カンキツ病害虫の共同防除地区における捕食性甲虫類

The relationship between predator density, community composition, and field predation of Colorado potato beetle eggs

Field plot tests during two seasons show that augmentative releases of Perillus bioculatus can control first-generation eggs and larvae of the Colorado potato beetle (CPB) under Quebec short-season conditions. Stinkbugs mass-reared on CPB were introduced manually as 2nd- and 3rd-stage nymphs during spring oviposition of the beetle at densities of one nymph per 50–225 CPB eggs recruited per plant, in 0.025-ha plots. Sampling at intervals of 1–3 days measured predator establishment, CPB egg and larval mortality, and foliage protection level. Direct observations were used to document predator-prey relationships and to determine weather conditions favourable to P. bioculatus.In the 1 st-year test, with predators released over all plants within plots, CPB control was compared among: (1) stinkbugs alone, (2) the bioinsecticide Bacillus thuringiensis (BT) as Trident™, (3) a combination of both control alternatives, and (4) no protection against the CPB. BT and stinkbugs, both alone and in combination, produced significant control as measured by percentage reductions in prepupal drop to the ground, new adult emergence, and foliage protection. Only treatments involving P. bioculatus reduced CPB egg eclosion which was the key control factor; it is strongly correlated with overall control level.In the 2nd-year test, predators were released in a central area comprising only 25% of all plants within plots. Predator and CPB egg mass densities were manipulated to produce predator: prey ratios of 0:1, 0:2, 1.5:2, 1.5:1, 3:2, and 3:1, representing average ratios of 0, 1.5,or 3 P. bioculatus per plant, and 1 or 2 CPB egg masses per plant at release time. As expected, central release produced complex interactions between control, and predator and prey densities. High beetle density slowed predator emigration from the centre, more so at low predator density than at high predator density. Predators moved more quickly within the same row than across rows. CPB eggs were destroyed in large numbers in both years but in 1993, final control correlated with larval rather than egg predation. A maximum 80% reduction in prepupal drop to the ground was obtained at the 3:1 predator:prey ratio (1 P. bioculatus:95 CPB eggs recruited per plant).The results prove the efficacy of P. bioculatus for biological control of first-generation L. decemlineata populations, at densities resulting in approximately 300 eggs laid per plant during spring oviposition in the study area. Despite low natural populations of P. bioculatus and unclear prospects for commercial availability at reasonable cost, it is evident that stinkbug releases have potential as a non-chemical control measure within an IPM program in Quebec potato production.

Augmentative release of predators is used in agriculture to suppress pest populations and minimise crop damage. However, predators affect prey populations not only through consumption but by inducing changes to prey morphology, physiology, behaviour and life history. These risk‐induced trait responses can increase prey fitness, potentially reducing the efficacy of certain predators as biocontrol agents. We investigated how non‐consumptive effects contribute to the overall influence of predators by modelling the effect of the predator Podisus maculiventris on the population dynamics of a major agricultural pest, the Colorado potato beetle ( Leptinotarsa decemlineata ). We developed a demographic model incorporating both consumption and non‐consumptive Podisus ‐induced shifts in beetle reproductive strategy. Our model combines data from multiple mechanistic experiments showing that predator‐exposed beetles produce fewer offspring but increase offspring provisioning, and that provisioned larvae have increased survival when predators are present. We simulated beetle densities across multiple beetle generations and a range of predator densities. The influence of non‐consumptive effects depended on predator density. At low predator densities, non‐consumptive effects strengthened the negative effect of predators by up to 45%, and risk‐induced changes to offspring provisioning had a stronger effect on prey densities than reduced offspring quantity. In contrast, at high predator densities, non‐consumptive effects changed the effect of predators by <5%, likely because beetle densities were very low both with and without non‐consumptive effects. Our results suggest that even adaptive responses to predation risk by prey do not necessarily reduce the ability of predators to suppress pest populations.

Pollinators and their predators share innate and learned preferences for high quality flowers. Consequently, pollinators are more likely to encounter predators when visiting the most rewarding flowers. I present a model of how different pollinator species can maximize lifetime resource gains depending on the density and distribution of predators, as well as their vulnerability to capture by predators. For pollinator species that are difficult for predators to capture, the optimal strategy is to visit the most rewarding flowers as long as predator density is low. At higher predator densities and for pollinators that are more vulnerable to predator capture, the lifetime resource gain from the most rewarding flowers declines and the optimal strategy depends on the predator distribution. In some cases, a wide range of floral rewards provides near-maximum lifetime resource gains, which may favor generalization if searching for flowers is costly. In other cases, a low flower reward level provides the maximum lifetime resource gain and so pollinators should specialize on less rewarding flowers. Thus, the model suggests that predators can have qualitatively different top-down effects on plant reproductive success depending on the pollinator species, the density of predators, and the distribution of predators across flower reward levels.

