Genetic diversity allows species to adapt to change in the environment. Imagine if the world had only one type of cow adapted to a climate like Virginia's. If the world-wide climate became very hot or cold, this type of cow might not survive the change. Then we would not have the milk or beef that a cow provides for us. The variety of species in the world provides many methods of nutrient and energy cycling in ecosystems.
Plants use the sun's energy and provide many animals with food.
Vultures and cockroaches help breakdown decaying matter, offering nutrients and energy for plants to use for growth. Man inhales oxygen and exhales carbon dioxide. Mammal species come in last with only about 4000 kinds in the world. As an example, cockroaches provide a nutritious food source for birds, reptiles, amphibians and mammals. So imagine all the colorful rainforest creatures that might be affected by the loss of insect life.