Predation Rates Research Articles

Evaluation of release rates of predator, <i>Apertochrysa astur</i> (Banks) (Neuroptera: Chrysopidae) against Rugose Spiraling Whitefly (RSW), <i>Aleurodicus rugioperculatus</i> Martin

Evaluation of release rates of a generalist predator, Apertochrysa astur was carried out against Rugose Spiraling Whitefly (RSW) during 2020-21 and 2021-22 at Dr. YSRHU - SKPP Polytechnic College, Ramachandrapuram and Dr. YSRHU - Horticultural Research Station (HRS), Ambajipeta (100, 200, 300, 400, 500 and 600 eggs per palm). The overall and pooled results during the years 2020-21 and 2021-22, indicated that clipping of A. astur at 600 eggs/palm (T6) recorded the lowest number of RSW spirals, nymphs and pupae, whereas the control palms (T8) recorded with a maximum number of RSW spirals, nymphs and pupae per leaflet.

Predation potential and life history of three nabid species as biological control agents of pests in Canadian greenhouses

Nabids are hemipteran generalist predators commonly associated with agroecosystems. In this study, the predation rate of Nabis americoferus Carayon, N. roseipennis Reuter, and Hoplistoscelis pallescens Kerhzner on several common greenhouse pests was assessed in the laboratory, compared to the most closely related commercially available predator in North America, Dicyphus hesperus Knight (Heteroptera: Miridae). In addition, life history parameters of the nabids were determined to estimate their capacity for population increase, an important data set when considering their mass rearing and population establishment in crops. Our results showed that the three nabid species are generally more voracious predators than D. hesperus, especially when fed adult green peach aphids, adult western flower thrips and adult greenhouse whiteflies. Dicyphus hesperus preyed more on two spotted spider mites and greenhouse whitefly nymphs. Nabis americoferus consumed more western flower thrips larvae than all other species. Of the three nabids, N. americoferus also performed significantly better as a predator of western flower thrips. Additionally, N. americoferus had a significantly shorter egg to adult development time, and had a shorter pre-oviposition period than the other two species. Based on its predation capacity and favourable life history characteristics, N. americoferus was selected for further development as a new biological control agent for the North American market.

Defensive behaviour plasticity in Ananteris mauryi Lourenço, 1982 (Scorpiones: Buthidae) facing different predator species

Abstract Small species often fall prey to a wide range of predators in their natural habitats, and therefore require behavioural strategies to mitigate predation rates. In this study, we investigated the defensive behaviour of Ananteris mauryi, a small-bodied scorpion, against different natural predator species. Behavioural trials were conducted with A. mauryi individuals facing two different predators, spider and scorpion. Our results show that A. mauryi altered their defensive acts depending on the predator type, swinging their telson, cleaning their pedipalps, and run more frequently when facing spiders than scorpions. Additionally, we observed variation in the duration of behaviours according to predator type, with stinging attempts being performed more frequently against scorpions and run and metasoma swinging against spiders. Our findings suggest that scorpions have the ability to modulate their defensive behaviour according to the type of predator they face.

Increasing landscape heterogeneity as a win–win solution to manage trade-offs in biological control of crop and woodland pests

Agriculture and forestry cover more than 75% of Europe, and invertebrate pests are a costly challenge for these two economic sectors. Landscape management is increasingly promoted as a solution to enhance biological pest control, but little is known on its effects on adjacent crop fields and woodlands. This study aims to explore the effect of the proportion of woodlands and permanent grasslands as well as crop diversity on biological pest control simultaneously in cereals fields and woodland patches, in south-western France. We used different types of sentinel prey as well as bird and carabid community metrics to assess biological pest control potential in these two ecosystems. We first show that land cover variables influence biological pest control both in cereal fields and woodland patches, but have antagonistic effects in the two ecosystems. Although results vary according to the biological control indicator considered, we show that increasing landscape heterogeneity represents a valuable solution to manage trade-offs and promote higher average predation rates across forests and cereal fields. Our study therefore calls for more integrative studies to identify landscape management strategies that enable nature-based solutions across ecosystems.

