Niels Holst

Grain injury models for Prostephanus truncatus (Coleoptera: Bostrichidae) and Sitophilus zeamais (Coleoptera: Curculionidae) in rural maize stores in West Africa.

Abstract Prostephanus truncatus (Horn) and Sitophilus zeamais Motschulsky have been reported as the two most serious pests of stored maize in sub-Saharan Africa and smallholder farmers are in urgent need of guidelines for their proper management. In this article we investigate the injury rates attributable to these two species in terms of percentage weight loss and percentage grain damage, and we derive functional response models for the two species on maize. The models successfully described the progression of grain injury in an extensive data set compiled from previously published studies, comprising 46 time series of data relating maize injury and insect pest density. The grain injury models can be used in conjunction with predictive models of pest population dynamics to guide the development of integrated management strategies for postharvest maize pests in West Africa and comparable regions elsewhere.

Sensitivity of Prostephanus truncatus (Coleoptera: Bostrichidae) Flight Activity to Environmental Variables in Benin, West Africa

Abstract Based on pheromone trap catches, a model of weekly Prostephanus truncatus (Horn) flight activity was generated for southern Benin. Using response surface regression, the following environmental variables were examined: number of rainy days per week, precipitation, minimum and maximum temperatures, minimum relative air humidity, and daylength. A time-variable, year, was included to account for the variance between years. From step-wise exclusion of variables with the lowest contribution to the model fit, a model was generated which included three environmental variables (daylength, minimum relative air humidity, and minimum temperature) that explained 55% of the total variance, and the yearly variable explaining 8%. The response surface regression analysis of P. truncatus flight activity revealed the following: (1) it was positively correlated with daylength when daily minimum temperature and relative air humidity were low, (2) it was positively associated with minimum relative air humidity when lower than 75%, (3) it was negatively associated with minimum temperature, (4) unexplained yearly variation was important for the predictive strength of the model, (5) interactions of environmental variables contributed substantially to the model fit, and (6) precipitation, both as mm rain and as number of rainy days, had little influence on P. truncatus flight activity. Independent data showed that the model predicted P. truncatus flight activity well elsewhere in southern Benin, whereas in central Benin new coefficients for the same environmental variables were needed to produce an adequate prediction. The model did not fit pheromone baited trap catches from northern Benin.

Duration and Spread of an Entomopathogenic Fungus, Beauveria bassiana (Deuteromycota: Hyphomycetes), Used to Treat Varroa Mites (Acari: Varroidae) in Honey Bee (Hymenoptera: Apidae) Hives

Abstract A strain of the fungus Beauveria bassiana (Balsamo) Vuillemin (Deuteromycota: Hyphomycetes) isolated from varroa mites, Varroa destructor Anderson & Trueman (Acari: Varroidae), was used to treat honey bees, Apis mellifera L. (Hymenoptera: Apidae), against varroa mites in southern France. Fungal treatment caused a significant increase in the percentage of infected varroa mites compared with control treatments in two field experiments. In the first experiment, hives were treated with a formulation containing 0.37 g of B. bassiana conidia per hive and in the second experiment with a dose of 1.0 g of conidia per hive. The percentage of infected varroa mites also increased in the nontreated (control) hives, suggesting a movement of conidia, probably via bee drift, among the hives. Mite fall was significantly higher among treated hives compared with control hives on the sixth and eighth days after treatment in the first experiment. These days correspond to previously published data on the median survivorship of mites exposed to that fungal solate. The interaction of treatment and date was significant in the second experiment with respect to mite fall. Increases in colony-forming unit (cfu) density per bee were observed in all treatments but were significantly higher among bees from treated hives than control hives for at least a week after treatment. The relationship between cfu density per bee and proportion infected was modeled using a sigmoid curve. High levels of infection (>80%) were observed for cfu density per bee as low as 5 × 102 per bee, but the cfu density in hives treated with 0.37 g generally dropped below this level less than a week after treatment.

