Grooming and hygienic behaviours of the honey bee (Apis mellifera) toward the parasitic mite Varroa destructor

Despite a multitude of environmental stressors, the Varroa mite is still regarded as the greatest cause of honey bee mortality in its invaded range. Breeding honey bees that are resistant to the mite is an important area of research. This thesis aimed to gain a better understanding of the grooming and hygienic behaviours of Russian honey bees (RHB). The effect of a break in the synchrony of a mite’s life cycle on reproductive success was tested through brood inoculation experiments. Mites released by hygienic behaviour and forced to enter a new cell are less likely to lay male offspring. Through laboratory cage assays it was found that daughter mites are more susceptible to grooming behaviour. A new method of marking Varroa mites was developed which would enable a single cohort of mites to be followed after inoculation. A strong brood removal trait was noticed in RHB colonies, therefore they were tested for Varroa sensitive hygienic (VSH) behaviour. RHB demonstrated levels of VSH as high as the USDA line bred specifically for this behaviour. In addition the same QTL found to be responsible for the trait in VSH bees, was associated with VSH in RHB stock. Previous work showed that the ratio of older mites to total trapped mites (O/T) in the debris of honey bee colonies demonstrated the strongest association with colony infestation. This research showed that O/T is associated with VSH and brood removal behaviour. In addition, bees that displayed high levels of VSH in this study were also more likely to spend a longer amount of time grooming in laboratory assays. This indicates that both grooming and hygienic behaviours play important roles in the resistance of RHB stock. Their likelihood to be expressed by other stocks is discussed and recommendations for further research are provided.

Interactions between nematodes, potato and soil-borne micro-organisms and their effect on the management of potato cyst nematodes

Potato cyst nematodes (PCN) cause significant damage to the potato crop worldwide and growers experience economic losses related to yield loss and the cost of control measures. Experiments were set up to further elucidate the complex tritrophic PCNpotato-soil bacteria relationship. Bacterial strains isolated from the sugar beet rhizosphere were shown to be hatch active towards Globodera pallida and to be capable of successfully colonising the sugar beet rhizosphere when applied exogenously. A trap-crop system, based on these isolates, was proposed. Ridge and bulk soil taken from a commercial potato field were incubated with sterile potato root leachate (sPRL) and subsequent in vitro hatching assays showed that PCN hatch was influenced by microorganisms present in the ridge, but not in the bulk soil. Community level physiological profiling (CLPP) of ridge and bulk soil, using BIOLOG EcoplatesTM, demonstrated differences in bacterial functional diversity between the two soil types. An investigation of the inter-species competition between G. pallida and G. rostochiensis showed that G. pallida performed significantly better, in terms of multiplication rate, in competition with G. rostochiensis compared to its multiplication rate in single-species populations. Effectively removing the early hatch of G. rostochiensis in pot trials led to the removal of this competitive advantage of G. pallida suggesting that this advantage was due, at least in part, to morphological changes to the root caused by the early hatching of G. rostochiensis.

A simulation-based design method to transfer surface mount RF system to flip-chip die implementation

The flip-chip technology is a high chip density solution to meet the demand for very large scale integration design. For wireless sensor node or some similar RF applications, due to the growing requirements for the wearable and implantable implementations, flip-chip appears to be a leading technology to realize the integration and miniaturization. In this paper, flip-chip is considered as part of the whole system to affect the RF performance. A simulation based design is presented to transfer the surface mount PCB board to the flip-chip die package for the RF applications. Models are built by Q3D Extractor to extract the equivalent circuit based on the parasitic parameters of the interconnections, for both bare die and wire-bonding technologies. All the parameters and the PCB layout and stack-up are then modeled in the essential parts' design of the flip-chip RF circuit. By implementing simulation and optimization, a flip-chip package is re-designed by the parameters given by simulation sweep. Experimental results fit the simulation well for the comparison between pre-optimization and post-optimization of the bare die package's return loss performance. This design method could generally be used to transfer any surface mount PCB to flip-chip package for the RF systems or to predict the RF specifications of a RF system using the flip-chip technology.

