Comparison of leaf processing rates under different temperature regimes in three headwater streams

1. We studied the effects of different temperature regimes on leaf litter processing in three forested Appalachian headwater streams of different pH (mean pH = 4.2, 6.5, 7.5).
2. We compared leaf breakdown rates, microbial biomass and macroinvertebrate shredder density and biomass between two 12-week processing periods (October–January and November–February) in each stream. Leaf processing rates were calculated both as k (day^–1) and k _d (degree day^–1).
3. There were no significant differences in processing rates ( k day^–1) between the two study periods for any leaf species in any stream. The average difference in temperature between the two study periods was 175 degree days. Shredder density was significantly higher during the earlier study period on 40% of the sample dates, but shredder biomass was not significantly different between the two study periods. ATP concentration was significantly higher during the early study period for 60% of the sample dates.
4. More significant differences in these variables (shredder density and biomass, ATP concentration) were seen among the three study streams than between the two study periods. This indicates that in this study other factors, particularly stream pH, contributed more to processing rate variation than did differences in thermal regime.     

Litter breakdown in streams of the Agüera catchment: influence of dissolved nutrients and land use

1. The breakdown of oak ( Quercus robur L.), chestnut ( Castanea sativa Miller) and eucalypt ( Eucalyptus globulus Labill.) litter enclosed in 5-mm mesh bags was compared between first-order headwaters (two with native riparian forest and two with eucalypt plantations) and a third-order reach of Agüera stream. Weight loss and dynamics of phosphorus and nitrogen in litter were studied for a period of 155 days.
2. Among the different sites, processing rates ranged from 0.0045 to 0.0080 day^–1 for chestnut leaf litter, from 0.0036 to 0.0051 day^–1 for oak, and from 0.0027 to 0.0158 day^–1 for eucalypt.
3. The availability of nutrients in water clearly influenced nitrogen and phosphorus dynamics in litter. In headwater reaches, net immobilization was not observed and losses of phosphorus and nitrogen followed mass loss. However, there was an enrichment of litter at the low reach, where influence of human settlements—located upstream—could lead to a greater availability of phosphorus in water.
4. The enhancement of litter decay by the exogenous nutrient supply depended on leaf quality, as only the processing rate of eucalypt increased at the nutrient-rich site.
5. The processing rates differed little among headwaters, suggesting that riparian forest type, i.e. deciduous forest v eucalypt plantations, did not affect litter decay in the stream.     

Litter breakdown in streams of the Agüera catchment: influence of dissolved nutrients and land use

1. The breakdown of oak ( Quercus robur L.), chestnut ( Castanea sativa Miller) and eucalypt ( Eucalyptus globulus Labill.) litter enclosed in 5-mm mesh bags was compared between first-order headwaters (two with native riparian forest and two with eucalypt plantations) and a third-order reach of Agüera stream. Weight loss and dynamics of phosphorus and nitrogen in litter were studied for a period of 155 days.
2. Among the different sites, processing rates ranged from 0.0045 to 0.0080 day^–1 for chestnut leaf litter, from 0.0036 to 0.0051 day^–1 for oak, and from 0.0027 to 0.0158 day^–1 for eucalypt.
3. The availability of nutrients in water clearly influenced nitrogen and phosphorus dynamics in litter. In headwater reaches, net immobilization was not observed and losses of phosphorus and nitrogen followed mass loss. However, there was an enrichment of litter at the low reach, where influence of human settlements—located upstream—could lead to a greater availability of phosphorus in water.
4. The enhancement of litter decay by the exogenous nutrient supply depended on leaf quality, as only the processing rate of eucalypt increased at the nutrient-rich site.
5. The processing rates differed little among headwaters, suggesting that riparian forest type, i.e. deciduous forest v eucalypt plantations, did not affect litter decay in the stream.     

Catchment land-use, macroinvertebrates and detritus processing in headwater streams: taxonomic richness versus function