Interference competition driven by co‐occurrence with tigers Panthera tigris may increase livestock predation by leopards Panthera pardus: a first step meta‐analysis

Abstract In coexisting carnivorans (Carnivora) relying on the same food resources, the dominant species imposes a cost on the inferior competitor by limiting its foraging ability. Tigers Panthera tigris and leopards Panthera pardus live in sympatry in most Asian countries and, because of their similar trophic niche, ‘interference competition’ may exist between these two predators. In fact, since tigers generally occupy prime habitats, leopards could be forced to roam into peripheral areas that are heavily used by humans to avoid competition, consequently increasing the risk of human‐leopard conflicts. Using information collected from the reviewed scientific literature, the purposes of this work were: 1) to assess if livestock predation by leopards increases in areas of coexistence with tigers, and 2) to characterise leopard attacks on livestock to discern the main factors involved in the human‐leopard conflict. Our findings showed that the leopard's ‘overall’ livestock predation rate (i.e. individuals taken/year) was higher in the absence of tigers than in their presence, and the same was observed for the ‘sheep and goat’ predation rate. These results confirm the leopard's tendency to take livestock and, especially, smaller prey. Conversely, the ‘cattle’ and ‘other’ predation rates were higher in the presence of tigers than in their absence, suggesting the existence of a sort of spatial segregation between predators in certain contexts. Lower levels of predation by leopards were observed on farms in which more prevention measures were used, than in those in which only one measure was implemented. We stress the importance of using proper prevention measures to mitigate human‐leopard conflicts. However, because their implementation may not be easy or economically feasible, the financial support given by carnivoran‐policy makers assumes remarkable importance to minimise the economic impact on local families and, in turn, to foster the coexistence between leopards and humans in shared landscapes.

Co-parasitism in the face of predation: Effects of natural enemies on a neotropical mockingbird.

Co-parasitism is ubiquitous and has important consequences for the ecology and evolution of wild host populations. Studies of parasite co-infections remain limited in scope, with few experimental tests of the fitness consequences of multiple parasites, especially in natural populations. We measured the separate and combined effects of Philornis seguyi nest flies and shiny cowbirds Molothrus bonariensis on the fitness of a shared host, the chalk-browed mockingbird (Mimus saturninus) in Argentina. Using a two-factor experimental approach, we manipulated the presence of nest flies and cowbirds in mockingbird nests and assessed their effects on mockingbird haemoglobin levels, begging and provisioning rates, body size, and fledging success. We also monitored rates of nest predation in relation to parasitism by flies and cowbirds. Nest flies reduced the haemoglobin concentration, body size, and fledging success of mockingbirds, likely because mockingbirds did not compensate for parasitism by begging more or feeding their nestlings more. Cowbirds also reduced the fledging success of mockingbirds, even though they had no detectable effect on haemoglobin or body size. Nests with cowbirds, which beg more than mockingbirds, attracted more nest predators. There was no significant interaction between the effects of flies and cowbirds on any component of mockingbird fitness. The combined effects of nest flies and cowbirds were strictly additive. In summary, we show that nest flies and cowbirds both reduce host fitness, but do not have interactive effects in co-parasitized nests. Our results further suggest that predators exacerbate the effects of nest flies and cowbirds on their hosts. Our study shows that the fitness consequences of co-parasitism are complex, especially in the context of community-level interactions.

Efficacy of Duddingtonia flagrans (Bioverm®) on the biological control of buffalo gastrointestinal nematodes

