-exposure for early instars (first and second). Significant declines in the survival of early instars were observed for all concentrations at 7 d, and 95% mortality by 10 d, with the exception of the fifth instars that experienced a less severe reduction in survival (35%) when exposed to any concentrations used in the study. Survival of late instars (third to fifth) ranged from 44% to 68% on day 10, while adult survival was near 99% across the duration of the experiment. The relatively narrow range observed for both the lethal concentration and sporulation of second, third, and fifth instar cotton bollworms exposed to the <i>C. militaris</i> strain may demonstrate potential field application for control of larval populations of cotton bollworms.
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