Biological control of Trialeurodes vaporariorum by Encarsia formosa on tomato in unheated greenhouses in the high altitude tropics

Biological control of Trialeurodes vaporariorum (Westwood) by Encarsia formosa Gahan was tested during three consecutive production cycles (16-28 weeks) on a beef tomato (Solanum lycopersicum L.) crop in a glasshouse and a plastic greenhouse on the Bogota Plateau in Colombia. During the course of this study over the period 1997-1999, the mean temperature was around 16 °C in the plastic greenhouse and around 17 °C in the glasshouse. E. formosa was introduced at a rate of 3 adults per m2 per week in the 1997 production cycle, and at a rate of 3 and 5 pupae per m2 per week in 1998 and 1999, respectively. In 1997, the adult whitefly population increased exponentially to a peak of 76 adults per plant in the plastic greenhouse, while the whitefly population in the glasshouse reached a peak of only 12 adults per plant. The percentage parasitism fluctuated between 42 and 82% in the glasshouse and between 28 and 47% in the plastic greenhouse. In 1998, the T. vaporariorum population could not be brought under control in both greenhouses and reached a peak of 80 and 53 T. vaporariorum adults per plant in the plastic greenhouse and the glasshouse, respectively. Parasitism fluctuated between 55 and 97% in the glasshouse and between 32 and 84% in the plastic greenhouse. In 1999, biological control was successful in both greenhouses. Most of the time, populations of T. vaporariorum were lower than 1.2 adults per plant and parasitism by E. formosa was 80% or higher. We suggest that the higher temperature is the main reason for better parasitism in the glasshouse when compared to the plastic greenhouse. The successful results of 1999 show that biological control is possible under the short day and low temperature conditions of greenhouses situated in the high altitude tropics such as the Bogota Plateau. Recommendations are given for the application of E. formosa based on the results of these experiments

Electroweak Baryogenesis and the Standard Model Effective Field Theory

We investigate electroweak baryogenesis within the framework of the Standard Model Effective Field Theory. The Standard Model Lagrangian is supplemented by dimension-six operators that facilitate a strong first-order electroweak phase transition and provide sufficient CP violation. Two explicit scenarios are studied that are related via the classical equations of motion and are therefore identical at leading order in the effective field theory expansion. We demonstrate that formally higher-order dimension-eight corrections lead to large modifications of the matter-antimatter asymmetry. The effective field theory expansion breaks down in the modified Higgs sector due to the requirement of a first-order phase transition. We investigate the source of the breakdown in detail and show how it is transferred to the CP-violating sector. We briefly discuss possible modifications of the effective field theory framework.Comment: 21 pages + appendices. V2: Corrected a factor-2 mistake which has changed the results for the baryon asymmetry quantitatively. Main conclusions of the v1 still hol

