Predation potential and biology of Protogamasellopsis posnaniensis Wisniewski & Hirschmann (Acari: Rhodacaridae)

Rhodacaridae are cosmopolitan mites mentioned as predators, although nothing is known about their potential as biological control agents. One of the objectives of the work reported in this paper was to evaluate the potential of Protogamasellopsis posnaniensis (Acari: Rhodacaridae) as predator of representative species of insects of the families Sciaridae (Bradysia matogrossensis (Lane)) and Thripidae (Frankliniella occidentalis (Pergande)), of mites of the family Acaridae (Tyrophagus putrescentiae (Schrank) and Rhizoglyphus echinopus (Fumouze & Robin) and of nematodes of the family Rhabditidae (Protorhabditis sp.). Another objective was to determine the biological cycle of P. posnaniensis when fed the prey on which it performed best in the preceding predation test. The study was conducted in a laboratory where the experimental units were maintained at 25 ± 1 °C, 97 ± 3% RH and in the dark. Although the predator was able to kill all prey species considered in this study, the most favorable prey were T. putrescentiae, F. occidentalis and Protorhabditis sp. Survivorship of the predator in predation tests was always 98% or higher. Life table biological parameters when the predator was fed T. putrescentiae were: R_o = 109.29; T = 19.06 days; λ = 1.28 e r_m = 0.32 female/female/day. Despite preying upon larvae of B. matogrossensis, eggs of the former can also be killed by the latter. The results indicated that P. posnaniensis is a promising biological control agent, deserving additional studies on its possible use for the control of soil pests.     

Do leaf domatia mediate intraguild predation and host plant resistance to Oligonychus aceris (Shimer) on Red Sunset Maple (Acer rubrum)?

The predatory mites Neoseiulus fallacis (Garman) (Acarina: Phytoseiidae) and Zetzellia mali (Ewing) (Acarina: Stigmaeidae) have the potential to suppress populations of Oligonychus aceris (Shimer) (Acarina: Tetranychidae) on maple cultivars under field conditions. Red Sunset red maples (Acer rubrum) are more resistant to O. aceris than ‘Autumn Blaze’ Freeman maple (Acer × fremanii). Examination of leaves indicated that the mite resistant Red Sunset trees had more leaf domatia than those from Autumn Blaze. Laboratory assays found that maple cultivars did not affect rates of O. aceris consumption by N. fallacis or Z. mali in a 24 h period. Each predator exhibited distinct preferences for O. aceris life stages. N. fallacis consumed significantly more protonymphs and adults of O. aceris, whereas Z. mali consumed more eggs. In contrast, maple cultivars significantly influenced rates of intraguild predation between phytoseiids and stigmaeids. Adult N. fallacis consumed more immature stages of Z. mali on Autumn Blaze than on Red Sunset maple, but adult Z. mali consumed the same numbers of N. fallacis nymphs on both cultivars. These findings provide a potential mechanism to explain the resistance of Red Sunset maples to O. aceris. On Red Sunset maples, where domatia provide Z. mali with refugia from predation by N. fallacis, both predators can contribute to the mortality of O. aceris. In contrast on Autumn Blaze maples Z. mali have no place to hide from N. fallacis, so the contribution of this stigmaeid to O. aceris mortality is greatly diminished. Thus, differential susceptibility of these cultivars to spider mites may be mediated by the capacity of leaf domatia to influence rates of intraguild predation among phytoseiid and stigmaeid predators.     

Seasonal,spatial and diel partitioning of Acyrthosiphon pisum (Hemiptera: Aphididae) predators and predation in alfalfa fields

