A comparative study of cannibalism and predation in seven species of flour beetle

Abstract 1. The present study quantified egg and pupal cannibalism, and interspecific predation on eggs and pupae, by larvae and adults of seven species of flour beetle (Tribolium spp.) under laboratory conditions: T. anaphe, T. brevicornis, T. castaneum, T. confusum, T. destructor, T. freemani, and T. madens. 2. Variation among species in cannibalism and predation propensities did not reflect taxonomic affinities within the genus, indicating that these behaviours were shaped by ecology at species level. 3. Within species, larvae and adults displayed different propensities for cannibalism and predation, leading to the conclusion that these behaviours evolve independently in the two life stages. 4. All species behaved as intraguild predators to some degree, especially in the adult stage. 5. Three general patterns of cannibalism and predation were described by principal component mapping and cluster analysis. 6. The first group comprised three cosmopolitan pest species that were more voracious as adults than as larvae: T. castaneum, T. confusum, and T. destructor. It is proposed that stored product environments select for high adult voracity because the costs associated with emigration from such rare, but resource‐rich, habitats intensifies interference competition among adults. 7. The second group consisted of species that inhabit natural environments and that were more voracious as larvae: T. anaphe, T. freemani, and T. madens. Habitats for these species are probably numerous, but generally poor in quality, a situation that intensifies larval competition, while favouring earlier adult emigration. 8. The largest species, T. brevicornis, demonstrated inconsistent voracity between life stages and was the only species with chemically defended pupae. 9. It is proposed that consumption of eggs provides primarily nutritional benefits, whereas consumption of pupae has a more important role in interference competition.     

Is the spatial pattern of a tree population in a seasonally dry tropical climate explained by density‐dependent mortality?

Spatial pattern of tropical plants is initially generated by limited seed dispersal, but the role of density‐dependent and independent mechanisms as modifiers of these patterns across ontogeny is poorly understood. We investigated whether density‐dependent mortality (DDM) and environmental heterogeneity can drive spatial pattern across the ontogeny of a tree in a seasonally dry tropical climate. We used Moran's I correlograms and spatial analysis by distance indices (SADIE) to assess the spatial patterns of the pre‐ and post‐germinative stages of Cordia oncocalyx (Boraginaceae), an abundant tree endemic in the deciduous thorny woodland in the northeastern Brazilian semiarid region. We also used RDA to analyse the effect of DDM and environmental heterogeneity (measured by microtopography and canopy openness) in the mortality and recruitment. Seeds, seedlings, juveniles and adults showed aggregated spatial patterns; infants and immatures were randomly distributed; adults, seeds and seedlings attracted each other while adult, juveniles and immatures repulsed each other. Infant and seedling mortality rates were related to DDM and the recruitment from infant to juvenile was more influenced by spatial heterogeneity. Attraction was determined by local dispersal; repulsion was related to DDM and environment heterogeneity, which allowed the return to aggregation in adult stage. Together, these results indicated that spatial pattern can change across ontogeny, in which the initial stages are responsive to DDM and the final stages are influenced by spatial heterogeneity.     

Bacteria abundance and diversity of different life stages of Plutella xylostella (Lepidoptera: Plutellidae), revealed by bacteria culture‐dependent and PCR‐DGGE methods

Microbial abundance and diversity of different life stages (fourth instar larvae, pupae and adults) of the diamondback moth, Plutella xylostella L., collected from field and reared in laboratory, were investigated using bacteria culture‐dependent method and PCR‐DGGE analysis based on the sequence of bacteria 16S rRNA V3 region gene. A large quantity of bacteria was found in all life stages of P. xylostella. Field population had higher quantity of bacteria than laboratory population, and larval gut had higher quantity than pupae and adults. Culturable bacteria differed in different life stages of P. xylostella. Twenty‐five different bacterial strains were identified in total, among them 20 strains were presented in larval gut, only 8 strains in pupae and 14 strains in adults were detected. Firmicutes bacteria, Bacillus sp., were the most dominant species in every life stage. 15 distinct bands were obtained from DGGE electrophoresis gel. The sequences blasted in GenBank database showed these bacteria belonged to six different genera. Phylogenetic analysis showed the sequences of the bacteria belonged to the Actinobacteri, Proteobacteria and Firmicutes. Serratia sp. in Proteobacteria was the most abundant species in larval gut. In pupae, unculturable bacteria were the most dominant species, and unculturable bacteria and Serratia sp. were the most dominant species in adults. Our study suggested that a combination of molecular and traditional culturing methods can be effectively used to analyze and to determine the diversity of gut microflora. These known bacteria may play important roles in development of P. xylostella.     

