Entomopathogenicity of ascmycete fungus Cordyceps militaris on the cotton bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae)

Authors: Glover, James; Nufer, Marissa; Perera, Omaththage; Portilla, Maribel; George, Justin

Submitted to: The Journal of Fungi
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2023
Publication Date: 5/26/2023
Citation: Glover, J.P., Nufer, M., Perera, O.P., Portilla, M., George, J. 2023. Entomopathogenicity of ascmycete fungus Cordyceps militaris on the cotton bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae). The Journal of Fungi. https://doi.org/ 10.3390/jof9060614.
DOI: https://doi.org/10.3390/jof9060614

Interpretive Summary: The cotton bollworm, Helicoverpa zea, is a cosmopolitan and highly polyphagous pest that feeds on numerous wild and cultivated crops across the globe. Bollworms are significant economic pests of southern row crops including cotton, corn, and soybean causing yield losses in excess of 35 percent annually. Here we investigate the insecticidal effects of the entomopathogen Cordyceps militaris on the cotton bollworm. The objective of this study was to compare the survival, pupation, mortality, and lethal dose on all life stages of the cotton bollworm. Cotton bollworms across all developmental stages showed little to no mortality or infection when exposed to fungal spores by topical contact. However, insects who were exposed to treated corn leaf tissues showed a significant steep decline in survival for all concentrations assayed in this experiment. First, second, third, and fourth instar larvae were highly susceptible to all concentrations of cordyceps militaris spores. Of the four concentrations, the strongest effect on mortality and sporulation was observed for individuals treated with the second highest concentration of spores 5x10^8 on day five after treatment when compared to treatments. Older fourth and fifth instars began to show significant mortality on seven days post exposure to the fungal entomopathogen at any concentration. Pupae were highly sensitive to attack and colonization of fungal spores irrespective of spore concentration and contributed to significantly high mortality rates. Adult bollworms moths experienced little to no mortality during the ten-day observation period regardless of exposure method or concentration. These data have management implications and may provide alternative and supplementation to traditional synthetic insecticides for the control of bollworm larval and pupal populations.

Technical Abstract: This study investigated the exposure of the cotton bollworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae) to a novel pathogenic fungal agent historically associated with ancient and traditional Chinese medicine with human value, a commercial strain of Cordyceps militaris (Bals.-Criv.) Vuill. (Hypocreales: Cordycipitaceae). A series of comparative studies were conducted to evaluate the efficacy of two different exposure methods using four different concentrations (n × 109, n × 108, n × 107, n × 106) of C. mili-taris, where (n × 109) provided a concentration of approximately 420 ± 37 spores per mm2 with 398 ± 28 viable spores. Survival of cotton bollworms of all stages was not af-fected by C. militaris 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 (1st and 2nd). Significant declines in survival of early in-stars were observed for all concentrations at 7 d, and 95% mortality by 10 d, with the exception of 5th instars that experienced a less severe reduction in survival (35%) when exposed to any concentrations in the study. Survival of late instars (3rd to 5th) 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 LC50 2.01– 11.82 and LS50 of 2.14 – 10.36 spores/mm2 for 2nd, 3rd, and 5th instars cotton bollworms exposed to the C. militaris strain may demonstrate potential field application for control of larval populations of cotton bollworm.