摘要:

Abstract.Information on 4049 cases of sheep blowfly strike on 495 farms in England and Wales was gathered in a longitudinal survey conducted in 1991. The breech was the most commonly infested area, accounting for 70.9% of all strikes recorded. Body strikes accounted for 19.7% and foot strikes 11.4% of all strikes. Early in the season the incidences of both breech and body strikes were higher in ewes than in lambs, but from June to October lamb strikes predominated. The incidence of foot strike was greater in ewes than lambs throughout the year, with a peak incidence in September. Regional differences in strike incidence were evident; the highest overall incidences were recorded in the southern regions of England where peak incidence occurred earlier in the year. The highest monthly incidence risk was recorded in August in the south‐east of England where there were 14.2 strikes per 1000 lambs and 4.0 strikes per 1000 ewes at risk. The importance of faecal soiling and ambient temperature are discusse

ISSN:0269-283X    

DOI:10.1111/j.1365-2915.1995.tb00110.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.Dissection of the ovaries of the mosquitoAedes aegypti(Diptera: Culicidae) revealed, in each ovariole, a group of seven to nine specialized epithelial cells in a region of the calyx wall that is enclosed by the end of the ovariolar sheath. This group of cells is termed the basal body. During ovulation, the mature oocyte passes from the ovariole into the calyx lumen through the basal body. Subsequently, granulation occurs in the basal body cells. The granular basal bodies differ from all previously described ovarian structures. In multiparous females the size and optical density of the granular basal bodies increase after each ovulation. Examination of the granular basal bodies in intact ovaries, stained with neutral red, provides an easy method for distinguishing parous from nulliparous females, and has potential as a new method of age grading.

ISSN:0269-283X    

DOI:10.1111/j.1365-2915.1995.tb00111.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.Age‐dependent changes in the ovarioles ofSimulium woodi(Diptera: Simuliidae) and the age structure of a wild population of this species in the Amani hills of north‐eastern Tanzania were studied using the ovarian oil injection technique. Contrary to previous theories, egg sacs degenerate completely and do not form dilatations. The physiological age of the females could be determined only by gonotrophic dilatations formed from degenerating follicles during gonotrophic cycles. In individual females, the proportions of ovarioles with degenerating follicles were 3–54% (mean 22%) in the first cycle and 8–61% (mean 36%) in the second gonotrophic cycle. Agonotrophic degenerating follicles occurred in 2% of ovarioles in 12% of females. Additional information with regard to the degree of parity is given by the level of granulation in the basal body of each ovariole, a group of six to eight cells in the calyx wall enclosed by the end of the ovariolar sheath. Their granulation progressively increased in intensity following each subsequent ov

ISSN:0269-283X    

DOI:10.1111/j.1365-2915.1995.tb00112.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.Crude neem products have earlier shown considerable promise for control of culicine mosquito vectors in rice fields as a by‐product of their agricultural use as fertilizers, but suffer from disadvantages of bulkiness and lack of stability in storage. Relatively stable lipid‐rich fractions of neem were shown to be as effective as good‐quality crude neem products in control of breeding of culicine vectors of Japanese encephalitis, and also produced a slight but significant reduction in populations of anopheline pupae. Neem‐based formulations coated over urea significantly increased grain yield, but used alone did not, whereas combining the use of neem‐coated urea and water management by intermittent irrigation had a greater effect on grain yield than that of water management alone. The neem fractions were relatively cost‐effective, and the combined water management and neem‐coated urea strategy is acceptable to farmers, who are already aware of the benefits of the use of neem‐coated urea, and of water management. This technology therefore has considerable promise as an environmentally benign method of rice‐field mosquito control that could be sustainably imple

ISSN:0269-283X    

DOI:10.1111/j.1365-2915.1995.tb00113.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.In a 3‐year study during 1990–92, larval collections of theSimulium damnosumcomplex from the River Corubal system in Guinea Bissau revealed that the only sibling species present wereS. sirbanumand the Konkouré form ofS. konkourense, but notS. damnosum s.s.which had been found at some of the localities (Saltinho and Cusselinta) in a previous survey by Quillévéréet at.(1981). Their differential distributions were seasonally consistent between years.S. sirbanumwas concentrated in the upper reaches of the Corubal, moving downstream at the end of the dry season to exploit new breeding grounds, whereasS. konkourenseseemed to be concentrated in the lower reaches and moved upstream in the middle of the dry season.Since the previous survey, it appears thatS. konkourensehas largely replacedS. sirbanumandS. damnosum s.s.in the lower reaches of the Corubal.S. sirbanumwas consistently associated with man‐biting behaviour and, although infection studies were not performed, it is likely thatS. sirbanumis the main vector of onchocerciasis in Guinea Bissau asS. konkourensedoes not seen to be anthropophilic.Among five polymorphic inversions inS. sirbanum, the frequency of inversion IL‐B increased during the dry season; IL‐2 and IIL‐7 showed homozygous disadvantage whereas IIL‐3 and IIIL‐6 did not; IS‐2 tended to be fixed in all populations.Simulium konkourensepopulations in the River Corubal differ from those found upstream in its tributary the River Koumba, in the Fouta Djallon of Guinea, by their sex chromosomes (having no sex‐linked inversions) and biting preferences, indicating that the populations are not freely interbreeding. Inversion IIIL‐X was found for the first time in populations ofS. konkourenseoutside the Fouta Djallon area and a new inversion IIL‐Y was identified in samples from th

