Ontogenetic shifts in the functional response and interference interactions of Rhyacophila dorsalis larvae (Trichoptera)

1. Ontogenetic shifts in predator behaviour can affect the assessment of food‐web structure and the development of predator–prey models. Therefore, it is important to establish if the functional response and interference interactions differ between life‐stages. These hypotheses were tested by (i) comparing the functional response of second, third, fourth and fifth larval instars of Rhyacophila dorsalis, using three stream tanks with one Rhyacophila larva per tank and one of 10 prey densities between 20 and 200 larvae of Chironomus sp.; (ii) using other experiments to assess interference within instars (two to five larvae of the same instar per tank), and between pairs of different instars (one, two or three larvae per instar; total predator densities of two, four or six larvae per tank). 2. The first hypothesis was supported. The number of prey eaten by each instar increased with prey density, the relationship being described by a type II model. The curvilinear response was stronger for fourth and fifth instars than for second and third instars. Mean handling time did not change significantly with prey density, and increased with decreasing instar number from 169 s for fifth instars to 200 s for second instars. Attack rate decreased progressively with decreasing instar number. Handling time varied considerably for each predator–prey encounter, but was normally distributed for each predator instar. Variations in attack rate and handling time were related to differences in activity between instars, fourth and fifth instars being more active and aggressive than second and third instars, and having a higher food intake. 3. The second hypothesis was partially supported. In the interference experiments between larvae of the same instar or different instars, mean handling time did not change significantly with increasing predator density, and attack rate did not change for second and third instars but decreased curvilinearly for fourth and fifth instars. Interference between some instars could not be studied because insufficient second instars were available at the same time as fourth and fifth instars, and most third instars were eaten by fourth and fifth instars in the experiments. Prey capture always decreased with decreasing attack rate. Therefore, interference reduced prey consumption in fourth and fifth instars, but not in second and third instars. The varying feeding responses of different instars should be taken into account when assessing their role in predator–prey relationships in the field.     

Effects of prey density and spatial distribution on prey consumption of the adult predatory ladybird beetle

The effects of prey density and spatial distribution on prey consumption of the adult predatory ladybird, Harmonia axyridis , were investigated by using a 2 × 2 factorial design in large scale cages. Prey density influenced prey consumption of the ladybirds, and the frequency with which predation occurred was quite different between the prey distributions. The ladybirds consumed a relatively constant and small number of aphids when the prey were uniformly distributed, whereas the number of prey consumed per day when predation occurred was large and much more variable when the prey were contagiously distributed. At high prey density, the number of prey consumed was highest during the first day of the experiment; thereafter, only 10–20 aphids were consumed during the following 3 days. However, these patterns of prey consumption were not observed at low prey density. The percentage of aphids that remained on the host plants when the experiments were terminated was higher at low prey density than at high prey density, suggesting that predator foraging efficiency at low prey density was lower than at high prey density. Ladybirds foraging for high prey density were more frequently observed on the plants with aphids than ladybirds foraging for low prey density. Prey distribution also influenced the frequency of residence of ladybirds on the plants. The different predation patterns observed in the two spatial distributions, in which prey consumption was much more variable for the contagious distribution, might be explained by the difference in prey encounter rate of the predator between the distributions. This study indicated that the ladybirds had limited ability to search out prey over large spatial scales.     

The effects of host plant on the coccinellid functional response: Is the conifer specialist Aphidecta obliterata (L.) (Coleoptera: Coccinellidae) better adapted to spruce than the generalist Adalia bipunctata (L.) (Coleoptera: Coccinellidae)?