1. We used a litter bag technique to assess the effect of catchment land-use (forest, wetland, agriculture, urban) on the processing of red maple ( Acer rubrum L.) litter in 17 streams in Maine, U.S.A. Litter processing by fungi was predicted to increase with nutrient concentrations along a gradient of land use, from relatively unmodified to highly modified. Litter processing by litter-shredding macroinvertebrates was predicted to decline along this gradient because of a decline in their taxonomic richness and biomass.
2. Land use was associated with the anticipated gradient in nutrient and macroinvertebrate attributes, and a significant relationship was found between land use and nitrate concentration. There was, however, no significant relationship between land use and soluble reactive phosphorus (SRP) concentration. Similarly, shredder taxonomic richness was significantly related to land use type, whereas shredder biomass showed no significant relationship to land use.
3. Attributes of the shredder assemblage structure and nutrient concentrations were both strong determinants of litter processing. Increasing biomass and taxonomic richness of shredders was significantly related to increasing rates of litter mass loss. Increasing concentrations of nitrate and SRP were significantly related to increasing rates of litter softening below threshold concentrations (approximately 0.20 mg NO₃-N L^–1 and 5 μg SRP L^–1).
4. The potentially additive effects of nitrate and SRP concentrations or shredder richness and biomass on litter processing rates were confounded by the lack of significant correlation between these pairs of variables. Consequently, rates of litter processing (as rates of softening or mass loss) did not vary systematically among different land use regimes.     

Production and litter processing by crayfish in an Appalachian mountain stream

SUMMARY 1. Mean annual density and biomass () of Cambarus bartonii in an Appalachian mountain stream (U.S.A.) was 12 individuals m⁻² and 1669 mg (ash-free dry weight) m⁻².
2. Annual production ( P ) of C bartonii was 961 mg AFDW m⁻². Despite high biomass, low growth rates resulted in low production and a low P/ ratio of 0.58.
3. While C bartonii constituted 61% of the total macroinvertebrate biomass, it contributed only 13% of annual community secondary production.
4. Litter processing was positively related to temperature and crayfish size. Cambariis bartotnii was estimated to comminute 36 g m⁻² y⁻¹ of leaf litter (>1 mm²) to 24 g m−^>2 y⁻¹ fine particulate material (<1 mm²). The annual pattern of litter comminution by crayfish was regulated by temperature. As a result, >5()% of shredding activity by crayfish occurred from June to September which was also the period of lowest litter standing crops and activity of other shredding macroinvertebrates.
5. We speculate that during summer crayfish play an important role in temperate woodland streams by converting slowly processed leaf litter species (e.g. Rhododendron ) to fine particles which are then available to collector-gatherers (e.g. Chironomidae, Oligochaeta).     

Production of a stream shredder, Peltoperla maria (Plecoptera: Peltoperlidae) in disturbed and undisturbed hardwood catchments

SUMMARY. (1) The average benthic density of Peltoperla maria in an undisturbed southern Appalachian stream was more than twice that of a nearby stream draining a previously clear-cul catchment in its tenth year of natural secondary succession.
(2) Peltoperla production estimates, using three methods, do not show a significant difference in production between streams draining the two catchments. We attribute these results to quicker growth and slightly higher densities of larger nymphs in the disturbed stream. Production estimates for the disturbed stream ranged from 498 to 560 mg (ash free dry weight) m⁻²y⁻¹ while those for the undisturbed stream were 41–4–515 mg m⁻² y⁻¹.
(3) Our results reinforce the view that conclusions based solely upon numerical densities may lead to erroneus interpretations about the roles organisms play in ecosystems.
(4) Annual frass production by this shredder is about 20 times (10 g m⁻² y⁻¹) the secondary production of P. maria.     

Long-term effects of successive Ca(OH)2 and CaCO3 treatments on the water quality of two eutrophic hardwater lakes

1. Whole-lake experiments were conducted in two hardwater lakes (Halfmoon and Figure Eight) in Alberta, Canada, to investigate the effectiveness of repeated lime (slaked lime: Ca(OH)₂ and/or calcite: CaCO₃) treatments (5–78 mg L^–1) for up to 7 years.
2. Randomized intervention analysis of intersystem differences between the experimental and three reference lakes demonstrated a decline in euphotic total phosphorus and chlorophyll a concentrations in the experimental lakes after repeated lime treatments.
3. After the second lime application to Halfmoon Lake, mean winter total phosphorus release rates (TPRR) decreased to < 1 mg m^–2 day^–1 compared with 3.6 mg m^–2 day^–1 during the winter after initial treatment. In the final year of lime application, mean summer TPRR decreased to 4.5 mg m^–2 day^–1 compared with 7.6 mg m^–2 day^–1 in the pre-treatment year.
4. Mean macrophyte biomass declined and species composition was altered at 1 and 2 m depths in Figure Eight Lake during lime application. Over the first 6 years of treatment, macrophyte biomass at 2 m declined by 95% compared with concentrations recorded during the initial treatment year. In the last year of the study, macrophyte biomass at 2 m reached initial treatment concentrations, which coincided with the greatest water transparency. Over the treatment period, macrophyte species shifted from floating to rooted plants.
5. Multiple lime applications can improve water quality in eutrophic hardwater lakes for periods of up to 7 years.     