Soil nutrients can influence the population dynamics of arthropod pests and their natural enemies. Previous research has revealed that overfertilization increases the likelihood of pest outbreak in a subsequent soybean [Glycine max (L.) Merr.] crop following winter wheat (Triticum aestivum L.). Improving biological control from natural enemies is an important aspect of integrated pest management. Our objectives in this field study were to (i) determine the effect of soil nutrition on population densities of the predators Geocoris spp. (bigeyed bugs), Nabis and Hoplistoscelis spp. (damsel bugs), and spiders (Araneae) in a soybean canopy and (ii) relate densities of each predator to pest densities and determine if previously reported effects of overfertilization on pest densities were the indirect result of influences of soil nutrients on predator populations. Soil nutrient levels were four levels of P and three levels of K and Mg. The study was conducted in 1986 and 1987. High P favored population density of damsel bug nymphs in 1986 only, but populations were not significantly affected by K or Mg. High P significantly affected population densities of bigeyed bug nymphs each year. Density estimates of spiders were significantly increased by P only in 1986. Densities of spiders were not affected by K and Mg either year. Increased pest outbreaks from overfertilization of soybean were not the result of fertility effects on population densities of these major predators.

1. Predator and alternative food density are important factors influencing herbivore suppression by generalist predators. Herbivore suppression can be reduced if predators forage preferentially on alternative foods. Cannibalism can increase at high predator densities, further reducing herbivore suppression. However, complex interactions are possible, as alternative food can increase predator abundance and survival restoring top‐down effects on herbivores. 2. In two species of carabid larvae ( Poecilus chalcites and Anisodactylus ovularis ), we studied how alternative foods (fly pupae and grass seeds) and predator density affect predation of black cutworm larvae and how alternative foods affect cannibalism among carabid larvae. 3. Adding alternative food to microcosms generally reduced total predation of cutworms. However, the strength of this effect was dependent on carabid species, larval density, and food type. 4. Increasing larval density from one to three per microcosm reduced per‐capita predation by both species irrespective of alternative food treatment. 5. Alternative food reduced cannibalism in both carabid species and increased survival of carabid larvae in field plots, such that twice as many were captured in plots subsidised with pupae than plots with no alternative food. 6. These results provide new insight into the complex interactions that influence predator survival and herbivore suppression in resource diverse habitats by demonstrating the primacy of intraguild interactions among carabid larvae.

Wildlife population dynamics are modulated by abiotic and biotic factors, typically climate, resource availability, density‐dependent effects, and predator–prey interactions. Understanding whether and how human‐caused disturbances shape these ecological processes is helpful for the conservation and management of wildlife and their habitats within increasingly human‐dominated landscapes. However, many jurisdictions lack either long‐term longitudinal data on wildlife populations or measures of the interplay between human‐mediated disturbance, climate, and predator density. Here, we use a 50‐year time series (1962–2012) on mule deer (Odocoileus hemionus) demographics, seasonal weather, predator density, and oil and gas development patterns from the North Dakota Badlands, USA, to investigate long‐term effects of landscape‐level disturbance on mule deer fawn fall recruitment, which has declined precipitously over the last number of decades. Mule deer fawn fall recruitment in this study represents the number of fawns per female (fawn:female ratio) that survive through the summer to October. We used this fawn recruitment index to evaluate the composite effects of interannual extreme weather conditions, energy development, and predator density. We found that density‐dependent effects and harsh seasonal weather were the main drivers of fawn fall recruitment in the North Dakota Badlands. These effects were further shaped by the interaction between harsh seasonal weather and predator density (i.e., lower fawn fall recruitment when harsh weather was combined with higher predator density). Additionally, we found that fawn fall recruitment was modulated by interactions between seasonal weather and energy development (i.e., lower fawn fall recruitment when harsh weather was combined with higher density of active oil and gas wells). Interestingly, we found that the combined effect of predator density and energy development was not interactive but rather additive. Our analysis demonstrates how energy development may modulate fluctuations in mule deer fawn fall recruitment concurrent with biotic (density‐dependency, habitat, predation, woody vegetation encroachment) and abiotic (harsh seasonal weather) drivers. Density‐dependent patterns emerge, presumably due to limited quality habitat, being the primary factor influencing fall fawn recruitment in mule deer. Secondarily, stochastic weather events periodically cause dramatic declines in recruitment. And finally, the additive effects of human disturbance and predation can induce fluctuations in fawn fall recruitment. Here we make the case for using long‐term datasets for setting long‐term wildlife management goals that decision makers and the public can understand and support.

