The use of fecundity, lobe biometry and the RAPD-PCR technique in order to compare strains of Tetranychus sp.

In Belgium, recently two new red carmine forms of Tetranychus sp. have appeared on tomato crops in glasshouses and in maize crops. These forms maintain their red colour even during summer and on other host plants such as French bean. Our aim was to establish their status and to compare them with strains of Tetranychus urticae and Tetranychus cinnabarinus. A strain of Tetranychus kanzawai, a distant relative of the same genus, was used as a control. The five strains tested were characterized by their own demographic parameters, probably because of a long separated evolution on different host plants. The white eye strain of ir: urticae was differentiated from the four other strains by scanning electron microscopy studies of the dorsal integument folds. An investigation using the random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) showed T. cinnabarinus as a distinct group. However, the mixing of the individuals of the four other strains raises the question of the role of hybridization and host plant selection in the evolution of the Tetranychus complex. Exp Appl Acarol 22: 649-666 (C) 1998 Kluwer Academic Publishers