Academy of Science of South Africa (ASSAf): Open Journal Systems
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The sustainable use of wild species benefits biodiversity and human well-being in South Africa
No full textEye morphology and colour preferences in a semi-field test of the pine pest, Sirex noctilio (Hymenoptera: Siricidae)
No full textThe woodwasp, Sirex noctilio, is a global pest of pines. Although it is known to be attracted to light and possess sexually dimorphic body colouration, the visual ecology of S. noctilio is poorly understood. Photoreceptor sensitivity of the compound eyes in S. noctilio is not sexually dimorphic. These previous results suggest that colour tracking of one sex by the other might not be an important input for mate searching. This study aimed to expand our knowledge of the visual system of S. noctilio by means of i) morphological description of the compound eyes and ocelli; and ii) semi-field behavioural tests of the colour preference of newly emerged wasps. Eye and ocellus morphological features were investigated in 21 males and 21 females. Measurement of male and female median ocellus diameter, compound eye surface area, number of ommatidia and facet diameter varied from 0.22 to 0.40 mm, 0.589 to 2.277 mm2, 1820 to 4207 and 1.88 × 10–2 to 2.82 × 10–2 mm, respectively. In addition, all traits significantly correlated with body size. Male and female wasps emerged from infested host material in a flight cage with five traps, each reflecting a different colour. Analysis of trap captures did not identify any colour preference, but an effect of trap location was observed with traps in the north-eastern position capturing more woodwasps, suggesting that other factors, e.g., global landmarks or other non-colour visual cues might guide initial flight behaviour of S. noctilio
Phytochemicals, bioactivity, and ethnopharmacological potential of selected indigenous plants
No full textThe coastal regions of Africa are endowed with indigenous wild fruit plants rich in nutritional and medicinal phytochemicals and micronutrients. South African wild fruit plants complement the diet and health needs of rural poor households by providing vital dietary nutrients and remedies for various health concerns, and alleviating food insecurity. Milk plum, Natal plum, wild custard apple, and wild medlar medicinal plants are found mainly in the coastal provinces of South Africa. Studies have established that these plants are good sources of vitamins, essential elements, and bioactive phytocompounds such as flavonoids, phenolic acids, and terpenoids, which demonstrate significant antioxidant, antimicrobial and anti-inflammatory activities. The plants studied possess anti-epileptic, antiplasmodial, and snake antivenom qualities. Here we highlight the views of different reports on ethnopharmacological relevance, phytochemistry, and bioactivity of the selected South African indigenous medicinal plants. We found a research gap in the phytochemical composition and phytopharmacological activity evaluation of Carissa macrocarpa and Englerophytum magalismontanum.Significance:
South African indigenous medicinal plants augment the dietary and other health needs of the rural populace. The phytochemistry and phytopharmacological activities of C. macrocarpa and E. magalismontanum have been only partially studied, hence the need for further studies to examine their worth and possible use in cosmetic product enrichment
The effect of elevated temperatures on trichomes, essential oil composition and yield of Lippia javanica: A chemometric approach
No full textExtreme changes in climate, especially in temperature, could have implications for herbal plants in various world regions. Medicinal plants often produce a wide variety of natural phytochemicals to enhance their defence and survival mechanisms against harsh environmental conditions, and when these mechanisms fail, plants consequently die. We investigated the impact of high temperatures coupled with the specific duration of exposure on the yield and composition of essential oils and trichomes in leaves of Lippia javanica. Plants were exposed to increasing temperatures (25 °C to 47 °C) for different durations (48 h to 144 h). Response surface methodology was applied to assess the interaction between temperature and length of exposure on the essential oil yield, trichome length, and trichome diameter. Essential oils were recovered from the control and treated leaf samples using hydrodistillation and volatile compounds were identified through gas chromatography–mass spectrometry (GC-MS). Multivariate analysis modelling allowed different clustering patterns to be detected. That is, increasing temperatures raised the oil yield, trichome length, and diameter from 1.007 mg/100 g to 3.58 mg/100 g, 50 µm to 160 µm, and 25 µm to 60 µm, respectively. Significant chemical differences between the essential oils were confirmed by the principal component and orthogonal projections to latent structures, which identified separate clusters for the control and treated samples. The current findings indicate that L. javanica has coping mechanisms against high temperatures.Significance:
High temperatures significantly alter the trichome morphology and secretion of essential oils in L. javanica, which adversely affects the shrub’s medicinal properties. Regardless of climate change, this finding could have major implications for indigenous people who continue to use the shrub for therapeutic purposes.
L. javanica showed coping mechanisms against high temperatures for a maximum of six days; however, a prolonged exposure would be more detrimental. As a result, climate change will negatively influence the plant’s developmental and defence mechanisms
Deep learning for photovoltaic defect detection using variational autoencoders
No full textFaults arising in photovoltaic (PV) systems can result in major energy loss, system shutdowns, financial loss and safety breaches. It is thus crucial to detect and identify faults to improve the efficiency, reliability, and safety of PV systems. The detection of faults in large PV installations can be a tedious and time consuming undertaking, particularly in large-scale installations. This detection and classification of faults can be achieved using thermal images; use of computer vision can simplify and speed up the fault detection and classification process. However, a challenge often faced in computer vision tasks is the lack of sufficient data to train these models effectively. We propose the use of variational autoencoders (VAEs) as a method to artificially expand the data set in order to improve the classification task in this context. Three convolutional neural network (CNN) architectures – InceptionV3, ResNet50 and Xception – were used for the classification of the images. Our results provide evidence that CNN models can effectively detect and classify PV faults from thermal images and that VAEs provide a viable option in this application, to improve model accuracy when training data are limited.Significance:
Faults in PV systems can be labour and time consuming to detect and classify. This process can be automated by using computer vision and thermal images.
