It is well recognised that interactions among multiple species of natural enemies can have important consequences for the population dynamics of the species involved, particularly when intra-guild ...predation (IGP) occurs. However, these interactions are highly dependent on the type and behaviour of the prey, an aspect of IGP that is frequently overlooked. Here we demonstrate how a parasitoid (Dolichogenidea tasmanica) facilitates attack on a lepidopteran larva (Epiphyas postvittana) by a predatory mite (Anystis baccarum). We show that anti-predator behaviour of the lepidopteran larva is the mechanism that facilitates this. E. postvittana is protected by its silken leaf roll which limits predation by the mite except when the larva is attacked by the parasitoid causing the larva to leave its shelter. We explored the implications of the interactions among these three species for pest suppression by modelling changes in mite density and mite predation intensity. The presence of mites (the IG predator) always leads to a decrease in ability of the parasitoid to control E. postvittana and, as mite predation intensity increases, the ability of the parasitoid to suppress E. postvittana decreases. The results from the experiment show a synergistic interaction, but results from the population model show an interaction resulting in pest release. These findings support the general idea that if uni-directional IGP occurs, and competition is strong between the top and intermediate predator, then a single best control agent will likely be more effective at suppressing the prey population than multiple control agents combined. These findings have important implications for the management of E. postvittana in vineyards across Southern Australia and for other multi-species systems.
Es ist gut bekannt, dass die Interaktionen zwischen mehreren Arten von Fressfeinden wichtige Konsequenzen für die Populationsdynamik der beteiligten Arten haben können, insbesondere, wenn es zu intra-guild predation (IGP) kommt. Indessen hängen diese Interaktionen entscheidend von Typ und Verhalten der Beute ab, ein Aspekt, der häufig übersehen wird. Wir zeigen hier, wie ein Parasitoid (Dolichogenidea tasmanica) den Angriff auf eine Schmetterlingsraupe (Epiphyas postvittana) durch eine räuberische Milbe (Anystis baccarum) begünstigt. Wir zeigen, dass das gegen den Räuber gerichtete Verhalten der Schmetterlingsraupe der Mechanismus ist, der dies ermöglicht. Epiphyas postvittana wird durch ihre seidene Blattrolle vor den Angriff der Milbe geschützt, außer wenn die Larve vom Parasitoiden angegriffen wird, der die Larve veranlasst, ihr Refugium zu verlassen. Wir erkundeten die Folgen der Interaktionen zwischen diesen drei Arten für die Schädlingskontrolle indem wir Änderungen in der Milbendichte und des Räuberdrucks durch die Milbe modellierten. Die Anwesenheit der Milben mindert stets die Fähigkeit des Parasitoiden E. postvittana zu kontrollieren. Mit steigendem Räuberdruck durch die Milbe, sinkt die Fähigkeit des Parasitoiden zur Kontrolle. Die experimentellen Ergebnisse zeigten eine synergistische Interaktion, aber die Ergebnisse des Populationsmodels zeigen eine Interaktion, die zu einer Entlastung des Schädlings führt. Diese Befunde unterstützen den Gedanken, dass, wenn einseitige IGP stattfindet und die Konkurrenz zwischen dem Spitzenräuber und dem untergeordneten Räuber stark ist, ein einziger bester Kontrollagent die Beutepopulation vermutlich effektiver kontrollieren wird als mehrere Kontrollagenten zusammen. Diese Befunde haben wichtige Implikationen für das Management von E. postvittana in Weinbergen in ganz Süd-Australien und für andere Mehr-Arten-Systeme.
Agricultural systems have been continuously intensified to meet rising demand for agricultural products. However, there are increasing concerns that larger, more connected crop fields and loss of ...seminatural areas exacerbate pest pressure, but findings to date have been inconclusive. Even less is known about whether increased pest pressure results in measurable effects for farmers, such as increased insecticide use and decreased crop yield. Using extensive spatiotemporal data sampled every 2 to 3 d throughout five growing seasons in 373 cotton fields, we show that pests immigrated earlier and were more likely to occur in larger cotton fields embedded in landscapes with little seminatural area (<10%). Earlier pest immigration resulted in earlier spraying that was further linked to more sprays per season. Importantly, crop yield was the lowest in these intensified landscapes. Our results demonstrate that both environmental conservation and production objectives can be achieved in conventional agriculture by decreasing field sizes and maintaining seminatural vegetation in the surrounding landscapes.