不同林分白蜡树云斑白条天牛种群空间格局地统计学分析

云斑白条天牛是我国重要林业害虫,在黄河三角洲地区对白蜡树造成严重危害。利用地统计学方法,通过调查城市行道绿化林、庭院绿化林、公路林和片林4种不同林分类型的白蜡树林地,以产卵刻槽、排粪孔和羽化孔为调查指标,对危害白蜡云斑白条天牛种群卵、幼虫、成虫(蛹)的空间格局进行了研究。结果表明:除片林样点成虫(蛹)的半变异函数模型为指数模型外,危害白蜡云斑白条天牛种群卵、幼虫、成虫(蛹)在不同林分类型下的半变异函数模型均为球形模型,其指明空间分布均为聚集分布,种群的聚集分布习性与林分类型相关性不强。但不同林分类型云斑白条天牛种群的空间相关性地统计学参数存在差异,片林调查样点的卵、幼虫和成虫(蛹)的变程a、块金值C0和基台值C0+C均小于其他3种林分类型的统计值,片林样点成虫(蛹)的半变异函数模型不同于其他林分类型为指数模型。     

Conditions for noise reduction and stable encoding of spatial structure by cortical neural networks

Cortical circuits have been proposed to encode information by forming stable spatially structured attractors. Experimentally in the primary somatosensory cortex of the monkey, temporally invariant stimuli lead to spatially structured activity patterns. The purpose of this work is to study a recurrent cortical neural network model with lateral inhibition and examine what effect additive random noise has on the networks' ability to form stable spatially structured representations of the stimulus pattern. We show numerically that this network performs edge enhancement and forms statistically stationary, spatially structured responses when the lateral inhibition is of moderate strength. We then derive analytical conditions on the connectivity matrix that ensure stochasticly stable encoding of the stimulus spatial structure by the network. For stimuli whose strength falls in the near linear region of the sigmoid, we are able to give explicit conditions on the eigenvalues of the connection matrix. Finally, we prove that a network with a connection matrix, where the total excitation and inhibition impinging upon a neural unit are nearly balanced, will yield stable spatial attractor responses. Received: 16 October 1998 / Accepted in revised form: 25 November 1999     

Dynamics of diluted attractor neural networks with delays

We present an analysis of the attractors of a deterministic dynamics in formal neural networks characterized by binary threshold units and a nonsymmetric connectivity. It is shown that in these networks a stored pattern or a pattern sequence is represented by a cloud of attractors rather than by a single attractor. Dilution, which we describe by a power-law scaling, and delayed couplings are shown to equip this type of network with a dynamic behaviour that is interesting enough for simplified models of biological motor systems. Received: 27 November 1992/Accepted in revised form: 22 September 1993     

