Red harvester ants (Pogonomyrmex barbatus) do not distinguish between sorghum head mold symptomatic and asymptomatic seeds

Authors: ELLIOTT-VIDAURRI, LILLY - Cornell University; Penn, Hannah; CHOUDHURY, ROBIN - University Of Texas Rio Grande Valley

Submitted to: bioRxiv
Publication Type: Other
Publication Acceptance Date: 7/23/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Red harvester ants, common in arid parts of Texas, eat primarily seeds that they collect from areas near their nests. These nests are commonly found in farmer’s fields, meaning that ants can collect crop seeds. Some of these crop seeds may be infected with fungus that can reduce crop yield. But we do not know if ants will ignore infected seeds or if they will collect them. If they collect the seeds, the ants would be spreading and storing the fungus by moving the seeds to their nests. By storing infected seeds, this may spread fungus to other seeds in the nest and cause problems for farmers in later years when they till the fields. To find out if harvester ants will collect infected crop seeds, we used a seed depot containing 10 grain sorghum seeds with and 10 without visible head mold. We counted how many seeds of each type were taken by ants after 1, 2, 4, and 24 hours and did this for 20 ant colonies. We found that red harvester ants did not prefer seeds with and without head mold but collected all seeds of both types by 24 hours. Given this, ants may be storing infected seeds next to uninfected seeds within their nests, which may pose a risk to crop fields. Future work is needed to find out if this is the case.

Technical Abstract: Red harvester ants, Pogonomyrmex barbatus (Smith) (Hymenoptera: Formicidae), common in the Lower Rio Grande Valley of Texas, are known to gather seeds from areas around their nests and store the seeds inside their nests until later consumption. As these ants often nest in and near agricultural fields, some of these seeds may be from crops and may also be infected with fungal plant pathogens. These pathogens can degrade seed coats and may cause the seeds to rot within the ant nests, decreasing storage time and potentially spreading to other stored seeds. We studied how head mold, a common sorghum disease, changed ant preferences for sorghum seeds. Using seed depots, we evaluated foraging preferences for sorghum seeds with and without head mold, then we monitored how many seeds of each type were collected by the colonies after 1, 2, 4, and 24 hours. We found that red harvester ants did not have any significant preference for infected or uninfected seeds, taking both equally over time. Given this non-preference, ants were assumed to be storing infected seeds next to uninfected seeds within their colonies. However, the risk that stored pathogen-infected seeds will pose as a source of future seed infection to seeds within the nest and plants in the surrounding field needs to be further examined.