Conditional sex allocation theory predicts that under poor conditions parents should produce more of the cheaper sex. Alternatively, females could provide less food for the single progeny or store resources (and thus decrease their rate of reproduction) when food is scarce. These non exclusive options were experimentally tested in the European beewolf where females provision brood cells with paralysed honey bees. Depending on the severity of the food restriction (number of available prey bees per day) females made use of one or more of the different options. In accordance with conditional sex allocation theory the investment ratio was biased towards the cheaper sex (sons) under poor conditions. Females also decreased the amount of food per progeny at very low food availability and stored food under one condition.