Impact of Woolly Apple Aphid (Homoptera: Aphididae) on the Growth of Potted Apple Trees

Abstract

The impact of woolly apple aphids (WAA), Eriosoma lanigerum (Hausmann), on growth and nutrient content of plant tissues was investigated with young apple trees grown in growth chambers. One hundred forty-four individually potted and caged tissue cultured ‘M.7’ apple trees were divided equally into two treatments (infested with five first-instr WAA on the shoot or infested with five first-instar WAA on the roots) and an uninfested control. Root galls and stem splits began forming as a result of WAA feeding after only 4 and 8 wk, respectively. Four weeks after infestation, trees in the WAA-infested treatments had significantly greater shoot and root dry weight than the control trees. After 16 wk, the growth rate of infested trees had decreased and the dry weights of roots, shoots, and leaves were greater in control trees than in treated trees. The difference in dry weight increased at 21 wk. In general, roots were more severely affected by WAA; populations of WAA on roots caused a greater reduction in tissue weights than WAA feeding on the shoot. WAA feeding also caused a decrease in foliar nitrogen and phosphorus; results from the other elemental analyses were variable. Results from the elemental analysis of root tissue indicated that WAA disrupted the nutrient balance of these apple trees.