Female Aphidecta obliterata consumed an average of 26.6 ± 5.8 Elatobium abietinum and males consumed an average of 19.9 ± 3.2 Elatobium abietinum, but there was no significant difference in the number consumed between the sexes. In Petri dish trials, the larval stages of A. obliterata and all stages of Adalia bipunctata appeared to exhibit a Type II response to prey density, although A. obliterata adults showed a more linear response to prey density. There was no significant difference between the functional responses of the 3rd instars of the two coccinellid species, but there was a significant difference between the responses shown by the 1st instars, with A. obliterata larvae consuming more than those of A. bipunctata, especially at low densities, suggesting that the two species respond differently to an increase in prey density.At low prey densities, adults and 4th instars of both species exhibited a similar response to an increase in prey density but at higher densities the 4th instars and adult stages of A. bipunctata showed higher attack rates when compared with the same stages of A. obliterata.Adult and 4th instar A. obliterata exhibited Type II functional responses on spruce sections. The 4th instar A. obliterata larva appeared to be a more effective predator than the adult of the species, and was more effective when compared with adult A. bipunctata at lower prey densities but A. bipunctata adults appeared to be a more effective predator at higher prey densities.The host plant affected the rate of consumption by adult A. obliterata as adults on Sitka spruce sections consumed significantly higher numbers of aphids than their counterparts on Norway spruce. This was most noticeable at densities above 16 aphids.The distributions of the two coccinellid species in the olfactometer were significantly affected by the presence of host plant material. Aphidecta obliterata adults were found in significantly higher numbers in the Sitka spruce chambers than the control chambers (those without plant material). Adalia bipunctata adults were found in significantly lower numbers in the Norway spruce chamber than the control chamber.Although A. bipunctata has a higher level of voracity than A. obliterata, the latter is more adapted to the spruce environment and the boom and bust population dynamics of E. abietinum.     

Relationship between predation by Podisus nigrispinus and developmental phase and density of its prey,Plutella xylostella

This study evaluated the predation by Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae) at various densities of larvae and pupae of the pest Plutella xylostella (L.) (Lepidoptera: Plutellidae). We tested predator behavior of female P. nigrispinus at six experimental densities (1, 5, 10, 15, 20, or 25 prey items in a 1‐l transparent plastic container, replicated 15 times for each density) of both the fourth instar and pupae of P. xylostella. The number of prey consumed was monitored every 15 min for 12 h and was subsequently monitored at 24 h. Podisus nigrispinus females were weighed before and after the experiments to determine the effect of different densities of prey on their weight gain. Female predators had a Type‐II functional response, with attack rate estimated at 1.387 and 0.260 and a handling time of 0.091 and 0.183 h^?1 for larvae and pupae, respectively. Podisus nigrispinus consumed on average 10.9 larvae or 5.5 pupae in 24 h. Despite the similarity of the response type, P. nigrispinus preferred to feed on larvae, rather than on pupae.     

Preference and consumption of Macrolophus pygmaeus preying on mixed instar assemblages of Myzus persicae

This study examines the effects of changes in the prey frequency and abundance on prey selection among the four instars of Myzus persicae by the predator Macrolophus pygmaeus under laboratory conditions. The central hypothesis was that M. pygmaeus will become more selective as prey density increases. It was also observed that M. pygmaeus can occasionally abandon a prey item that had already been killed (non-consumptive prey mortality). It was assumed that the frequency of this behavior would increase with the prey size and prey density. For these purposes prey selection was evaluated by simultaneously presenting all instars of M. persicae to the predator in equal proportions and at increasing densities. M. pygmaeus showed a higher predation rate and a higher preference for smaller prey instars at all prey densities. However, if the predation rate by the predator is expressed in terms of biomass consumed, then biomass gain was higher when feeding on the larger instars of M. persicae. The prey selectivity was indicated by the total prey mortality (consumptive plus non-consumptive prey mortality) as well as by the non-consumptive prey mortality, was associated with relatively high prey densities, depending on the prey instar. Therefore, we argued that the predatory impact of M. pygmaeus on the various instars of the aphid depends not only on prey traits but also on their relative abundance in a patch. Observed decreases in biomass gain from larger prey were likely the result of high prey availability at densities before saturation, which might have caused confusion in the predator’s prey selection.     

