Parasitism of Plutella xylostella (Lepidoptera, Plutellidae): field and laboratory observations
- Authors: Waladde, S M , Leutle, M F , Villet, Martin H
- Date: 2001
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/442239 , vital:73969 , https://doi.org/10.1080/02571862.2001.10634397
- Description: Investigations carried out at Alice and its rural environs in the Eastern Cape province of South Africa, showed that parasitoids affecting the diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae) were Cotesia plutellae, Apanteles eriophyes, Diadegma sp., Diadromus collaris, Oomyzus sokolowskii and Hokeria sp. Cotesia plutellae was active all year round and accounted for 30–50% parasitism of P. xylostella. Field experiments using three cabbage cultivars, grown under pesticide-free conditions, indicated that C.plutellae achieved rates of parasitism as high as 90–95% for at least eight months of the year. In winter and early spring parasitism by C. plutellae was less than 30% in the field. This level of parasitism coincided with rising pest density resulting in a pest increase in early spring when C. plutellae appeared unable to control the high pest numbers. Towards the latter part of spring and early summer, C. plutellae parasitism and that of the other parasitoids increased. The possibility of using indigenous parasitoids especially C. plutellae in the management of P. xylostella in this area requires further investigation.
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- Date Issued: 2001
Preliminary observations on the effects of hydrocortisone and sodium methohexital on development of Sarcophaga (Curranea) tibialis Macquart (Diptera: Sarcophagidae), and implications for estimating post mortem interval
- Authors: Musvasva, E , Williams, Kirstin A , Muller, Nikite W J , Villet, Martin H
- Date: 2001
- Language: English
- Type: text , Article
- Identifier: vital:7075 , http://hdl.handle.net/10962/d1009532
- Description: Larvae of Sarcophaga (Curranea) tibialis (S. tibialis) were reared at constant temperature on chicken liver treated with a steroid or a barbiturate at concentrations that would be lethal, half-lethal and twice-lethal doses for humans. Trends to greater mortality at higher drug concentrations were not statistically significant. Larvae exposed to either drug took significantly longer to reach pupation compared to those in the control, while larvae exposed to sodium methohexital passed through pupation significantly faster than those in the control. No systematic relationship was found between drug concentration and development time of larvae or pupae. The total developmental period from hatching to eclosion did not differ between treatments, implying that estimates of post mortem intervals- (PMI) based on the emergence of adult flies will not be affected by the involvement of these drugs in a case. On the other hand, anomalous pupation spans may indicate the presence of barbiturates. These findings are compared with patterns found in another fly fed other contaminants.
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- Date Issued: 2001
Cicadas (Hemiptera, Homoptera: Cicadoidea) of Mkomazi
- Authors: Villet, Martin H , van Noort, Simon , Packer, M
- Date: 1999
- Subjects: To be catalogued
- Language: English
- Type: text , book chapter
- Identifier: http://hdl.handle.net/10962/442756 , vital:74030 , ISBN , https://doi.org/10.1046/j.1472-4642.2001.00094.x
- Description: The cicadas are a group of insects belonging to the order Hemiptera which comprises a diverse range of insects including the bugs, leafhoppers, aphids, scale insects etc. The Hemiptera are characterised by specialised mouth parts that are adapted for piercing and sucking up sap from host plants or animal juices from their prey. All cicadas are plant feeders and can be extremely camouflaged when sitting and feeding on a branch, although the males give themselves away by their persistent, often high pitched calls.
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- Date Issued: 1999
On two species of Paectira Karsch (Hemiptera: Cicadidae) from Kenya
- Authors: Villet, Martin H
- Date: 1999
- Language: English
- Type: Article
- Identifier: vital:6850 , http://hdl.handle.net/10962/d1011131
- Description: During an ongoing revision of the genera of southern African Cicadidae (Hemiptera), examination of the holotype of Xosopsaltria fuliginosa Distant, 1905, showed that this species is not a member of Xosopsaltria Karsch, 1890, but that it belongs in the genus Paectira Karsch, 1890 (= Inyamana Distant, 1905). It is redescribed and illustrated here. As Heller's (1980) revision of this genus highlighted the paucity of records of species in this endemic East African taxon, details of material of Paectira jeanuaudi Boulard, 1977, from the Rhodes University Entomological Collection are recorded here. The specimens are in the Natural History Museum, London (BMNH), and the Albany Museum, Grahamstown (AMGS). All drawings were made using a Wild M5 stereomicroscope and camera lucida, and morphometric details of specimens were measured with vernier callipers. Anatomical terminology follows Boulard (1972) and Villet (1987,1997).
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- Date Issued: 1999
Reproductive behaviour of Plectroctena mandibularis F. Smith (Hymenoptera: Formicidae), a ponerine ant with ergatoid queens
- Authors: Villet, Martin H
- Date: 1999
- Language: English
- Type: Article
- Identifier: vital:6890 , http://hdl.handle.net/10962/d1011650
- Description: [From the text]: The present study reports on new observations on the reproductive biology of P. mandibularis, particularly the phenology of males, mating behaviour and colony founding, that may help in deciding between alternative explanations for the occurrence of ergatoid queens in this species.
