Efficient conifer seedling protection against pine weevil damage using neonicotinoids

Abstract

The large pine weevil Hylobius abietis (L.) is the most important pest of coniferous plantations in Europe. Two neonicotinoid insecticides, acetamiprid and thiacloprid, have been tested in field conditions to check to what extent they can protect softwood seedlings from injuries caused by this pest. The experiment was organized in a randomized complete block design, included five treatments (two concentrations of 0.5% and 1.0% of each insecticide, and a control) and was performed on four experimental clear-cut sites, three recently-felled, and one of 1-year old, with high populations of large pine weevil. The seedlings were treated by dipping their aerial parts into insecticide emulsion before planting.
The tested treatments diminished only to a moderate extent (by 36.4-¬89.8%) the proportion of the attacked seedlings, but greatly reduced the size of the wounds and the mortality of the seedlings, by more than 82.7% and 89.7-100%, respectively. In three of the four experimental sites, no treated seedlings were killed through weevil attack, while 36% of the untreated plants died during the first vegetation season after planting. There were no statistically significant differences between the 0.5% and 1% treatment concentrations of either commercial product, suggesting that under similar conditions the 0.5% concentration could be used to diminish the costs of the treatments. The treatments are highly effective up to the end of the first growing season (5 months after application), even when the density of weevil populations increases through the emergence of new adult beetles from root stumps.