Binomial sequential sampling plans have been used widely for monitoring invertebrate pest populations. Such plans are typically based upon a single action threshold (AT), which represents the level ...of infestation that the grower is prepared to accept before using a control measure. For many cropping systems this acceptable infestation level is likely to vary, being dependent on factors such as the growth stage of the crop and the value or demands of the destination market (e.g., local or high-quality export). We developed and validated a computer-assisted plan that uses a dynamic AT. The plan has been developed for monitoring diamondback moth, Plutella xylostella (L.) on broccoli (Brassica oleracea variety botrytis L.) and cauliflower (Brassica oleracea variety botrytis L.), but the concepts and methodologies could be readily applied to other systems.
Predators that have an increasing numerical response for aggregation, attack and oviposition to increasing prey density are thought to be ideal for biological control. However density‐dependent ...processes are infrequently detected and explanations include differences in the scales at which observations are made, behavioral differences among species, and habitat features. We examined the aggregation of four species of colonizing adult coccinellids to varying prey densities at two spatial scales in a maize system. Three of the species, Adalia bipunctata, Hippodamia tredecimpunctata, and Hippodamia convergens, responded to aphid abundance at the plant scale, and one species, Coleomegilla maculata, responded to the average aphid density at the plot (10×10 m) scale. In addition, H. convergens responded to individual plants with high aphid abundance in those plots with many plants of high aphid abundance. These results suggests that C. maculata (and possibly H. convergens) may be better able to colonize fields before aphid populations reach high levels, whereas A. bipunctata and H. tredecimpunctata may only be able to respond to high aphid abundance at the plant scale. This study suggests that spatial scale can affect predator–prey dynamics in a species‐specific manner. However, the differences among coccinellid species in the community appear to be complementary, potentially contributing to greater aphid suppression.
Fixed sample-size plans for monitoring Plutella xylostella (L.) (Lepidoptera: Plutellidae) on broccoli and other Brassica vegetable crops are popular in Australia for their simplicity and ease of ...application. But the sample sizes used are often small, ≈10–25 plants per crop, and it may be that they fail to provide sufficient information upon which to base pest control decisions. We tested the performance of seven fixed sample-size plans (10, 15, 20, 30, 35, 40, and 45 plants) by resampling a large data set on P. xylostella in commercial broccoli crops. For each sample size, enumerative and presence-absence plans were assessed. The precision of the plans was assessed in terms of the ratio of the standard error to the mean; and at least 45 and 35 samples were necessary for the enumerative and presence-absence plans, respectively, to attain the generally accepted benchmark of ≤0.3. Sample sizes of 10–20 were highly imprecise. We also assessed the consequences of classifications based on action thresholds (ATs) of 0.2 and 0.8 larvae per plant for the enumerative case, and 0.15 and 0.45 proportion of plants of infested for the presence-absence case. Operating characteristic curves and investigations of the frequency of correct decisions suggest improvements in the performance of plans with increased sample size. In both the enumerative and presence-absence cases, the proportion of incorrect decisions was much higher for the lower of the two ATs assessed, and type II errors (i.e., failure to suggest pest control upon the AT is exceeded) generally accounted for the majority of this error. Type II errors are the most significant from a producer’s standpoint. Further consideration is necessary to determine what is an acceptable type II error rate.
Hospital-acquired infections are on the rise and represent both, a clinical and financial burden. With resistance emerging and an ever-dwindling armamentarium at hand, infections caused by ...Acinetobacter baumannii are particularly problematic, since these bacteria have a high level of resistance and resilience to traditional and even last-resort antibiotics. The antibiotic rifabutin was recently found to show potent in vitro and in vivo activity against extensively drug resistant A. baumannii. Building on this discovery, we report on the synthesis and activity of rifabutin analogs, with a focus on N-functionalization of the piperidine ring. The antimicrobial testing uncovered structure activity relationships (SAR) for A. baumannii that were not reflected in Staphylococcus aureus. The cellular activity did not correlate with cell-free transcription inhibition, but with bacterial intracellular compound accumulation. Mass spectrometry-based accumulation studies confirmed the involvement of the siderophore receptor FhuE in active compound translocation at low concentrations, and they showed a strong impact of the culture medium on the accumulation of rifabutin. Overall, the study underlines the structural feature required for strong accumulation of rifabutin in A. baumannii and identifies analogs as or more potent than rifabutin against A. baumannii.
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•35 spiropiperidyl rifabutin analogs were synthesized and tested.•Structural features for active internalization by A. baumannii were identified.•The role of FhuE in the transport of rifabutine analogs was confirmed.
