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Interactions between the Fungal Entomopathogen Zoophthora radicans Brefeld (Entomophthorales) and Two Hymenopteran Parasitoids Attacking the Diamondback Moth, Plutella xylostella L.

Treatment of the hymenopteran parasitoids Diadegma semiclausum and Cotesia plutellae with a strain of the entomopathogenic fungus Zoophthora radicans, which was initially isolated from Plutella xylostella, showed that D. semiclausum was susceptible to the pathogen but that C. plutellae was not. In leaf shower bioassays, the susceptibility of D. semiclausum adults to Z. radicans was 70- and 133-fold less than the susceptibility of P. xylostella larvae and adults, respectively. When adult D. semiclausum were held in petri dishes with P. xylostella cadavers producing Z. radicans conidia the subsequent level of fungal infection in the parasitoids (20.3% became infected) was independent of the number of cadavers to which they were exposed. Female parasitoids were not shown to vector conidia of Z. radicans directly from sporulating cadavers to the susceptible P. xylostella larvae upon which they foraged. However, the presence of a foraging D. semiclausum female enhanced the level of Z. radicans infection in P. xylostella larvae feeding in proximity to a source of Z. radicans inoculum. Video analysis of the movement of P. xylostella larvae in the presence and absence of the parasitoids indicated that the increased levels of fungal infection in the presence of foraging D. semiclausum could be accounted for by the greater movement of larvae (in terms of both the total distance moved and the number of new "infective units" visited) when disturbed by this parasitoid. Although C. plutellae foraging also increased larval movement when compared with larvae not foraged upon, the increase was not sufficient to exceed a presumed threshold level required to enhance the fungal infection level of the larvae. The results are discussed in terms of the likely interactions between Z. radicans and field populations of D. semiclausum.

Journal Article↗

Mineral status of grazing beef cattle in the warm climate region of Florida.

An experiment was conducted to determine the mineral status of purebred Brahman beef cattle grazing Bermuda--Bahia pastures grown on sandy, well-drained soils in Central Florida. Soil, plant, blood serum and liver tissue concentrations of calcium, potassium, sodium, magnesium, manganese and cobalt were generally adequate. Sixty-nine per cent of forages and 40% of serum samples were deficient in phosphorus. Seventy-five per cent of soils, 38% of forages and 18% of liver samples were deficient in copper. Sixty-nine per cent of forage samples were low, less than 30 ppm, in iron. All samples of forage, liver and serum were deficient in selenium. Likewise, all soil and forage samples and 47 and 88% of serum and liver samples, respectively, were deficient in zinc. Mineral elements most likely deficient and needed in supplements for grazing cattle on sandy, well-drained soils in the warm climate region of Central Florida are phosphorus, copper, selenium and zinc.

Animals↗

Protein supplementation of grazing cattle in the semi-arid zone of Cameroon.

The effects of cottonseed meal (CSM) supplementation on forage dry matter intake (FDMI), forage dry matter digestibility (FDMD) and average daily gain (ADG) of steers on pasture in the semi-arid zone of northern Cameroon were evaluated during 120 d in the dry season and the residual effects during 120 d in the rainy season. Thirty steers (229 kg and 2.6 years) were randomly assigned to a complete block design of 3 treatments (0, 0.5 and 1.0 kg of CSM as a protein supplement per steer per day). After feeding CSM to individual steers in the mornings, all were allowed to free graze a pasture of Andropogon spp. Every month, 2 steers per treatment were put into digestion crates and ad lib fed hand-clipped forage of similar botanical composition as that grazed by the remaining steers. Cottonseed meal supplementation increased crude protein absorbed (CPA), rumen turn over rate (RTO) and ADG. Forage intake was increased only with 0.5 kg CSM. Forage dry matter and cell wall (NDF and ADF) digestibility tended to be decreased with 1.0 kg of CSM compared with 0.5 kg or no supplement. Cottonseed meal supplementation during the dry season increased FDMI and RTO, but had no effect on cell wall digestibility, FDMD, CPA and ADG during the rainy season. Data from this study suggest that 0.5 kg of CSM can increase FDMI, RTO, and ADG of cattle during the dry season and that improvement can be maintained throughout the subsequent rainy season.