Aequidens paraguayensis is a cichlid fish with biparental care that spawns on a leaf taken from substrate litter and, after the eggs have hatched, broods the progeny orally. We tested the hypothesis that increasing predator density causes proportional changes in the frequency or duration of parental care activities, including moving the spawn. We predicted that at high predator densities, the parents would pick up the eggs and begin mouthbrooding earlier than usual to prevent egg loss.Increasing predator density led to greater parental sex-role differentiation, the males defending the spawning site while the females tended the eggs. Leaf tugging was performed by the females only and did not increase significantly with predator density. Pairs that spawned on a fixed substrate did not exhibit this sex-role differentiation.Predator density and type of spawning substrate did not affect brood survival or time between spawning and beginning of mouthbrooding. Hatching time is temperature dependent and parents apparently must wait for the egg membranes to break before picking up the hatchlings.

Citrus red mite ( Panonychus citri) is a common sensitizing allergen among children living around citrus orchards

The citrus red mite Panonychus citri (McGregor) is a major pest that can reduce the quality and yield of citrus crops. However, information regarding the local and landscape factors that influence its population dynamics remains limited. This study aimed to analyse the influence of local and landscape factors on citrus red mite population density. The research was conducted in nine citrus orchards in Malang, East Java, Indonesia. Data collected included local factors (pesticide application frequency and plant canopy density) and landscape factors (landscape composition, encompassing the number of patches (NP) and class area (CA) of semi-natural habitats). Pesticide application frequency data were obtained through farmer interviews, while canopy density was measured using a photographic method and analysed with ImageJ2 software. Landscape composition data were by digitizing land-use types within a 500-meter radius of the plot center using QGIS software and subsequently analysed using LecoS (QGIS add-ins) to obtain the NP and CA of semi-natural habitats. The generalized linear model (GLM) analysis indicated no overall significant influence of both local and landscape factors on P. citri population density. However, it was found that the variation in mite population density was significantly influenced by citrus plant canopy density. These findings suggest that local factors, particularly the canopy microhabitat conditions, are more critical in affecting the P. citri population compared to landscape factors. Therefore, the management strategy for citrus red mite should be focused on the local, on-farm scale.

Cannibalistic interactions in two co-occurring decapod species: Effects of density, food, alternative prey and habitat

The influence of biotic and abiotic factors on species interactions and overall community structure has long interested ecologists. Despite a legacy of interest, there is still ambiguity into the role of biotic and abiotic factors due to highly nuanced, complex networks of interactions that are difficult to comprehend. Yet, understanding how such nuances is an essential goal to determine how they affect population and community structure. Thus, the goal of my dissertation was to understand how multiple biotic and abiotic mechanisms alter interactions among larval stages of two pond-breeding salamanders. Larval stages of pond-breeding salamanders represent an excellent system for understanding how species interactions vary along abiotic and biotic gradients. Intra-and interspecific interactions are frequently determined by size differences among individuals, where larger larvae are predators of smaller larvae and can out-compete them for shared resources. However, when size differences are minimized, only competition occurs. Such conjoined competition and predation is termed intraguild predation, and is a common interaction in many taxa. The factors that determine size differences among individuals (both within and between species) are critical towards to determining both the type of interaction, as well as the strength of such interactions. The focal species I used were the ringed salamander (Ambystoma annulatum) and spotted salamander (A. maculatum). The former breeds earlier than the latter, creating a larval size advantage which results in predation as the dominant interaction between species. However, factors that influence growth rates of ringed salamanders could result in minimized size differences, resulting in a change to the strength or type of interaction that occurs. For my dissertation, I experimentally investigated three different processes that were expected to affect the relative importance of predation and competition: density dependence, food web structure, and phenological shifts. In my first chapter, I tested whether the density of ringed salamanders influenced their growth rates to such a degree that the interaction type with spotted salamanders would switch from predation to competition. I found that increased intraspecific competition in ringed salamanders reduced their body size and increased their larval period length. However, intraspecific competition did not reduce their size to such a degree that predation on spotted salamanders was precluded. Spotted salamanders showed decreased survival and increased size at higher predator densities, indicative of thinning effects. The period of overlap in ponds also increased at higher predator densities, resulting in a larger temporal window for interactions to occur. In my second chapter, I tested how six different top predator food webs would influence intraguild predation between ringed and spotted salamanders. I also tested whether food web configuration would be simultaneously impacted by increased habitat complexity. I found that ringed salamander body size and survival were unaffected by habitat complexity, and that only certain combinations of predators affected these demographic rates. Spotted salamander body size and survival showed positive and negative relationships with ringed salamander survival, but the strength of these relationships varied depending on the predator and habitat complexity treatment. Thus, pairwise interactions may not exemplify typical interactions when embedded in more complex food webs with other predators. For my third chapter, I investigated whether phenological shifts in both the ringed and spotted salamanders, simultaneous to density dependence in the ringed salamander would influence the type and strength of their interactions. I found ringed salamander survival varied with phenological shifts but only when at high intraspecific densities. Spotted salamanders were relatively unaffected by phenological shifts, and that their interactions were, similar to the previous chapters, influenced primarily by survival of ringed salamanders. As phenological shifts are predicted for many species with climate change, this study highlights that not all species interactions will be subsequently affected, and that other underlying factors (e.g. density dependence) may be more important. Thus, the most important findings of my dissertation include 1) predator density can be a dominant factor in species interactions, 2) pairwise interactions may change when embedded in different habitats or food webs in non-intuitive ways, and 3) simultaneously testing multiple mechanisms can elicit a greater understanding of the relative importance of different ecological processes.