Population dynamics and feeding of mayfly larvae in some acid and alkaline New Zealand streams

SUMMARY. 1. Population dynamics (density, biomass, annual production), gut contents and feeding rates of mayflies ( Deleatidium spp.; Leptophlebiidae) were compared in two naturally acid (mean pH≃4.8). brownwater streams and two alkaline (mean pH 7.5), clearwater streams in South Westland, New Zealand.
2. Mean densities of larvae (range 234–2318 m⁻²) were higher in alkaline streams on most of the six bimonthly sampling dates. Mean biomass (range 0.020–0.376 g larval dry weight (LDW) m⁻²) was always highest at the stable, spring-fed, alkaline site and was lower at the acid sites and another alkaline site where the population was always dominated by small larvae.
3. Annual production was high at the more stable, alkaline site (10.35 gLDW m⁻²) but much lower at the other sites (2.49–3.77 g m⁻²).
4. Gut contents of larvae were dominated by fine (45–75 μm widest diameter) paniculate matter (69–99%), diatoms (up to 21%) and. at one site, filamentous algae (8–13%).
5. Grazing rates of mayflies on epilithon were significantly higher on stones taken from acid than alkaline streams and material grazed from the former contained a higher proportion of inorganic material (87–93% and 61–83% inorganics, respectively).
6. Higher grazing rates may reflect lower quality of epilithic food in acid, brownwater streams, a factor that could contribute to the lower productivity of Deleatidium populations at these sites.     

Detrital processing in streams exposed to acidic precipitation in the Central Appalachian Mountains

Continuing high rates of acidic deposition in the eastern United States may lead to long-term effects on stream communities, because sensitive catchments are continuing to lose anions and cations. We conducted a two-year study of the effects of pH and associated water chemistry variables on detrital processing in three streams with different bedrock geology in the Monongahela National Forest, West Virginia. We compared leaf pack processing rates and macroinvertebrate colonization and microbial biomass (ATP concentration) on the packs in the three streams. Breakdown rates of red maple and white oak leaf packs were significantly lower in the most acidic stream. The acidic stream also had significantly lower microbial and shredder biomass than two more circumneutral streams. Shredder composition differed among streams; large-particle detritivores dominated the shredder assemblages of the two circumneutral streams, and smaller shredders dominated in the acidic stream. Within streams, processing rates for three leaf species were not significantly different between the two years of the study even though invertebrate and microbial communities were different in the two years. Thus, macroinvertebrate and microbial communities differed both among streams that differed in their capacity to buffer the effects of acidic precipitation and among years in the same stream; these differences in biotic communities were not large enough to affect rates of leaf processing between the two years of the study, but they did significantly affect processing rates between acidic and circumneutral streams.The Unit is jointly sponsored by the National Biological Service, the West Virginian Division of Natural Resources, West Virginia University, and the Wildlife Management Institute.The Unit is jointly sponsored by the National Biological Service, the West Virginian Division of Natural Resources, West Virginia University, and the Wildlife Management Institute.     

Colonization and processing of leaf litter by macroinvertebrate shredders in streams of contrasting pH

• 1 Leaf litter processing rates and macroinvertebrate shredder assemblages in leaf packs were compared in four streams on the Allegheny plateau in the central Appalachian Mountains, U.S.A.; these streams were characterized by different bedrock geology and streamwater pH.
• 2 Leaf litter processing rates were fastest in the neutral streams, slowest in the acidic stream, and intermediate in the most alkaline stream.
• 3 Slower processing rates in the acidic stream were associated with lower total shredder biomass, made up predominantly by small leuctrid and nemourid stoneflies.
• 4 The differences in processing rates between the more alkaline stream and the neutral streams were not associated with differences in shredder biomass, but appeared to be related to taxonomic differences in the shredder assembiages. Insects were dominant in the neutral streams, and amphipods were dominant in the more alkaline stream.

