A comparison is made between testing techniques for examination of spider mites on their host plants. The female fecundity is related to chemical composition of different rose and strawberry cultivars using Tetranychus urticae and Panonychus ulmi. From stepwise regression analysis it is shown that a number of amino acids and minerals are correlated with mite fecundity, but the effects vary with the host plant species and cultivar. Mineral nutrition of the plant increases fecundity, while certain phenolic compounds apparently decrease it. An attempt was made to correlate female fecundity with the amounts of feeding, using plants which were radio-labelled. The pattern of food plant finding and acceptance by the females of the two spotted spider mite, Tetranychus urticae Koch was demonstrated by Dabrowski (1976). Female mites exhibited differences in gustatory response to the extracts from different plant species and the observed order of preference was the same as the mite fecundity when feeding on fresh leaves from these plants. The aim of the present study was to investigate the suitability of various methods used in the study of spider mite/host plant relationships and especially to investigate the effect of the biochemical and physiological state of plant species or cultivars upon the behaviour and biology of T. urticae and the fruit tree spider mite, Panonychus ulmi (Koch). Comparison of some techniques used in the experiments The effect of the host plant on the behaviour and reproduction of spider mites is most readily investigated using leaf discs, 25-50 mm in diameter, placed on moist cotton wool in glass or plastic dishes, but a defect of this method is that soluble compounds from the plant tissue diffuse out into the surrounding water and some biochemical degradation may occur. These changes may affect the palatability of the test plant for the mites. Because of this problem, comparisons were made between five different methods. Females of T. urticae and P. ulmi were reared on the strawberry cultivar Purpuratka × Senga Sengana (cross). Females of P. ulmi were reared on four apple cultivars, Golden Delicious, Fantazja, Bankroft and Jonathan, to establish the
Distinct differences in Panonychus ulmi population densities on various apple cultivars have been observed under natural field infestations. Various laboratory techniques may be used to determine the differences in susceptibility or resistance to P. ulmi of different apple cultivars. The lowest variation in P. ulmi behaviour, and fecundity between replications was observed for females reared on leaf discs 20-25 mm in diameter and for females reared in the small plastic cages placed on the leaves of potted young apple trees. The leaves used for bioassays should be collected from the same part of the trees. The density of P. ulmi populations and their fecundity should be observed on leaves growing on short spurs. Preconditioning P. ulmi on various cultivars did not influence the female's fecundity on the new plants.There is no individual, singly-acting mechanism responsible for the moderate resistance of apples to P. ulmi. The resistance is caused by a number of morphological, anatomical and biochemical leaf properties, expressed differently in different cultivars.Resume-En conditions d'infestation naturelle au champ, des variations ont ete observees au niveau des densites de population de P. ulmi selon les cultivars consideres. De nombreuses techniques de laboratoire permettent de determiner les ecarts de sensibilite ou de resistance a l'encontre de P. ulmi chez les differents cultivars. En termes de comportement et de fecondite de P. ulmi en fonction des repetitions, la variation minimale fut observee pour les insectes femelles eleves sur des disques foliaires de 20-25 cm de diametre, ou dans de petites cages en matiere plastique installees sur les feuilles de jeunes pommiers en pots. Les feuilles utilisees dans le cadre des essais bioecologiques doivent etre prelevees au meme endroit sur les arbres. En outre, il convient d'etudier la densite et la fecondite des populations de P. ulmi au niveau des feuilles portees par les bois de retour courts. Signalons egalement qu'un conditionnement preable aux divers cultivars n'eut aucun effet sur la fecondite de l'insecte femelle lorsque celle-ci fut mise en presence de nouvelles plantes. La resistance moyenne des pommiers vis-a-vis de P. ulmi n'est pas le resultat d'un mecanisme unique agissant independamment. Elle est le fruit d'un nombre considerable d'attributs morphologiques, anatomiques et chimiques des feuilles, lesquelles s'expriment differemment suivant les cultivars.
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