Is sunflower (Helianthus annuus) at risk to damage from Ophraella communa, a natural enemy of common ragweed (Ambrosia artemisiifolia)?

Abstract

Ophraella communa is being studied for augmentative releases in eastern Canada for Ambrosia artemisiifolia (common ragweed) control. Host specificity studies with cohorts of insects and a life table approach with individual insects were utilized to evaluate the risk of damage to sunflower. Predicting relative non-target attack and when and where this may occur is based on relative acceptability, suitability, and availability of host and non-host plants. We conclude the risk of O. communa adult-stage beetles attacking sunflower plants is negligible. In 20% open cages, over 98% of the adult O. communa left sunflower plants with few or no eggs laid. When the preferred host plants (A. artemisiifolia) are completely defoliated, the first instar larvae move to nearby sunflower plants in the immediate vicinity (up to 20–30 cm) and begin foraging. O. communa larvae can significantly damage sunflower, but 50% of the first instar larvae will die feeding on sunflower plants. The effect of low oviposition and high mortality will result in no increase in the O. communa population. Within 30 days, the O. communa population increased 208 times when feeding on ragweed and decreased 4.2 times when feeding on sunflower. Newly emerged adults leave the sunflower plants in search of ragweed. Damage to sunflower could occur during augmentative releases of O. communa, but this would only occur when a significantly large, advancing insect population has completely defoliated A. artemisiifolia within or adjacent to a sunflower field.