We evaluated the efficacy of Bioverm®, a commercial product containing Duddingtonia flagrans, on the control of buffalo (Bubalus bubalis) gastrointestinal nematodes. We randomly divided 12 buffaloes into two groups of six animals. In the treated group, each animal received a Bioverm®ˋs single dose of 1g (105 chlamydospores of D. flagrans) to 10 kg of live weight; in the control group, each animal received 1g of corn bran for each 10 kg of live weight as a placebo. Fecal samples were individually collected from 12, 24, 36, 48, 60 and 72 h after treatments. To examine 1) viability of chlamydospores passed through the gastrointestinal tract, 2 g of faeces and 1000 infective larvae (L3) were added to Petri dishes with 2% water-agar, and 2) to examine larval predation by D. flagrans during fecal cultures, 2000 L3 were added. In the Petri dishes, were observed significant reductions (p < 0.01) in the treated group after 48 (56.7%) and 60 h (91.5%). In the fecal cultures, significant reductions (p < 0.01) occurred in the treated group from 36 h (75%), with larval reduction up to 72 h. High larval predation rate occurred 60 h after Bioverm® administration. Bioverm® maintained viability and predation capacity after passage through the buffalo's gastrointestinal tract, showing efficacy on gastrointestinal nematodes.

Sympatric primate seed dispersers and predators jointly contribute to plant diversity in a subtropical forest.

Mutualistic and antagonistic plant-animal interactions differentially contribute to the maintenance of species diversity in ecological communities. Although both seed dispersal and predation by fruit-eating animals are recognized as important drivers of plant population dynamics, the mechanisms underlying how seed dispersers and predators jointly affect plant diversity remain largely unexplored. Based on mediating roles of seed size and species abundance, we investigated the effects of seed dispersal and predation by two sympatric primates (Nomascus concolor and Trachypithecus crepusculus) on local plant recruitment in a subtropical forest of China. Over a 26month period, we confirmed that these primates were functionally distinct: gibbons were legitimate seed dispersers who dispersed seeds of 44 plant species, while langurs were primarily seed predators who destroyed seeds of 48 plant species. Gibbons dispersed medium-seeded species more effectively than small- and large-seeded species, and dispersed more seeds of rare species than common and dominant species. Langurs showed a similar predation rate across different sizes of seeds, but destroyed a large number of seeds from common species. Due to gut passage effects, gibbons significantly shortened the duration of seed germination for 58% of the dispersed species; however, for 54% of species, seed germination rates were reduced significantly. Our study underlined the contrasting contributions of two primate species to local plant recruitment processes. By dispersing rare species and destroying the seeds of common species, both primates might jointly maintain plant species diversity. To maintain healthy ecosystems, the conservation of mammals that play critical functional roles needs to receive further attention.

EXPERIMENTAL INFECTIONS WITH EUHAPLORCHIS CALIFORNIENSIS AND A SMALL CYATHOCOTYLID INCREASE CONSPICUOUS BEHAVIORS IN CALIFORNIA KILLIFISH (FUNDULUS PARVIPINNIS).

Some parasites manipulate their host's phenotype to enhance predation rates by the next host in the parasite's life cycle. Our understanding of this parasite-increased trophic transmission is often stymied by study-design challenges. A recurring difficulty has been obtaining uninfected hosts with a coevolutionary history with the parasites, and conducting experimental infections that mimic natural processes. In 1996, Lafferty and Morris provided what has become a classic example of parasite-increased trophic transmission; they reported a positive association between the intensity of a brain-infecting trematode (Euhaplorchis californiensis) in naturally infected California killifish (Fundulus parvipinnis) and the frequency of conspicuous behaviors, which was thought to explain the documented 10-30× increase in predation by the final host birds. Here, we address the primary gap in that study by using experimental infections to assess the causality of E. californiensis infection for increased conspicuous behaviors in F. parvipinnis. We hatched and reared uninfected F. parvipinnis from a population co-occurring with E. californiensis, and infected them 1-2 times/week over half their life span with E. californiensis and a small cyathocotylid trematode (SMCY) that targets the host's muscle tissue. At 3 time points throughout the hosts' lives, we quantified several conspicuous behaviors: contorting, darting, scratching, surfacing, and vertical positioning relative to the water's surface. Euhaplorchis californiensis and SMCY infection caused 1.8- and 2.5-fold overall increases in conspicuous behaviors, respectively. Each parasite was also associated with increases in specific conspicuous behaviors, particularly 1.9- and 1.4-fold more darting. These experimental findings help solidify E. californiensis-F. parvipinnis as a classic example of behavioral manipulation. Yet our findings for E. californiensis infection-induced behavioral change were less consistent and strong than those previously documented. We discuss potential explanations for this discrepancy, particularly the idea that behavioral manipulation may be most apparent when fish are actively attacked by predators. Our findings concerning the other studied trematode species, SMCY, highlight that trophically transmitted parasites infecting various host tissues are known to be associated with conspicuous behaviors, reinforcing calls for research examining how communities of trophically transmitted parasites influence host behavior.

