Nitrogen availability and defense of tomato against two-spotted spider mite

The aim of this work was to study how nitrogen availability affects within- plant allocation to growth and secondary metabolites and how this allocatio n affects host selection by herbivores. Tomato plants (Lycopersicon esculen tum) were grown at six levels of nitrogen availability. When nitrogen avail ability increased, plant relative growth rate increased, but tissue carbon/ nitrogen ratio in the second oldest true leaf and allocation to large gland ular trichomes (type VI) as well as to the defense compounds rutin and chlo rogenic acid decreased. Leaf protein concentration increased. Two-spotted s pider mite (Tetranychus urticae) females responded significantly to these c hanges: in dual choice tests they preferred leaf disks from plants grown at high nitrogen availability, with a low C/N ratio. This preference persiste d in an olfactometer in which the mites were offered only the odors release d by leaves with damaged trichomes. We conclude that in a tomato leaf incre ased nitrogen availability leads to decreased allocation to defenses, and t hat repellent volatiles released by trichomes play a key role in affecting leat selection by two-spotted spider mite females.