not in Young Changes in trophic level interactions due to global climate change and the increasing occurrence of pollution are likely to have consequences for natural enemies. Specifically, information regarding the effects of these factors on insect parasitoids is relatively sparse. We examined the individual and joint effects of temperature and the pollutant selenium on the fitness correlates of the parasitoid wasp Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), parasitizing Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae). Our specific objective was to determine in a factorial experiment how three temperatures (constant 28.6[degree]C, constant 33[degree]C and a fluctuating temperature between 28.6 and 33[degree]C) and three concentrations of seleno-DL-methionine (0.00, 21.21, and 42.42 [mu]g/g) affected the parasitoid's fitness and life history. Parasitoids failed to complete development at the constant 33[degree]C, but developed significantly faster at the fluctuating temperature compared to the constant 28.6[degree]C. There were significant declines due to increased temperature, but not selenium, on C. marginiventris survival time, adult body weight, body size, hind tibia length, female life span and number of progeny that survived to adulthood. Mean generation times and the intrinsic rate of increase (r) further show that both of these life table statistics declined under conditions of increased temperatures. We discuss the implications of these results in helping to understand and predict the effectiveness of biological control programs and pest management strategies as climate changes in the presence of metal and metalloid pollution. BR Animals and man. Control. Life cycle and development. Evolution. Parasites diseases and disorders. Parasites. Insect parasites. Hosts. Insect hosts. Pollution. Chemical pollution. Abiotic factors. Physical factors. Land zones. Nearctic region. North America. USA. Cotesia marginiventris (Braconidae): Parasite; Spodoptera exigua (Noctuidae): Host. Cotesia marginiventris: Biological control, Life cycle, Life history, Natural selection, Fitness, Lepidopteran hosts, Spodoptera exigua, Metal pollution, Selenium pollution, Temperature, California, Central Valley; Spodoptera exigua: Biological control, parasite fitness and life history, Hymenopteran parasites, Cotesia marginiventris, Metal pollution, Selenium pollution, Temperature, California, Central Valley. ST Animalia, Arthropoda, Insecta, Hymenoptera, Apocrita, Terebrantia, Ichneumonoidea, Braconidae; Animalia, Arthropoda, Insecta, Lepidoptera, Glossata, Heteroneura, Noctuoidea, Noctuidae. Arthropods; Hymenopterans; Insects; Invertebrates; Lepidopterans. none