If I plant the pitcher plant in a very fertile land and provide it with every nutrient it requires, will it stop to trap insects ?

Insectivorous plants generally grow in low marshy areas where the nutrients especially nitrogen content are very less and the quality of soil is very poor. To fulfil the requirements of nutrients of their body, they eat insects. These plants trap the insects and digest them by secreting some enzymes and obtain the nutrients from their body. Because pitcher plant is adapted to such environment that it only feeds on insects and therefore, it does not require fertile soil and thus such plants are able to grow on low nutrients and acidic medium conditions. If in any case these pants are provide with fertile soil containing nutrients, the plants stops producing carnivorous leaves and produces a flat non-carnivorous leaf which is called as phyllodia.

Regards