Animal Feed↗

Heat-balling wasps by honeybees.

Defensiveness of honeybee colonies of Apis cerana and Apis mellifera (actively balling the wasps but reduction of foraging) against predatory wasps, Vespa velutina, and false wasps was assessed. There were significantly more worker bees in balls of the former than latter. Core temperatures in a ball around a live wasp of A. cerana were significantly higher than those of A. mellifera, and also significantly more when exposed to false wasps. Core temperatures of bee balls exposed to false wasps were significantly lower than those exposed to V. velutina for both A. cerana and for A. mellifera. The lethal thermal limits for V. velutina, A. cerana and A. mellifera were significantly different, so that both species of honeybees have a thermal safety factor in heat-killing such wasp predators. During wasps attacks at the hives measured at 3, 6 and 12 min, the numbers of Apis cerana cerana and Apis cerana indica bees continuing to forage were significantly reduced with increased wasp attack time. Tropical lowland A. c. indica reduced foraging rates significantly more than the highland A. c. cerana bees; but, there was no significant effect on foraging by A. mellifera. The latency to recovery of honeybee foraging was significantly greater the longer the duration of wasp attacks. The results show remarkable thermal fine-tuning in a co-evolving predator-prey relationship.

Animals↗

The ant's estimation of distance travelled: experiments with desert ants, Cataglyphis fortis.

Foraging desert ants, Cataglyphis fortis, monitor their position relative to the nest by path integration. They continually update the direction and distance to the nest by employing a celestial compass and an odometer. In the present account we addressed the question of how the precision of the ant's estimate of its homing distance depends on the distance travelled. We trained ants to forage at different distances in linear channels comprising a nest entrance and a feeder. For testing we caught ants at the feeder and released them in a parallel channel. The results show that ants tend to underestimate their distances travelled. This underestimation is the more pronounced, the larger the foraging distance gets. The quantitative relationship between training distance and the ant's estimate of this distance can be described by a logarithmic and an exponential model. The ant's odometric undershooting could be adaptive during natural foraging trips insofar as it leads the homing ant to concentrate the major part of its nest-search behaviour on the base of its individual foraging sector, i.e. on its familiar landmark corridor.

Animal Migration↗

Mechanisms promoting higher growth rate in arctic than in temperate shorebirds.

We compared prefledging growth, energy expenditure, and time budgets in the arctic-breeding red knot (Calidris canutus) to those in temperate shorebirds, to investigate how arctic chicks achieve a high growth rate despite energetic difficulties associated with precocial development in a cold climate. Growth rate of knot chicks was very high compared to other, mainly temperate, shorebirds of their size, but strongly correlated with weather-induced and seasonal variation in availability of invertebrate prey. Red knot chicks sought less parental brooding and foraged more at the same mass and temperature than chicks of three temperate shorebird species studied in The Netherlands. Fast growth and high muscular activity in the cold tundra environment led to high energy expenditure, as measured using doubly labelled water: total metabolised energy over the 18-day prefledging period was 89% above an allometric prediction, and among the highest values reported for birds. A comparative simulation model based on our observations and data for temperate shorebird chicks showed that several factors combine to enable red knots to meet these high energy requirements: (1) the greater cold-hardiness of red knot chicks increases time available for foraging; (2) their fast growth further shortens the period in which chicks depend on brooding; and (3) the 24-h daylight increases potential foraging time, though knots apparently did not make full use of this. These mechanisms buffer the loss of foraging time due to increased need for brooding at arctic temperatures, but not enough to satisfy the high energy requirements without invoking (4) a higher foraging intake rate as an explanation. Since surface-active arthropods were not more abundant in our arctic study site than in a temperate grassland, this may be due to easier detection or capture of prey in the tundra. The model also suggested that the cold-hardiness of red knot chicks is critical in allowing them sufficient feeding time during the first week of life. Chicks hatched just after the peak of prey abundance in mid-July, but their food requirements were maximal at older ages, when arthropods were already declining. Snow cover early in the season prevented a better temporal match between chick energy requirements and food availability, and this may enforce selection for rapid growth.

Adaptation, Physiological↗

Estimating the latitudinal origins of migratory birds using hydrogen and sulfur stable isotopes in feathers: influence of marine prey base.