     

The energetic importance of terrestrial arthropod inputs to three warm-water streams

1. Inputs of terrestrial arthropods (number and mass m^–2 d^–1) from riparian corridors to three streams representing different orders were highly variable among seasons and sites, with significantly greater ( P < 0.05) inputs at the headwater stream during summer months, compared with other sites and seasons.
2. No significant differences in estimates of stream retention of terrestrial arthropods (number and mass m^–2 d^–1) were observed among sites; however, retention of terrestrial arthropods at all sites was significantly greater during summer months, compared with other periods.
3. The gravimetric proportion of terrestrial arthropods present in the stomachs of redbreast sunfish ( Lepomis auritus ) and bluegill ( L. macrochirus ) was equivalent among sites. However, estimates of the dietary importance of terrestrial arthropods at all study sites were significantly greater in the summer, compared with other seasons.
4. Estimates of the potential annual energetic contribution (kJ m^–2 d^–1) of terrestrial arthropod inputs to the stream system were comparable with published rates of total annual production of aquatic macroinvertebrates in other Virginia headwater streams.
5. Results of this study supported the hypothesis that terrestrial arthropods represented an important energetic subsidy to stream fish during periods of low aquatic macroinvertebrate availability, and suggest that this component of allochthonous input is a potentially significant, but poorly understood energetic linkage between riparian landscapes and stream ecosystems.     

The energetic importance of terrestrial arthropod inputs to three warm-water streams

1. Inputs of terrestrial arthropods (number and mass m^–2 d^–1) from riparian corridors to three streams representing different orders were highly variable among seasons and sites, with significantly greater ( P < 0.05) inputs at the headwater stream during summer months, compared with other sites and seasons.
2. No significant differences in estimates of stream retention of terrestrial arthropods (number and mass m^–2 d^–1) were observed among sites; however, retention of terrestrial arthropods at all sites was significantly greater during summer months, compared with other periods.
3. The gravimetric proportion of terrestrial arthropods present in the stomachs of redbreast sunfish ( Lepomis auritus ) and bluegill ( L. macrochirus ) was equivalent among sites. However, estimates of the dietary importance of terrestrial arthropods at all study sites were significantly greater in the summer, compared with other seasons.
4. Estimates of the potential annual energetic contribution (kJ m^–2 d^–1) of terrestrial arthropod inputs to the stream system were comparable with published rates of total annual production of aquatic macroinvertebrates in other Virginia headwater streams.
5. Results of this study supported the hypothesis that terrestrial arthropods represented an important energetic subsidy to stream fish during periods of low aquatic macroinvertebrate availability, and suggest that this component of allochthonous input is a potentially significant, but poorly understood energetic linkage between riparian landscapes and stream ecosystems.     

Effects of chronic chlorine exposure on litter processing in outdoor experimental streams

SUMMARY 1. The effects of chlorine on litter ( Potamogeton crispus L.) processing were examined using six outdoor experimental streams. Downstream portions of two streams were dosed at c . 10 μg l⁻¹ Total Residual Chlorine (TRC), one stream at 64 μgl¹, and one stream at 230μg l⁻¹. Two control streams were not dosed; upstream riffles of each stream served as instream controls.
2. Two 35 day litter breakdown (per cent AFDW remaining) experiments indicated significantly lower decay rates in the high dose riffle. No other concentration of chlorine significantly affected decay rate.
3. A third experiment, conducted in medium and high dose streams, indicated that high dose chlorine exposure reduced litter decomposition rates significantly, and reduced microbial colonization, microbial electron transport system activity, and microbial litter decomposition after 4 days but not after 11 days of exposure. The number of amphipod shredders colonizing litter bags was also reduced significantly with high chlorine dose.
4. A fourth experiment, after dosing was terminated, provided direct evidence that amphipod shredders were important in facilitating litter decomposition: litter bags stocked with amphipods had significantly higher decomposition rates than bags which excluded shredders.
5. Overall results indicate that the high dose (c. 230 μgl⁻¹ TRC) of chlorine reduced litter processing rates partly by reducing initial microbial conditioning, but primarily by reducing the colonization of amphipod shredders.     

Differences in processing dynamics of fresh and dried leaf litter in a stream ecosystem

