Zoology and Entomology
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Browsing Zoology and Entomology by Subject "Activity patterns"
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Item Open Access Aspekte van die biologie van tuinduiwe (Columba livia) in die Bloemfonteinse stadsgebied(University of the Free State, 2007-05) Le Roux, Pieter Daniël Stephanus; Kok, O. B.; Butler, H. J. B.English: Owing to the increase of complaints in the city of Bloemfontein concerning the damage being caused to buildings by birds, different aspects of the biology of feral pigeons (Columba livia) was investigated. Close to 400 pigeons, which included nearly 50 lost racing pigeons, were collected on a regular basis within the city boundaries over a period of one year (March 2005 - February 2006). Although slightly more male birds were obtained, no significant variance from a balanced sex ratio in the population structure was distinguished. Feral pigeons moult continuously throughout the year at a relatively low intensity rate. Conspicuous peaks in the moulting of primary, secondary and tail feathers were observed for both sexes, however, the period for replacement was slower for females. Leucism was displayed by more than a quarter of the birds. Feral pigeons are more frequently infected with parasitic louse flies compared to local rock pigeons (Columba guinea), with the highest infection occurring during the summer months. Apart from measurements of the beak, the standard body measurements of adult males are significantly larger compared with their female counterparts. A similar trend applies in the different sexes of juvenile feral pigeons as well as racing pigeons. The seasonal variation in the body weight and visible fat deposits of adult feral pigeons probably coincides with the birds' breeding activity and the temporary availability of abundant food supplies. A prominent peak in the activity of the ovarian cycle of female birds, based on the weight and diameter of macroscopic follicles, coincides with the gonad cycle of male feral pigeons which occurs during the early winter months, followed by a smaller peak during spring. Based on the presence of nests, eggs and chicks, feral pigeons breed throughout the year with a decrease in breeding activity during the wetter summer months. Nest types vary from dried droppings on which eggs are laid to firmly-built, dry stick nests. After hatching from a typical clutch of two eggs the weight of the chicks increase daily on a linear scale. Both parents are involved in the hatching and raising of the chicks. Second or subsequent clutches are laid regularly throughout the year at the same nesting site. Rock and feral pigeons may interbreed, however this phenomenon is rarely documented. Agricultural crops including maize (Zea mays), sunflower (Helianthus annuus) and wheat (Triticum aestivum) are the most important components of the diet of feral pigeons living at the SASOL library on the campus of the University of the Free State. The diet of birds living within the city centre consists mainly of natural vegetation of which seeds of the Camdeboo stinkwood (Celtis africana) constitutes the most important component. The low percentage of animal matter consists largely of pupae of Diptera and egg cocoons of unidentified earthworms, while grit constitutes the largest component of inorganic matter. No significant statistical difference was found in the composition of the different sexes' diet. Under experimental conditions feral pigeons show a definite affinity towards maize in comparison with sorghum (Sorghum almum), sunflower and wheat. Associated with the latter, yellow food items are preferred above blue, green and red coloured items. Single birds eat on average more over a short term (10 minutes) than individuals which feed in groups, but almost equal amounts of food are ingested by individuals over a longer period (2 hours). Feral pigeons living on the university campus leave their nesting sites daily just after sunrise to go and feed on agricultural crops on the surrounding farmlands, returning approximately two hours later. Birds feeding in the city were mainly found on the ground during the early morning hours and to a lesser extent during the afternoon. The birds usually spend the hot midday hours in the shade. Lost racing pigeons regularly join local feral populations in urban areas. With the consideration of appropriate national and/or municipal laws, the shooting of feral pigeons with airguns and/or the provision of alpha-chloralose treated bait seems to be the most effective way in which their numbers in urban areas may be controlled. The introduction of natural enemies such as owls and/or falcons into urban areas could also be considered as a method of control of feral pigeon numbers.Item Open Access Biology and control of the mango seed weevil in South Africa(University of the Free State, 2008) Louw, Cornelia Estelle; Van der Merwe Louw, S.English: The mango seed weevil (MSW), Sternochetus mangiferae (Fabricius) (Coleoptera: Curculionidae), generally causes few problems on early-season cultivars, since the fruit are marketed and consumed before adult emergence from the fruit. Adult emergence from late-hanging cultivars, however, results in unattractive lesions that influence the marketability of the fruit. There is little evidence that MSW influences yield, although some authors argue that MSW development in the seed may lead to premature fruit drop. The economic impact of the MSW is primarily based on the fact that it is a major phytosanitary pest, restricting access to new foreign markets and contributing to substantial rejections of fruit destined for existing export countries. The MSW has no natural enemies, is monophagous on mango and completes its entire life cycle within the mango seed. The impact of this pest can, therefore, be greatly reduced by orchard sanitation. Sanitation practices, however, are labour intensive, necessitating producers to rely on alternative or additive control measures. Several semi-penetrant and contact pesticides are registered for MSW control. However, with trans-laminar products it is imperative that treatments coincide with, or are applied just after, the onset of weevil oviposition. This requires intensive and accurate scouting programmes, with an in-depth knowledge regarding the duration of oviposition necessary to ensure seasonal control. When using contact insecticides, applications should coincide with seasonal and daily activity peaks to ensure direct contact. Since adult weevils are extremely inactive, this necessitates an in-depth knowledge of MSW activity patterns. It is also imperative to understand the development cycle and life strategies of the insect in order to know at which time intervention would prove to be the most effective. The product most generally used for MSW control in the Hoedspruit magisterial district of the Limpopo Province is fenthion (Lebaycid® EC 500g/ℓ a.i.). This product is very effective, but does not provide 100% control and can lead to secondary infestations of mango scale, Aulacaspis tubercularis (Newstead) (Hemiptera: Diaspididae), and mealybug (various species). The use of organophosphates on fruit destined for certain overseas markets is also under investigation by the EU. It is for this reason that Westfalia Technological Services, over the past four years, investigated various aspects of MSW general biology, reproduction and control. The investigation into the activity patterns of adult weevils indicated that MSW were crepuscular – nocturnal insects. For this reason, applications with contact insecticides aimed at controlling the adult weevil would be expected to be more efficacious when applied at dusk. During the study investigating MSW development, it was found that the majority of MSW eggs hatched between 7 and 14 days, with some of the first instar larvae already having penetrated into the seeds between 7 and 14 days after oviposition, depending on whether the eggs were laid early or late in the season. This implies that chemical control with contact and semi-penetrant chemicals, aimed at controlling the MSW larvae, should preferably not commence later than 7 days after observing the first eggs in the orchards. However, it was found during the course of this study that MSW oviposition commenced during the latter part of September and continued up to the latter part of January, a period considerably longer than previously stated in the literature. For this reason, more than one chemical application would be warranted. While investigating alternative chemical control measures, it was found that a single application with the systemic insecticide, thiamethoxam (Actara™ SC 240g/ℓ a.i.), applied during flowering in the root zone, rendered seasonal MSW control. The use of this product, therefore, negates the necessity of tedious fruit inspections and an in-depth understanding of the pest in order to determine the most appropriate time for chemical intervention.