Design and implementation of the embedded capacitance layers for decoupling of wireless sensor nodes

In this paper, the embedded capacitance material (ECM) is fabricated between the power and ground layers of the wireless sensor nodes, forming an integrated capacitance to replace the large amount of decoupling capacitors on the board. The ECM material, whose dielectric constant is 16, has the same size of the wireless sensor nodes of 3cm*3cm, with a thickness of only 14μm. Though the capacitance of a single ECM layer being only around 8nF, there are two reasons the ECM layers can still replace the high frequency decoupling capacitors (100nF in our case) on the board. The first reason is: the parasitic inductance of the ECM layer is much lower than the surface mount capacitors'. A smaller capacitance value of the ECM layer could achieve the same resonant frequency of the surface mount decoupling capacitors. Simulation and measurement fit this assumption well. The second reason is: more than one layer of ECM material are utilized during the design step to get a parallel connection of the several ECM capacitance layers, finally leading to a larger value of the capacitance and smaller value of parasitic. Characterization of the ECM is carried out by the LCR meter. To evaluate the behaviors of the ECM layer, time and frequency domain measurements are performed on the power-bus decoupling of the wireless sensor nodes. Comparison with the measurements of bare PCB board and decoupling capacitors solution are provided to show the improvement of the ECM layer. Measurements show that the implementation of the ECM layer can not only save the space of the surface mount decoupling capacitors, but also provide better power-bus decoupling to the nodes.

Impact of non-optimal grounding of the CC2420 RFIC on a 802.15.4 Tyndall sensor wireless mote

The performance of an RF output matching network is dependent on integrity of the ground connection. If this connection is compromised in anyway, additional parasitic elements may occur that can degrade performance and yield unreliable results. Traditionally, designers measure Constant Wave (CW) power to determine that the RF chain is performing optimally, the device is properly matched and by implication grounded. It is shown that there are situations where modulation quality can be compromised due to poor grounding that is not apparent using CW power measurements alone. The consequence of this is reduced throughput, range and reliability. Measurements are presented on a Tyndall Mote using a CC2420 RFIC todemonstrate how poor solder contact between the ground contacts and the ground layer of the PCB can lead tothe degradation of modulated performance. Detailed evaluation that required the development of a new measurement definition for 802.15.4 and analysis is presented to show how waveform quality is affected while the modulated output power remains within acceptable limits.

The ecology of the Irish stoat

The Irish stoat, Mustela erminea hibernica (Thomas and Barrett-Hamilton), has been regarded as an intermediate between the British stoat and the weasel. In this study Irish stoats, mainly from road casualties, were collected and studied. A small number were also live-trapped and radio-tracked. Thus information was gathered on the stoat’s ecology, in particular its form (size and coat colours), reproduction, food habits, parasites, habitat utilisation mortality and predation. The Irish stoats studied were clearly not intermediate in size between British stoats and weasels. They showed considerable size overlap with British stoats, and marked size variation within Ireland. It is argued that size of stoats is determined by food supply early in life. The ventral coat pattern of Irish stoats is apparently unique in the Palaearctic, being similar to that of some stoats found on the west coast of North America. It is argued that this is an example of parallel evolution resulting from adaptation to similar climatic conditions. The stoats were reproductively active in spring and summer. Food consisted mainly of rabbits, but rats, birds, shrews mice and voles were also consumed. Mites were the most numerous ectoparasites, followed by lice, ticks and fleas. Damage by the parasitic nematode Skrjabingylus nasicola was found more frequently in female stoat skulls. Stoats were frequently found in a variety of habitats, both open and wooded. Some of the radio-tracked stoats climbed trees. Dens used were often rat holes. Only one home range, that of a breeding female, was considered to have been accurately measured. It was 22 ha. in size. Mortality is known to have been caused by road accidents and domestic carnivores. It is argued that predation by raptorial birds is important to stoat populations. Results of this study are compared with information available from elsewhere.

Evaluation of rhizobacterial colonisation and the ability to induce Globodera pallida hatch

Three bacterial isolates, SB13 (Acinetobacter sp.), SB14 (Arthrobacter sp.) and SB15 (Bacillus sp.), were previously isolated from the rhizosphere of sugar beet (Beta vulgaris ssp. vulgaris) plants and shown to increase hatch of potato cyst nematodes in vitro. In this study, the three isolates were assayed for rhizosphere competence. Each isolate was applied to seeds at each of four concentrations (105-108 CFU ml−1) and the inoculated seeds were planted in plastic microcosms containing coarse sand. All three isolates were shown to colonise the rhizosphere, although to differing degrees, with the higher inoculation densities providing significantly better colonisation. The isolates increased sugar beet root and shoot dry weight. Isolates SB14 and SB15 were analysed for their ability to induce in vivo hatch of Globodera pallida in non-sterile soil planted with sugar beet. After 4 and 6 weeks, both isolates had induced significantly greater percentage hatch compared to controls.