Size of orchard trees as a factor affecting behavioural control of apple maggot flies (Dipt, Tephritidae) by traps

Over a 3-year period (1997-1999), we examined the influence of tree size on effectiveness of traps for behaviourally controlling apple maggot flies, R hagoletis pomonella (Walsh), in small blocks of trees in Massachusetts comm ercial apple orchards. Traps were red spheres coated with Tangletrap and ba ited with an attractive synthetic host fruit odour (butyl hexanoate). Traps were placed 6 m apart on perimeter apple trees of each block and were desi gned to intercept apple maggot flies immigrating into blocks from unmanaged host trees. Based on captures of adults by unbaited red spheres placed nea r the centre of each block to monitor degree of adult penetration into the interior and on percentages of fruit injured by apple maggot, traps surroun ding blocks of small trees (1.5 m canopy diameter) planted at high density were more effective in controlling apple maggot flies (relative to control obtained by insecticide sprays used in comparison blocks) than were traps s urrounding blocks of large trees (3.7 m canopy diameter) planted at low den sity, with traps surrounding blocks of medium-size trees (2.5 m canopy diam eter) planted at medium density generally providing an intermediate level o f control.