The effects of different oxygen regimes on the feeding and vertical distribution of Nephelopsis obscura (Hirudinoidea)

The feeding rates and vertical distribution of the freshwater leech Nephelopsis obscura, fed on different densities of third instar Chironomus riparius, were determined in the laboratory at three different constant dissolved oxygen regimes (10%, 100%, 300% saturation) at 15 °C. The rate of feeding increased linearly with prey density up to maximal field prey densities, with no satiation response. Analysis of covariance showed that the rate (slope) at which prey were consumed was not significantly different among oxygen regimes but the amount eaten at any given prey density was higher in higher dissolved oxygen saturations. Analysis of the vertical distribution of N. obscura at different oxygen saturations and prey densities showed a higher proportion of N. obscura on or in the mud substrate compared to the water column at 100% and 300%. No correlation was found between prey density and the vertical distribution of N. obscura, but the numbers of prey eaten were correlated with the proportion of N. obscura on the mud substrate. These results indicate that higher percentage dissolved oxygen regimes increase the feeding of N. obscura and are of potential importance in explaining the seasonal depth distribution and microdistribution patterns recorded for N. obscura.     

Effect of prey size on attack components of the functional response by Notonecta undulata

The number of encounters per prey, the proportion of encounters resulting in attacks, and the proportion of attacks that were successful were observed while fourth-instar Notonecta undulata nymphs preyed on smaller N. undulata nymphs. While encounters per prey and proportion of encounters resulting in attacks increased with prey size, the proportion of attacks that were successful decreased. The increase in encounter rate per prey was due in part to an increase in the predator's reactive distance to prey as prey size increased. While none of the attack parameters varied significantly with prey density, logarithmic regression of the number of encounters per unit search time on prey density suggested that prey density tends to have a positive effect on encounters per first-instar prey but a negative effect on encounters per second-instar prey. A functional response model is presented that incorporates components of the predator's attack rate as exponential functions of prey density and allows for effects of the time the predator may spend evaluating prey encountered but not attacked and time spent attacking prey not captured. Estimates of the attack parameters derived from the experimental data are used in the model to generate functional response curves for fourth-instar N. undulata preying on first- or second-instar conspecifics. The predicted curve for second-instar prey is typical type II but the curve for firstinstar prey is slightly positively density dependent at low prey densities, i.e., type III.     

The effect of prey density on the developmental time of larvae of an aquatic beetle: <Emphasis Type="Italic">Tropisternus setiger</Emphasis> (Insecta,Coleoptera: Hydrophilidae)

Predaceous larvae of the water scavenger beetle Tropisternus setiger (Germar) are common inhabitants of variable environments in which prey availability may vary widely. We conducted laboratory experiments to assess the effect of prey density on developmental times and survivorship of the preimaginal stages of T. setiger. We also examined the effect of the number of consumed prey on the larval size of instar III. Four different prey densities (one, two, four, and eight preys a day) were tested and both developmental time and survivorship differed significantly among them. Larvae fed one or two preys daily showed a longer developmental time and a lower survivorship than larvae fed four or eight preys a day. Moreover the consumption of four preys a day increased larval developmental success, and to consume one prey a day affected survivorship through the larval period. On the other hand, prey density had no effect on the final larval size. Handling editor: K. Martens     

FUCTIONAL RESPONSE AND PLANT PREFERENCE OF NEPHASPIS OCULATUS (COLEOPTERA: COCCINELLIDAE), PREYING ON BEMISIA ARGENTIFOLII (HOMOPTERA: ALEYRODIDM) IN THE LABORATORY

Abstract The predatory behavior and functional response of all larval stages and adults of Nephpis oculatus (Blatchley), a predacious coccinellid, on various egg densities of Bemisia argentgolii Bellows & Pemng, and prey preference of adult N. oculatus , were studied in the laboratory. Daily consumption of eggs of B. argentifolii by N. oculatus was evaluated at six different densities to obtain functional response curves for all active stages of the coccinellid. Bemisia argentifolii eggs were offered to N. oculatus on collard leaf disks in Petri dish arenas over a 24-h period at 26.7 ∀ 2°C: and a photoperiod of 14:10 (L: D) h. Linear relationship were observed between percentage prey consumed and prey density, with r ² values between 0.82–0.99 for all stages except for the fourth instar that had a smaller r² value (0.64). Functional response curves of prey consumption by N. oculatus against density of B. argentifolii eggs fitted the type II model of Holling's disc equation for all larval stages and both the male and female adults. Adult females consumed more prey than adult males. The maximum theoretical number of prey consumed per day increased with larval development. The fourth instar was the most effective larval predator, followed by the third instar, the second instar, and finally, the first instar. Based on the functional response parameters, a maximum of 321, 312, 237, 229, 73, and 34 B. argentifolii eggs could be attacked by an adult female, a fourth instar, an adult male, a third instar, a second instar, and a first instar of N. oculatus , respectively. Nephaspis oculatus adults strongly preferred collard to tomato, soybean, eggplant or sweet-potato for oviposition and foraging. Nephaspis oculatus did not deposit any eggs on soybean and tomato.     