Native predators can learn new prey cues to overcome naivete and hunt novel alien prey

Biological invasions continue to rise globally, increasing the frequency of novel ecological interactions and the potential for naivete. Native predators can defend against invasion by alien prey species through biotic resistance, but initial predator naivete towards novel alien prey can allow prey to establish. Here we test if predator naivete can be overcome via a learned association between novel prey cues and a food reward, and if this conditioning increases predator motivation to hunt novel alien prey. We exposed free-living native bush rats (Rattus fuscipes) to repeated bouts of novel alien cockroach (Nauphoeta cinerea) odour and food rewards over an 11-day training period. We then conducted a simulated invasion, comparing the survival rates of sentinel cockroach prey in sites with trained and untrained rats. Cockroaches in sites with trained rats were 46 % more likely to be found and consumed over the invasion period than prey in sites with untrained rats. Also, the number of food rewards taken during training was correlated with the number of prey consumed on the first night of the invasion. Our results suggest that predators can overcome their naivete to novel prey through learning and that pre-exposing free-living predators to novel prey cues can subsequently increase predation rates on novel alien prey.

Hedgerows interact with forests to shape the abundance of mesopredators and their predation rate on eggs in farmland landscapes

Nest predation is the main cause of reproductive failure, particularly in ground-nesting birds on farmlands. Understanding the links between nest predation and habitat change can help design effective management schemes to constrain the negative impact of predation pressure on birds. However, the mechanisms underlying the relationships between landscape attributes, predator distribution, and nest predation are still unclear. Here, we use an experimental approach to examine the effects of distance to the hedgerow as well as hedgerow and forest densities on the abundance of major mesopredators of ground nests of our study area (i.e., corvids) and on the predation rate of artificial ground nests (n = 2576). We found evidence that landscape configuration influenced predation patterns differently depending on the predator species. Nest predation by corvids was more likely in homogeneous and open agricultural landscapes with a low density of forest and hedgerows, whereas predation by other predators was more likely close to hedgerows. Nest predation by corvids and the abundance of corvids also tended to be lower in landscapes dominated by grasslands. Other variables such as road density and distance to human settlements had contrasted effects on the likelihood of a nest being depredated by corvids, i.e., no effect with proximity to human settlements and decreasing trend with road density. Altogether, our results suggest that landscape features interact with mesopredator distribution and their predation rates of ground nests. Therefore, from a conservation and management perspective, a heterogeneous agricultural landscape that includes a mixture of crops associated with patches of forests, hedgerows, and grasslands offering alternative food to generalist predators should contribute to reducing ground-nesting bird predation.

Predation rate of dragonfly (Odonata: Libellulidae) on tilapia (Oreochromis niloticus Linnaeus 1758) and the availability of alternative preys (Insecta: Diptera: Chironomidae) to increase fish survival

The objective of this work was to evaluate the predation rates of two genera of Odonata Miathyria Kirby, 1889 and Erythemis Hagen, 1861 in post-larviculture of tilapia with and without availability of Chironomidae. For that, 3 experiments were carried out, the first to analyze which size scale of these two genera would be more efficient in the predation of tilapia and the other 2 experiments with the selected size scales, to analyze the predation rates on tilapia with different Odonata densities, with and without availability of the aquatic insect Chironomidae. For statistical analysis of the data, an analysis of variance (ANOVA) was applied with the Duncan test searching for the means in all experiments. In experiments 2 and 3 a linear regression model was also applied. In experiment 1, there were significant differences between treatments, and in the phase with Miathyria the predation of tilapia post-larvae was higher among odonates that corresponded to the size scale from 7.1 to 9.9 mm and therefore the scale was also selected for the next experiments. For Erythemis, the consumption of tilapia was higher in the size scale between 12.1 to 14,2 mm. In the following experiments, there were significant differences between treatments. With the increase in Odonata densities the predation of the fish was greater. With the availability of Chironomidae, the consumption of tilapia post-larvae decreased. The consumption of Chironomidae was higher than the consumption of fish in experiment 3. Miathyria proved to be more efficient than Erythemis in predation and the use of Chironomidae can be a sustainable alternative for post-larvae predation control on fish farms.

