Viability of Claviceps africana spores ingested by adult corn earworm moths, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae)

A study was conducted in College Station, TX, to determine the viability of Claviceps africana spores in the digestive tract of adult corn earworm moths, Helicoverpa zea (Boddie). Both sexes were exposed to ergot-infected sorghum panicles for 30 min, and spores were recovered from excreta of the moths at 24-, 48-, and 72-h intervals after feeding. Recovered spores were quantified, and viability was determined by the germination rate of macroconidia. Nearly a 100-fold greater concentration of spores was recovered from female excreta at the three time intervals compared with male excreta. Concentration of spores in female and male excreta was greatest at 24 h, with a significant reduction at the later time intervals. Spore germination rates for both sexes were greater at 24 h, with survival being significantly reduced at the 72-h interval. Spores in female excreta survived longer than those from male excreta. Spore survival over time was significantly reduced in male excreta. Spore concentration and survival were greater from female excreta, which is key, because egg-laying activities on sorghum panicles intensify during flowering, and this source of ergot spores could contribute to the spread of the disease. This study demonstrates that corn earworm moths can internally carry viable ergot spores for several days and can act as primary dispersal agents for the fungus. This is important because contaminated moths migrating from areas in Mexico and southern Texas where ergot is endemic could transmit and spread the disease to other sorghum growing regions of the United States.