SUMMARY. 1. Although the bulk of litter input to stream ecosystems is in the form of fresh leaves, current understanding of organic matter processing is largely founded on experimental studies made with pre-dried leaves. This paradox points to the critical need for evaluating to what extent those experiments with dried leaves reflect natural litter decomposition.
2. The mass loss rates, patterns of mass loss, and chemical changes during processing of fresh leaf litter were compared with air-dried leaf litter in a stream ecosystem.
3. Although overall mass loss rates were similar between treatments ( k = 0.0213 day⁻¹ and 0.0206 day⁻¹), fresh leaves lost mass at a constant rate, whereas the decay of dried leaves proceeded in two distinct phases. Soluble organic carbon, phosphorus, and potassium were rapidly leached from dried litter, but were largely retained in fresh material for more than a week. Kinetics of concentrations of cellulose and changes in amounts of lignin remaining per leaf pack revealed further differences in decomposition dynamics between treatments, apparently related, either directly or indirectly, to differences in leaching behaviour.
4. Dynamics of nitrogen and protein contents were similar between treatments, indicating that microbial colonization was not greatly delayed on fresh leaves.
5. It is concluded that the retention of labile carbon and nutrients in fresh leaf litter facilitates their utilization by leaf-associated micro-organisms and invertebrates, resulting in an increased importance of biotic processes relative to physical processes such as leaching.
6. At the ecosystem level, retention of carbon and nutrients in streams would be increased, allowing greater overall productivity. Conversely, the availability of labile organic carbon would be reduced in compartments such as the epilithon, fine sediments, and the water column.     

Influence of invasive macrophytes on channel morphology and hydrology in an open tropical lowland stream, and potential control by riparian shading

1. The catchments of many tropical lowland streams in far north Queensland have been extensively cleared for the cultivation of sugar cane to the extent where very little of the native riparian vegetation remains. Stream channels are often choked by a matrix of introduced pasture grass ( Brachiaria mutica , or para grass) and accumulated sediment from cropland erosion.
2. Detailed transects across Bamboo Creek, a fourth order cane-land stream, revealed an estimated sediment load of 20 000 t km^–1. This has resulted in an estimated 85% reduction in the predicted bankful discharge of the original stream channel. Channel capacity has been reduced from 2.3 times to 0.3 times the predicted Q₅₀ flood discharge of 140 m³ s^–1.
3. Shade cloth treatments of 50% and 90% across the stream were used to mimic the effect of shading by riparian vegetation. Three months of shading resulted in a substantial reduction in the height and standing biomass of para grass in both shade treatments, compared to open plots (0% shade). The most dramatic effect was in the 90% treatment, where a mean reduction of 63% in height and 52% in total biomass was recorded. This was despite high net primary production of para grass in the open plots of 2.8 g dry wt m^–2 day^–1, which resulted in a overall increase of 11% and 28% in plant height and total biomass, respectively.
4. These data suggest that restoration of native riparian vegetation will be an effective long-term means of controlling invasive macrophytes in disturbed cane-land stream channels. Reduction of excessive macrophyte growth and the mobilisation of accumulated sediment are essential to the restoration of natural hydrological and ecological processes.     

The utilization of lightflecks for growth in four Australian rain-forest species

1. The ability of rain-forest plants to utilize sunflecks for growth was investigated using the following species: Alocasia macrorrhiza, Diploglottis diphyllostegia, Micromelum minutum and Omalanthus novo-guinensis.
2. Growth analysis and gas-exchange measurements were used to assess performance of the four species when exposed to either constant or fluctuating light.
3. Final biomass (g dry wt) in D. diphyllostegia and M. minutum grown under the lightfleck regime (total daily PFD = 7·02 mol m^–2 day^–1) was significantly greater than in the same species grown under constant low PFD (total daily PFD = 4·86 mol m^–2 day^–1). In contrast, final biomass in lightfleck O. novo-guinensis and A. macrorrhiza was significantly reduced in comparison with the same species grown under constant low PFD.
4. When grown under either constant or fluctuating light but with the same total daily PFD, A. macrorrhiza and O. novo-guinensis had significantly lower final biomass in fluctuating light as compared to constant light. Final biomass in D. diphyllostegia was not significantly different in either regime, while M. minutum had significantly higher final biomass in the fluctuating light regime.
5. Responses of the four species to fluctuating or constant light appeared to be the result of physiological rather than morphological acclimation as net assimilation rate was more closely correlated with relative growth rate than was leaf area ratio.     

Effects of shredding amphipod density on watercress Nasturtium officinale breakdown

Shredding stream invertebrates should have a positive influence on the breakdown rates of leaf litter via direct consumption and particle fragmentation. To determine the effects of shredder density on litter breakdown, breakdown of the emergent stream macrophyte, Nasturtium officinale , was investigated using three litter bag mesh sizes [fine (0.2 mm), medium (1 mm) and coarse (3 mm) mesh] and four stocking densities of the shredder, Gammarus pseudolimnaeus , (0, 4, 8 and 16 per bag). Watercress decayed very rapidly, with breakdown rates ( k values) ranging from 0.075 d^-1 for fine mesh with no shredders to 0.24 d^-1 for coarse mesh. Stocked Gammarus increased breakdown rates significantly in fine mesh bags (p < 0.001), but only marginally in medium mesh bags (p < 0.1). Breakdown rates also increased significantly with mesh size. A regression model showed a significant relation of breakdown rate to Gammarus density and mesh size. These results clearly show that shredders can significantly influence breakdown rates and can account for up to 30% of breakdown, but that mesh size effects such as particle size reduction and loss are also very important.     