Application of continuous monitoring of honeybee colonies

Monitoring physical variables associated with honeybee colonies, including weight, temperature, humidity, respiratory gases, vibration, sound, and forager traffic, in a continuous manner is becoming feasible for most researchers as the cost and size of electronic sensors decrease while their precision and capacity increase. Researchers have taken different approaches to collecting and analyzing the resulting datasets, with a view toward extracting information on colony behavior and phenology. The objective of this review is to examine critically the different kinds of data and data analyses, providing researchers with better-informed options for obtaining information on colony phenology in the field without disturbing the hive, and for combining information from different kinds of sensors to obtain a more complete picture of colony status. Wireless sensor networks and powering sensors are briefly discussed.

Within-day variation in continuous hive weight data as a measure of honey bee colony activity*

Hourly weight data, from 4 honey bee hives placed on balances linked to dataloggers, were divided into two independent parts: (1) daily running average and (2) detrended weights, obtained by subtracting the running average from raw data. Weekly changes in running average weights, WCRAW, were correlated with food store changes but not adult or brood weights. Detrended weights showed daily fluctuation due to water and foraging bee movement and were modeled using sine curves, which fit all weekly subsets. Adult and brood populations, measured independently, were expressed as colony consumption rates via published per capita rates, and those consumption rates were correlated with sine amplitudes. Amplitudes were more sensitive to hive activity than WCRAW and unlike WCRAW detected high activity when foraging success was masked by high consumption Estimating food store changes with WCRAW and colony consumption with amplitudes reveals hive growth and activity without disturbing bees.ZusammenfassungWir analysierten hier wie stündlich aufgenommene Gewichtsdaten Hinweise auf dynamische Veränderungen in Honigbienenvölkern liefern können. Das Wiegen von Völkern ist zwar eine schnelle und eingriffsfreie Massnahme, andererseits aber muss in regelmässigen Abständen und mit ausreichender Präzision gewogen werden, wenn man zuverlässige Informationen über Stockaktivität und Volksdynamik erhalten will. In dieser Studie wurden Bienenvölker in 2005 und im Frühjar 2006 in zweiwöchigen Abständen inspiziert. Die einzelnen Waben wurden gewogen und das Gewicht der verdeckelten Brut, der erwachsenen Bienen und der eingelagerten Futtervorräte wurden bestimmt. Die Völker waren auf elektronischen Waagen aufgestellt und mit Dataloggern verbunden. Stündlich registrierten Gewichtsdaten wurden aufgeteilt in einen Mittelwert über 25 Stunden hinweg, als Langzeitmittel, und einen trendfreien Gewichtswert, als Kurzzeitinformation. Letzterer gibt die Abweichung der Rohdaten für die jeweilige Stunde von dem laufenden Mittelwert für die entsprechende Stunde an. Laufende Mittelwerte wurden auch benutzt, um die Wöchentliche Änderung im Laufenden Mittel (WCRAW, übersetzt WÄLM) zu berechnen, indem Wochenmittel von dem der jeweils folgenden Woche subtrahiert wurden. Die WCRAW-Daten wurden mit denen der Inspektionsdaten von 2005 für Gewichte der verdeckelten Brut und der adulten Bienen, sowie der Futtervorräte verglichen, und diese Vergleichsergebnisse wurden gegen die der in 2006 vorgenommenen Inspektionen verglichen. An die trendfreien Gewichtsdaten wurde eine Sinuskurve angepasst und die Parameter dieser Kurvenanpassungen wurden für WCRAW-ähnliche Analysen benutzt, ausser dass hier die Daten über die Brut- und Adultpopulationen in Verbrauchsraten umgerechnet worden waren.Die WCRAW-Daten zeigten eine gute Korrelation mit den täglichen Veränderungen im Gewicht der Futtervorräte (Tab. I), aber nicht mit den Gewichtswerten für die Brut und für adulte Bienen. Die trendfreien Daten zeigten klare aber variable Tagesverlaufsmuster. Sinuskurven konnten an alle trendfreien Daten angepasst werden und diese wiesen stets eine Periodik zwischen 22 und 26 Stunden auf. Die Futtergewichtsdaten und die geschätzten Werte der Verbrauchsraten wurden für 2005 und 2006 mit den jeweiligen täglichen Amplituden der Sinuskurven und den WCRAW-Schätzwerten verglichen (Abb. 6 und 7). Die Amplituden und die Gewichte der meisten Komponenten zeigten eine signifikante Beziehung (Tab. I). Insbesonders die Beziehung zwischen den Verbrauchsraten für die Brut und adulte Bienen war signifikant mit der jeweiligen Amplitude korreliert (Abb. 8) und kann damit wichtige Informationen über den Volkszustand geben. Die Kombination der Wägungen mit der kontinuierlichen Datalogger-Information wurde hier benutzt, um Rückschlüsse über die Sammelaktivität, Wasserbewegungen, Schwarmvorgänge, Ruhezustände, sowie über Veränderungen in Futtervorräten und Futterverbrauch zu treffen. Diese Methode ist damit in der Lage, sowohl die Notwendigkeit invasiver Inspektionen zu reduzieren, als auch die Information aus solchen Inspektionen umfassender auszuwerten.