Effect of prey density on the performance of Eupeodes corollae and its predation rate against the cabbage aphid, Brevicorynae brassicae (L.).

Eupeodes corollae (F.) (Diptera: Syrphidae) is the most abundant syrphid fly which is distributed worldwide and is the sole predator of aphids. Therefore, the present study was conducted to evaluate the predation rate and functional response of E. corollae against the cabbage aphid, Brevicoryne brassicae (L.). The experiment was carried out under laboratory conditions at 25 ± 2°C with 60-70% relative humidity. The results revealed that age-specific net predation rate (qx) increased after the 4th day and a peak was recorded on the 10th day of pivotal age in the third larval instar. The stable host kill rate and finite host kill rate of E. corollae were 18.63 and 21.07, respectively, against the B. brassicae and predicted that a mean of 20.78 aphids was needed for E. corollae to produce one offspring. A negative linear coefficient (P < 0) indicated the type II functional response for all larval instars of E. corollae against the B. brassicae. At higher prey density, the prey consumption was significantly at par with second and third instar larvae of E. corollae as the prey consumption was increased with increasing the prey density, which then decreased after attaining the upper asymptote (76.40 and 81.40% consumption, respectively). The Roger's predator random equation for type II functional response was fitted to estimate attack rate (a) and handling time (Th). The maximum prey consumption was recorded for third instar of E. corollae with a higher attack rate (0.336 h-1) and lower handling time (0.514 h) against B. brassicae, followed by the second and first instar. Thus, it is concluded that the third larval instar of E. corollae was the voracious feeder and used as an efficient biocontrol agent in the IPM programme.

Bacillus thuringiensis-based bioinsecticides affect predation of Euborellia annulipes on diamondback moth larvae.

Interactions between earwigs and entomopathogens, such as Bacillus thuringiensis (Bt), are still poorly understood. This study tested whether Bt-based bioinsecticides have any effect on the predation of Euborellia annulipes (Lucas) (Dermaptera: Anisolabididae) on Plutella xylostella (L.) (Lepidoptera: Plutellidae), one of the pests with the largest number of cases of use and resistance to Bt. Fourth instar larvae were Bt infected by feeding on collard green leaves treated with Dipel®WG and XenTari®WG at the manufacturer-recommended doses. We used one no-choice condition, in which the predator had access to uninfected or Bt-infected larvae separately, and four free-choice conditions: uninfected vs Dipel®-infected larvae, uninfected vs XenTari®-infected larvae, Dipel®-infected vs XenTari®-infected larvae, and uninfected vs Bt-infected larvae with both bioinsecticides. Uninfected larvae were less consumed than those infected by both Bt-bioinsecticides in the no-choice condition. There was a higher consumption of uninfected over Dipel®-infected larvae in the free-choice condition. Overall, uninfected larvae were preferred over both Bt-based bioinsecticides infected larvae. We also used six different prey densities. The ringlegged earwig's predation rate enhanced as the prey population density increased, but the functional response was not affected by Bt-infection, being type II. The predator invested a low amount of handling time on Bt-fed prey and increased the maximum predation rate. Bt-based bioinsecticides cause effects on E. annulipes predation by altering their feeding preference and some aspects of its predatory behavior. The results of our study provide an important background for understanding interactions between earwigs and Bt. In addition, they can be used for decision making during approaches to integrated P. xylostella management.

Flowering Coriander (Coriandrum sativum) Strips Do Not Enhance Ecosystem Services in Azorean Orchards.