Hydrogen stable isotope analysis of feathers is an important tool for estimating the natal or breeding latitudes of nearctic-neotropical migratory birds. This method is based on the latitudinal variation of hydrogen stable isotope ratios in precipitation in North America (deltaD(p)) and the inheritance of this variation in newly formed feathers (deltaD(f)). We hypothesized that the typically strong relationship between deltaD(p) and deltaD(f) would be decoupled in birds that forage in marine food webs because marine waters have relatively high deltaD values compared to deltaD values for local precipitation. Birds that forage on marine prey bases should also have feathers with high delta(34)S values, since delta(34)S values for marine sulfate are generally higher than delta(34)S values in terrestrial systems. To examine this potential marine effect on feather stable isotope ratios, we measured deltaD and delta(34)S in the feathers of nine different species of raptors from both inland and coastal locations across North America. Feathers from coastal bird-eating raptors had consistently higher deltaD and delta(34)S values than feathers from inland birds. Birds that had high delta(34)S values also deviated strongly from the typical relationship between deltaD(p) and deltaD(f). We recommend measuring both sulfur and hydrogen stable isotope ratios in feathers when some members of a migrant population could potentially forage in marine habitats. We suggest using a practical cutoff of delta(34)S >10 per thousand to remove marine-foraging birds from a migrant sample when using stable isotopes of hydrogen to estimate the latitudinal origins of migrants because high deltaD(f) values for marine-foraging birds could potentially distort estimates of origins.

Animals↗

The role of predation in the decline and extirpation of woodland caribou.

To select appropriate recovery strategies for endangered populations, we must understand the dynamics of small populations and distinguish between the possible causes that drive such populations to low numbers. It has been suggested that the pattern of population decline may be inversely density-dependent with population growth rates decreasing as populations become very small; however, empirical evidence of such accelerated declines at low densities is rare. Here we analyzed the pattern of decline of a threatened population of woodland caribou (Rangifer tarandus caribou) in British Columbia, Canada. Using information on the instantaneous rate of increase relative to caribou density in suitable winter foraging habitat, as well as on pregnancy rates and on causes and temporal distribution of mortalities from a sample of 349 radiocollared animals from 15 subpopulations, we tested 3 hypothesized causes of decline: (a) food regulation caused by loss of suitable winter foraging habitat, (b) predation-sensitive foraging caused by loss of suitable winter foraging habitat and (c) predation with caribou being secondary prey. Population sizes of caribou subpopulations ranged from < 5 to > 500 individuals. Our results showed that the rates of increase of these subpopulations varied from -0.1871 to 0.0496 with smaller subpopulations declining faster than larger subpopulations. Rates of increase were positively related to the density of caribou in suitable winter foraging habitat. Pregnancy rates averaged 92.4% +/-2.24 and did not differ among subpopulations. In addition, we found predation to be the primary cause of mortality in 11 of 13 subpopulations with known causes of mortality and predation predominantly occurred during summer. These results are consistent with predictions that caribou subpopulations are declining as a consequence of increased predation. Recovery of these woodland caribou will thus require a multispecies perspective and an appreciation for the influence of inverse density dependence on population trajectories.

Animals↗

Theory of oviposition strategy of parasitoids. I. Effect of mortality and limited egg number.

The optimal oviposition strategies of parasitoids, the host range, and the number of eggs laid per host which result in the maximum lifetime performance of reproduction, are investigated. To study the effects of parasitoid mortality and of limiting total number of eggs laid by a parasitoid, a standard criterion used in previous theories of optimal diet and optimal patch use, the maximization of the foraging rate, is no longer suitable. The model is solved analytically by using dynamic programming. The results are as follows: The host preference of solitary parasitoids depends on the mortality during handling times; i.e., the forager tends to avoid hosts with high risk of foraging mortality. If the total number of eggs produced by a parasitoid is limited, and if the mortality during handling is negligible, the host range is wider when a larger number of eggs remains in the parasitoid's body. In general, however, the mortality-cost of forager and the egg-cost interplay, because the loss of future reproduction by mortality increases with the number of available eggs. In an example with two host types, host range is widest with an intermediate number of eggs available in the body. The optimal number of eggs per host laid by a gregarious parasitoid is also affected by the differential mortality of the forager, and by the number of available eggs.