Impact of a treatment of Beauveria bassiana (Deuteromycota: Hyphomycetes) on honeybee (Apis mellifera) colony health and on Varroa destructor mites (Acari: Varroidae)*

In 2 experiments bee colonies in southern France were treated with conidia of a Beauveria bassiana isolate collected from Varroa mites in the region. Objectives were to evaluate treatment effect on colony weight, adult bee mass, and capped brood and honey, and on Varroa fall onto sticky boards. Treatments included conidia formulated with either wax powder or wheat flour, flour alone, or control. Treatment did not affect colony health. Colonies treated with conidia and wax powder had higher mite fall compared to controls while those treated with conidia and wheat flour did not. The proportion fallen, infected mites in both conidia treatments was higher than controls for up to a week. Higher mite fall and infection rates were observed in treated hives in the 2nd, smaller experiment. The relationships between dosage and proportion fallen, infected mites, and between ambient temperature and infection duration, were examined. Future experiments will explore Varroa control using conidia.ZusammenfassungIn zwei Experimenten wurden Honigbienenvölker in Südfrankreich mit Konidiensporen eines aus Varroamilben der Region gesammelten Isolates behandelt. Ziel war die Erfassung der Auswirkung der Behandlung auf das Gewicht der Völker, das Gesamtgewicht an adulten Bienen, auf die verdeckelte Brut und auf die Honigmenge, sowie auf den Totenfall von Varroamilben auf klebrige Bodeneinlagen. Die Behandlungen umfassten Formulierungen von Konidiensporen entweder mit Wachspulver oder mit Weizenmehl, sowie Weizenmehl alleine und unbehandelte Kontrollvölker. Die Behandlungen hatten keinen Einfluss auf die Gesundheit der Bienenvölker. Die mit Konidiensporen und Wachspulver behandelten Völker hatten einen höheren Milbentotenfall als die Kontrollvölker, bei den mit Konidiensporen und Weizenmehl behandelten Völkern war dies nicht der Fall. Der Anteil an infizierten Milben im Totenfall war bei beiden Behandlungen mit Konidiensporen über den Zeitraum von etwa einer Woche höher als bei den Kontrollen. Ein erhöhter Milbentotenfall und erhöhte Infektionsraten wurden auch in dem zweiten, kleineren Experiment gefunden. Die Beziehung zwischen der Dosierung und dem Anteil infizierter Milben im Totenfall und zwischen der Umgebungstemperatur und der Infektionsdauer wurden untersucht. Zukünftige Experimente sollen die Möglichkeit einer Behandlung der Varroose mittels Konidiensporen untersuchen.

A universal simulator for ecological models

To most modellers, ecological models are primarily about ecology. A model is a condensed summary of an ecosystem written in the language of mathematics and logic. While modellers with a mathematical inclination may prefer stringent model formulations, that allow formal mathematical analysis, most modellers in ecology prefer heterogeneus, composite models permitting only numerical analysis; they are computational modellers who implement their models in software, which then itself becomes both tool and object in the ensuing analysis. The design and implementation details of this software is largely neglected. But this paper is only about this: the proper design and implementaion of ecological models.