Coccinellid larvae are known to prey upon conspecific and heterospecific eggs, larvae, prepupae, and pupae. This behavior may depend on both the aggregation and intensive search of potential ...cannibals and predators near aphid colonies and the disappearance of aphids before coccinellid larvae have completed their development. We examined how coccinellid density and prey availability influence cannibalism and interspecific predation of larvae and pupae of 4 species of coccinellids. We determined whether coccinellid mortality and dispersal were density-dependent when prey become scarce, and estimated the leaving rates of Coleomegilla maculata (DeGeer), Adalia bipunctata (L.), and Hippodamia convergens (Guerin) larvae from plants with aphids and plants without aphids. Our results show that larval and pupal cannibalism and interspecific predation occur more frequently when aphid populations crash, but we found no evidence of coccinellid density-dependent mortality or density-dependent larval dispersal among species. However, A. bipunctata and H. convergens were significantly more aggressive and more likely to leave a plant without aphids than was C. maculata. These results suggest that the decision to stay on a plant is not strongly aphid- or pollen-mediated for C. maculata, but the decision to stay or leave does appear to be aphid-mediated for H. convergens and to some extent A. bipunctata. Whether a coccinellid larva stays or leaves and its tendency to cannibalize can affect larval and pupal survival and the population dynamics of each species.
There is increasing evidence that biological control of agricultural pests is affected by the landscape context, although the mechanisms behind this pattern have received little attention. Ecological ...theory predicts that one key mechanism mediating successful pest suppression is early predator immigration to agricultural fields. However, the importance of this population process under different landscape contexts remains unknown. Here, we elucidate the relative importance of landscape context and timing of predator immigration on aphid suppression by manipulating exposure to predation in agroecosystems located across a gradient of landscape complexity in a subtropical horticultural region in Australia. Aphid suppression varied with landscape context, from populations escaping control to almost complete pest suppression. In general, we found higher aphid suppression when predators were allowed immediate and continuous access to aphids than when predators were delayed or excluded for a week, but responses varied in each landscape. Contrary to previous reports from temperate agricultural landscapes, aphid suppression was neutral or negatively associated with natural and seminatural vegetation, whereas aphid suppression was positively associated with landscapes with a higher proportion of alfalfa. When landscapes were classified according to their levels of complexity, we showed that early predation resulted in similar levels of pest suppression in simplified landscapes (i.e., with low proportions of alfalfa and habitat diversity) as late predation in complex landscapes (i.e., with high proportions of alfalfa and habitat diversity). Our data show that timing of predator arrival to agricultural fields is as important as landscape complexity for mediating pest control in agroecosystems. Furthermore, our results suggest that key distributions of suitable habitats that facilitate natural enemy movement can enhance biological control in simplified landscapes.
Purpose
We investigated the cardiovascular individual response to 6 weeks (3×/week) of work-matched within the severe-intensity domain (high-intensity interval training, HIIT) or moderate-intensity ...domain (moderate-intensity continuous training, MICT). In addition, we analyzed the cardiovascular factors at baseline underlying the response variability.
Methods
42 healthy sedentary participants were randomly assigned to HIIT or MICT. We applied the region of practical equivalence-method for identifying the levels of responders to the maximal oxygen uptake (V̇O
2max
) response. For investigating the influence of cardiovascular markers, we trained a Bayesian machine learning model on cardiovascular markers.
Results
Despite that HIIT and MICT induced significant increases in V̇O
2max
, HIIT had greater improvements than MICT (
p
< 0.001). Greater variability was observed in MICT, with approximately 50% classified as “non-responder” and “undecided”. 20 “responders”, one “undecided” and no “non-responders” were observed in HIIT. The variability in the ∆V̇O
2max
was associated with initial cardiorespiratory fitness, arterial stiffness, and left-ventricular (LV) mass and LV end-diastolic diameter in HIIT; whereas, microvascular responsiveness and right-ventricular (RV) excursion velocity showed a significant association in MICT.
Conclusion
Our findings highlight the critical influence of exercise-intensity domains and biological variability on the individual V̇O
2max
response. The incidence of “non-responders” in MICT was one third of the group; whereas, no “non-responders” were observed in HIIT. The incidence of “responders” was 11 out of 21 participants in MICT, and 20 out of 21 participants in HIIT. The response in HIIT showed associations with baseline fitness, arterial stiffness, and LV-morphology; whereas, it was associated with RV systolic function in MICT.
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