- an evolved relationship between plants and insects

Mutualism is the symbiotic relationship where both species involved benefit in the exchange. However, the relationship between plants and insects may have begun with the plants are the primary benefactor initially. Plant evolution before their relationship with insects was limited by the ability of the plants to spread genetic material through wind or water borne pollen. Therefore the majority of the plant species were forms that were asexual, in that they produced complete gametes. The spreading of the spores would then not be as risky as spreading the pollen to the wind. Those species that did spread pollen did so with the following limits, the distance to the receiving member and the likelihood of success. Therefore, the insects being able to acts as a more precise transporter of the genetic material then increased the success rate and the diversity of the mixing of the gene pool of the plants. So the Plants task was to generate a reward for the insects to collect in exchange for visiting the flower and picking up the cargo.

How plants enticed insects to become, their transit system is as diverse of the varity of relationships.
Relationship Example
The most commonly identified example are the bees and flowering plants. Here the insects are acquiring food and in the process pickup and transport pollen.
Honey bee
There are various species of flies and moths that mimic the role of the bees - picking up pollen in exchange for food.
Clearwing Moth
There are cases where the relationship is far more one-sided. The plant mimics a chemical attractant - such as a pheromone and the insect in the process of searching for the source of the pheromone and inmost cases not finding the desired result, disturbs the pollen and picks up a certain amount for transportation.