Dust and gas in local galaxies in the equatorial H-ATLAS fields

One of the main challenges for extragalactic astronomy is to understand how the baryonic components of galaxies evolve from simple clouds of unenriched atomic gas into complex systems consisting of stars, dust, heavy elements and the different gas phases we observe today. This transformation is driven by the ongoing star formation in galaxies, yet there are many other poorly understood interactions between the different constituents that strongly affect the evolution. The physical properties of the galaxy population have been observed to change over time. For example, the stellar mass is built up monotonically, and the star formation rate within galaxies has changed drastically over the past ∼ 10 billion years. The main challenge in galaxy evolution is to procure a more detailed understanding of the various physical and chemical processes responsible for the observed changes in the physical properties of galaxies. Galaxies evolve over cosmic time, and thus much too slow to observe any changes directly. In order to study how the physical properties of a galaxy change, they need to be compared to the physical properties of galaxies at different evolutionary stages. There are two approaches to achieve this. The first one is to study the average change in the galaxy properties with redshift. Many studies (see next sections) have used this approach to study the redshift-evolution of various galaxy properties and these have dramatically changed our understanding of galaxy evolution. However, because of the difficulties of observing very distant objects, this method can only be used to study the evolution out to a given limiting redshift, which is determined by the used wavelength and telescope. Especially for atomic hydrogen (HI) gas, which has a hyperfine emission line at 21 cm, the current generation of telescopes strongly restricts the observations to the relatively nearby Universe. And since the HI gas is a key component in galaxy evolution, it is hard to get a detailed understanding of galaxy evolution beyond the local Universe. One way to extract information for HI beyond the most nearby sources is to use a ‘stacking’ analysis technique. Stacking is the process of combining many low signal-to-noise observations of different individual objects in order to retrieve a high-significance statistical detection (e.g. Delhaize et al., 2013). This technique enables studies of the changes in average galaxy properties out to larger distances (and thus larger lookback times). Part III of this thesis describes the ‘HI-stacking’ analysis of dust-selected sources. The second approach to study galaxy evolution is to investigate the differences in galaxy properties between galaxies at different evolutionary stages, rather than between galaxies at different times. In this context, the evolutionary stage of a galaxy can be defined by its gas fraction, i.e. by how much gas has been converted into stars. So as galaxies evolve, they move from high to low gas fractions and the changes in the physical galaxy properties are studied as a function of gas fraction rather than as a function of time. The rate at which galaxies evolve is determined by their star formation rate, which is in turn dependent on the galaxy’s halo mass and environment. Galaxies span a wide range of halo masses and environments, and hence a correspondingly large range in star formation rates. By the current epoch, some galaxies have converted most of their gas into stars, whereas others still mainly consist of gas. Galaxies in the local Universe span a range of different evolutionary stages due to the differences in their star formation histories. Depending on how the sources are selected, a sample can consist of more evolved or more unevolved sources. In Part I of this thesis, we present a local HI-selected sample and compare to a local stellar mass selected and local dust-selected sample in order to study the changes in galaxy properties over as much of the evolutionary track as possible. Galaxy evolution entails much more than the formation of stars from the available gas. As stars evolve, they synthesise metals (i.e. all elements except hydrogen and helium) in their cores, and subsequently expel them into the interstellar medium (ISM) at the end of the stars’ lives. About half of these metals are locked up in dust grains (Whittet, 1992). This dust absorbs about 30 to 50% of the optical light emitted by galaxies (e.g. Driver et al., 2016; Viaene et al., 2016) and enshrouds some of the most interesting environments in these galaxies. It is therefore difficult to develop a thorough understanding of galaxy evolution without also understanding how dust affects the observations. In Part I of this thesis we will put additional focus on the dust content of galaxies selected by their HI, dust and stellar content. In Part II, we determine the metal content of the same galaxies and study how dust is formed and destroyed by comparing dust and chemical evolution models (that predict the build-up of dust, gas and metals) with observed galaxy properties. This thesis describes three distinct, but closely related, research projects I conducted during the course of my PhD, all dealing with cosmic dust and HI gas in the context of galaxy evolution. This introductory chapter briefly summarises the current theoretical and observational framework of galaxy evolution, with a focus on cosmic dust and HI gas. Chapter 2 explains how we have selected the HIGH sample (HI-selected Galaxies in H-ATLAS) and dealt with observational issues. Chapter 3 describes the pipeline that was developed to perform the photometry and the SED fitting code that was used to determine the galaxy properties. Chapter 4 details the scaling relations between the different galaxy properties and how the galaxy properties of HIGH compare to a stellar selected and dust-selected sample. Chapter 5 explains how metallicities have been derived using fibre optical spectroscopy. In Chapter 6, we study dust sources and sinks by comparing models of the build-up of dust, gas and metals with the observed properties of galaxies. Chapter 7 presents the HI-stacking methods and preliminary results. Finally, in Chapter 8 we summarise our conclusions and describe potential future work

Differential responses of Nile tilapia (Oreochromis niloticus) to fin clip wounding and related stress: perspectives

The debate around fish welfare is intensifying in The Netherlands. As a result, more research is carried out to enhance knowledge on fish welfare in aquaculture. Detailed information is lacking on how production procedures causing discomfort to the fish may affect welfare. That fish must perceive adversive stimuli follows from the fact that nociceptive mechanisms similar to those in mammals are present in fish. However, whether and how nociceptive stimuli are perceived or interpreted by a fish is a far more difficult question that requires significantly more effort from fundamental research, both neurophysiological and behavioural studies, than now available. The study presented in this report aimed to define selected readout for the acute response to a supposedly painful stimulus: a standardised tailfin clip to a common carp. In conclusion, we succeeded to demonstrate differential, stronger responses to a presumed painful stimulus than to the handling stress per se associated with the administration of the pain stimulus. These parameters will be the focus of future research within this welfare project

The effects of pulse stimulation on biota - Research in relation to ICES advice - Effects on dogfish

Onderzoek naar het welzijn van hondshaaien bij de vangst. Er is onderzocht of de methode van het gebruik van stroom wel diervriendelijk is. De conclusie is dat dit geen beletsel voor de diervriendelijkheid oplever