Dispersal and population dynamics of Amblyseius womersleyi Schicha(Acari:Phytoseiidae) and Tetranychus urticae Koch(Acari:Tetranychidae) in apple orchards

Abstract

Study was conducted to determine dispersal pattern of Tetranychus urticae Koch and Amblyseius womersleyi Schicha in the orchard in early, mid-, and late season, and determine diapause induction conditions for A. womersleyi, and elucidate the overwintering sites of various mites including T. urticae and A. womersleyi in apple and pear orchards in 2002 and 2003. Overwintered adult T. urticae movement from the tree trunk to the ground mostly occurred from late March to mid-April with a daily peak activity from noon to 4 p.m. Movement of overwintered A. womersleyi was not found from the tree trunk to the ground. T. urticae began to move from the ground vegetation to the tree canopy via trunk from early May, and A. womersleyi began to move to the tree canopy via trunk from early June. In 2002 when populations of T. urticae and A. womersleyi were high in the tree canopy, downward ambulatory movement of T. urticae from the canopy began to occur from late May while that of A. womersleyi occurred from late June. In 2003 when populations of T. urticae and A. womersleyi were low in the tree canopy, significant downward movements occurred much later (early July and late July, respectively). On the tree canopy peak densities of T. urticae and A. womersleyi occurred in mid-late July and late July, respectively in 2002, and in early July and late July, respectively in 2003. Thus, A. womersleyi population followed the T. urticae population 1-3 weeks behind. Since the times of peak populations of T. urticae and A. womersleyi significant aerial movement as well as downward movement of both species were detected.