|Lopez, Juan De Dios|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2004
Publication Date: 6/1/2004
Citation: Prom, L.K., Lopez, J. 2004. Viability of Claviceps africana spores ingested by adult corn earworm moths, Helicoverpa zea. Journal of Economic Entomology. 97:764-767. Interpretive Summary: Sorghum ergot is a major threat to sorghum production, especially in hybrid seed production fields. The disease can result in major losses to farmers because it reduces both grain yield and quality. Since ergot is a new disease of sorghum in the United States, it is important to learn as much about the ability of mobile flying insects that frequent sorghum plants during flowering to spread the disease from field to field, in order to develop cost-effective control measures. We have shown in this work that once these flying insects feed on the reproductive components (called spores) of the fungus from diseased sorghum plants, they will be able to spread the disease from one sorghum field to the next for up to 72 hours. Therefore, reducing the impact of these insects in sorghum production fields will minimize or avoid the spread of the disease within the field and to other areas.
Technical Abstract: A study was conducted at the USDA-ARS, Southern Plains Agriculture Research Center, College Station, Texas to determine the viability of Claviceps africana spores in the digestive tract of adult corn earworm moths. Both sexes were exposed to ergot-infected sorghum panicles for 30 min and spores were recovered from the excreta of the moths at 24, 48, and 72 h intervals after feeding. Recovered spores were quantified and viability determined by the germination rate of macroconidia. Excreta from female moths contained a greater concentration of ergot spores compared to excreta from males. Nearly a 100 fold greater concentration of spores was recovered from female excreta at the three time intervals versus male excreta. The concentration of spores in female and male excreta was greater at 24 h with a significant reduction at the later time intervals Spore germination rates for both sexes were greater at the 24 h collection interval with survival being significantly reduced at the 72 h interval. Spores survival over time was observed for male excreta. Spore concentration and survival were greater for female moths, which is significant since the egg-laying activities of females intensify during sorghum 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 secondary dispersal agent for the fungus. This is important because contaminated moths migrating from areas in Mexico and southern Texas where ergot is endemic will be able to transmit and spread the disease to other sorghum regions of the U.S.