Assessing the spatial variability of density dependence in waterfowl populations

Population models commonly assume that the demographic parameters are spatially invariant, but there is considerable evidence that population growth rate (r) and the strength of density dependence (β) can vary over a species' range. To address this issue we developed a spatially explicit Gompertz population model based on the spatially varying coefficients approach to assess the spatial variation in population drivers. The model was fit to spatially stratified time series population estimates of the mallard Anas platyrhynchos in western North America. We included precipitation during the previous year and spring maximum temperature in the current year as environmental factors in the density dependent population model. Because density dependent models can give biased estimates for time series of abundance data, we fit a naïve model without informative priors and a model where we constrained the mean and variance of r to biologically realistic values that were derived via a comparative demography approach. In the naïve model, r and β were not separately identifiable and their values were overestimated, leading to unrealistic population growth. The naïve model also implied spatial variation in population r and the return time to equilibrium [1?(– β)] across the survey area. In contrast, in the informative model, r and the return time to equilibrium did not vary markedly among populations and were generally equal across populations. The effects of the climatic factors were similar across models. Population growth rates in the Prairie‐pothole region were positively correlated with precipitation, while in Alaska rates were positively correlated with spring temperature. Although it has been argued in the past that adding ecological realism could help avoid the pitfalls associated with density dependent models, our results demonstrate that imposing constraints on the population parameters is still the best course of action.     

The spatio-temporal distribution of adult Ceutorhynchus assimilis in a crop of winter oilseed rape in relation to the distribution of their larvae and that of the parasitoid Trichomalus perfectus

The spatio-temporal distribution of Ceutorhynchus assimilis Payk. (Coleoptera: Curculionidae) adults caught in a rectangular grid of flight traps in a crop of winter oilseed rape (Brassica napus L.) was mapped and was analysed using Spatial Analysis by Distance IndicEs (SADIE). Their distribution was compared to that of their larvae and that of their parasitoid Trichomalus perfectus (Walker) (Hymenoptera: Pteromalidae) in pods. The distribution of immigrating C. assimilis adults was consistent with their arrival at the crop boundaries and movement within the crop towards its centre. Adult C. assimilis were aggregated at all times, invasion being on two fronts, leading to the formation of two major clusters within the crop. Large areas of the crop remained relatively unpopulated. During the emigration phase, numbers declined simultaneously in all parts of the crop. The distributions of adult and larval C. assimilis and of larval T. perfectus were spatially associated. The distribution of the parasitoid did not show a density dependent relationship with that of its host. We discuss the movements of insects which underlie their population distributions, the value of integrating spatial information into improved management strategies for C. assimilis and the potential for the spatial targeting of insecticides to reduce the amount applied and to conserve T. perfectus.     

The spatial distribution of the wheat-bulb fly,Leptohylemyia coarctata (fall.) (Diptera: Anthomyiidae)

The spatial distribution of the eggs, larvae, pupae and adults of the wheat-bulb fly was investigated by fitting 42 sets of data comprising 1334 samples to the Poisson and negative binomial distributions, and by using the power law (S²=am^b). In general, the tests indicated that all stages were aggregated and fitted the negative binomial model.     

Aggregated seed dispersal by spider monkeys limits recruitment to clumped patterns in Virola calophylla

The initial spatial pattern of seed deposition influences plant population and community structure, particularly when that pattern persists through recruitment. In a vertebrate‐dispersed rain forest tree, Virola calophylla, we found that spatially aggregated seed deposition strongly influenced the spatial structure of later stages. Seed dispersion was clumped, and seed densities were highest underneath V. calophylla females and the sleeping sites of spider monkeys (Ateles paniscus), the key dispersal agent. Although these site types had the lowest per capita seed‐to‐seedling survival, they had the highest seedling/sapling densities. Conversely, seed and seedling/sapling densities were lowest, and seed survival was highest, at sites of diurnal seed dispersal by spider monkeys. Negative density‐dependent and positive distance‐dependent seed survival thinned seed clumps. Nonetheless, the clumped dispersion at sleeping and parental sites persisted to the seedling/sapling stage because differences in seed deposition were large enough to offset differences in seed survival among these site types.     