ISSN:0269-283X    

DOI:10.1111/j.1365-2915.1995.tb00114.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.A village‐scale field trial of pyrethroid‐impregnated mosquito nets was undertaken in The Gambia, West Africa, in the Mandinka village of Saruja (13o13'N, 14o55'W) during July‐November 1989. Nearly all the villagers possessed and used their own bednets.Anopheles gambiaeis the main vector of human malaria in the area.An experimental wash‐resistant formulation of permethrin was compared with standard emulsifiable concentrate (EC) formulations of permethrin and lambda‐cyhalothrin, versus placebo‐treated bednets. Target concentrations of pyrethroids on bednets were permethrin 500mg/m2and lambda‐cyhalothrin 25 mg/m2. The experimental design involved random allocation of a treatment to one net per family. Whereas 68% of people questioned said they washed their nets fortnightly, observations during the 16‐week trial period showed that only 4/130 (3%) of nets involved in the trial had been washed as frequently as once per month.Early morning searches for mosquitoes under bednets (1 day/week for 16 weeks) found significantly more mosquitoes (60%An. gambiae) in placebo‐treated nets than in pyrethroid‐treated nets. The numbers found with each of the three pyrethroid treatments did not differ significantly from each other. Insecticidal efficacy of the treatments was tested by bioassays using wild‐caught unfed mosquitoes exposed to netting for 3min. Linear regression analysis of bioassay mortality against number of times that a net had been washed by villagers showed that nets impregnated with the wash‐resistant permethrin retained their insecticidal properties better than nets impregnated with lambda‐cyhalothrin or with the standa

ISSN:0269-283X    

DOI:10.1111/j.1365-2915.1995.tb00115.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.Variation in exposure of children to malaria vectors of theAnopheles gambiaecomplex was recorded in a Gambian village situated near an irrigated area of rice cultivation. Observations were made in 1987 and 1988 during two dry seasons, when pumped water was used to grow rice, and two rainy seasons, when rice was produced using a combination of irrigated and rainfed paddies. Routine collections of mosquitoes were made from under bednets. Most of these specimens were assumed to have fed on the occupants of the net and thus represented a crude measure of exposure to malaria. Most nets in the village were in good condition, but even these were a poor defence against blood‐seeking mosquitoes.Two annual peaks in the numbers ofAn. gambiae s.l.corresponded with the irrigation of rice paddies in the dry and wet seasons. When there were few vectors in the village the frequency distribution of mosquitoes caught under nets was described best by a Poisson process. When high numbers were present the daily distributions were over‐dispersed and fitted a negative binomial model. The spatial distribution of mosquitoes varied between dry and wet seasons and was related to the predominant wind direction at night, suggesting that wind assisted the dispersal of mosquitoes from their breeding sites.For individual children in the rainy season, increased exposure to malaria vectors was associated with living adjacent to a mosquito breeding site, being resident in larger compounds, having open eaves in the house, a store‐room adjacent to the bedroom, the absence of a ceiling in the bedroom, the absence of wood smoke indoors and leaving the bednet untucked at night. In the dry season a high level of exposure was associated with living close to a mosquito breeding site, having an unfenced compound, sleeping in a room without a ceiling and using insecticide aerosols. These observations demonstrate that within a village there are systematic and persistent differences in the level of exposure to malaria parasites experienced by individual chi

ISSN:0269-283X    

DOI:10.1111/j.1365-2915.1995.tb00116.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.Synthetic pyrethroid (SP) resistance has developed in Australian field populations of the sheep body louse,Bovicola(Damalinia)ovis.Laboratory bioassays were used to measure the susceptibility of lice to cypermethrin and the other registered SPs. Results of these bioassays indicated resistance to cypermethrin, deltamethrin, cyhalothrin and alphacypermethrin. So far, high‐level resistance has been diagnosed in only a few strains. The toxicological responses of these strains were clearly separated from those of the majority of louse strains tested. Furthermore, these strains had survived immersion in commercial SP dips. The level of resistance described in some strains was sufficient to cause pour‐on products to fail despite the fact that the LC50s of these strains fell within the normal range of field respon

ISSN:0269-283X    

DOI:10.1111/j.1365-2915.1995.tb00117.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.Ovitraps were exposed outdoors during wet and dry seasons in Trinidad to determine the proportions of eggs laid on three substrates: the widely‐used hardboard ‘paddle’ (P), the water surface (W) and the inside surface of the ovitrap wall (S) in three types of blackened ovitrap: round, glass (RG), round, plastic (RP) and rectangular, plastic (SP). Of the 3556 eggs obtained, most (86.4%) were laid during the wet season when statistically significant differences were detected between substrates but not between ovitrap types. Most eggs (>80%) were laid on P, significantly fewer (P<0.005) on W, on S and on W + S, thus confirming the superiority of the paddle as a device for monitoring oviposition activity. Implications of these findings for the interpretation ofAedesstudies using ovitraps are disc

ISSN:0269-283X    

DOI:10.1111/j.1365-2915.1995.tb00118.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.Culicoides variipennis sonorensisfemales were fed bluetongue virus serotype 11 mixed in sheep blood and were held at constant temperatures of 32, 27, 21 and 15oC. Virogenesis, as measured by enzyme‐linked immunosorbent assay (ELISA), proceeded significantly faster at higher temperatures. Based on ELISA absorbance ≥0.2, some flies first were categorized as infected after 1 day, 2 days and 4 days at 32, 27 and 21oC, respectively. Peak levels of virus antigen were seen after 5–7, 7–13 and 18–22 days for flies held at 32, 27 and 21oC, respectively. There was no significant virus replication in flies held at 15oC for 22 days, but latent virus replicated and was detected easily (44% infection) 4–10 days after these flies were transferred to 27oC. The implications for temperature effects on bluetongue epizootiology ar

ISSN:0269-283X    

DOI:10.1111/j.1365-2915.1995.tb00119.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY