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.

The results of five experiments on maize resistance to Chilo partellus, suggest that there are at least five levels of relationships affecting plant colonization, larval survival and damage level: non-acceptance for oviposition shown by Inbred D and G and CIMMYT lines 125, 33, 324 and 178 (s3). Preferred Inbred A was oviposited 2–3 times higher. Feeding of young larval instars on young leaves or leaf sheaths, reduced on CIMMYT lines 324, 125 and 33; concentration of feeding of young larval instars on the upper growing part of plant, extensive on the highly susceptible Inbred A and reduced on all resistant lines tested; penetration of young larval instars into stem, reduced on CIMMYT lines 34 and 125 and Inbred G; and feeding of older larval instars in stem, reduced on CIMMYT lines 324, 178, 125 and Inbred G.