Effect of heat stress on survival and reproduction of the olive fruit fly Bactocera (Dacus) oleae

The olive fruit fly Bactrocera (Dacus) oleae Gmelin is a major olive pest in Greece and other Mediterranean countries. Its population density and respective olive infestation is usually low in many areas of northern Greece during summer months. To some extent, this may be due to the prevailing high temperature and low relative humidity conditions. In the present work the effects of short term exposure to high temperatures on the survival and egg production of B. oleae pre‐imaginal stages and adults were studied under laboratory conditions. Different larval instars within infested green olive fruits, adults and pupae and were exposed for 2 h to a series of different high constant temperatures ranging from 34 to 42°C. Subsequently, survival percentages of pre‐imaginal stages and adults as well as the number of eggs laid by females previously exposed to high temperatures were determined. At temperatures up to 38°C high survival percentages of larvae and adults were observed, whereas pupae displayed a relatively increased heat tolerance up to 40°C. Female longevity and egg production were substantially reduced after heat stress. Prior acclimation at 33°C for 1 and 3 days resulted in increased adult survival following heat stress. We discuss the results with respect to the ability of the fly to survive and reproduce under high summer temperatures.     

The distribution and density of a lycaenid butterfly in relation to Lasius ants

Summary Larvae and pupae of lycaenid butteflies are often associated with ants: this is usually a mutualism in which ants guard the lycaenids from natural enemies, and the lycaenid larvae and pupae provide sugars and amino acids for the ants. A possible consequence of the interaction is spatially correlated ant and lycaenid distributions, but the phenomenon is poorly documented. We examined the lycaenid Plebejus argus, which is tended by Lasius ants. Within habitat patches, P. argus eggs, larvae and pupae were all spatially associated with Lasius. On a larger scale, the densities of butterflies in different habitat patches and populations, and whether the butterfly was present or not, were correlated with Lasius ant densities. The association of P. argus with Lasius ants is consistent among populations, and occurs at several spatial scales. Other aspects of the ecology of P. argus are more variable.     

Overwintering stages of Callosobruchus chinensis (L.) in the field

Adzuki bean beetle, Callosobruchus chinensis, is a worldwide oligophagous and a field‐to‐storage pest of legumes including adzuki beans (Vigna angularis). Its over‐wintering stage is yet to be confirmed. A series of experiments was carried out at Jinju, in the southern part of the Republic of Korea, to elucidate the overwintering stages. Top‐ and sub‐soil samplings followed by pod and seed samplings from left over plants from adzuki bean fields in the winter of 2015, and an outdoor overwintering test (during Nov 2018 to Jun 2019) by exposing bean seeds harboring different stages (eggs, larvae, pupae, pharates and adults) of laboratory reared C. chinensis to the winter environment were carried out. None of the C. chinensis stages was detected from the top‐ and sub‐soil samples. When the pods and seeds from left over plants were sampled, only a few live pupae were obtained. In the outdoor test with laboratory reared C. chinensis, all the stages (larvae, pupae, and adults), except eggs, were detected on every other weekly samples of infested adzuki bean seeds throughout the winter. These results showed that the overwintering stages of C. chinensis in Jinju, southern Korea, are larvae, pupae, pharates and adults.     

Foraging time and spatial patterns of predation in experimental populations

Summary Responses of the predaceous mites Phytoseiulus persimilis, Typhlodromus (=Metaseiulus) occidentalis, and Amblyseius andersoni to spatial variation in egg density of the phytophagous mite, Tetranychus urticae, were studied in the laboratory.The oligophagous predator P. persimilis showed initially a direct density dependent foraging time allocation and variation in foraging time increased with prey density. With changes in prey density due to predation, predator foraging rates (per hour) decreased with time and density dependent foraging gradually became density independence, because P. persimilis continued to respond to initial prey density, instead of the changing prey density and distribution. The consequent spatial pattern of predation by P. persimilis was density independent, although slopes of predation rate-prey density regressions increased with time.Compared with P. persimilis, the narrowly polyphagous predator T. occidentalis responded relatively slowly to the the presence or absence of prey eggs but not to prey density: the mean and variation of foraging time spent in patches with prey did not differ with prey density, but was significantly greater in patches with prey eggs than in patches without eggs. Prey density and distribution changed only slightly due to predation and overall foraging rates remained more or less constant. The consequent spatial pattern of predation by T. occidentalis was inversely density dependent. As with P. persimilis, slopes of predation rate-prey density regressions increased with time (i.e. the inverse density dependence in T. occidentalis became weaker through time).The broadly polyphagous predator A. andersoni showed density independent foraging time allocation with variation independent of prey density. With changes in prey density over time due to prey depletion, overall foraging rates decreased. The consequent spatial pattern of predation by A. andersoni also changed through time; it initially was inversely density dependent, but soon became density independent.Overall, P. persimilis and T. occidentalis spent more time in prey patches than A. andersoni, suggesting that A. andersoni tended to spend more time moving outside patches. The overall predation rates and searching efficiency were higher in P. persimilis than in A. andersoni and T. occidentalis. Predator reproduction was highest in P. persimilis, lower in T. occidentalis and the lowest A. andersoni.The differences in response to prey distribution among the three predaceous species probably reflect the evolution of these species in environments with different patterns of prey distribution. The degree of polyphagy is a major determinant of the aggregative response, but other attributes such as handling time are also important in other aspects of phytoseiid foraging behavior (e.g. searching efficiency or predation rate).     