Predators are important natural enemies, often responsible for preventing pest population outbreaks of in many crops. Complementarity in resource use involves spatial or temporal segregation of predators, which can result in better biological control when several species of natural enemies share a prey. In this study, we investigated the seasonal, spatial and diel segregation of Acyrthosiphon pisum predators and its predation in alfalfa fields, by setting out cards with sentinel aphids, and making observations every 3 h for a 24 h period. A temporal and spatial segregation of predators was observed. Coccinellids were the most abundant predators, representing 51% of the total observations, followed by syrphid larvae. Coccinellids were also responsible for high levels of predation throughout the year, although the species responsible varied from spring to summer and autumn. On the other hand, syrphids were only found in spring and summer, while spiders only in autumn. Predator species also differed on their preferred sites for predation, with Heteropterans and syrphids found on the foliage, the spider Neomaso articeps only on the ground, and coccinellid and Anyphaenidae species on both sites. The two main predator groups also showed distinct diel patterns, with coccinellids observed only during day and syrphids only during night. This predatory activity corresponded with aphid predation, observing more predation in spring, on the foliage and during the day time. The proportion of predators observed preying on cards in the different seasons did not corresponded tightly with their field abundance, particularly in the case of coccinellids, which maintained high levels of predation in spite of great variations in its field abundance. Our results support the hypothesis of a spatio-temporal segregation of the predators associated with A. pisum in alfalfa, which might be beneficial for the outcome of biological control of this pest.     

Two-sex life table and predation rate of Cybocephalus flavocapitis Smith (Coleoptera: Cybocephalidae) reared on Aulacaspis yasumatsui Takagi (Hemiptera: Diaspididae), in Taiwan

Development, survival, and fecundity of the predator, Cybocephalus flavocapitis Smith, reared on its host Aulacaspis yasumatsui Takagi, were studied at 24 °C, 70 ± 10% RH, and photoperiod of 12:12 (L:D) h under laboratory conditions. Developmental periods for egg, larval, and pupal stages were 6.4, 12.1 and 14.3 d, respectively. The mean longevity of adults was 85.1 d. Raw life history data of all individuals were pooled and analyzed according to the age-stage, two-sex life table theory. The intrinsic rate of increase (r) was 0.05 d^? 1, the finite rate of increase (λ) was 1.05 d^? 1, the net reproductive rate (R₀) was 29.1 offspring, and the mean generation time (T) was 63.3 d. When we incorporated the age-stage variability of predation rate with the two-sex life table, our results indicated that the predation rates of larvae and adults were 743 eggs and 1595 scales, respectively. The net predation rate of C. flavocapitis is 1874 scales. Additionally, we compared life table results of C. flavocapitis with those of a previous life table study on Cybocephalus nipponicus because both species are currently used for the biological control of A. yasumatsui in Taiwan.     

Habitat effects on second-order predation of the seed predator Harpalus rufipes and implications for weed seedbank management

Seed predators provide a valuable ecosystem service to farmers by reducing densities of weed seeds, and, in turn, densities of weed seedlings they must manage. The predominant invertebrate weed seed predator in Maine, USA, agroecosystems is the carabid beetle Harpalus rufipes DeGeer. Pitfall trapping has shown that H. rufipes prefers sites with vegetative cover to fallow sites, preference speculated to be driven by predator avoidance behavior. To test this hypothesis, ‘second-order predation assays’ were developed, in which live H. rufipes prey were presented to second-order predators. Field experiments were conducted to determine foremost if H. rufipes was subject to second-order predation, and secondly, whether (a) vegetative cover affords H. rufipes protection from second-order predators, and (b) high rates of second-order predation correspond with decreased invertebrate seed predation rates. Two 72-h experiments were conducted (mid August and September 2012) at crop and non-crop sites across a 28 ha diversified farm in Stillwater, ME, USA.Second-order predation was 2.8% per day. Based on images from motion-sensing cameras, H. rufipes’ predators included birds and small mammals. Neither a relationship between second-order predation and vegetative treatment, nor an empirical relationship between second-order predation and invertebrate seed predation were detected. However, a simulation model predicted that 2.8% per day second-order predation could increase the number of seeds entering the seedbank by more than 17% annually. Additionally, complex habitats supported higher rates of second-order predation than did simple habitats.     

