Comparison of Methods for Monitoring Mindarus abietinus (Homoptera: Aphididae) and Their Potential Damage in Christmas Tree Plantations

Abstract

The balsam twig aphid, Mindarus abietinus Koch, causes distortion, loss, or both, of needles on balsam fir Christmas trees. Insecticides are often applied for control of twig aphids with little monitoring of population levels or their subsequent damage. This study compared the utility of 2 techniques (beating discs and visual counts of infested shoots) that could easily be used by Christmas tree growers to monitor aphids. A beating technique was better than visual counts for detecting numbers of fundatrices before and during budbreak, whereas visual counts of midcrown infested shoots were more feasible for estimating aphid abundance after budbreak. Sample size analysis indicated that a minimum of 15 trees could be used for either method to estimate mean numbers of fundatrices or mean proportions of potentially infested shoots. Correlation analyses between mean numbers of aphids or proportions of infested shoots and resulting proportions of undamaged shoots were variable with a significant and negative correlation between infested shoots and subsequent undamaged shoots ( r = −0.83). Paired comparisons were also made between selected and nonselected Choose-and-Cut Christmas trees to evaluate public perception of aphid damage. The public did not differentiate between aphid-damaged and undamaged trees, but they did show a preference for larger trees. Our results indicate that growers need to monitor aphids before budbreak and limit insecticide applications to trees with predictable levels of infestation (e.g., 2 or more fundatrices per disc results in ≈50% infested shoots) that will be harvested for shipment rather than grown for Choose-and-Cut.