Impact of the predatory mite Anystis baccarum (Prostigmata: Anystidae) on apple rust mite Aculus schlechtendali (Prostigmata: Eriophyidae) populations in Northern Ireland Bramley orchards

Summary Anystis baccarum is a common predatory mite in Northern Ireland Bramley orchards. To determine its effect on Aculus schlechtendali populations, sticky traps and sprays of demeton‐S‐methyl were used to exclude A. baccarum from branches. Out of four trials, exclusion of A. baccarum by sticky traps alone resulted in significantly greater numbers of A. schlechtendali in one trial. In the other trials where A. schlechtendali numbers were lower, there was either no effect, or possible evidence of fewer A. schlechtendali. The combination of demeton‐S‐methyl treatments and sticky traps to exclude A. baccarum resulted in significantly more A. schlechtendali in two trials out of three in 1998. It seems likely that this resulted from the dual effects of stimulation of A. schlechtendali reproduction by the acaricide and the absence of predation by A. baccarum, because acaricide treatment alone in 1999 resulted in significant reductions in A. schlechtendali numbers at the end of the season. This effect could have resulted from A. baccarum re‐invading the treatment branches after the effects of the acaricide had worn off. It is recommended that growers are encouraged to conserve A. baccarum within their orchards.