Increased control of thrips and aphids in greenhouses with two species of generalist predatory bugs involved in intraguild predation

The combined release of species of generalist predators can enhance multiple pest control when the predators feed on different prey, but, in theory, predators may be excluded through predation on each other. This study evaluated the co-occurrence of the generalist predators Macrolophus pygmaeus Rambur and Orius laevigatus (Fieber) and their control of two pests in a sweet pepper crop. Both predators consume pollen and nectar in sweet pepper flowers, prey on thrips and aphids, and O. laevigatus is an intraguild predator of M. pygmaeus. Observations in a commercial sweet pepper crop in a greenhouse with low densities of pests showed that the two predator species coexisted for 8 months. Moreover, their distributions in flowers suggested that they were neither attracted to each other, nor avoided or excluded each other. A greenhouse experiment showed that the predators together clearly controlled thrips and aphids better than each of them separately. Thrips control was significantly better in the presence of O. laevigatus and aphid control was significantly better in the presence of M. pygmaeus. Hence, combined inoculative releases of M. pygmaeus and O. laevigatus seem to be a good solution for controlling both thrips and aphids in greenhouse-grown sweet pepper. The predators are able to persist in one crop for a sufficiently long period and they complement each other in the control of both pests. This study also provides further evidence that intraguild predation does not necessarily have negative effects on biological control.     

A new method to study the functional response of Scymnus syriacus (Coleoptera: Coccinellidae) to different densities of Aphis gossypii

Functional response is basic to any investigation of predator–prey relationships. In this study, the functional response of female Scymnus syriacus Marseul (Col.: Coccinellidae) to different densities (10, 20, 40, 60, 80, 100) of third instar nymphs of Aphis gossypii Glover as prey was studied in an open patch experiment in a growth chamber (25 °C, 65 ± 5% RH and a photoperiod of 16L:8D h ). Using logistic regression, a type II functional response for female Scymnus syriacus was determined. The searching efficiency (a') and handling time (T_h) of the female predator using non linear least-square regression were estimated as 0.0769 ± 0.0136 h^? 1 and 0.3103 ± 0.0438 h., respectively. Mean times required for the female predator to settle in a patch were 10.20 ± 4.28, 6.58 ± 2.58, 12.58 ± 4.50, 4.53 ± 1.48, 5.14 ± 2.59, 3.87 ± 3.52 min at different prey densities, respectively. Maximum theoretical predation rate (T/T_h) estimated by Rogers' model for the female predator was 77.34. The proportion of female predators remaining in open patches at the end of the experiment was dependent on prey density (R² = 0.876). The type of functional response obtained here agrees with studies on this predator in closed patches.     

The effect of diet on longevity,fecundity, and the sex ratio of Clitostethus arcuatus (Rossi) (Coleoptera: Coccinellidae)

Clitostethus arcuatus is a major, cosmopolitan predator of some Aleyrodidae. Field collected adult beetles were reared in the laboratory on different diets: Siphoninus phillyreae eggs, Trialeurodes vaporariorum eggs, Sitotroga cerealella eggs, or an artificial diet consisting of honey, yeast, and pollen. All experiments were conducted at 25 ± 2 °C, 65 ± 5% RH and a photoperiod of 16:8 (L:D) h. Female and male C. arcuatus consumed a mean (± SE) of 61 ± 0.6 and 27 ± 0.9 T. vaporariorum eggs d^? 1, respectively, and a mean of 56 ± 2.2 and 29 ± 1.1 S. phillyreae eggs d^? 1, respectively. Significant differences were noted between sexes and between hosts consumed by female C. arcuatus. No feeding occurred on S. cerealella eggs. Although there was a significant difference between rates of oviposition due to diet, fertility rates on different diets did not show significant differences. The sex ratio of C. arcuatus (female:male) was 51.4:48.6, 55.2:44.8, and 54.6:45:4 when adults fed on T. vaporariorum, S. phillyreae, and artificial diet, respectively. These differences were not significantly different. Average longevity (± SE) was 66.4 ± 2.6, 54.9 ± 2.5; 77.3 ± 6.9, 67.5 ± 7.2; and 86.4 ± 4.5 70.3 ± 3.6 days for female and male C. arctuatus, respectively, on T. vaporariorum, S. phillyreae and artificial diet, respectively, with significant differences between sexes and diets. Although developmental duration on T. vaporariorum was longer than ash whitefly, this difference was not significant (mean 27.68 ± 0.31 and 25.09 ± 0.21 days for predators reared on T. vaporariorum and S. phillyreae, respectively). Given its longevity and fecundity on T. vaporariorum, C. arcuatus may be a good choice for mass release on glasshouse crops infected by greenhouse whitefly.     