The effect of flower strips on ecosystem services (ESs) and disservices (EDs) is routinely assessed following changes in service provider densities without measuring the associated levels of ES/EDs. By using the sentinel approach (i.e., exposing a plant, seeds, and prey models in a standardized way), we tested how coriander (Coriandrum sativum) strips planted in mixed orchards on Terceira Island (Azores, Portugal) affected herbivory on lettuce plants, seed predation on wheat and weed seeds, and predation on artificial caterpillars. Vertebrates had more influence than invertebrates on ESs/EDs. Herbivory (ED) after 2 weeks was similar in the coriander and the control plots (mean ± SD; 2.3% ± 3.3% vs. 2.2% ± 2.9%, n = 32 for both). Seed predation was higher in the control than in the coriander plots for both grain (ED; 30.8% ± 38.9% vs. 15.3% ± 10.8%, n = 18 for both) and weed seeds (ES; 2.5% ± 4.1% vs. 0.4% ± 0.5%, n = 18 for both). Vertebrate predation (ES) rates after 48 h were significantly higher in the control (estimate 9%, 95% CI: 4-20%) than in the coriander plots (3%, 1-8%), while no difference was observed for invertebrate predation. Coriander strips did not support increased ES/reduced ED levels in this setting. The tools used can be effective to quantitatively compare multiple ESs/EDs under different farming management strategies.

Changes in prey body size differentially reduces predation risk across predator and prey abundances

Trophic interactions underpin the structure of ecological communities by describing the rates at which consumers exploit their resources. The rates at which predators consume their prey are influenced by prey traits, with many species inducing defensive modifications to prey traits following the threat of predation. Here we use different clonal lines of the protist Paramecium being consumed by Stenostomum predators to highlight how differences in prey traits impact rates of predation. Clonal lines differed in their body width traits, and in their ability to induce changes in body width. By using a factorial cross of predator and prey abundances for different clonal lines we demonstrate how evolutionary or induced alterations in prey traits can impact the relative threat of predation. Our experiments show how interference among predators impacts predation rate, and how increased body width increased predator handling times. Given that reductions in the strength of interspecific interactions are associated with increased levels of overall community stability, our results indicate how individual level changes may scale up to impact whole communities.

Multiparasitism and repeated parasitism by the great spotted cuckoo Clamator glandarius on its main host, the magpie Pica pica: effects on reproductive success, nest desertion and nest predation

Brood parasites are expected to lay only one egg per parasitized nest, as the existence of several parasitic nestlings in a brood increases competition and can lead the starvation of some of them. However, multiparasitism (laying of two or more eggs by one or more parasitic females in a single host nest) is surprisingly frequent. Here, we study multiparasitism by different females or by the same female (repeated parasitism) in the great spotted cuckoo Clamator glandarius, a non‐evictor brood parasite that mainly parasitizes the magpie Pica pica, and whose chicks may be raised together with host nestlings in the same nest. We used a total of 262 magpie nests found during four breeding seasons. Multiparasitism and repeated parasitism are very frequent because this brood parasite is less virulent than other cuckoo species and magpie hosts can successfully raise more than one parasitic nestling per nest. The total number of cuckoo chicks fledged was higher in multiparasitized nests than in single‐ or double‐parasitized magpie nests. Magpie breeding success (i.e. the proportion of eggs that produce young that leave the nest) did not differ between single‐, double‐, and multiparasitized magpie nests. These results suggest that multiparasitism is an adaptation in the great spotted cuckoo. The intensity of parasitism (number of cuckoo eggs per nest), after controlling for the potential effect of year, did not affect nest desertion or nest predation rate, neither during the incubation nor the nestling periods. This implies that nest concealment does not affect the susceptibility of one nest being parasitized and predated, as nest predation rate was similar regardless of the intensity of parasitism. Predation rate during the nestling phase did not vary according to intensity of parasitism, which does not support either the ‘mutualism' hypothesis or the ‘predation cost of begging' hypothesis.