Diet↗

Pelagic food-web structure influences probability of mercury contamination in lake trout (Salvelinus namaycush).

An empirical model predicting probability of encountering levels of mercury in excess of 0.5 p.p.m. in lake trout (Salvelinus namaycush) is developed using logistic regression and two published data sets on food-web structures and elevated levels of mercury in sport fish. Probability of mercury contamination is a function of lake trout length and presence of pelagic forage fish. Presence of forage fish in a lake increased the odds that a lake trout of a given size would contain elevated levels of mercury in excess of eight times the expected level in lakes without pelagic forage fish. The model predicted a less than 5% probability of encountering elevated mercury levels in lake trout less than 30 cm in length from lakes with pelagic forage fish. In lakes where pelagic forage fish were absent, there was a less than 5% probability that lake trout under 45 cm would contain levels of mercury above 0.5 p.p.m.

Animals↗

Effects of rooting medium and fertilizer rate on response of white clover to tropospheric ozone.

Two white clover (Trifolium repens L.) clones with varying sensitivity to O(3) are being developed as a system to indicate effects of ambient concentrations of tropospheric O(3) on plants. One clone (NC-S) is highly sensitive to O(3) and the other (NC-R) is highly resistant. The system relies on periodic measurement of foliar injury, foliar chlorophyll, and forage production of NC-S and NC-R grown in 15-liter pots throughout a summer season. Relative amounts of foliar injury and ratios (NC-S/NC-R) for chlorophyll and forage weight can be used to estimate biologically effective ambient O(3) concentrations. The effect of variation in rooting media formulation and fertilizer rate on response of NC-S and NC-R to ambient O(3) was determined in the present study. In the rooting medium experiment, clover was grown in three mixtures of sandy loam topsoil:course washed sand:Metro Mix 220 (ratios (by volume) of 2:1:1, 2:1:5, and 6:1:1). In the fertilizer experiment, clover was grown in the 2:1:1 medium at four fertilizer rates (soluble 5-11-26 (N-P-K) at 0.0, 0.5, 1.0, or 2.0 g per pot). Ozone caused more foliar injury, more chlorosis, and a greater decrease in forage production of NC-S than of NC-R in all studies. Rooting media treatments affected both clones similarly and occasional clone x media interactions were judged to be random. Forage production by NC-S, relative to that of NC-R, was generally greater in the 0.0 fertilizer treatment, but the forage ratios were similar at all other fertilizer treatments. The relative response of NC-S and NC-R to O(3) is fairly stable under cultural conditions that support normal plant growth.

Journal Article↗

Influence of seed size and seed nature on recruitment in the polymorphic harvester ant Messor barbarus.

In the polymorphic harvester ant Messor barbarus, the colony modulates response during foraging according to seed characteristics. The easiness of picking up small seeds (oat fragments or canary seeds) shortens the time lapse between food discovery and the return of scouts to the nest, favouring the onset of recruitment and higher mobilisation rates than bigger seeds (whole oat). However, size is not the only criterion, as canary seeds are preferred among small ones. A modulation of the trail laid by the first scouts also plays a role in the shaping of harvesting patterns and in the enhancement of recruitment towards small and/or preferred seed. This flexibility extends to the relative participation of the three worker sizes classes, which differs according to seed. Media are the most numerous at the foraging arena and largely responsible for trail-laying. Minor participate in seed harvesting and trail-laying, mostly when they can be efficient in carrying seeds, such as oat fragments. Major scarcely participate in harvesting and trail-laying, but are involved in the exploitation of bigger and/or preferred seed species. When faced with different seed species, M. barbarus seems thus to collectively adopt a "foraging time minimisation" rather than an "energetic gain per item harvested maximisation" strategy. Dynamics of foraging and division of labour between foragers of different sizes are related to both the workers' ability to carry seed items, and the transfer of information to nestmates by trail-laying, all parameters that vary according to seed characteristics.

Animal Communication↗

What determines probability of surviving predator attacks in bird migration?: the relative importance of vigilance and fuel load.