Spatially varying density dependence drives a shifting mosaic of survival in a recovering apex predator (Canis lupus)

Understanding landscape patterns in mortality risk is crucial for promoting recovery of threatened and endangered species. Humans affect mortality risk in large carnivores such as wolves (Canis lupus), but spatiotemporally varying density dependence can significantly influence the landscape of survival. This potentially occurs when density varies spatially and risk is unevenly distributed. We quantified spatiotemporal sources of variation in survival rates of gray wolves (C. lupus) during a 21‐year period of population recovery in the Upper Peninsula of Michigan, USA. We focused on mapping risk across time using Cox Proportional Hazards (CPH) models with time‐dependent covariates, thus exploring a shifting mosaic of survival. Extended CPH models and time‐dependent covariates revealed influences of seasonality, density dependence and experience, as well as individual‐level factors and landscape predictors of risk. We used results to predict the shifting landscape of risk at the beginning, middle, and end of the wolf recovery time series. Survival rates varied spatially and declined over time. Long‐term change was density‐dependent, with landscape predictors such as agricultural land cover and edge densities contributing negatively to survival. Survival also varied seasonally and depended on individual experience, sex, and resident versus transient status. The shifting landscape of survival suggested that increasing density contributed to greater potential for human conflict and wolf mortality risk. Long‐term spatial variation in key population vital rates is largely unquantified in many threatened, endangered, and recovering species. Variation in risk may indicate potential for source‐sink population dynamics, especially where individuals preemptively occupy suitable territories, which forces new individuals into riskier habitat types as density increases. We encourage managers to explore relationships between adult survival and localized changes in population density. Density‐dependent risk maps can identify increasing conflict areas or potential habitat sinks which may persist due to high recruitment in adjacent habitats.     

Environmental thermal levels affect the phenological relationships between the chestnut gall wasp and its parasitoids

Studies of thermal level‐related asynchrony in a host–parasitoid relationship are necessary to understand the effects of climate change on new host–parasitoid interactions. In the Asian chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae) and its Chalcidoidea parasitoids, phenological synchrony is assumed to be weather‐dependent in a new area of expansion. To evaluate the effects of environmental thermal regimes on the host, a phenology model for different cynipid stages (larvae, pupae, adults, and adult emergence) and a host–parasitoid phenological estimator are developed in three chestnut fields during two successive growth seasons and subsequently validated in areas with chestnut fields at two different altitudes. Comparisons of the timings of the juvenile and adult stages with those of the parasitoid complex demonstrate that the shortest period of occurrence for cynipids within galls has negative effects on the host–parasitoid relationships at higher temperature levels, thereby increasing phenological asynchrony for some parasitoids species. Reducing the development time of pupae and adults decreases the likelihood of success for some parasitoid species at higher temperature levels. We also record the extension of the gall wasp development time (approximately 15 days) at higher altitudes (linked to a lower mean temperature of approximately 1.5 °C). These results highlight how parasitization on the new hosts is dependent on the host phenology and, in the present study, is limited by the short duration of the presence of the host in galls, which could explain the considerable differences in cynipid gall wasp parasitization recorded at different altimeters.     

