Interactions of gulf cordgrass, Spartina spartinae (Trin.) Merr. ex Hitchc., habitat with ixodids on the South Texas coastal plain

Authors: Showler, Allan

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2023
Publication Date: 8/11/2023
Citation: Showler, A. 2023. Interactions of gulf cordgrass, Spartina spartinae (Trin.) Merr. ex Hitchc., habitat with ixodids on the South Texas coastal plain. Environmental Entomology. https://doi.org/10.1186/s40068-023-00311-w.
DOI: https://doi.org/10.1186/s40068-023-00311-w

Interpretive Summary: Many hard ticks of the South Texas coastal plains transmit medical and veterinary disease agents. Ecology of hard ticks involves living and nonliving factors, such as plants. Substantial areas of the coastal plains are dominated by Gulf cordgrass, which grows in dense clumps, each with a fountain-like canopy of thin leaves. Hard tick abundances on Gulf cordgrass in winter, spring, and summer were similar to those on mixed mesquite-thorn scrub typical of the region. At least five hard tick species were found on Gulf cordgrass. Gulf cordgrass provides favorable conditions for hard ticks because it is cooler and more humid inside the clump than in the canopy where questing occurs: hard ticks can take refuge in the same plant when canopy conditions are unfavorable. Also, the leaves mostly have a “V” shape or, during warm subtropical seasons, a tightly folded slot into which larvae crawl. Larval lone star ticks were more abundant in the concave side of “V”-shaped leaves than on the opposite, more exposed side of the leaves. It is likely that humidity and dew are better conserved in the “V” and slot than on more exposed parts of the leaves. Gulf cordgrass offers ticks opportunities to rehydrate on the leaf at or near the place of questing and inside the basal grass clump. We suggest that most published studies reporting tick populations based on flag samples are inaccurate because flag sampling does not account for ticks periodically moving down or inside the plant to reabsorb moisture between questing times.

Technical Abstract: Many ixodid species of the South Texas coastal plains transmit medical and veterinary disease agents. Ixodid ecology involves abiotic and biotic factors including interactions with plants. Substantial areas of the coastal plains are dominated by Gulf cordgrass, Spartina spartinae (Trin.) Merr. ex Hitchc., which grows in dense clumps, each with a fountain-like canopy of thin leaves. Ixodid abundances on S. spartinae in winter, spring, and summer were similar to those on mixed mesquite-thorn scrub typical of the region. At least five species of ixodids were collected from S. spartinae. Spartina spartinae provides favorable conditions for ixodids because it is cooler and more humid inside the clump than in the canopy where questing occurs: ixodids can take refuge in the same plant when canopy conditions are unfavorable. Also, the leaves mostly have a “V” shape or, during warm subtropical seasons, a tightly folded slot into which larvae crawl. Larval lone star ticks, Amblyomma americanum Koch, were more abundant in the concave side of “V”-shaped leaves than on the opposite, more exposed side of the leaves. It is likely that humidity and dew are better conserved in the “V” and slot than on more exposed parts of the leaves. Spartina spartinae offers ixodids opportunities to rehydrate on the leaf at or near the place of questing and inside the basal grass clump. We suggest that most published studies reporting ixodid populations based on flag samples are inaccurate because flag sampling does not account for ixodids periodically moving down or inside the plant to reabsorb moisture between questing times.