Pk. Kleintjes et al., Comparison of methods for monitoring Mindarus abietinus (Homoptera : Aphididae) and their potential damage in Christmas tree plantations, J ECON ENT, 92(3), 1999, pp. 638-643
The balsam twig aphid, Mindarus abietinus Koch, causes distortion, loss, or
both, of needles on balsam iir Christmas trees. Insecticides are often app
lied for control of twig aphids with little monitoring of population levels
or their subsequent damage. This study compared the utility of 2 technique
s (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 d
uring budbreak, whereas visual counts of midcrown infested shoots were more
feasible for estimating aphid abundance after budbreak. Sample size analys
is indicated that a minimum of 15 trees could be used for either method to
estimate mean numbers of fundatrices or mean proportions of potentially inf
ested shoots. Correlation analyses between mean numbers of aphids or propor
tions of infested shoots and resulting proportions of undamaged shoots were
variable with a significant and negative correlation between infested shoo
ts and subsequent undamaged shoots (r = -0.83). Paired comparisons were als
o made between selected and nonselected Choose-and-Cut Christmas trees to e
valuate 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 predictabl
e levels of infestation (e.g., 2 or more fundatrices per disc results in ap
proximate to 50% infested shoots) that will be harvested for shipment rathe
r than grown for Choose-and-Cut.