Life-history parameters of two closely related forms of the Tetranychus urticae-complex on different host plants

Abstract

Life-history parameters of two closely related forms of the Tetranychus urticae-complex, Tetranychus urticae Koch and Tetranychus cinnabarinus Boisduval, were compared on four different host plants, i.e. bean cv Sizal, cucumber cv Picobello, tomato cv W 3298, and gerbera cv Porto. The experiments were conducted at 24±2°C, L:D=16:8 hand 60-70% RH, using leaf discs of the host plants in Petri dishes. Life table analysis showed that the reproductive potential of T. cinnabarinus and T. urticae varied on different host plants. Tetranychus cinnabarinus had the highest rm (day·l) on cucumber (0.21) and bean (0.19), and the lowest on tomato (0.16) and gerbera (0.15). Tetranychus urticae showed the highest fm on bean (0.18) and cucumber (0.16) and the lowest on gerbera (0.12) and tomato (0.08). The higher reproductive potential of T. cinnabarinus compared to T. urticae may explain the displacement of the latter by T. cinnabarinus, as observed in the glasshouse on some plant species (e.g. cucumber, gerbera). Introduction The two-spotted spider mite and the car-mine spider mite are two forms belonging to the T. urticae complex. They may inhabit the same host plant under glasshouse conditions. The carmine spider mite, often referred to as T. cinnabarinus, has red females, orange eggs and usually lacks the ability to enter diapause. Despite these differences, hybridisation may occur readily (Dupont, 1979). Dupont considers T. cinnabarinus Boisduval synonymous with T. urticae Koch and it is now common practise to speak of the T. urticae species complex. Results of recent research (Gotoh et aI., 1993) on host race formation in the T. urticae complex based on cross-breeding experiments , showed that gene flow between the red (tomato) and green (cucumber) form is possible. Hence, it was concluded that both