Assessing ground predation by invertebrates in crops: Camera observations clarify the relevance of aphid cards and coleopteran sentinel prey

Redesigning cropping systems to promote natural pest control requires a sound understanding of the regulation potential of natural enemies. Sentinel preys are useful to quantify biological control, but the use of aphid cards (aphids glued to a sandpaper card) is controversial for their lack of realism. The objectives here were: (1) to compare aphid cards to non-fixed beetle larvae resembling coleopteran pests, with respect to the consumers attracted; and (2) to ascertain whether predation on coleopteran prey larvae responds to different invertebrates communities.We used cameras to identify the consumers of two types of sentinel prey on the ground, and compared aphid cards to an original sentinel prey, bruchid beetle larvae. Aphids glued to predation cards attracted opportunistic consumers and scavengers with very long handling times, and even scavengers, including harvestmen (33% of consumption events), spiders and slugs, and a very few carabid beetles. Unattached bruchid beetle larvae were consumed largely by carabids (64%), and secondarily by rove beetles, ants and chilopods. As the sentinel prey were not consumed by the same organisms, these findings demonstrate the importance of the choice of organisms exposed to estimate pest predation.Knowing the identity of the bruchid larvae consumers from the images, we investigated whether the assemblages of epigeic arthropods could explain their predation rates under contrasting field conditions. Accounting for all the expected consumers, sentinel prey disappearance rates could be explained statistically with a satisfactory goodness-of-fit. Slugs and ants contributed more strongly to the disappearance of sentinel prey than carnivorous carabids and chilopods. Finally, alternative prey (especially Collembola) reduced consumption by diverting consumers from their usual prey. Camera observations were valuable to assess the relevance of two different sentinel preys and of the consumers involved. With this knowledge, it is possible to estimate the pest control potential from the ground-dwelling communities present.

Sub-lethal Competition of Joint Predators (Pardosa pseudoannulata and Menochilus sexmaculatus) when Predating Nilaparvata lugens at Different Densities

Pardosa pseudoannulata and Menochilus sexmaculatus are two predators of the brown planthopper (BPH, Nilaparvata lugens, Hemiptera: Delphacidae) in rice fields. The research aimed to determine the predation and the competition model of P. pseudoannulata and M. sexmaculatus on different BPH densities. This study used a completely randomized design (CRD) factorially. The first factor was the difference in predator species (P. pseudoannulata, M. sexmaculatus, and a combination of predators P. pseudoannulata + M. sexmaculatus), and the second was the difference in N. lugens density (0, 30, 50, and 70 individuals). The treatment was repeated in 4 repetitions. The parameters observed were predatory and competitive behavior, predation rate, body weight gain, and competition model. The research showed that P.pseudoannulata was more aggressive in finding and catching prey than M. sexmaculatus. The more prey provided, the higher the predation rate of the two predators. The combination of them as joint predators has increased the pressure on BPH and the predation rate, although it was still below its potential. Sub-lethal competition occurred between the two predators; it did not affect P.pseudoannulata but affected the behavior and reduced body weight of M. sexmaculatus. The competition between the two predators was not influenced by BPH density but by the intensity of meeting time. Both as joint predators in rice fields are safe and beneficial for BPH control.

Adaptive host responses to infection can resemble parasitic manipulation.

Using a dynamic optimisation model for juvenile fish in stochastic food environments, we investigate optimal hormonal regulation, energy allocation and foraging behaviour of a growing host infected by a parasite that only incurs an energetic cost. We find it optimal for the infected host to have higher levels of orexin, growth and thyroid hormones, resulting in higher activity levels, increased foraging and faster growth. This growth strategy thus displays several of the fingerprints often associated with parasite manipulation: higher levels of metabolic hormones, faster growth, higher allocation to reserves (i.e. parasite-induced gigantism), higher risk-taking and eventually higher predation rate. However, there is no route for manipulation in our model, so these changes reflect adaptive host compensatory responses. Interestingly, several of these changes also increase the fitness of the parasite. Our results call for caution when interpreting observations of gigantism or risky host behaviours as parasite manipulation without further testing.