Sunflower headclipping weevil, Haplorhynchites aeneus
Adults of sunflower headclipping weevil measure about 8.5 mm (1/3 inch) in length and are shiny, black, and slightly hairy. Like all weevil species, adults have a snout-like protrusion that extends from their head and contains antennae and mouthparts. Larvae of the sunflower headclipping weevil are yellow or cream colored, C-shaped, and have a brown head capsule.
- The sunflower headclipping weevil is a species of beetle that is widespread in eastern Colorado. It is occasionally a pest of gardens and cultivated sunflower crops. Feeding injuries include clipped sunflower heads that hang from the stem. Injuries are typically limited to field edges and do not require management.
- Adults are small, black beetles that have a long snout protruding from their head. The snout contains the mouthparts and antennae and is on other weevil species. Larvae are yellow or cream colored and can be found developing in the fallen heads of sunflowers.
- Chemical management of sunflower stem weevil is not usually necessary. When applying pesticides, it is recommended that it be applied to the back of sunflower heads.
Adult sunflower headclipping weevil. Note the shiny black body and elongated snout protruding from the head. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Adult sunflower headclipping weevil on a flower. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Sunflower head injured by sunflower headclipping weevil. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Life history and habits
In October, mature larvae burrow in the soil to overwinter. After pupating the following spring, adults emerge in early summer and can be observed on young buds and emerging flowers by July. Adults feed on pollen and make cuts on the stem underneath the head of the flower, causing it to droop noticeably Adults are most likely to be observed on the cut flower head since they are generally active in the summer months while the sunflowers are in the reproductive stage.
After mating, females cut the stem below a developing flower and lay eggs at the base. Newly emerged larvae feed on flowers, pollen, and decaying tissues. Often, the severed flower head will fall to the ground and larvae will continue developing in the fallen head until overwintering in the soil. This species produces one generation each year and is usually associated with the common sunflower (Helianthus anuus) but will occasionally attack other related plants.
Feeding injuries include girdling of flower peduncles and leaf petioles, resulting in partially severed flower heads. In agricultural fields, sunflower headclipping weevil typically only affects a small portion of plants within border rows. Feeding injuries are generally aesthetic, especially in home gardens, and typically do not require management.
To monitor sunflower headclipping weevil, fields can be scouted for sunflowers that have clipped heads. In some states such as Kansas, management is recommended when weevils are observed on sunflowers and over 10% of the heads within a field are clipped.
Sunflower headclipping weevils are considered a minor pest of commercially grown sunflowers and can be difficult to manage in smaller home gardens. Injury in Colorado is usually limited to field edges and treatment is not typically necessary. In situations where treatment is necessary, the insecticide should be applied to the back of the flower heads rather than the front.
Colorado State University. (n.d.). Sunflower Headclipping Weevil. Colorado State University – Extension. Available https://webdoc.agsci.colostate.edu/bspm/arthropodsofcolorado/Sunflower-Headclipping-Weevil.pdf
Davis, H. 2020. Managing Insect Pests of Texas Sunflowers. Texas A&M – Extension. Available https://extensionentomology.tamu.edu/resources/management-guides/managing-insect-pests-of-texas-sunflowers/
Michaud, P. 2013. Sunflower Insects. Kansas State University – Department of Entomology. Available https://entomology.k-state.edu/extension/insect-information/crop-pests/sunflowers/sunflower-headclipping-weevil.html#:~:text=This%20is%20a%20black%20weevil,leaves%20hanging%20on%20the%20plant.
Varenhorst, A. 2021. Headclipping Weevils in Sunflower. South Dakota State University – Extension. Available https://extension.sdstate.edu/headclipping-weevils-sunflower