Motorway verges: Paradise for prey species? A case study with the European rabbit

Roads have many effects on the mammal populations of their surroundings. Prey species are thought to establish dense populations in road verges due to a predation release effect, which arise as a side-effect of roadside avoidance by predators and/or predator roadkill. A species that has been suggested to benefit from predation release and attain high densities near roads is the European rabbit, a keystone species in Mediterranean ecosystems. We monitored rabbit relative abundance at three distances from a motorway (50, 450 and 850 m) during a 6 month period, as well as hunting and predator pressures, in a suitable area for rabbits. The lowest rabbit abundance was found next to the motorway (6.76 ± 8.87 pellets/m² per month) and the highest abundance at an intermediate distance (17.65 ± 23.11 pellets/m² per month). Hunting and carnivore pressures were highest at the sampling transect located farthest from the infrastructure. Thus, variability in rabbit abundance did not match the predation release effect found close to the motorway, and some sort of road avoidance or other process must underlie the observed abundance pattern. We advocate for a formal measurement of prey populations response to roads prior to any generalization as, in the case of rabbit, the response to roads and the potential cascading effects on other species may depend on landscape characteristics.     

Ambulatory dispersal of the susceptible and propargite-resistant strains of Tetranychus urticae and its influence on pesticide resistance dynamics

The distribution of resistant individuals is determined by the amount of movement between populations. The differential rate of dispersal of a susceptible and a pesticide-resistant strain could influence the resistance dynamics under field conditions. The dispersal rate and dispersal efficiency of the susceptible and propargite-resistant strains of Tetranychus urticae were measured in separate-release and mixed-release experiments. The diffusion coefficient (D) of both strains did not differ significantly (P > 0.344) and an estimate of the asymptotic rate of advance (2 √ rD) (for one generation) was estimated at 0.1047 and 0.0930 cm per degree day for the susceptible and propargite-resistant strains, respectively. The dispersal efficiency of the two strains differed significantly (P < 0.005) as more susceptible mites than propargite-resistant mites crossed into specified zones more quickly after 290 and 366 degree days. Significantly (P < 0.05) higher number of susceptible adults, immatures and eggs were found in the outer most zone of an arena as compared to that of the propargite-resistant mites. The bioassay of the two strains showed a similar pattern of the spread of the adult females across the specified zones in the mixed-release experiment. The relatively lower dispersive tendency of the propargite-resistant T. urticae and the smaller proportion of adult females exhibiting that behaviour increase the chances of developing resistant ‘hotspots’ in field specially after an acaricide application.     

Intraguild predation of Orius tristicolor by Geocoris spp. and the paradox of irruptive spider mite dynamics in California cotton

It is paradoxical when a community of several natural enemies fails to control a pest population when it can be shown experimentally that single members of the natural enemy community are effective control agents when tested individually. This is the case for spider mites, Tetranychus spp., in California cotton. Spider mites exhibit irruptive population dynamics despite that fact that experiments have shown that there are at least four predators (Galendromus occidentalis, Frankliniella occidentalis, Orius tristicolor, and Geocoris spp.) that, when tested singly, can suppress mite populations. One possible explanation for the paradox is intraguild predation, wherein one predator consumes another. Here, I evaluate the hypothesis that intraguild predation is a strong interaction among spider mite predators. I report manipulative field experiments, focal observations of freely foraging predators in the field, and population survey data that suggest that the minute pirate bug O. tristicolor, is subject to strong predation by other members of the predator community, and in particular by Geocoris spp. These results, combined with the results of prior work, suggest that pervasive intraguild predation among spider mite predators may explain the pest status of Tetranychus spp. in cotton.     

