The effects of selenium (Se) accumulation in phytophagous insects on predators in the next trophic level were investigated. The generalist predator Podisus maculiventris Say (Hemiptera: Pentatomidae) was fed an herbivore Spodoptera exigua Hübner (Lepidoptera: Noctuidae) larvae from control diet and diets at two Se levels (0, 109, and 135 mg/g sodium selenate dry weight added). Predators reared on larvae grown on diets with sodium selenate took longer to complete each developmental stage and had significantly higher mortality rates. Predators achieving the adult stage on Se-containing hosts weighed 20% less than those feeding on control larvae. Reduced adult weights have been associated with reduced fitness (longevity, egg production, etc.), which would have long-term negative impacts on population dynamics. These developmental and mortality effects resulted from biotransfer of Se, not biomagnification. Host larvae in Se-treatments contained significantly more total Se (9.76 and 13.04 mg/g Se dry weight host larvae) than their predators (8.34 and 11.19 mg/g Se dry weight predatory bugs, respectively). Host larvae and predators in the control groups did not differ in their Se content (0.89 and 1.10 mg/g Se dry weight, respectively). For both herbivores and predators, Se content increased when Se was increased in the diet. For host larvae, Se content also increased with development stage (stadia 2-4), but no difference was found in Se accumulation between fifth-instar and adult bugs. These data demonstrate that Se in the food chain may have detrimental population level effects on insects, even in the absence of biomagnification.
Species 1: Heteroptera Pentatomidae Podisus maculiventris (spined soldier bug)
Species 2: Lepidoptera Noctuidae Spodoptera exigua (beet armyworm)
Keywords: biotransfer selenium, tritrophic interactions
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