The effect of density and mutual interference by a Predator: A laboratory study of predation by the Nudibranch Coryphella rufibranchialis on the hydroid Tubularia larynx

The nudibranch Coryphella rufibranchialis (JOHNSTON) feeds on a variety of hydroids, including Tubularia larynx Ellis & Solander. Experiments in which density of prey and predators were altered showed that more prey were eaten as prey density increased. However, more prey were consumed at low predator densities, presumably because of mutual interference among nudibranchs at the higher predator densities. The number of prey consumed per nudibranch was maximal with low predator densities and a ratio of 25–50 polyps per predator. Coryphella seems to show an opportunistic feeding strategy involving solitary predators rapidly depleting hydroid colonies and moving on to new colonies.     

Prey to predator size ratio influences foraging efficiency of larval Aeshna juncea dragonflies

We investigated foraging behaviour of larval dragonflies Aeshna juncea in order to examine the significance of prey density and body size in predator-prey dynamics. A. juncea were offered separately three size-classes of Daphnia magna at low and high densities. The data were collected with direct observations of the foraging individuals. We found that large A. juncea larvae could better enhance their intake of prey biomass as prey size and prey density increased than their smaller conspecifics. However, increasing feeding efficiency of both larval instars was constrained by declining attack success and search rate with increasing prey size and density. With small D. magna, in contrast to large A. juncea, small A. juncea increased their searching efficiency as prey density increased keeping D. magna mortality rate at a constant level. In a predator-prey relationship this indicates stabilizing potential and feeding thresholds set by both prey density and prey-predator size ratio. Attack success dropped with prey size and density, but did not change in the course of the foraging bout. For both A. juncea sizes prey handling times increased as more medium and large prey were eaten. The slope of the increase became steeper with increasing prey-predator size ratio. These observations indicate that components of the predator-prey relationship vary with prey density, contrary to the basic assumptions of functional response equations. Moreover, the results suggest that the effects of prey density change during the ontogeny of predators and prey.     

The functional response of a predatory plant preying on swarming zooplankton

In a laboratory study, we determined the functional response of the carnivorous aquatic plant Utricularia vulgaris feeding on Polyphemus pediculus, a cladoceran zooplankton that forms swarms. The number of prey eaten increased linearly with prey density up to a density of 35 prey per 125 ml and decreased slightly above this density. Independent estimates of handling time showed that the number eaten was not limited by handling. Thus, we hypothesized that the functional response levelled off because attack rate decreased with increasing density. Direct observations of the predation act at high and low prey densities showed that prey per capita mortality rate was markedly lower at high densities. An analysis of the components of the predation cycle showed that encounter rate and attack probability but not capture success decreased with increasing prey density. We, then, studied the degree of aggregation and the movement behaviour of Polyphemus . The tendency to form swarms increased with density and this was associated with reduced swimming speed and swimming along a more tortuous path. Presence of Utricularia leaves did not influence the spatial distribution and swimming behaviour of Polyphemus . We concluded that the unusual shape of the functional response was due to density dependent prey mortality rates that resulted from a density dependent tendency to form swarms. We, therefore, suggested a modification of Holling's type II functional response model that included density dependent attack rate and this model fitted data significantly better than the original model.     

