A survey of the prevalence of blowfly strike and the control measures used in the Rûens area of the Western Cape Province of South Africa.

Blowfly strike and the methods used to combat blowfly strike were recorded on 33 properties in the Rûens area of South Africa during 2003/2004. Data were recorded on Merino and Dohne Merino hoggets (n = 4951) with at least 3 months' wool growth. The following data were captured: presence or absence of strike, site of the strike (body or breech), presence or absence of dermatophilosis as well as subjective scores for wool quality and wool colour. Control measures recorded include: chemical treatment (preventative and spot treatment), crutching, mulesing and the use of the Lucitrap system. Blowfly strike was not significantly influenced by gender or breed. Hoggets suffering from dermatophilosis were more likely to be struck, compared with contemporaries not suffering from the skin disorder (0.057 vs 0.027; P < 0.05). Merino hoggets generally had higher scores than their Dohne Merino contemporaries for wool quality (32.6 vs 27.4; P < 0.05) and wool colour (29.0 vs 27.2; P < 0.05). There was an indication that the Lucitrap system may have reduced flystrike, but the effect was not statistically significant (P = 0.19 for overall strikes and P = 0.12 for body strike). The Mules operation benefited overall flystrike (0.013 vs 0.110; P < 0.05); mainly through an effect on breech strike (0.010 vs 0.109; P < 0.05). The proportion of fly strikes increased with wool length, and declined with an increase in farm size in wool colour score. None of the ethically acceptable control measures assessed could substantially reduce blowfly strike on their own, and an integrated pest management programme was proposed.

The oral susceptibility of South African field populations of Culicoides to African horse sickness virus.

Twenty-two isolates of African horse sickness virus (AHSV), representing its distinct serotypes, geographical and historical origins, were fed to three populations of South African livestock-associated Culicoides spp. (Diptera, Ceratopogonidae). Infective blood meals included 12 recent isolates, nine historical reference strains and one live attenuated vaccine strain serotype 7 (AHSV-7) of the virus. Field-collected midges were fed through a chicken-skin membrane on sheep blood spiked with one of the viruses, which concentrations ranged from 5.4 to 8.8 log(10)TCID(50)/mL of blood. After 10 days incubation at 23.5 degrees C, AHSV was isolated from 11 Culicoides species. Standard in vitro passaging of AHSV-7, used for the preparation of live attenuated vaccine, did not reduce its ability to infect Culicoides species. Virus recovery rates in orally infected Culicoides midges differed significantly between species and populations, serotypes, isolates and seasons. Significant variations in oral susceptibility recorded in this study emphasize a complex inter-relationship between virus and vector, which is further influenced by multiple intrinsic and extrinsic factors. As it is not possible to standardize all these factors under laboratory conditions, conclusive assessment of the role of field-collected Culicoides midges in the transmission of orbiviruses remains problematic. Nevertheless, results of this study suggest the potential for multi-vector transmission of AHSV virus in South Africa.

Seasonal occurrence and production effects of the biting louse Damalinia limbata on Angora goats and 2 treatment options.

Adult biting lice Damalinia limbata (Gervais 1844) were most numerous on Angora goats in southwestern Free State Province from November to May with the smallest numbers present during August. Nymphs were most numerous from January to March with the smallest numbers present during July. The largest proportion of adult lice was present on the ventral surface of goats during winter, when population numbers were lowest, and the largest proportion of nymphs during summer, when population numbers were highest. Infestation did not affect the body weight of goats, but adversely affected both the quantity and quality of mohair produced. A single treatment with deltamethrin, applied as a pour-on along the mid-line of the backs of the goats, effectively controlled infestation and resulted in a significant increase in mohair production compared with untreated goats. Deltamethrin sprayed along the sides of the animals was equally effective in controlling infestation.

Aspects of excretion of antlion larvae (Neuroptera: myrmeleontidae) during feeding and non-feeding periods.

The main nitrogenous excretory products were determined for third instar Cueta sp. and Furgella intermedia larvae during periods of food abundance and for F. intermedia during starvation periods. Biochemical analysis indicated that allantoin was the main nitrogenous excretory product, with smaller quantities of ammonia, urea and uric acid. Respectively 9 and 13amino acids of low concentrations (0.005-0.329g/l) were detected by high pressure liquid chromatography in the excreta of Cueta sp. and F. intermedia larvae. The volume of urine produced and concentrations of the nitrogenous excretory products of fed Cueta sp. and fed F. intermedia larvae did not differ. F. intermedia excreted smaller volumes of urine and smaller quantities of nitrogenous excretory products during starvation than during periods of food abundance. Feeding conditions rather than the pitbuilding or non-pitbuilding lifestyles seem to be the major influence on the excretory products of these antlion larvae.

Utilisation of prey by antlion larvae (Neuroptera: Myrmeleontidae) in terms of energy and nutrients.