Seasonal patterns of nitrogen fixation in termites

1. Termite nitrogenase activity was highest in autumn and spring (≈ 3 μg N₂ fixed termite fresh mass (g)^–1 day^–1) and lowest in winter and summer (≈ 0·8 μg N₂ fixed termite fresh mass (g)^–1 day^–1).
2. The nitrogenase activity of worker termites was significantly higher than all other castes (1·58 ± 0·27 μg N₂ fixed termite fresh mass (g)^–1 day^–1).
3. Worker termites constituted the largest proportion of all the castes throughout the study period (≈ 90%).
4. The localized input of fixed nitrogen by termites may reach 15·3 mg N log^–1 day^–1 and 5·6 g N log^–1 year^–1.     

Input, movement and exchange of organic matter within a subtropical coastal black water river-flood plain system

SUMMARY. 1. Inputs, movements and exchanges of particulate organic matter were measured on two contrasting floodplains of the Ogeechee River, Georgia, U.S.A. A model, which incorporated measurements of standing crop, respiration, litterfall, inundation, and litter processing rates, was used to estimate annual exchanges of organic matter between the river and floodplains.
2. Annual litterfall was higher on the East floodplain than on the lower elevation West floodplain (902 v. 784 g ash-free-dry-mass [AFDM] m⁻²).
3. Experiments with tagged leaves and sticks demonstrated that litter was readily displaced during floods. The distance and direction of displacement varied within and between floodplains but tended to be higher closer to the river and was generally parallel to the river.
4. The model indicated that both floodplains lost organic matter to the river. The lower elevation floodplain (East) lost more organic matter to the river (208 g AFDM m⁻² year⁻¹) than did the higher elevation (West) floodplain (79g AFDM m⁻² year⁻¹).
5. Inputs of organic matter from the floodplain to the river exceeded the amount of litterfall typically entering heavily forested high gradient headwater streams (5.5 v. 0.4-0.6 kg AFDM m⁻² year⁻¹).
6. Floodplain organic matter inputs may exert a greater influence upon structure and function within these streams than do upstream inputs or primary production. Consequently, current conceptualizations of stream structure and function need to be modified to account for the effects of floodplain inputs on stream channel processes within large, low-gradient rivers.     

Contribution of fungal biomass to the growth of the shredder, Pycnopsyche gentilis (Trichoptera: Limnephilidae)

1.  1. It has been accepted that aquatic hyphomycetes colonising submerged leaves increase the nutritional value of leaf detritus and suggested that fungal biomass plays a greater role in the growth of shredders than leaf tissue itself. However, it is not clear what proportion of the nutritional needs of shredders is met by fungal biomass.
2.  We fed Pycnopsyche gentilis larvae with tulip poplar ( Liriodendron tulipifera ) leaf discs colonised by the aquatic hyphomycete, Anguillospora filiformis , which had been radiolabelled to quantify the contribution of fungal carbon to the growth of the shredder at different larval developmental stages. Instantaneous growth rates of larvae on this diet were also estimated.
3.  When provided with fungal-colonised leaves (14–16% fungal biomass), the third and the fifth instar larvae of P. gentilis grew at the rates of 0.061 and 0.034 day⁻¹, respectively, but on a diet of sterile leaves, both larval instars lost weight. The incorporation rates of fungal carbon were 31.6 μg C mg⁻¹ AFDM day⁻¹, accounting for 100% of the daily growth rate of the third instar larvae and 8.6 μg C mg⁻¹ AFDM day⁻¹, accounting for 50% of the daily growth rate of the fifth instar larvae.
4.  These results suggest that leaf material colonised by A. filiformis is a high quality food resource for P. gentilis larvae, and that fungal biomass can contribute significantly to the growth of these larvae. Differences in feeding behaviour and digestive physiology may explain the significantly greater assimilation of fungal biomass by the earlier instar than the final instar. To satisfy their nutritional needs the fifth instar larvae would have to assimilate detrital mass that may have been modified by fungal exoenzymes.