Resource modification by ecosystem engineers generates hotspots of stream community assembly and ecosystem function

Ecosystem engineers can generate hotspots of ecological structure and function by facilitating the aggregation of both resources and consumers. However, nearly all examples of such engineered hotspots come from long-lived foundation species, such as marine and freshwater mussels, intertidal cordgrasses, and alpine cushion plants, with less attention given to small-bodied and short-lived animals. Insects often have rapid life cycles and high population densities and are among the most diverse and ubiquitous animals on earth. Although these taxa have the potential to generate hotspots and heterogeneity comparable to that of foundation species, few studies have examined this possibility. We conducted a mesocosm experiment to examine the degree to which a stream insect ecosystem engineer, the net-spinning caddisfly (Tricoptera:Hydropsychidae), creates hotspots by facilitating invertebrate community assembly. Our experiment used two treatments: (1) stream benthic habitat with patches of caddisfly engineers present and (2) a control treatment with no caddisflies present. We show that compared to controls, caddisflies increased local resource availability measured as particulate organic matter (POM) by 43%, ecosystem respiration (ER) by 70%, and invertebrate density, biomass and richness by 96%, 244%, and 72%, respectively. These changes resulted in increased spatial variation of POM by 25%, invertebrate density by 76%, and ER by 29% compared to controls, indicating a strong effect of caddisflies on ecological heterogeneity. We found a positive relationship between invertebrate density and ammonium concentration in the caddisfly treatment, but no such relationship in the control, indicating that either caddisflies themselves or the invertebrate aggregations they create increased nutrient availability. When accounting for the amount of POM, caddisfly treatments increased invertebrate density by 48% and richness by 40% compared to controls, suggesting that caddisflies may also enhance the nutritional quality of resources for the invertebrate assemblage. The caddisfly treatment also increased the rate of ecosystem respiration as a function of increasing POM compared to the control. Our study demonstrates that insect ecosystem engineers can generate heterogeneity by concentrating local resources and consumers, with consequences for carbon and nutrient cycling.

Measured efficacy, bioaccumulation, and leaching of a transfluthrin-based insecticidal paint: a case study with a nuisance, nonbiting aquatic insect

BACKGROUND

Pest management professionals will require a diverse, adaptive abatement toolbox to combat advanced challenges from disease vector and nuisance insect populations. Designed for post-application longevity, insecticidal paints offer extended residual effects on targeted insect pest populations; a measured understanding of active ingredient bioavailability over time is valuable to fully assess treatment efficacy and potential environmental risks. This study was initiated because a nuisance net-spinning caddisfly, Smicridea fasciatella, is lowering the quality of life for riverfront residents at the type locality.

RESULTS

We tested the efficacy and potential mobility of a transfluthrin-based paint (a.i. 0.50%), comparing the impacts of UV exposure and substrate texture over time. Direct UV exposure decreased efficacy (β ± S.E. = 0.008 ± 0.001, P < 0.001) and a coarse texture maintained greater efficacy (β ± S.E. = -3.7 ± 1.3, P = 0.004) over time. Notably, the coarse texture + indirect UV treatment maintained 100% mortality after 240 days. UV exposure and substrate texture did not have a significant impact on leachate concentrations over time, and successive immersion tests indicated a two-phase emission pattern. Bioaccumulation increased with time on the cuticle of dead adult S. fasciatella; after 24 h of direct exposure the concentration of transfluthrin was 25.3 ± 0.9 ng/caddisfly with a maximum concentration of 345 ng/caddisfly after 7 days.

CONCLUSION

Our predictions were validated with measured, time-dependent impacts on efficacy, leachability, and bioaccumulation. Because of the mobility of active ingredient in the environment, insecticidal paints merit low-impact protocols to improve public health outcomes and environmental safety. © 2022 Society of Chemical Industry.

Intra- and interspecific competition resulting from spatial coexistence among larvae of closely-related caddisflies from the genus Hydropsyche

Caddisfly larvae commonly inhabit freshwater ecosystems, where they often create multi-species aggregations. However, while several strategies have been developed to avoid or reduce inter- and intraspecific interactions, most species choose the same time to seek a suitable place for pupation, which can increase competition. The current study assesses the competitive interactions among larvae (5^th instar) of three co-existing Hydropsyche species, viz. H. contubernalis, H. pellucidula, and H. modesta, analysing their direct one-on-one interaction and various morphological features, such as size, weight, and mandibles. More than half of the interspecific conflicts ended with a draw, and 80% of intraspecific interactions with a decisive outcome. In fights between species, H. pellucidula was the most successful, and H. modesta the weakest. Our results confirm that among the larvae, competitive interactions were usually decided by body size, especially that of the head capsule. Although wider head capsule and higher weight were advantageous for ~60% of winning larvae, there were no distinct winning species. The chewing mouthpart turned out to be supportive in the fight: regardless of the species, longer and wider mandibles were significant for winning specimens, but not the distance between mandibles. Hence, acquiring a suitable place for pupation is determined by the possession of certain features enhancing the fighting potential of individual larvae, which does not exclude any species from the possibility of closing the life cycle. Future studies on interactions among caddisfly larvae could include experience in fights, volitional features and stridulation (not tested).