Life Cycle and Predation Potential of the Black Cricket,Methioche vittaticollis (Orthoptera: Gryllidae) and Its Population Density in the Rice Field

Life cycle and predation potential of a predatory black crickets, Methioche vittaticollis (Stal), were studied in the laboratory at the conditions of 27±1°C and 70±5% RH with a photoperiod of 14: 10 (L: D). Average life cycle was 90 days. The cylindrical eggs were laid singly within the leaf sheath and hatched in 17 days. Total nymphal period lasted 33 days. There were four nymphal stadia that lasted for 7.2, 7.7, 8.7, and 9.0 days, respectively. Adult male and female lived an average of 35 and 43 days, respectively. The female lay an average of 45 eggs during her life span. The number of striped stemborer (SSB) eggs consumed per day by 1st, 2nd, 3rd and 4th instar nymphs of M. vittaticollis was 1.7, 2.5, 13.3 and 184.3, respectively. Also, The number of SSB eggs consumed per day by male and female adults were 102.7 and 158.7, respectively. The fourth instar nymph consumed the most number of preys. The functional response curve of 4th instar nymph, male and female adults of M. vittaticollis to the densities of SSB eggs indicated Holling's TYPE II. The consumption of prey by the M. vittaticollis increased with the prey density but the consumption rate decreased. The attack rate of 4th instar of M. vittaticollis was the highest compared to the adults, and handling time was the shortest. Population densities of hoppers and lepidoptera in unsprayed field consisted of rice variety “PSBRc 20” were very low throughout the cropping period. This could be due to the high density of M. vittaticollis. M. vittaticollis was collected from the field and bunds, its population inside the field increased as crop matures. Bunds served as refuge for predators when the crop is maturity stage.     

Temperature and the biology and predation of Ilione albiseta (Diptera: Sciomyzidae) — Potential biological control agent of liver fluke

The effect of temperature on predation by Ilione albiseta (Diptera: Sciomyzidae) on Lymnaea peregra was investigated at 14°, 17°, 20°, 23° and 26°C. The mean dry weight of snail tissue (Lymnaea peregra) attacked and consumed per day by first and second instar I. albiseta larvae was highest at 20°C while for third instar and total larval duration period it was greatest at 23°C. The mean number of snails killed per day during the third instar was also highest at 23°C. The total amount of snail tissue consumed by I. albiseta larvae increased significantly from first to second instar and from second to third instar at each constant temperature. Mean survival period of unfed first instar larvae decreased from 28.4 days at 14°C to 11 days at 26°C and the mean length of the second instar cephalopharyngeal skeleton decreased with increasing temperatures. As temperature increased the rate of consumption of oxygen (dissolved in water) by first and third instar larvae rose.     

Habitat complexity reduces aggression and enhances consumption in crayfish

We tested the hypothesis that increased habitat complexity would reduce intraspecific interactions among crayfish (Orconectes propinquus), and result in an increase in the consumption rate of prey at different crayfish densities. The effect of crayfish density, food level (trout eggs), and habitat complexity on prey consumption by crayfish was quantified in the laboratory. There was a significant difference in the consumption rate between different food levels. When food was scarce, almost all trout eggs were consumed regardless of crayfish density or habitat complexity. When food was unlimited, there was a significant positive linear relationship between eggs consumed per crayfish and habitat complexity. However, the relationship was not significant when trials without habitat were deleted from the analysis. We found that habitat complexity significantly reduced intraspecific aggression. Our findings suggest that a minimal amount of habitat complexity can reduce interactions among predators, ultimately resulting in increased prey consumption.     

Prey stage preference and feeding behaviour of Oligota kashmirica benefica (Coleoptera: Staphylinidae), an insect predator of the spider mite Tetranychus urticae (Acari: Tetranychidae)

We studied the prey stage preference and feeding behaviour of the first to third instar larvae and adult females of Oligota kashmirica benefica Naomi (Coleoptera: Staphylinidae), a predator of the spider mite Tetranychus urticae Koch (red form) (Acari: Tetranychidae), on leaves of the kudzu vine (Pueraria lobata (Wild.) Ohwi (Leguminosae)) under laboratory conditions. The number of mites eaten increased with the growth of predator larvae. Third instar larvae preyed on all stages of spider mite, whereas first instar larvae preyed mainly on immobile stages (eggs and quiescent stages). The predator larvae showed two types of foraging behaviour (active searching and ambush behaviour) when targeting the mobile stages (larval, nymph and adult stages of prey). Although no difference was found in the number of prey consumed by adult females and third instar larvae of the predator, the adult females mainly attacked and consumed the immobile stages.     

