Our research has investigated the individual and joint effects of increased temperatures and the anthropogenic pollutant selenium (Se) on the life history on the parasitoid Cotesia marginiventris (Cresson) under controlled laboratory conditions. Previous research has indicated that some parasitoids may be more sensitive to environmental pollutants, and that changes in insect-plant interactions due to global climate change are likely to have consequences for higher trophic levels. However, information regarding the effects of these factors on insect natural enemies is relatively sparse. Our specific objectives were to test the following novel hypotheses: 1) increases in temperatures predicted to occur in the next few decades will alter host-parasitoid interactions between the beet armyworm, Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae), a major agricultural pest, and C. marginiventris, which is important for the biological control of this species; 2) selenium transferred from the host to the parasitoids will be detrimental to the life history of this biological control agent and alter the fitness of C. marginiventris; and 3) increased temperatures and selenium biotransference from host to parasitoid will interact antagonistically on the life history of this parasitoid. By defining critical elements of environmental concern, these data can be used to increase the potential for the success of biological control programs for S. exigua, and support the establishment of more sustainable agricultural systems.