Functional Feeding Groups of Aquatic Insects Influence Trace Element Accumulation: Findings for Filterers, Scrapers and Predators from the Po Basin

For this study, we measured the concentrations of 23 trace elements (Al, As, Ba, Bi, Cd, Cr, Co, Cu, Fe, Ga, Hg, In, Li, Mn, Mo, Ni, Pb, Se, Sr, Ti, Tl, V, and Zn) in the whole bodies of three functional feeding groups (FFG) (filterers-Hydropsychidae, scrapers-Heptageniidae, and predators-Odonata) of aquatic insects collected from two sites in the Po basin (Po Settimo and Malone Front, Northwest Italy) to determine: (a) how FFG influence trace element accumulations, (b) if scrapers accumulate higher elements compared to the other FFG, since they graze on periphyton, which represents one of the major sinks of metals, and (c) the potential use of macroinvertebrates to assess the bioavailability of trace elements in freshwater. The hierarchical clustering analysis generated three main groups based on trace element concentrations: the most abundant elements were Fe and Al, followed by Sr, In, Zn, V, Mo, and Cu. Tl was below the limit of detection (LOD) in all FFG. Ga was detected only in scrapers from both sites and Hg only in predators from Po Settimo. The principal component analysis showed that concentrations of Al, As, Bi, Cd, Co, Cr, Ga, Fe, In, Mn, Pb, Ni, and Sr were highest in scrapers, suggesting that trace elements accumulate from the ingestion of epilithic periphyton (biofilm). Odonata (predators) accumulate certain elements (Ba, Hg, Li, Se, V, Ti, and Zn) in higher concentrations by food ingestion composed of different aquatic organisms. Differently, Cu and Mo concentrations were the highest in filterers due to their bioavailability in the water column. Non-metric multidimensional scaling clearly differentiated the FFG based on their ability to accumulate trace elements. The findings from this study represent an important step toward the definition of an innovative approach based on trace element accumulation by macroinvertebrates.

DNA barcode-based survey of Trichoptera in the Crooked River reveals three new species records for British Columbia

Anthropogenic pressures on aquatic systems have placed a renewed focus on biodiversity of aquatic macroinvertebrates. By combining classical taxonomy and DNA barcoding we identified 39 species of caddisflies from the Crooked River, a unique and sensitive system in the southernmost arctic watershed in British Columbia. Our records include three species never before recorded in British Columbia: Lepidostoma togatum (Lepidostomatidae), Ceraclea annulicornis (Leptoceridae), and possibly Cheumatopsyche harwoodi (Hydropsychidae). Three other specimens may represent new occurrence records and a number of other records seem to be substantial observed geographic range expansions within British Columbia.

Persistence in the longitudinal distribution of lotic insects in a changing climate: a tale of two rivers

The longitudinal distribution of many taxa in rivers is influenced by temperature. Here we took advantage of two older datasets on net-spinning caddisflies (Hydropsychidae) from contrasting European rivers to assess changes in species occurrence and relative abundance along the river by resampling the same sites, postulating that an increase in river temperature over the intervening period should have resulted in cool-adapted species retreating into the headwaters and warm adapted species expanding upstream. Distributional changes in the Welsh Usk were slight between 1968/69 and 2010, one rare species appearing at a single headwater site and one warm-adapted species disappearing from the main river. Distributional changes in the French Loire, between 1989-93 and 2005, were similarly modest, with no consistent movement of species up- or downstream. We estimate that the decadal rate of increase in the mean summer daily maximum in the Usk was only 0.1°C at one 'summer cool' headwater site, while a neighbouring 'summer warm' tributary increased by 0.16°C per decade, and the main river by 0.22°C. The Loire is warmer than the Usk and the mean decadal rates of increase, over the period 1989-2005, at three sites along the lower reaches were 0.39, 0.48 and 0.77°C. Increases in stream and river temperature, therefore, were spatially variable and were not associated with consistent upstream movement of species in either of these (very different) rivers. We conclude that either the temperature increases have hitherto been insufficient to affect species distribution or, more speculatively, that it may not be possible for river organisms (that do not respond only to temperature) to move upstream because of a developing spatial mismatch between key habitat characteristics, some of them changing with the climate but others not.