Capitate glandular trichomes fail to provide significant resistance to banded sunflower moth (Lepidoptera: Tortricidae)

Authors: Prasifka, Jarrad; Hulke, Brent

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2019
Publication Date: 1/21/2020
Citation: Prasifka, J.R., Hulke, B.S. 2020. Capitate glandular trichomes fail to provide significant resistance to banded sunflower moth (Lepidoptera: Tortricidae). Environmental Entomology. 49(2):444-448. https://doi.org/10.1093/ee/nvaa002.
DOI: https://doi.org/10.1093/ee/nvaa002

Interpretive Summary: Chemicals inside specialized plant hairs have been shown to kill or repel several types of insects that feed on sunflowers. Lines with very low or very high numbers of these hairs were grown in North Dakota to see whether the hairs would limit damage to sunflower seeds by caterpillars of the banded sunflower moth. Over two years, results did not show any benefit to higher numbers of hairs on the plants. In one year, the strength of sunflower hulls was also tested to see whether it could explain differences in damage to the lines, but the hull strength also did not explain why some lines were damaged less than others. Though neither test explained the amounts of damage to sunflower lines, sunflower hybrids do differ in the amount of damage caused by the banded sunflower moth, which means plant breeding is a valuable part of management along with late-planting, pest scouting, and insecticides.

Technical Abstract: Extracts from capitate glandular trichomes (CGT) of wild and cultivated sunflowers, Helianthus spp., have been shown to have repellent or toxic effects on sunflower specialists and generalist herbivores less closely associated with sunflower. Though CGT have been primarily examined for their potential to provide partial resistance to the sunflower moth, Homoeosoma electellum Hulst (Lepidoptera: Pyralidae), a floret- and seed-feeding pest, the banded sunflower moth (Cochylis hospes Walsingham [Lepidoptera: Tortricidae]) is a similar species more common in the primary sunflower-producing states of North Dakota and South Dakota. Replicated field trials using partially-inbred lines with low or high CGT densities were used to evaluate possible reductions to seed damage by C. hospes larvae in 2016–2017. Results failed to support the hypothesis that CGT are a useful defense against larvae of C. hospes; the putative plant defense of high trichome density corresponded to slightly more, rather than less, insect damage. A test of a secondary hypothesis, that strength of sunflower hulls could help explain patterns of seed damage among tested lines, produced similarly negative results. Though timing of bloom differed between groups of most- and least-damaged lines, prior research and pheromone-trapping data suggest differences in plant maturity also cannot adequately explain the observed results. Though the specific mechanisms remain unclear, significant differences in susceptibility to C. hospes exists for cultivated sunflower and limits losses from this primary insect pest.