Migrating birds must accumulate fuel during their journeys and this fuel load should incur an increased risk of predation. Migratory fuelling should increase individual mass-dependent predation risk for two reasons. First, acquisition costs are connected to the increased time a bird must spend foraging to accumulate the fuel loads and the reduced predator detection that accompanies foraging. Second, birds with large fuel loads have been shown to suffer from impaired predator evasion which makes them more vulnerable when actually attacked. Here, I investigate the relative importance of these two aspects of mass-dependent predation risk and I have used published data and a hypothetical situation for a foraging bird to investigate how much migratory fuelling in terms of escape performance and natural variation in predator detection contribute to individual risk during foraging. Results suggest that for birds foraging close to protective cover the negative impact of fuel load on flight performance is very small, whereas variation in time to predator detection is of great importance for a bird's survival. However, the importance of flight performance for predation risk increases as the distance to cover increases. Hence, variation in predator detection (and vigilance) probably influences individual survival much more than migratory fuel load and consequently, to understand risk management during migration studies that focus on vigilance and predator detection during fuelling are much needed.

Animal Migration↗

Optimal diving behaviour and respiratory gas exchange in birds.

This review discusses the advancements in our understanding of the physiology and behaviour of avian diving that have been underpinned by optimal foraging theory and the testing of optimal models. To maximise their foraging efficiency during foraging periods, diving birds must balance numerous factors that are directly or indirectly related to the replenishment of the oxygen stores and the removal of excess carbon dioxide. These include (1) the time spent underwater (which diminishes the oxygen supply, increases carbon dioxide levels and may even include a build up of lactate due to anaerobic metabolism), (2) the time spent at the surface recovering from the previous dive and preparing for the next (including reloading their oxygen supply, decreasing their carbon dioxide levels and possibly also metabolising lactate) and (3) the trade-off between maximising oxygen reserves for consumption underwater by taking in more air to the respiratory system, and minimising the energy costs of positive buoyancy caused by this air, to maximise the time available underwater to forage. Due to its importance in avian diving, replenishment of the oxygen stores has become integral to models of optimal diving, which predict the time budgeting of animals foraging underwater. While many of these models have been examined qualitatively, such tests of predictive trends appear fallible and only quantifiable support affords strong evidence of their predictive value. This review describes how the quantification of certain optimal diving models, using tufted ducks, indeed demonstrates some predictive success. This suggests that replenishment of the oxygen stores and removal of excess carbon dioxide have significant influences on the duration of the surface period between dives. Nevertheless, present models are too simplistic to be robust predictors of diving behaviour for individual animals and it is proposed that they require refinement through the incorporation of other variables that also influence diving behaviour such as, perhaps, prey density and predator avoidance.

Animals↗

The effects of birdsfoot trefoil (Lotus corniculatus) and chicory (Cichorium intybus) when compared with perennial ryegrass (Lolium perenne) on ovine gastrointestinal parasite development, survival and migration.

Two experiments were conducted to investigate the effects of birdsfoot trefoil and chicory on parasitic nematode development, survival and migration when compared with perennial ryegrass. In experiment one, sheep faeces, containing 10,385 Cooperia curticei eggs were added to 25 cm diameter pots containing birdsfoot trefoil, chicory or ryegrass, and the pots maintained under optimal conditions for nematode parasite development. Replicate pots of each forage type were destructively sampled on day 8, 16, 20, 28 and 37 to collect the nematode larvae. When forages were compared on a dry matter basis, by day 16 there were 31% and 19% fewer larvae on birdsfoot trefoil and chicory than on ryegrass, respectively (P<0.01). In the second experiment, replicate 1m(2) field plots of birdsfoot trefoil, chicory and ryegrass were sub-sampled on day 14, 21, 35 and 49 for larval counts following the application of sheep faeces containing 585,000 Teladorsagia circumcincta eggs to each plot on day 0. Results showed there were a minimum of 58% and 63% fewer infective stage parasitic larvae on birdsfoot trefoil and chicory, respectively, compared with ryegrass on day 14 and 35 when forages were compared on a forage dry matter, plot area sampled and leaf area basis (P<0.01). Overall, these results indicate that the number of infective stage larvae on birdsfoot trefoil and chicory pasture was reduced by the effect of their sward structure on the development/survival/migration of ovine parasitic nematodes. These effects may be one of the ways in which these forages may affect parasitic infections in grazing livestock.

