The ecological significance of tallgrass prairie arthropods.

Tallgrass prairie (TGP) arthropods are diverse and abundant, yet they remain poorly documented and there is still much to be learned regarding their ecological roles. Fire and grazing interact in complex ways in TGP, resulting in a shifting mosaic of resource quantity and quality for primary consumers. Accordingly, the impacts of arthropod herbivores and detritivores are expected to vary spatially and temporally. Herbivores generally do not control primary production. Rather, groups such as grasshoppers have subtle effects on plant communities, and their most significant impacts are often on forbs, which represent the bulk of plant diversity in TGP. Belowground herbivores and detritivores influence root dynamics and rhizosphere nutrient cycling, and above- and belowground groups interact through plant responses and detrital pathways. Large-bodied taxa, such as cicadas, can also redistribute significant quantities of materials during adult emergences. Predatory arthropods are the least studied in terms of ecological significance, but there is evidence that top-down processes are important in TGP.

Sublethal effects of three pesticides on activities of selected target and detoxification enzymes in the aquatic midge, Chironomus tentans (diptera: chironomidae).

Sublethal effects of three pesticides including atrazine (triazine herbicide), DDT (organochlorinated insecticide), and chlorpyrifos (organophosphate insecticide) on acetylcholinesterase (AChE), general esterase (GE), glutathione S-transferase (GST), and cytochrome P450 monooxygenase (P450) activities were evaluated in the aquatic midge Chironomus tentans. Exposures of midges to atrazine at 30 and 150 micrograms per liter (microg/L) for 20 d (i.e., from the first- to fourth-instar larvae) enhanced P450 O-deethylation activity by 12.5- and 15.5-fold, respectively, but did not significantly change AChE, GST, and GE activities. Similar exposures to DDT at 0.01 and 0.05 microg/L did not significantly affect AChE, GE, and P450 activities; however, DDT at 0.05 microg/L enhanced GST activity toward the substrate 1-chloro-2, 4-dinitrobenzene by 33.6%. Exposures of midges to chlorpyrifos at 0.10 microg/L for 20 d reduced AChE activity by 59.8%, and GE activities toward the substrates alpha-naphthyl acetate and beta-naphthyl acetate by 30.7 and 48.8%, respectively. The reduced GE activities appear to be due to the inhibition of several esterases, particularly the one with a slow migration, by chlorpyrifos as demonstrated by non-denaturing polyacrylamide gel electrophoresis. Furthermore, exposure of midges to chlorpyrifos at 0.10 microg/L for 20 d enhanced the P450 O-deethylation activity by 3.3-fold although no significant effect was observed at 0.02 microg/L for the same enzyme. These results provide insights into the sublethal effects of these commonly detected pesticides in aquatic environments on important enzymes in aquatic midges.

Sublethal effects of three pesticides on larval survivorship, growth, and macromolecule production in the aquatic midge, Chironomus tentans (diptera: chironomidae).

Effects of long-term exposure to each of three pesticides including atrazine, DDT, and chlorpyrifos on larval survivorship, growth, and macromolecule (total body protein and RNA) production were evaluated in the aquatic midge, Chironomus tentans, under laboratory conditions. Newly hatched larvae were exposed to atrazine at 30 and 150 microg/L, DDT at 0.01 and 0.05 microg/L, or chlorpyrifos at 0.02 and 0.10 microg/L throughout one life cycle. Larval survivorship was evaluated at 20 d and the end of the test, and larval growth at 20 d. Chlorpyrifos at 0.1 microg/L reduced the midge survivorship by 67% after 20-d exposure. However, neither atrazine nor DDT affected larval survivorship. The ash-free dry weight of midge larvae exposed to chlorpyrifos at 0.1 microg/L was 1.5-fold greater than that of the control whereas neither atrazine nor DDT showed a significant effect on the ash-free dry weight. In addition, exposures of midges to chlorpyrifos at 0.1 microg/L increased the adult emergence rate by 81% as compared to the control although the actual number of adults that emerged from chlorpyrifos-treated larvae was significantly decreased. Both the increased ash-free dry weight of larvae and increased adult emergence rate were likely caused by reduced competition for both food and space among the survivors due to increased larval mortality. Although neither total protein nor total RNA production was significantly affected in larvae exposed to each pesticide for 20 d, a significantly higher number of males over females (ratio = 4) emerged from midges exposed to DDT at 0.05 microg/L. Our study indicates that chronic exposure to low concentrations of chlorpyrifos and DDT results in significant mortality of midge larvae and alteration of the sex ratio of adult emergence, respectively. Because midges are important components of the food web, our results suggest that effects elicited directly or indirectly by long-term pesticide exposures may potentially disrupt both food chains and community structure in aquatic environments.