This thesis examines the population trends and habitat requirements of the endangered northern bettong (Bettongia tropica) (Wakefield 1967) within wet to moist Eucalyptus woodland in their core population on the Lamb Range in north-eastern Queensland, Australia. This research has implications for managing habitat used by B. tropica and increasing their long-term population viability. Management recommendations to improve the conservation of B. tropica are presented. Effective management strategies depend upon identifying and mitigating against the key threats to population stability. However, the ability to devise suitable management strategies is often impeded by a lack of data. This is frequently the case for endangered species, including B. tropica. In Chapter two I overcome this problem by using simulation models to make projections of the future impacts on B. tropica under various scenarios. The population viability and survival probability of B. tropica populations on the Lamb Range was modelled in response to 1) increased predation; 2) changes in drought and fire frequency predicted with anthropogenic climate change; and 3) synergistic effects of predation, fire, and drought. Population viability analysis (PVA) models suggest that populations were resilient to substantial declines (up to 75%) and recovered to carrying capacity within 10 years when no threats impacted upon the population. However, modelling showed that a ≥40% increase in predation by cats, Felis catus, resulted in the population declining to extinction within 20 years. In contrast, populations were resilient to increases in droughts and fires. However, the impacts of predation could be more severe if predation and fire were to interact to increase the mortality of B. tropica. Interestingly, juvenile mortality was the main age class driving population viability, although mortality would need to double from the current rate before extinction was assured. To assist in maximising the long-term viability of B. tropica populations, it is recommended that the density of predators (especially cats and foxes) and B. tropica populations be regularly and consistently monitored. Predator control measures should be undertaken if high densities of predators are detected. Bettongia tropica is a keystone species within Eucalyptus woodlands on the Lamb Range. The longterm viability of B. tropica is important for maintaining ecosystem function within these woodlands. The population density of B. tropica was previously assessed between 1994 and 1996 within the three main sub-populations (Davies Creek, Emu Creek and Tinaroo Creek) of the core population on the Lamb Range. During that previous study, the majority of sampling occurred at one sub-population, Davies Creek. No consistent monitoring of B. tropica's core population had been undertaken since 1996, although inconsistent monitoring between 2000 and 2009 at Davies Creek suggested a possible decline. In Chapter three, I re-assessed the population density, fitness (survival rates, body condition and…

Since its introduction fewer than 20 yr ago, the spread of the Asian shore crab Hemigrapsus sanguineus along the east coast of the US has been remarkable. By many accounts it is now the numerically dominant brachyuran in rocky intertidal sites in Long Island Sound. Evidence from several laboratory studies has suggested that H. sanguineus could have significant consequences for barnacle abundance and distribution. In this study we used field caging experiments to determine the effect of this invader on recruitment (sampled at weekly intervals) of the indigenous barnacle Semibalanus balanoides. We found that although H. sanguineus readily consumed settling cypris larvae and early post-settlement juveniles, crab predation did not have a negative impact on barnacle recruitment when predator density was low (15 crabs 0.25 m–2). We also found a measurable decrease in barnacle density at medium (45 crabs 0.25 m–2) and high (90 crabs 0.25 m–2) predator densities after the larval settlement period had ended, but this effect was short-lived. Based on available estimates of Asian shore crab abundance in Long Island Sound, we conclude that crab predation will not have a significant impact on the recruitment success of S. balanoides populations.

Does the “Enemies Hypothesis” operate by enhancing natural enemy evenness?