A user-friendly simulation tool for determining the impact of the sterile insect technique/inherited sterility technique (SIT/IS) on populations of the African sugarcane stalk borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) is described in this paper. The simulation tool is based on a spatio-temporal model. The design of the simulation tool is such that it is applicable for use in a number of pest/crop and pest control scenarios. It uses 4 interacting subsystems (pest species population dynamics, crop dynamics, environmental dynamics and economics) within a specified spatial domain. Furthermore, the spatial domain describes the layout of the agricultural crop (position, size, shape, crop age and variety of the different fields contained within the crop area). The pest species population subsystem describes E. saccharina population dynamics (but is designed to also include population dynamics of other pest species) under the influence of the IS technique. The E. saccharina module developed utilizes mean-field and spatio-temporal models, and includes dynamics of all E. saccharina life stages under the influence of the control measure. Only temperature and damage caused by E. saccharina are currently included as variables in the sugarcane dynamics subsystem. This subsystem estimates stalk length as a function of time and temperature, and sucrose percentage as a function of damage caused by E. saccharina boring. Interaction between E. saccharina population growth and sugarcane growth is described by a decreasing s-shaped density-dependent mortality function-the older the cane, the higher the carrying capacity (more food resources) and corresponding infestation and damage levels. The only environmental factor considered as an independent variable in the environmental dynamics subsystem is temperature. Possible extensions to this subsystem are discussed. The economics subsystem developed includes the estimation of the recoverable value, percentage, expected revenue and the cost of control. No other farm expenditures are taken into account. As such only profit or loss expected from applying the IS technique is estimated. The profit or loss is defined as the increase in revenue expected less the cost of applying a pest control measure. An example of using the simulation tool is presented in the context of a real field scenario of a simulated SIT/IS program against E. saccharina at a pilot site near the Eston area of KwaZulu-Natal, South Africa.
Concentrations of noradrenaline (NA), homovanillic acid, 5-hydroxyindoleacetic acid and cyclic nucleotides were determined in lumbar cerebrospinal fluid (CSF) from acute and chronic schizophrenics and various groups of psychiatric and non-psychiatric control subjects. Statistically significant increases in NA and cyclic adenosine monophosphate were found in CSF from chronic schizophrenics compared to all other groups. These results were shown by statistical analyses to be unrelated to medication. They may be interpreted as evidence for noradrenergic overactivity as a possible primary abnormality in chronic schizophrenia.
A mathematical model is formulated for the population dynamics of an Eldana saccharina Walker infestation of sugarcane under the influence of partially sterile released insects. The model describes the population growth of and interaction between normal and sterile E.saccharina moths in a temporally variable, but spatially homogeneous environment. The model consists of a deterministic system of difference equations subject to strictly positive initial data. The primary objective of this model is to determine suitable parameters in terms of which the above population growth and interaction may be quantified and according to which E.saccharina infestation levels and the associated sugarcane damage may be measured. Although many models have been formulated in the past describing the sterile insect technique, few of these models describe the technique for Lepidopteran species with more than one life stage and where F1-sterility is relevant. In addition, none of these models consider the technique when fully sterile females and partially sterile males are being released. The model formulated is also the first to describe the technique applied specifically to E.saccharina, and to consider the economic viability of applying the technique to this species. Pertinent decision support is provided to farm managers in terms of the best timing for releases, release ratios and release frequencies.
gamma-Aminobutyric acid (GABA) concentration was determined in cerebrospinal fluid (CSF) of acute and chronic schizophrenic patients, in persons with psycho-organic or personality disorders, and in nonpsychiatric controls. The mean CSF GABA level in the chronic schizophrenic patients was found to be significantly higher than in any of the other groups. No other statistically significant differences were found. Statistical analysis revealed that the elevated CSF GABA concentration in the chronic schizophrenic patients was unlikely to be caused by medication. These results are interpreted as evidence for possible primary or secondary GABAergic overactivity in the brain in chronic schizophrenia.
Eldana saccharina Walker (Lepidoptera: Pyralidae) is a stalk borer pest plaguing the sugar producing industry in South Africa . The pest feeds on the internal tissue of sugarcane stalks, causing yield losses in sucrose. Various control methods have been proposed in an attempt to suppress the pest. These control methods are, however, often difficult and costly to test, implement, and develop further in an iterative manner. In an attempt to better understand the behavior and population dynamics of E. saccharina, an agentbased simulation model is presented in this paper which simulates the stalk borer's biology, feeding habits, mating behavior, dispersal patterns, and various other characteristics as accurately as possible. The flexibility and validity of the model are then ascertained by subjecting the model to expert opinion and parameter variation analysis. A simplified control measure is then implemented in order to demonstrate the possibility for using the agent-based model in the future for developing and testing integrated pest management strategies against E. saccharina. Recommendations for Resource Managers• The use of agent-based simulation modeling is investigated as a possible means for accurate capturing of the behavior of E. saccharina.• The ability to accurately recreate pest behavior poses the opportunity for the detailed testing and development of control strategies to combat this sugarcane pest. Natural Resource Modeling. 2018;31:e12153. wileyonlinelibrary.com/journal/nrm
The tumultuous inception of an epidemic is usually accompanied by difficulty in determining how to respond best. In developing nations, this can be compounded by logistical challenges, such as vaccine shortages and poor road infrastructure. To provide guidance towards improved epidemic response, various resource allocation models, in conjunction with a network-based SEIRVD epidemic model, are proposed in this article. Further, the feasibility of using drones for vaccine delivery is evaluated, and assorted relevant parameters are discussed. For the sake of generality, these results are presented for multiple network structures, representing interconnected populations—upon which repeated epidemic simulations are performed. The resource allocation models formulated maximise expected prevented exposures on each day of a simulated epidemic, by allocating response teams and vaccine deliveries according to the solutions of two respective integer programming problems—thereby influencing the simulated epidemic through the SEIRVD model. These models, when compared with a range of alternative resource allocation strategies, were found to reduce both the number of cases per epidemic, and the number of vaccines required. Consequently, the recommendation is made that such models be used as decision support tools in epidemic response. In the absence thereof, prioritizing locations for vaccinations according to susceptible population, rather than total population or number of infections, is most effective for the majority of network types. In other results, fixed-wing drones are demonstrated to be a viable delivery method for vaccines in the context of an epidemic, if sufficient drones can be promptly procured; the detrimental effect of intervention delay was discovered to be significant. In addition, the importance of well-documented routine vaccination activities is highlighted, due to the benefits of increased pre-epidemic immunity rates, and targeted vaccination.
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