Combining a weed traits database with a population dynamics model predicts shifts in weed communities

A functional approach to predicting shifts in weed floras in response to management or environmental change requires the combination of data on weed traits with analytical frameworks that capture the filtering effect of selection pressures on traits. A weed traits database (WTDB) was designed, populated and analysed, initially using data for 19 common European weeds, to begin to consolidate trait data in a single repository. The initial choice of traits was driven by the requirements of empirical models of weed population dynamics to identify correlations between traits and model parameters. These relationships were used to build a generic model, operating at the level of functional traits, to simulate the impact of increasing herbicide and fertiliser use on virtual weeds along gradients of seed weight and maximum height. The model generated ‘fitness contours’ (defined as population growth rates) within this trait space in different scenarios, onto which two sets of weed species, defined as common or declining in the UK, were mapped. The effect of increasing inputs on the weed flora was successfully simulated; 77% of common species were predicted to have stable or increasing populations under high fertiliser and herbicide use, in contrast with only 29% of the species that have declined. Future development of the WTDB will aim to increase the number of species covered, incorporate a wider range of traits and analyse intraspecific variability under contrasting management and environments.

Simulation Modelling of Population Dynamics of Mosquito Vectors for Rift Valley Fever Virus in a Disease Epidemic Setting

Background Rift Valley Fever (RVF) is weather dependent arboviral infection of livestock and humans. Population dynamics of mosquito vectors is associated with disease epidemics. In our study, we use daily temperature and rainfall as model inputs to simulate dynamics of mosquito vectors population in relation to disease epidemics. Methods/Findings Time-varying distributed delays (TVDD) and multi-way functional response equations were implemented to simulate mosquito vectors and hosts developmental stages and to establish interactions between stages and phases of mosquito vectors in relation to vertebrate hosts for infection introduction in compartmental phases. An open-source modelling platforms, Universal Simulator and Qt integrated development environment were used to develop models in C++ programming language. Developed models include source codes for mosquito fecundity, host fecundity, water level, mosquito infection, host infection, interactions, and egg time. Extensible Markup Language (XML) files were used as recipes to integrate source codes in Qt creator with Universal Simulator plug-in. We observed that Floodwater Aedines and Culicine population continued to fluctuate with temperature and water level over simulation period while controlled by availability of host for blood feeding. Infection in the system was introduced by floodwater Aedines. Culicines pick infection from infected host once to amplify disease epidemic. Simulated mosquito population show sudden unusual increase between December 1997 and January 1998 a similar period when RVF outbreak occurred in Ngorongoro district. Conclusion/Significance Findings presented here provide new opportunities for weather-driven RVF epidemic simulation modelling. This is an ideal approach for understanding disease transmission dynamics towards epidemics prediction, prevention and control. This approach can be used as an alternative source for generation of calibrated RVF epidemics data in different settings.

A scientific note on the fungus Beauveria bassiana infecting Varroa destructor in worker brood cells in honey bee hives

We report on the isolation of the mitosporic fungus Beauveria bassiana from varroa mites, Varroa destructor, in capped worker brood cells of honey bees, Apis mellifera. To our knowledge, this is the first record of B. bassiana from mites collected from bee brood. The brood chamber is the area of the hive where bees maintain high constant temperatures of 33–36 ◦C (Le Conte et al., 1990). An entomopathogenic fungus may be less efficacious because of poor germination at the high temperatures inside brood cells. Natural enemies of the varroa mite are few and, until recently, included no records of fungal pathogens (Chandler et al., 2001). However, a number of studies have shown that varroa mites are highly susceptible to infection by a range of entomopathogenic fungi, including B. bassiana (James, 2009). Many entomopathogenic fungi have a ubiquitous distribution and a wide host range, thus one might expect foraging bees to frequently carry fungus conidia into the bee hive from their environment. The lack of observed natural infections of varroa mites by these fungi could be due to a combination of hygienic behaviour of worker bees and the harsh environmental conditions in bee colonies. Nevertheless, Meikle et al. (2006) isolated B. bassiana from approximately 0.2% of varroa mites collected from a number of apiaries in southern France and documented that natural infections could indeed be found. B. bassiana has also been reported from varroa mites in southern Spain (Garcia-Fernandez et al., 2008).