Host plant quality directly affects potential and achieved herbivore fecundity and reproductive strategies. Insect herbivores strongly regulate their nutrient intake including allochemicals. The nitrogenous nutrients are a limiting factor for herbivore survival, growth and fecundity. Herbivore insects usually exhibit enhanced performance and outbreak dynamics on stressed plants do to increased changes in plant physiology. Closely related. coocuring and generalist feeding herbivores eat protein and carbohydrate in different amounts and ratios even if they eat the same plant taxa. Plants in rban landscapes are subject to stress factors (pollutants, automobile exhaust, higher temperature) may reduce the abundance of natural enemies, parasitoids and predators. Many species of insects possess the capacity to learn to guide an active search for food and hosts. Both plants and arthropod herbivores generate select forces that lead to the evolution of plant defence against herbivores and pathogens.