Insect predators and augmentative biological control of balsam twig aphid (Mindarus abietinus Koch) (Homoptera: Aphididae) on Christmas tree plantations

Abstract

The balsam twig aphid (Mindarus abietinus Koch) (Homoptera: Aphididae) is a major insect pest of balsam and Fraser firs grown for Christmas trees. Few control methods other than chemical insecticides have been evaluated. In this study, we identified insect predators associated with M. abietinus in three fir Christmas tree fields in Michigan. We also conducted laboratory and field studies to assess the effectiveness of augmentative releases of Chrysoperla rufilabris Burmeister (Neuroptera: Chrysopidae) for M. abietinus control. A diverse complex of predators, primarily generalists including syrphids, coccinellids, and lacewings, was observed on infested trees. Predator abundance was generally low early in spring when M. abietinus fundatrices were present, but predators became more common as sexuparae and later aphid stages appeared. In controlled laboratory tests, C. rufilabris were capable of consuming at least 35 M. abietinus per day, but were able to develop on 10 aphids per day. Average adult weight of C. rufilabris increased with the number of aphids consumed by larvae. In field studies, release of one C. rufilabris larva onto caged branches with moderate M. abietinus infestations significantly reduced the density of M. abietinus overwintering eggs. In open field releases, C. rufilabris larvae significantly reduced the density of M. abietinus sexuparae and overwintering M. abietinus eggs in two of three fields.