The goal of this research was to determine the role of Lepidostoma hirtum Fabricius 1775 in the fragmentation of allochtonous organic material, in a segment of a mountain river in central Portugal. For this purpose, we measured leaf fragmentation and growth rates at four temperatures (9, 12, 15 and 18°C) and four leaf types (alder, Alnus glutinosa L.; oak, Quercus andegavensis Hy; poplar, Populus  canadensis Moench; and chestnut, Castanea sativa Mill.). Growth rates ranged from 0.012 to 0.049 mg AFDW day )1 with no significant effect of temperature and leaf type. Fragmentation/consumption rates were significantly higher for alder (1.62 mg animal )1 day )1 ) than for other leaf types, and significantly lower at 9°C (0.70 mg animal )1 day )1 ) than at any other temperature (1.12 mg animal )1 day )1 ). In the studied stream, L. hirtum larvae had a univoltine life history, with an asynchronous development. Secondary production of L. hirtum ranged from 53.95 mg m )2 year )1 (pools) to 63.12 mg m )2 year )1 (riffles). Annual P/B ratios differ between habitats: they were 4.01 year )1 for pools and 4.49 year )1 for riffles. Considering the average density of this species in the study river and their consumption rates, this species has the potential to fragment 8.6 times the mean annual standing stock of organic matter, in the study location.
Imidacloprid is a new insecticide that mimics nicotine, combining its insecticidal activity with a reduced persistence in the environment. The toxicity of imidacloprid to Chironomus riparius Meigen using the formulated product Confidor® from Bayer®, in pulse and continuous exposure, was evaluated in this study. The behavioural response of the midge after toxicant exposure using an online biomonitor was also investigated. Early second-instar C. riparius larvae were exposed in either constant (10 days) or pulse (4 days, followed by 6 days post exposure in clean medium) conditions. Imidacloprid constant exposure resulted in a decrease in growth and impairment of the behavioural pattern of the midge larvae. Pulsed exposure followed by a recovery period revealed a recovery of midge physiological conditions, by reaching a stabilisation of normal behavioural activities and growth among treatments. Moreover, ventilation showed to be a more sensitive parameter by revealing a faster recovery than locomotion. Behaviour alterations may weaken the ability to escape from predators, and reduce food acquisition with consequent growth impairment. These effects may have an impact at the population and community level.
Mercury is a pervasive toxicant that can be found in the environment due to anthropogenic activity as well as natural sources. The majority of studies in freshwater environments focus mainly on bioaccumulation, population dynamics, and biomagnification. Here, we study the effects of mercuric chloride on Chironomus riparius Meigen, simulating a mercury discharge on a freshwater ecosystem. Growth, emergence, development time, and behavior were the end points assessed. Growth was measured after 8 days of exposure and behavior was recorded on days 4 and 10 of the experimental period. The behavioral responses of C. riparius to different mercury treatments were recorded with an online biomonitor, which allows a more objective and precise behavioral understanding than visual observation. Mercury exposure resulted in reductions in growth and emergence, a delayed development time, and a decrease in locomotor activity of the larvae. Our results demonstrate that mercury exposure can impair life-history responses of chironomids.
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