Differentiating two species of sunflower seed weevils
While scouting sunflower, there are two types of seed weevils that you may encounter. They are the red sunflower seed weevil and the gray sunflower seed weevil. It is possible to observe both of these species on a single sunflower head (Figure 1), and determining their identities isn’t difficult. Generally, the populations of the red sunflower seed weevil are much higher than the populations of the gray sunflower seed weevil. For this reason, thresholds have been calculated for the red sunflower seed weevil (4-6 red sunflower seed weevils per head), while the gray sunflower seed weevil is considered a non-economic pest.
Red sunflower seed weevil
Like its name implies, the red sunflower seed weevil has an orange/red appearance due to small hairs that are present on its body (Figure 2). Often, these weevils will appear almost black because the hairs have been rubbed off. The red sunflower seed weevil has a black snout with small bent antennae originating from it. The adults will also have black legs. Of the two species, the red sunflower seed weevil is smaller.
When examining a plant, the red sunflower seed weevil will often be found down between the developing seeds in the head. It can also be observed climbing on the head or on the leaves and stem of the plant. Prior to flowering, pulling back the bracts can often uncover seed weevils. The red sunflower seed weevils are capable of flight and may drop from the plant when disturbed.
Gray sunflower seed weevil
Aptly named, the gray sunflower seed weevil adult has small gray hairs that cover the majority of its body (Figure 3). The gray sunflower seed weevil is larger in size than the red sunflower seed weevil, and will have gray legs instead of black. It also has a black snout that has small antennae originating from it. The gray seed weevil usually emerges about 10 days before the red sunflower seed weevil.
The larvae of both species are small and feed on the developing seeds. They are cream colored and take on a “C” shape when disturbed.