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Sunflower production depends on pollination by honey bees, Apis mellifera L., and wild bees. For wild sunflower oligoleges, preference for various sunflower lines seems to reflect the quantity (or accessibility) of floral rewards, with floret size (≈accessibility of sunflower nectar) appearing most important. However, it is less clear how honey bees, a key generalist, are affected by sunflower floral traits. The honey bee-sunflower interaction was explored to test if accessibility of nectar (≈floret size) and related floral traits explain foraging preferences and to assess potential nutritional variation in sunflower pollen. In the first two years, honey bee foraging preference increased with decreasing floret length similar to previous observations with wild pollinators. In the second year, no similar response was seen, though nectar rewards (by volume or volume × concentration) were remarkably low compared to the previous year. Pollen collected from bagged plants in the second year showed sunflower lines differed in concentrations (µg/mg ± SE) of total fatty acids and essential fatty acids. In general, it appears that honey bee responses to floral traits are similar to those of wild bees responsible for pollinating much of the sunflower crop in the central United States and that variation in the nutritional quality of sunflower pollen is greater than previously known. Because of the broad geographic distribution of the sunflower crop, additional research on how the environment influences floral rewards and sunflower-pollinator interactions may be needed. [ABSTRACT FROM AUTHOR]

Sunflower line HA 488 (where HA is Helianthus annuus) is resistant to the red sunflower seed weevil, Smicronyx fulvus LeConte, with ≈80% less seed damage compared to susceptible lines. To determine the value of resistance in single‐cross hybrids, six hybrids were created by pollinating weevil‐resistant (cms HA 488, where cms cytoplasmic male sterile) or susceptible (cms HA 412HO) inbred lines with three putatively susceptible restorer lines (RHA 274, RHA 464, or RHA 468) and artificially infesting each with 30 weevils head−1. In 2021–2022, resistant hybrids from cms HA 488 reduced seed damage by ≈40%–50% for hybrids with RHA 274 or RHA 464. However, cms HA 488 did not reduce damage when crossed with RHA 468. Infestation of male‐fertile isogenic lines HA 488 and HA 412HO with 60 weevils head−1 showed resistance remained effective at 12–20 times economic thresholds. Results confirm the value of resistance to S. fulvus for sunflower hybrids but also suggest a need to further examine the role of the male heterotic group in resistance to the red sunflower seed weevil. Core Ideas: Inbred cms HA 488 reduced seed weevil damage ≈40%–50% in single‐cross hybrids.Some male (RHA) parents may provide non‐complementary resistance.Field trials showed resistance in HA 488 per se was effective at 12–20 times economic thresholds. [ABSTRACT FROM AUTHOR]

The red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae), is the most destructive seed-feeding pest of sunflower in North America. The life history of S. fulvus (e.g., univoltine, overwintering within 6 cm of soil surface) suggests several strategies to limit crop damage, but insecticides remain the primary management tool. To facilitate broader management of S. fulvus, a degree-day model for adult emergence was developed and tested. Emergence of adults under controlled conditions produced a lower developmental threshold of 5 °C, ≈ 970 degree-days to first emergence, and ≈ 1160 degree-days to 50% emergence. Soil temperature data showed accumulated degree-days were similar 5 cm below turf and 10 cm beneath bare soil. Observed emergence of weevils in field plots occurred several days earlier than predicted (using 5 cm turf or 10 cm bare soil temperatures) when soil was kept free of vegetation. However, observed emergence was similar to predicted emergence when plots were shaded by spring wheat, which is representative of crops planted after sunflower for much of North America. Though access to soil (rather than ambient) temperature data is needed, this first degree-day model provides a tool to help growers avoid S. fulvus damage using early planting or early-maturing hybrids. [ABSTRACT FROM AUTHOR]

The red sunflower seed weevil, Smicronyx fulvus L. is a univoltine seed-feeding pest of cultivated sunflower, Helianthus annuus L. Artificial infestations of S. fulvus onto sunflowers with traditional (<25% oleic acid), mid-oleic (55–75%), or high oleic (>80%) fatty acid profiles were used to test if fatty acids could be used as natural markers to estimate the proportion of weevils developing on oilseed sunflowers rather than wild Helianthus spp. and confection (non-oil) types. Oleic acid (%) in S. fulvus confirmed the fatty acid compositions of mature larvae and weevil adults reflected their diets, making primary (oleic or linoleic) fatty acids feasible as natural markers for this crop-insect combination. Oleic acid in wild S. fulvus populations in North Dakota suggests at least 84 and 90% of adults originated from mid-oleic or high oleic sunflower hybrids in 2017 and 2018, respectively. Surveys in 2017 (n = 156 fields) and 2019 (n = 120 fields) extended information provided by S. fulvus fatty acid data; no significant spatial patterns of S. fulvus damage were detected in samples, damage to oilseed sunflowers was greater than confection (non-oil) types, and the majority of damage occurred in ≈10% of surveyed fields. Combined, data suggest a few unmanaged or mismanaged oilseed sunflower fields are responsible for producing most S. fulvus in an area. Improved management seems possible with a combination of grower education and expanded use of non-insecticidal tactics, including cultural practices and S. fulvus -resistant hybrids. [ABSTRACT FROM AUTHOR]