Lonicera maackii, a dominant invasive shrub in riparian zones, is known to have adverse affects on plant growth, reproduction, and terrestrial insects. Lonicera maackii grows prolifically along riparian corridors and contributes leaf litter into stream systems; however, the influence of these inputs on aquatic communities in unknown. We investigated linkages between this terrestrial invader and the aquatic macroinvertebrate community via a senesced leaf pack breakdown experiment including invasive, native and mixed leaf packs. Leaf loss and macroinvertebrate colonization were quantified over 43 days in two Midwestern streams during autumn and winter when natural L. maackii senescence occurs. Further, a laboratory microcosm toxicity experiment was conducted to determine the lethal and sub-lethal effects of L. maackii leachate on Trichoptera (Hydropsychidae). Two treatment concentrations (high and low) of L. maackii senesced leaves were compared to a native treatment of ash/sycamore and a control incubated in Midwestern autumn stream water at 15°C. Insect mortality, individual mass and behavior were measured at 24 hour intervals over seven day periods.
Results/Conclusions
Leaf breakdown rates for L. maackii were one order of magnitude faster than other leaf pack treatments, but differences depended on stream. Chironomidae were the dominant colonizers of invasive leaves in contrast to other packs. By day 7, gathering-collector densities were greater in invasive leaf packs compared to other treatments. Shredders were dominant by days 14 and 43, and were present in higher densities within the invasive compared to native and mixed leaf treatments by day 43. In laboratory microcosms there was no mortality for control Hydropsychidae after 96 hours. However, mean total mortality was 8.3%, 50% and 75% for native, low honeysuckle and high honeysuckle treatments, respectively. Standardized observations indicated insects in control microcosms were active and responsive while insects in treatment microcosms became less responsive over time, with the highest degree of negative change in low honeysuckle treatments. These preliminary results demonstrate that senesced L. maackii leaves rapidly break down, affect macroinvertebrate densities and colonization. Furthermore, these results are some of the first to indicate both lethal and non-lethal effects on a dominant aquatic insect taxon in streams heavily colonized by L. maackii. These findings indicate L. maackii may have significant impacts on stream communities and ecosystem processes.