Stage‐dependent responses to emergent habitat heterogeneity: consequences for a predatory insect population in a coffee agroecosystem

Interactions among members of biological communities can create spatial patterns that effectively generate habitat heterogeneity for other members in the community, and this heterogeneity might be crucial for their persistence. For example, stage‐dependent vulnerability of a predatory lady beetle to aggression of the ant, Azteca instabilis, creates two habitat types that are utilized differently by the immature and adult life stages of the beetle. Due to a mutualistic association between A. instabilis and the hemipteran Coccus viridis – which is A. orbigera main prey in the area – only plants around ant nests have high C. viridis populations. Here, we report on a series of surveys at three different scales aimed at detecting how the presence and clustered distribution of ant nests affect the distribution of the different life stages of this predatory lady beetle in a coffee farm in Chiapas, Mexico. Both beetle adults and larvae were more abundant in areas with ant nests, but adults were restricted to the peripheries of highest ant activity and outside the reach of coffee bushes containing the highest densities of lady beetle larvae. The abundance of adult beetles located around trees with ants increased with the size of the ant nest clusters but the relationship is not significant for larvae. Thus, we suggest that A. orbigera undergoes an ontogenetic niche shift, not through shifting prey species, but through stage‐specific vulnerability differences against a competitor that renders areas of abundant prey populations inaccessible for adults but not for larvae. Together with evidence presented elsewhere, this study shows how an important predator is not only dependent on the existence of two qualitatively distinct habitat types, but also on the spatial distribution of these habitats. We suggest that this dependency arises due to the different responses that the predator's life stages have to this emergent spatial pattern.     

Pupal deposition and ecology of bat flies (Diptera: Streblidae): Trichobius sp. (caecus group) in a Mexican cave habitat

We studied the deposition of pupae of the winged bat fly Trichobius sp. (caecus group; Diptera), an ectoparasite of Natalus stramineus (Chiroptera, Natalidae), in a natural cave in Tamaulipas, Mexico. For the first time, we show a strong spatial segregation of populations of a streblid bat fly at different stages of development. Using molecular techniques we were able to match developmental stages to adults. Only 5 pupae were present in the main bat roosts. The overwhelming majority occurred exclusively in the bat flyway passages at a considerable distance from roosting bats. Pupal density corresponded positively with the average flight height of bats in the cave passage. Taken together, observations suggest that these ectoparasites must actively seek out their hosts by moving onto passing or roosting bats. The scarceness of pupae in the main roost may be dictated by environmental constraints for their development. The estimated population of viable pupae far exceeds the population of imagoes on the bats, and predation on adults by spiders is common.     

A neural mechanism of hierarchical discrimination of odors in the olfactory cortex based on spatiotemporal encoding of odor information

We propose a neural mechanism for discrimination of different complex odors in the olfactory cortex based on the dynamical encoding scheme. Both constituent molecules of the odor and their mixing ratios are encoded simultaneously into a spatiotemporal activity pattern (limit cycle attractor) in the olfactory bulb [Hoshino O, Kashimori Y, Kambara T (1998) Biol Cybern 79:109–120]. We present a functional model of the olfactory cortex consisting of some dynamical mapping modules. Each dynamical map is represented by itinerancy among the limit cycle attractors. When a temporal sequence of spatial activity patterns corresponding to a complex odor is injected from the bulb to the network of the olfactory cortex, the neural activity state of each mapping module is fixed to a relevant spatial pattern injected. Recognition of an odor is accomplished by a combination of firing patterns fixed in all the mapping modules. The stronger the response strength of the component, the earlier the component is recognized. The hierarchical discrimination of an odor is made by recognizing the components in order of decreasing response strengths. Received: 28 November 1998 / Accepted in revised form: 17 December 1999