Prey utilisation at low prey densities was determined for third instar Cueta sp., Furgella intermedia (Markl) and Palpares annulatus (Stitz) larvae in terms of wet weight, dry weight, energy and nutrients. Prey utilisation was similar to other insects on a wet weight (42-47%), dry weight (46-49%), energetic (40-58%) and nutritive basis (62-79%). Lipids (33-36%) provided energetically the highest contribution of the nutrients ingested. The quantities of water, proteins, nucleic acids, lipids and carbohydrates extracted by the antlion larvae were in proportion to their availability in their prey, the Hodotermes mossambicus larvae. The quantities of nutrients extracted by the antlion larvae at low prey densities were not significantly influenced by the differences in mandible size, antlion body weight or the trapping method (building a pit or not) of the antlion species. It is proposed that a low metabolic rate and the accumulation of fat reserves, and not the extent of prey utilisation, enable P. annulatus larvae to tolerate a 123-d starvation period in which 22.3% of their body weight is lost.

Seasonal abundance and parity of stock-associated Culicoides species (Diptera: Ceratopogonidae) in different climatic regions in southern Africa in relation to their viral vector potential.

Seasonal abundance and parity in Culicoides populations, in the vicinity of livestock, were determined at seven sites in five different climatic regions with 220 V down-draught blacklight-traps. In 418 collections made between October 1983 and December 1986, a total of 2,134,171 Culicoides, of which 342,571 were identified to species level and sexed, were collected; 267 of these collections (182,321 Culicoides) were graded for parity. In the frost-free summer rainfall area, Culicoides were collected in large numbers in light-traps throughout the year; this implies breeding and possible virus transmission throughout the winter in certain parts of South Africa. However, where frost occurred, Culicoides numbers usually peaked in late summer and dropped sharply after the first frost. In the latter areas, small Culicoides collections during winter may be due to low winter temperatures and rainfall; low temperatures negatively affect adult activity and reduce the rate of development of larvae and pupae; low rainfall would lead to a reduction of available larval habitats. Relatively large numbers of Culicoides were collected in winter in the temperature frost-free winter rainfall area. In each of the four summer rainfall areas, one Culicoides species remained dominant throughout the year: at two of these areas this species was C. imicola. Other abundant species in some of these summer rainfall areas were C. schultzei s.l. and C. zuluensis. In the winter rainfall area, C. zuluensis, C. magnus, C. gulbenkiani and C. imicola shared abundance. It was established that abdominal pigmentation is an indicator of parity in C. imicola in South Africa. With the increase in Culicoides numbers towards the end of summer, there was also a rise in the proportion of parous (pigmented) females in most Culicoides species, which signifies a higher vector potential for African horsesickness and bluetongue towards the end of summer. This coincides with the seasonal occurrence of viral diseases transmitted by Culicoides species. Nulliparous (unpigmented) females of all Culicoides species were present throughout the year at all sites where Culicoides were continuously collected, confirming uninterrupted breeding in these areas.

Geographical distribution and relative abundance of stock-associated Culicoides species (Diptera: Ceratopogonidae) in southern Africa in relation to their potential as viral vectors.

To determine the geographical distribution and relative abundance of Culicoides species associated with livestock, 220-V down-draught light-traps equipped with 8-W blacklight tubes were operated at 34 sites in different climatic regions in South Africa and Lesotho. From January 1984 to September 1986, 3 041 631 Culicoides, belonging to at least 50 species, were collected in a total of 959 collections. Of these, 572 412 individuals were identified and sexed. Culicoides species were found to be widespread in South Africa and were collected in varying numbers at all the sites sampled. The average catch size, however, was larger in frost-free areas than in areas with extreme winters. The more abundant and widespread species, which have the potential to be vectors of stock-associated viruses such as bluetongue and African horsesickness, were C. imicola, C. leucostictus, C. schultzei s.l., C. pycnostictus, C. nivosus, C. similis, C. zuluensis, C. magnus, C. bedfordi, C. neavei, C. brucei, C. tropicalis, C. exspectator, C. gulbenkiani, C. bolitinos, C. ravus, C. coarctatus and C. onderstepoortensis. Of these, C. imicola was the most abundant species, being dominant at 17 of the 34 sites sampled and accounting for 71.4% of the specimens collected. As C. imicola is relatively uncommon in hot and dry as well as cool and wet areas, this species cannot be regarded as the only vector of stock-associated viruses in southern Africa. Further laboratory vector-competence studies, i.e. determination of viral-infection and -transmission rates, should first concentrate on the above-mentioned Culicoides species, especially those known to feed on livestock.

Establishment and characterization of a cell line from the mosquito Culex (Culex) theileri (Diptera: Culicidae) and its susceptibility to infection with arboviruses.

The mosquito Culex (Culex) theileri Theobald is probably the major vector of Rift Valley fever (RVF) virus during epizootics on the inland plateau of southern Africa. A cell line was established from the tissues of this mosquito species to facilitate laboratory studies on RVF and other arboviruses. After temperature pretreatment, egg rafts from a laboratory colony were disinfected, mechanically disrupted, and grown in preconditioned Eagles minimum essential medium supplemented with 10% fetal calf serum. The cells were characterized by their protein content, karyology, and their susceptibility to three arboviruses. Although high infectivity titers were obtained, no cytopathic effects were produced by these viruses. The cell line was shown to be free from latent viruses. These results show that this cell line may be employed fruitfully in arbovirus studies.