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- Date Issued: 1999
Systematic status of Plectroctena mandibularis Smith and P. conjugata Santschi (Hymenoptera: Formicidae: Ponerini)
- Authors: Villet, Martin H , McKitterick, L , Robertson, H G
- Date: 1999
- Language: English
- Type: text , Article
- Identifier: vital:6893 , http://hdl.handle.net/10962/d1011653
- Description: Plectroctena mandibularis Smith is the type species of Plectroctena F. Smith. Because there has been some doubt about its distinctness from P. conjugata, several techniques were used to assess the systematic status of the two species. Most crucially, several colony series contained workers of both phenotypes, and where these series included queens or males, the distinguishing feature of these specimens was not consistently related to those of the workers. Queens, males and workers did not manifest qualitative differences between the taxa, and morphological variation was continuous between the two. The putative morphological basis (funicular index) for distinguishing workers of the taxa arose from allometric variation. Putatively diagnostic colour variation in males was related to latitude, but no simple pattern of morphological variation could be correlated with geographical distribution. Plectroctena conjugata is therefore considered a junior synonym of P. mandibularis.
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- Date Issued: 1999
Clinal morphometric variation in wild honey bees (Hymenoptera: Apidae) in South Africa
- Authors: Steele, G R , Villet, Martin H , Radloff, Sarah E , Hepburn, H Randall
- Date: 1998
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/442622 , vital:74015 , https://www.jstor.org/stable/2999809
- Description: As a result of side effects of the accidental dispersal of the Cape honey bee, it has become of agroeconomic importance to delineate the region within South Africa where thelytokous worker honey bees occur so that apicultural movement of bees does not exacerbate the problem. Thelytokous workers are believed to be unique to Apis mellifera capensis, so that the problem is to find morphological markers distinguishing this race from its A. m. scutellata neighbours. However, no evidence of the expected hybrid zone demarcating races could be found. Factor analysis revealed only one spherical cluster of samples. Trend surfaces of the local mean morphometric factor scores showed a cline that paralleled latitude, with distortions relating to montane and continental effects. Discriminant function analysis implicated certain mountain ranges in amplifying the effects of latitude. Trend surfaces of local intercolony factor variance showed morphometric homogeneity across most of the country. We conclude that there is only a single population of honey bees in South Africa, and that it shows climate-correlated clinal variation. If the transportation of bees for commercial apiculture is to be successfully regulated to solve the `capensis calamity', further research should focus on the geographical distribution of thelytokous workers rather than on the capensis phenotype. Such workers have a wider distribution than capensis, occurring also at high frequencies around the type locality of A. m. scutellata.
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- Date Issued: 1998
Finding the optimum: fluoridation of potable water in South Africa
- Authors: Muller, Wilhelmine J , Heath, R G M , Villet, Martin H
- Date: 1998
- Subjects: Water SA
- Language: English
- Type: Article
- Identifier: vital:6921 , http://hdl.handle.net/10962/d1011904
- Description: Since the South African Department of Health has tabled legislation to make fluoridation of public water supplies mandatory, the issue of whether fluoride is beneficial or harmful has, once again, become controversial in South Africa. We reviewed the literature, the experiences of fluoridation in overseas countries and the latest WHO recommendations, and have found that fluoride is desirable at certain levels, and undesirable above these. The following recommendations are made for optimum fluoride levels in South Africa's potable water: The decision to fluoridate a public water supply must be a community decision taken after public consultation. However, it can only be reached when the public is properly informed about the issue. Optimum levels of fluoride for human health range from 0.4 to 0.7 mg F/l, depending on the maximum mean annual temperature. The maximum level of 0.7 mg F/l should not be exceeded. Accordingly, it is recommended that in areas where natural fluoride concentrations in the drinking water exceed 0.7 mg F/l steps be taken to defluoridate the water. As an interim measure, a scale of temperature-adjusted optimum fluoride levels should be adopted in South Africa, rather than a single level covering the wide-ranging ambient temperatures (and corresponding consumption rates of drinking water) in the country. A sliding scale would mean that the community within a water supply region can determine its own fluoride consumption within the optimum range. Fluoridation should be considered only a short-term measure, until economic conditions are such that all South Africans have access to proper dental health care. The duration of fluoridation of a community water supply, and the level of fluoridation (within the optimum range of fluoride levels) should both be considered community decision. However, defluoridation should be a permanent necessity in those areas where the drinking water exceeds levels of 0.7 mg F/l.
