Parasitoids are parasitic insects that kill their insect hosts in immature pre-reproductive stages. Parasitoids are employed in biological control programs worldwide to kill insect pests and are environmentally safe and benign alternatives to chemical pesticides. As resistance to chemical pesticides continues to escalate in many pest populations, attention is now refocusing on biologically-based strategies to control pest species in agriculture and forestry as well as insect vector populations that transmit human and animal diseases. Parasitoids are an economically critical element in this equation and ‘integrated pest management.’