Comparative demography and diet breadth of Brazilian and African populations of the predatory mite Neoseiulus baraki,a candidate for biological control of coconut mite

Neoseiulus baraki Athias-Henriot (Phytoseiidae) is one of the few predators associated with the coconut mite Aceria guerreronis Keifer (Eriophyidae), the most damaging pest of coconut fruits in the Americas, Africa and more recently in Oman, Sri Lanka and parts of India. As Brazil is presently considered the putative origin of A. guerreronis, a large effort is presently underway to develop a classical biological control strategy for this pest in Africa and Asia. In this study, we investigated the life history of a Brazilian (NbBr) and a Beninese (NbBe) population of N. baraki on prey and non-prey diets under laboratory conditions (25 ± 1 °C 70–90% RH and 12:12 h L:D). Both populations were able to complete juvenile development and reproduce when feeding on A. guerreronis, Tetranychus urticae Koch eggs—a prey commonly used in the maintenance of phytoseiid mite colonies—and maize pollen. The two predators developed faster on A. guerreronis than on any other diet. The longest developmental time was recorded for NbBe on castor bean pollen (12.3 days), which also was not suitable at all for the development of NbBr. The longest developmental time of NbBr was 8.94 days on T. urticae eggs, whereas NbBe needed only 5.86 days to develop from eggs to adult stage on the same diet. For both populations, oviposition rate and longevity as well as demographic parameters were most favorable on A. guerreronis, the target prey. Intrinsic rate of natural increase (r_m) and net reproductive rate (R_o) were significantly higher for NbBr (0.19 and 24.9) than for NbBe (0.16 and 18.0). Taken together, the life history data from this study predict that NbBr is a more specialized and efficient predator of A. guerreronis compared with NbBe. The ability of the latter to utilize alternative food types, however, predicts that it would be able to persist longer in coconut habitat in the absence of its primary prey A. guerreronis. Implications for the implementation of a sustainable control strategy against A. guerreronis are discussed.     

Biodiversity Loss following the Introduction of Exotic Competitors: Does Intraguild Predation Explain the Decline of Native Lady Beetles?

Exotic species are widely accepted as a leading cause of biodiversity decline. Lady beetles (Coccinellidae) provide an important model to study how competitor introductions impact native communities since several native coccinellids have experienced declines that coincide with the establishment and spread of exotic coccinellids. This study tested the central hypothesis that intraguild predation by exotic species has caused these declines. Using sentinel egg experiments, we quantified the extent of predation on previously-common (Hippodamia convergens) and common (Coleomegilla maculata) native coccinellid eggs versus exotic coccinellid (Harmonia axyridis) eggs in three habitats: semi-natural grassland, alfalfa, and soybean. Following the experiments quantifying egg predation, we used video surveillance to determine the composition of the predator community attacking the eggs. The extent of predation varied across habitats, and egg species. Native coccinellids often sustained greater egg predation than H. axyridis. We found no evidence that exotic coccinellids consumed coccinellid eggs in the field. Harvestmen and slugs were responsible for the greatest proportion of attacks. This research challenges the widely-accepted hypothesis that intraguild predation by exotic competitors explains the loss of native coccinellids. Although exotic coccinellids may not be a direct competitor, reduced egg predation could indirectly confer a competitive advantage to these species. A lower proportion of H. axyridis eggs removed by predators may have aided its expansion and population increase and could indirectly affect native species via exploitative or apparent competition. These results do not support the intraguild predation hypothesis for native coccinellid decline, but do bring to light the existence of complex interactions between coccinellids and the guild of generalist predators in coccinellid foraging habitats.     