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- Date Issued: 1998
Sexual dimorphism and tail-length in widowbirds and bishopbirds (Ploeeidae: Euplectes spp.): a reassessment
- Authors: Craig, Adrian J F K , Villet, Martin H
- Date: 1998
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/442306 , vital:73974 , https://doi.org/10.1111/j.1474-919X.1998.tb04551.x
- Description: No evidence for sexual selection in the evolution of tail‐length or wing‐length in widow birds and bishopbirds (genus Euplectes) was found when the methods used by previous authors were applied to a larger set of data. Nuptial tail‐length dimorphism scaled with body size dimorphism except in Euplectes progne, and interpopulation variation in taillength could be explained by genetic drift alone. Wing‐length appears to be under stabilizing selection and scales allometrically with body size, with no relation to tail‐length unless E. progne is included in the analysis.
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- Date Issued: 1998
The honeybees, Apis mellifera Linnaeus (Hymenoptera: Apidae) of woodland savanna of southeastern Africa
- Authors: Radloff, Sarah E , Hepburn, H Randall , Villet, Martin H
- Date: 1997
- Language: English
- Type: Article
- Identifier: vital:6829 , http://hdl.handle.net/10962/d1012341
- Description: The morphometric characters and sting pheromones of worker honeybees, Apis mellifera Linnaeus, were analysed by multivariate methods to identify discrete populations in the southeastern woodland savanna of Africa. A discrete population in Mozambique is classified as A. m. litorea Smith, a second in Zimbabwe as A. m. scutellata Lepeletier and a third group in southwestern Zambia as A.m. adansonii Latreille. A zone of introgression between the last two subspecies occurs in south-central Zambia and in the Zambezi Valley.
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- Date Issued: 1997
The use of wood ash for the protection of stored cowpea seed (Vigna unguiculata (L.) Walp.) against Bruchidae (Coleoptera)
- Authors: Katanga Apuuli, J , Villet, Martin H
- Date: 1996
- Language: English
- Type: Article
- Identifier: vital:6864 , http://hdl.handle.net/10962/d1011196
- Description: Dry wood-ash has been reported to provide effective, cheap and safe control of several pests of stored seeds by providing mechanical protection, especially if it is thoroughly mixed with the seed. Mixtures of seed and either clays, ash, talc, or sand are among the earliest recommendations for controlling bruchids in beans (Metcalf 1917; Headlee 1924; Subramanian 1935; Deay & Amos 1936; Lever 1941). Such use of ash has been reported on subsistence farms in Uganda (Davies 1970). However, little is known of the actual ratios of ash and beans needed for effective protection, or of the mechanism of protection. These issues motivated this investigation.
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- Date Issued: 1996
Description and identification of white grubs (Coleoptera: Scarabaeidae) attacking pineapple crops in South Africa
- Authors: Smith, Tamara J , Petty, G , Villet, Martin H
- Date: 1995
- Language: English
- Type: text , Article
- Identifier: vital:6853 , http://hdl.handle.net/10962/d1011134
- Description: Larvae of five species of scarabaeid beetles, Asthenopholis subfasciata Blanchard, Trochalus politus Moser, Macrophylla ciliata Herbst, Congela valida Peringuey and Adoretus ictericus Burmeister, and adults of a sixth species, Heteronychus arator (Fabricius), cause considerable economic damage to the root systems of pineapple plants. The biologies of the species differ, making reliable identification essential. Since no convenient method is available to identify them, both field and laboratory keys are provided for the identification of third instar larvae of the six species, and detailed, illustrated descriptions for confirming their identifications
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- Date Issued: 1995
Co-occurrence of mated workers and a mated queen in a colony of Platythyrea arnoldi (Hymenoptera Formicidae).
- Authors: Villet, Martin H
- Date: 1993
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447377 , vital:74619 , https://hdl.handle.net/10520/AJA00445096_510
- Description: A colony of Platythyrea arnold; was found to contain a functional queen and laying workers, both virgin and mated. This form of social organization has never been reported in ants before.
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- Date Issued: 1993
Winter absconding as a dispersal mechanism of the Cape honeybee
- Authors: Hepburn, H Randall , Villet, Martin H , Jones, G , Carter, A , Simon, V , Coetzer, W
- Date: 1993
- Language: English
- Type: Article
- Identifier: vital:6862 , http://hdl.handle.net/10962/d1011154
- Description: The dispersal characteristics of the African honeybee, Apis mellifera scutellata, resulted in a greatly mobile hybrid front in the New World, but in Africa its hybridization zone with the Cape honeybee, Apis mellifera capensis, appears very stable.The maintenance of stable hybrid zones is predicated on a balance between dispersal and selection Knowledge on the extent of gene flow from either race is in its infancy, and the probability of successful dispersal by either race has not yet been considered. Both capensis and scutellata are notorious for absconding, capensis the more so for resource-related seasonal absconding in winter. The two races also differ fundamentally in the ways they conserve heat both behaviourally and physiologically. We investigated the energy consumption and colony survival characteristics of capensis in terms of winter absconding in a climate with cycles of warm days interspersed with cold days. These are compared with calculated values for scutellata to assess whether capensis might have a directional gene flow advantage over scutellata in their zone of hybridization.
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- Date Issued: 1993