CNN models (InceptionV3, ResNet50 and Xception) are effective in the detection and classification of PV faults from thermal images.
Small data sets are a common barrier to entry for computer vision assessments. VAEs provide an effective method to artificially expand a limited data set to allow for the successful use of CNN models.
The expansion of training data using VAEs for CNN models can improve the prediction accuracy in these models.
Efficacy of Beauveria bassiana against adults of Prostephanus truncatus (Horn), Sitophilus zeamais Motschulsky and Teretrius nigrescens Lewis in stored maize
No full textThe larger grain borer, Prostephanus truncatus (Horn) and the maize weevil, Sitophilus zeamais Motschulsky continue to cause tremendous losses to stored maize. Research in the UK has identified Beauveria bassiana, IMI 389521 as a suitable control agent for grain storage pests in the UK. The pathogenicity of B. bassiana, IMI 389521 was evaluated against adult P. truncatus, S. zeamais and Teretrius nigrescens in Ghana. Fifty adults of each insect species were treated with 0.5 g dry conidia powder of this isolate at 8.65 × 108 conidia/g for 1 minute and mortality recorded daily for 14 days. The results indicated that B. bassiana, is pathogenic against P. truncatus and S. zeamais, inducing over 90% mortality by day 7. Teretrius nigrescens was, however less susceptible to the fungus with 30% mortality. To determine the most effective concentration of B. bassiana for the control of P. truncatus, a laboratory dose response experiment using four concentrations of B. bassiana (108–1011 cfu/kg maize) was also conducted. Maize grains (250 g) in separate jars were treated with the four concentrations of the product. Fifty adults of P. truncatus were placed into the jars containing the treated maize and mortality was assessed weekly for 3 weeks. The most effective dose was 1010 cfu/kg maize, which resulted in 96% and 100% mortality of P. truncatus after 2 and 3 weeks, respectively. This study shows that B. bassiana could effectively be integrated into bio-control programme of these two key pests of maize in Ghana after further field trials
“It’s easy to just be normal”: Performative masculinities in Die stropers
No full textIn post-apartheid South Africa, the representation of queer identities in Afrikaans-language films have become increasingly prominent. However, many such films focus on past contexts or serve as comedic depictions, failing to confront the complex issues faced by individuals in contemporary Afrikaner communities. Etienne Kallos’s 2018 coming-of-age film Die stropers (The Harvesters) candidly depicts the challenges faced by adoptive brothers Janno and Pieter, who must negotiate desire and gender in a conservative, Afrikaans farming community. Drawing on Judith Butler’s notion of gender performativity and recent reformulations of Raewyn Connell’s notion of hegemonic masculinity, we examine the discursive (re)production of hegemonic Afrikaner masculinity within the boys’ adoptive family and community. We investigate how the protagonists strategically deploy performative masculinities to achieve belonging and acceptance as heirs, even if the ideals they emulate oppress and restrict them. We propose that the protagonists’ strategic deployment of performative masculinities represents their claiming of agency in contexts where gender and desire are aggressively policed. Furthermore, their navigation of hegemony in this white, Afrikaner community through resistance and consent might point to a claiming of space for queer identities and the continued transmutation of hegemonic masculinity
The post-heroism of Stuur Groete aan Mannetjies Roux and Verraaiers
No full textThere is much scholarship on the linkages between Afrikaner nationalism and South African (Afrikaans-language) filmmaking. Within the context of a sustained post-apartheid renegotiation of Afrikaans or Afrikaner nationalism in the popular imagination, in this article we argue that two feature film historical dramas from the production company Bosbok Ses Films, Stuur groete aan Mannetjies Roux (2013) and Verraaiers (2013), resonate thematically and aesthetically with Thomas Elsaesser’s notion of post-heroic cinema. While a number of pre-1994 Afrikaans-language films celebrated Afrikaner nationalism as personified in the figure of the hero, this article positions and uses Elsaesser’s post-heroism as a critical lens through which to demonstrate the ways in which these two films call attention to a post-hero whose actions and behaviour (often inadvertently) renders a productive renegotiating of the hero figure within a post-apartheid cinematic context. To supplement Elsaesser, we also draw on Johan Degenaar’s writing on political pluralism. In this article, we find that an Elsaesserian post-heroic approach to the two films allows the following constitutive components of post-heroic cinema to surface: atemporality as opposed to linear narrative time, parapraxis (productive failure) as opposed to traditional iterations of heroic acts and valour, and conceiving of the film screen as a surface in flux as opposed to the screen as a mirror. The article’s contribution to existing scholarship on contemporary Afrikaans-language cinema is three-fold: it is the first to utilise an Elsaesserian approach to Afrikaans film and as such to foreground and investigate the figure of the post-hero, it provides a critical account of two independently-made feature films that remain under-researched in current South African film scholarship, and it contributes to discourse around the ways in which popular media inform and respond to the renegotiation of Afrikaans (or Afrikaans) identity