Laboratory and field tests of predation on the cereal leaf beetle,Oulema melanopus (Coleoptera: Chrysomelidae)

The cereal leaf beetle (CLB), Oulema melanopus (L.) (Coleoptera: Chrysomelidae), is an invasive pest in North America recently reported in the Canadian Prairies. We performed a series of laboratory assays to identify potential predators and a field study to quantify predation of CLB eggs. In no-choice Petri dish assays, ground beetles (Carabidae), rove beetles (Staphylinidae), and several common lady beetle species (Coccinellidae) were the most consistent predators of eggs and larvae. Nabis spp. (Hemiptera: Nabidae) and wolf spiders (Araneae: Lycosidae) consumed many larvae, but did not consume eggs. Hippodamia spp., Coccinella septempunctata (L.) (Coleoptera: Coccinellidae), and Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) also fed on CLB eggs on potted plants when an alternative food source was available, Sitobion avenae (Fabricius) (Hemiptera: Aphididae). In our field study, we found an average of 24.5% of sentinel eggs disappeared over a 24?h period, likely due to predation. Our results suggest that generalist predators can play an important role in the biological control of CLB, and warrant further study.     

Oviposition of Aedes aegypti Linnaeus, 1762 and Aedes albopictus Skuse, 1894 (Diptera: Culicidae) under laboratory and field conditions using ovitraps associated to different control agents,Manaus, Amazonas,Brazil

The aim of this study was to analyze the effectiveness of different control agents of Aedes aegypti and Aedes albopictus associated with ovitraps under laboratory and field conditions. Five treatments were used: grass infusion + Bacillus thuringiensis israelensis (gI + Bti), grass infusion + Saccharopolyspora spinosa (gI + Ss), grass infusion + Pyriproxyfen (gI + P), distilled water + Toxorhynchites haemorrhoidalis (dW + Th), and grass infusion (gI) (control). The highest mean number of eggs of both species were obtained with grass infusion in the laboratory. Among control agents, the lowest mean of A. aegypti eggs occurred with gI + Ss and the lowest mean of A. albopictus eggs occurred with dW + Th. There was no difference between treatments in A. aegypti (P = 0.4320) and A. albopictus (P = 0.7179). In the field, the highest mean number of eggs for both species were obtained with gI + Ss, and the lowest values were obtained with gI + P (P = 0.0124). The treatments can be applied to both the surveillance and the control, but ovitraps with biological larvicide Bti were more effective and safer considering the number of eggs laid and selectivity of pathogens for mosquitoes.     

Tracking aphid predation by lycosid spiders in spring-sown cereals using PCR-based gut-content analysis

Detection of prey DNA-remains in arthropod predators by polymerase chain reaction (PCR) is useful when investigating food webs. In this study we estimated how long after a feeding event it was possible to detect mitochondrial COII DNA (331 bp) from an important aphid pest, Rhopalosiphum padi (Homoptera: Aphididae), in spiders of the genus Pardosa (Araneae: Lycosidae). Following laboratory evaluations we tested spiders collected in spring-sown cereals for aphid predation during two seasons. Aphids were digested rapidly in laboratory-fed predators and the time point when prey DNA could be amplified from 50% of the spiders was estimated to be 3.7 h. A total of 372 field- collected predators were analyzed by PCR and despite low aphid densities many spiders (26% in 2004 and 19% in 2005) tested positive for R. padi, indicating consumption of at least one aphid within a few hours before capture. The percentage of spiders that tested positive for R. padi DNA varied considerably between fields and logistic regression analysis revealed that the probability of detecting aphid DNA was significantly influenced by location and year. We conclude that Pardosa spiders, under certain conditions, frequently feed on R. padi and deserve special attention in conservation biological control.     

Predator interference limits fly egg biological control by a guild of ground-active beetles

We examined whether predator interference could prevent effective conservation biological control of Delia spp. flies, important pests of cole crops, by an assemblage of carabid and staphylinid beetles. In laboratory feeding trials we found that the smaller (<1 cm) beetle species common at our site readily ate dipteran eggs, while the most common large carabid species, Pterostichus melanarius, rarely did. However, P. melanarius did eat several of the smaller beetle species. We conducted two field experiments where we manipulated immigration rates of the ground predator guild and then measured predation on fly eggs. Predation rates were consistently higher in cages where predators were added at ambient densities, compared to cages where ground predators were removed. However, in the second field experiment, when we quadrupled predator immigration rates neither beetle activity-density nor predation rate increased. High immigration rate plots had a higher proportion of P. melanarius in the predator community, compared to plots with beetles added at ambient densities, suggesting that P. melanarius was reducing activity-densities of the smaller beetles, perhaps through intraguild predation. Thus, tactics to improve the biological control of Delia spp. by conserving generalist predators, such as providing in- or extra-field refuges, could be thwarted if the primary predators of fly eggs, small carabids and staphylinids, are the targets of intraguild predation by also-conserved larger predators.     

