Temperature requirements may explain why the introduced parasitoid Quadrastichus citrella failed to control Phyllocnistis citrella in Spain
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Quadrastichus citrella Reina and La Salle (Hymenoptera: Eulophidae) is a parasitoid of Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), indigenous to South Eastern Asia where it is considered a key natural enemy of this pest. It was introduced in Spain in a classical biological control program and became established, but was not as successful as forecast. To check whether its biology could explain this lack of control, development and reproduction at different temperatures were studied. Quadrastichus citrella can survive at temperatures between 15 and 35°C. Lower development threshold was 12.3°C, which resulted in a thermal constant of 138.06 DD. The combination of development and reproduction into demographic parameters resulted in highest net reproduction occurring in the range 20-25°C (78.2 females per female), and highest intrinsic rate of increase at 30°C (0.2571 females per female per day). These values make Q. citrella an intrinsically superior natural enemy compared to other leaf miner parasitoids. However, overwintering of Q. citrella in Spain may present a barrier, especially in areas like Valencia, where average winter temperatures are around 11°C. This could account for the low recovery rates observed in Spain in spite of the key natural enemy status enjoyed by this species in its area of origin. © IOBC 2006.