|VAN TASSEL, DAVID - The Land Institute|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2017
Publication Date: 9/25/2017
Citation: Prasifka, J.R., Mallinger, R.E., Hulke, B.S., Larson, S.R., Van Tassel, D. 2017. Plant-herbivore and plant-pollinator interactions of the developing perennial oilseed crop, Silphium integrifolium. Environmental Entomology. 46(6):1339-1345. https://doi.org/10.1093/ee/nvx134.
Interpretive Summary: A perennial prairie plant, wholeleaf rosinweed (Silphium integrifolium, hereafter “Silphium”), is a relative of sunflower and being developed as an oilseed crop. Research in Kansas and North Dakota focused on determining which insect species might be significant pests, and explored the reliance of the crop on bees for pollination services to produce filled seed. Feeding by larvae of obscure moth, Eucosma giganteana, caused substantial loss of Silphium seed in Kansas, but this insect pest was not found in North Dakota. Field plots in Kansas also had damage to the growing points that delayed flowering; the cause of this damage was not clear, but it was consistent with the injury produced by the tarnished plant bug (Lygus lineolaris), which was common on plants in Kansas and occasionally observed in North Dakota. A sunflower pest, the sunflower seed maggot (Neotephritis finalis), was also common in Silphium heads in North Dakota. Controlled pollination experiments in the field and greenhouse confirmed that Silphium plants depend on bees for pollination, both because of physical and genetic limitations. A small amount (< 1%) of self-pollination was observed. However, even if plants were bred to be genetically self-compatible, the need for physical movement of pollen means this plant would still be reliant on pollination by wild and managed bees. Together, observations on Silphium show that both pest and pollinator management are important for seed production.
Technical Abstract: Sampling in Kansas and North Dakota documented the plant-herbivore and plant-pollinator interactions of the developing perennial oilseed crop, Silphium integrifolium Michx. The larva of the tortricid moth, Eucosma giganteana (Riley), was the most common floret- and seed-feeding pest in Kansas, with infested heads producing ˜85% (2015) or ˜45% (2016) fewer seeds than apparently undamaged heads. Necrosis of apical meristems caused stunting and delayed bloom in Kansas; though the source of the necrosis is not known, observations of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois)(Hemiptera: Miridae), in S. integrifolium terminals suggests a possible cause. In North Dakota, E. giganteana larvae were not found, but pupae of Neotephritis finalis (Loew)(Diptera: Tephritidae), a minor pest of cultivated sunflower, were common in heads of S. integrifolium. Bees appeared highly attracted to S. integrifolium, and in all but one observation, bees were seen actively collecting pollen. The most common bees included large apids (Apis mellifera L., Svastra obliqua [Say], Melissodes spp.) and small-bodied halictids (Lasioglossum dialictus spp.). Controlled pollination experiments demonstrated that S. integrifolium is pollinator dependent, due to both mechanical barriers (imperfect florets and protogyny) and genetic self-incompatibility. Subsequent greenhouse tests and AFLP confirmation of putative self progeny show a low (< 1%) level of self-pollination is possible. If genetic self-incompatibility is eventually reduced through breeding, mechanical barriers would maintain a reliance on bees to move pollen between male and female florets. Collectively, observations on S. integrifolium show that both herbivore and pollinator management are important to maximizing seed production.