Spider mite web mediates anti-predator behaviour

Herbivores suffer significant mortality from predation and are therefore subject to natural selection on traits promoting predator avoidance and resistance. They can employ an array of strategies to reduce predation, for example through changes in behaviour, morphology and life history. So far, the anti-predator response studied most intensively in spider mites has been the avoidance of patches with high predation risk. Less attention has been given to the dense web produced by spider mites, which is a complex structure of silken threads that is thought to hinder predators. Here, we investigate the effects of the web produced by the red spider mite, Tetranychus evansi Baker & Pritchard, on its interactions with the predatory mite, Phytoseiulus longipes Evans. We tested whether female spider mites recognize predator cues and whether these can induce the spider mites to produce denser web. We found that the prey did not produce denser web in response to such cues, but laid more eggs suspended in the web, away from the leaf surface. These suspended eggs suffered less from predation by P. longipes than eggs that were laid on the leaf surface under the web. Thus, by altering their oviposition behaviour in response to predator cues, females of T. evansi protect their offspring.     

The brown-world role of insectivores: Frogs reduce plant growth by suppressing detritivores in an alpine meadow

Predators of plant-suppressing herbivores have long been known to indirectly enhance plant biomass, while more recent work has revealed that predators of plant-facilitating detritivores can have the opposite effect on plant biomass. Generalist predators, such as frogs that typically facilitate plant growth in green food webs, may potentially negatively affect plant growth by consuming prey from brown food webs. In a marshy Tibetan alpine meadow, we tested the hypothesis that the locally abundant frog Rana kukunoris could negatively affect plant growth through suppression of dung-decomposing detritivores that promote plant growth by enhancing nutrient recycling. We conducted a factorial experiment (presence/absence of predators × presence/absence of dung) using replicate field enclosures over a growing season. Where dung was present, frogs significantly reduced the number of dung-feeding beetles and dung-feeding flies (including fly eggs and maggots) per dung pat, thereby decreasing dung mass loss and, indirectly, aboveground plant biomass (by 22%) surrounding dung pats. Where dung was absent, frogs did not affect plant biomass. Moreover, the number of dung beetles was positively associated with dung mass loss and soil soluble N concentration (but not total N concentrations), which in turn positively correlated with aboveground plant biomass. These results indicate that a generalist predator species standing in green food webs may play a contrasting role in brown food webs and indicate that a more nuanced appreciation of the functional role of predators in tri-trophic systems is required to accurately predict their cascading effects. Future studies must assess the relative strength of cascading effects mediated through brown and green channels in order to assess the net cascading effects of generalist predators in natural food webs.     

Oviposition patterns in a predatory mite reduce the risk of egg predation caused by prey

Abstract 1. Predatory arthropods lay their eggs such that their offspring have sufficient prey at their disposal and run a low risk of being eaten by conspecific and heterospecific predators, but what happens if the prey attacks eggs of the predator? 2. The egg distribution and time allocation of adult female predatory mites Iphiseius degenerans as affected by predation of their eggs by prey, the western flower thrips Frankliniella occidentalis, were studied on sweet pepper plants. The predatory mites attack the first instar of thrips but all active stages of thrips are capable of killing the eggs of the predator; however the predatory mite is used for biological control of thrips. 3. The majority of predatory mite eggs was laid on the underside of leaves in hair tufts (domatia). During the experiment, females spent increasing amounts of time in flowers where they fed on pollen and thrips larvae. The risk of predation on predator eggs by thrips was lower on leaves than in flowers where the majority of thrips resides. Moreover, predation risk was higher outside leaf domatia than inside. 4. This suggests that predators avoid ovipositing in places with abundant prey to prevent their eggs from being eaten by thrips.