Analysis of Variance↗

Aging and development in social insects with emphasis on the honey bee, Apis mellifera L.

Honey bee colonies typically consist of about 20-40 thousand workers, zero to few thousand males (drones), depending on the time of year, and a single queen, the mother of the colony. Workers typically live 3-6 weeks during the spring and summer and can live about 4months during the winter. Queens are longer lived. Anecdotes of queens living 2-3years are not unusual, though they normally live less than a year in commercial hives. Little is known about the life span of drones. Queens develop from fertilized eggs that are not different from the eggs that develop into workers. Queens are, however, twice as large, have specialized anatomy, live much longer, and develop faster from egg to adult. All of these differences are derived from differences in larval rearing environment, primarily nutrition. The developmental trajectory of a female larva from worker into a queen can be determined as late as the third day of larval development, after this time the developmental pathway is fixed for a worker phenotype. The total time of larval development is only 5-6 days, therefore, just 2-3 days of differential feeding can lead to profound differences in development, and longevity. Workers undergo age development after they become adults. Workers usually initiate foraging behavior when they are 2-3 weeks old. The age at which a worker initiates foraging is a strong determinant of her length of life. This is presumed to be a result of the hazards of foraging, but natural senescence also occurs. Some bees remain in the nest and are never observed to forage, thereby outliving their forager sisters. Corresponding to this behavioral development are changes in the sizes of glands and the production of glandular products, increases in biogenic amine titers within the brain, an increase in the volume of specific regions of the brain, and changes in the neural system that affect perception of stimuli, and learning and memory. These age-related changes in behavior are regulated by intrinsic and extrinsic factors. Genetic variation has been demonstrated for many of these life history and behavioral traits. Selection and genome mapping studies have demonstrated relationships between the neural system, behavior, and life history traits.

Aging↗

Nutritional and managerial considerations for range beef cattle production.

A number of nutritional and managerial schemes have been presented to help optimize range livestock production. Forage quality, animal requirements, and the animals' ability to meet their requirements from the forage is presented. After determining the nutritional value of the forages and animal requirements, prescription supplementation produces very efficient additional gains. Management alternatives to compensate for poor quality forage on range in late summer and early fall, such as selling market animals, moving to better feed, chemical curing of forages, time of calving, time of weaning, and using the range as a feedlot are discussed. Winter feeding programs using native flood meadow hay as a base were also presented for both growing animals and mature cows. Included were discussions on using rake-bunched hay, an ionophore, and feeding strategies for wintering cows. Material presented illustrates a philosophy of range nutrition with methods and procedures that are adaptable to grazing systems in all parts of the world. It should be noted, however, some data need to be extrapolated to fit local conditions.

Animal Feed↗

The functions of societies and the evolution of group living: spider societies as a test case.

Many models have been advanced to suggest how different expressions of sociality have evolved and are maintained. However these models ignore the function of groups for the particular species in question. Here we present a new perspective on sociality where the function of the group takes a central role. We argue that sociality may have primarily a reproductive, protective, or foraging function, depending on whether it enhances the reproductive, protective or foraging aspect of the animal's life (sociality may serve a mixture of these functions). Different functions can potentially cause the development of the same social behaviour. By identifying which function influences a particular social behaviour we can determine how that social behaviour will change with changing conditions, and which models are most pertinent. To test our approach we examined spider sociality, which has often been seen as the poor cousin to insect sociality. By using our approach we found that the group characteristics of eusocial insects is largely governed by the reproductive function of their groups, while the group characteristics of social spiders is largely governed by the foraging function of the group. This means that models relevant to insects may not be relevant to spiders. It also explains why eusocial insects have developed a strict caste system while spider societies are more egalitarian. We also used our approach to explain the differences between different types of spider groups. For example, differences in the characteristics of colonial and kleptoparasitic groups can be explained by differences in foraging methods, while differences between colonial and cooperative spiders can be explained by the role of the reproductive function in the formation of cooperative spider groups. Although the interactions within cooperative spider colonies are largely those of a foraging society, demographic traits and colony dynamics are strongly influenced by the reproductive function. We argue that functional explanations help to understand the social structure of spider groups and therefore the evolutionary potential for speciation in social spiders.

Animals↗

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