Abstract: The European cherry fruit fly Rhagoletis cerasi L. (Diptera: Tephritidae) is the most serious pest in European cherry production. The control of the pest is difficult, especially against the background of EU wide reduction programs for broad spectrum insecticides. To find alternative control measures, the biology and behaviour of the fly must be known in more detail. One option to control the pest might be bait sprays, which have to be applied repeatedly during the main infestation period. To achieve the optimal efficacy and with respect to the costs, timing and number of applications are important questions. For this reason we investigated the correlation between the maturity of female R. cerasi by analysing the ovary status of flies caught with yellow sticky traps, oviposition, larval development and ripeness of host fruits (varieties Sam, Van and Hedelfinger) by measuring colour, sugar content as well as solidity, recorded as pressure resistance.The 1st fly was trapped on May 9, whereas the 1st ripe eggs after dissection of ovaries were found on May 13. According to the cherry variety, the first deposited eggs were detected between May 28 and June 2. During this time, the cherries turned their colour from green to yellow/orange, pressure resistance ranged between 4.0 and 6.3kg/cm2 and sugar content between 8.4 and 13.8 Brix. Newly deposited eggs were found until mid of July, whereas 3rd instars occurred from mid of June until mid/end of July, depending on cherry harvest and variety.