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

In Belgium, recently two new red carmine forms of Tetranychus sp. have appe ared on tomato crops in glasshouses and in maize crops. These forms maintai n their red colour even during summer and on other host plants such as Fren ch bean. Our aim was to establish their status and to compare them with str ains of Tetranychus urticae and Tetranychus cinnabarinus. A strain of Tetra nychus kanzawai, a distant relative of the same genus, was used as a contro l. The five strains tested were characterized by their own demographic para meters, probably because of a long separated evolution on different host pl ants. The white eye strain of ir: urticae was differentiated from the four other strains by scanning electron microscopy studies of the dorsal integum ent folds. An investigation using the random amplified polymorphic DNA-poly merase chain reaction (RAPD-PCR) showed T. cinnabarinus as a distinct group . However, the mixing of the individuals of the four other strains raises t he question of the role of hybridization and host plant selection in the ev olution of the Tetranychus complex. Exp Appl Acarol 22: 649-666 (C) 1998 Kl uwer Academic Publishers.