Foraging behaviour of planktivorous fish in artificial vegetation: the effects on swimming and feeding

In the littoral zones of lakes, aquatic macrophytes produce considerable structural variation that can provide protection to prey communities by hindering predator foraging activity. The swimming and feeding behaviour of a planktivore, Pseudorasbora parva(Cyprinidae) on its prey (Daphnia pulex) was studied in a series of laboratory experiments with varying densities (0, 350, 700, 1400, 2100 and 2800 stems m^–2) of simulated submerged vegetation. Prey availability was varied from 0.5, 1.0, 2.0, 5.0, 10.0 and 25.0 prey l^–1. As the stem density increased, the predator's swimming speed and the number of prey captured decreased relative to feeding in open water. A good relation existed between the number of successful prey captures and swimming speed with the average stem distance to fish body length ratio (D). An abrupt reduction in feeding and swimming was recorded when D was reduced to values less than one.     

Consumption rate, functional response and preference of the predaceous mite Iphiseius degenerans to Tetranychus urticae and Eutetranychus orientalis

The functional response of females of the phytoseiid mite, Iphiseius degenerans (Berlese), to increasing densities of females of its prey, Tetranychus urticae Koch and Eutetranychus orientalis Klein, on bean leaves, were studied under laboratory conditions. Our results indicated that the predator consumed significantly more items of E. orientalis than of T. urticae at all densities treatments. Daily consumption of the predator increased with increasing prey density until a plateau was reached-maximum number of prey consumed was ca. 4 for T. urticae and ca. 12 for E. orientalis. A Type II functional response was determined by a logistic regression model. The highest estimated value a (instantaneous rate of attack) and the lowest value of T ( h ) (handling time) were found for the predator feeding on E. orientalis. Prey selection was evaluated by simultaneously presenting both prey species to the predator in various ratios and at increasing densities. I. degenerans showed a higher predation rate and higher preference for E. orientalis at all the ratios and prey densities tested. This may be due to the smaller size or the inactivity of E. orientalis and the inability of the predator to cope with the webbing of T. urticae. Our results suggest that I. degenerans can be considered a suitable biological control candidate based on its preference for E. orientalis in the Mediterranean region.     

Diel and density-related changes in food consumption and prey selection by brook charr in a New Hampshire stream

Synopsis We report the results of a field study testing influences of both density and changes over the diel cycle on food consumption and prey selection by brook charr,Salvelinus fontinalis. Charr density in replicate 35 m long sections of a New Hampshire stream was adjusted to either medium or high levels (relative to natural densities). Diets of charr and the availability of drifting prey were then sampled every four hours for 24 hours. There were no significant diel changes in the weight of prey consumed by charr per four hours, though there was some indication of reduced feeding at night. Chary fed selectively on different prey taxa, showing most preference for cased caddis larvae. Several species of mayflies and stoneflies were selected more strongly during the day than at night. Charr fed selectively on larger prey during the daytime but showed no size-selection at night. The density of charr had no significant effects on either their rate of food consumption or on selection for prey of different taxa or sizes.     

Effects of satiation on feeding and swimming behaviour of planktivores

Hunger affects the feeding and swimming behaviour in fish. After 36 h of food deprivation, the feeding and swimming behaviour of Pseudorasbora parva (Cyprinidae) was studied under different prey densities (0.5, 1, 2, 5, 10 and 25 of Daphnia pulex per liter). The initial feeding rates showed marked variations in relation to prey availability. Under high prey densities, the initial feeding rate of fish was higher and subsequently decreased faster, when compared to those feeding under low prey densities. At higher prey densities, two factors were involved: that of higher prey encounter rates and also the attainment of food satiation at a faster rate. Across all prey densities, the feeding rates of fish reached a plateau after satiation. The swimming speed of fish was found to be negatively related to the prey density and a significant change in swimming speed was noted as being directly related to the level of satiation. It was found that the increasing satiation level greatly influenced the handling time and reactive volume of predator, which finally caused reduced feeding rates.