Diapause induction in adults of three Rhipicephalus appendiculatus stocks

Newly-moulted adults of three Rhipicephalus appendiculatus stocks, originating from Kenya, Zambia and Zimbabwe, were kept in different photoperiods (12h : 12h, 13h : 11h and 14h : 10h light : dark). The stock originating from Kenya showed almost no behavioural diapause in any of these day lengths, whereas virtually all individuals of the Zimbabwean stock entered a behavioural diapause irrespective of day length. Adults from the Eastern Province of Zambia, a transition zone between the multivoltine phenology in equatorial Africa and the univoltine in southern Africa, exhibited a photoperiod-dependent diapause response. The possible mechanisms of diapause regulation and their origin are discussed.     

Distribution and phenology of ixodid ticks in southern Zambia

Distribution data for epidemiologically important ticks (Acari: Ixodidae) in the Southern Province of Zambia, one of the main cattle areas of the country, are presented. Boophilus microplus (Canestrini) was not recorded in southern Zambia, whereas Boophilus decoloratus (Koch) is present throughout the area. New distribution patterns for less economically important ixodid ticks are also discussed. Southern Zambia is a transition zone because it is the most northern area in Africa where mixed Rhipicephalus appendiculatus Neumann and Rhipicephalus zambeziensis Walker, Norval & Corwin populations were reported. Although a second generation of adult R. appendiculatus/R. zamnbeziensis was encountered, simulations indicated that this phenomenon is very rare in southern Zambia, mainly because of the colder temperatures during the early dry season and lower rainfall. These simulations were supported by a development trial under experimental conditions. Tick body size measurements showed that southern Zambian ticks are larger than eastern Zambian R. appendiculatus. It is hypothesized that body size is related to diapausing intensity in this species. The epidemiological consequences are that a different approach to control Theileria parva (Theiler) (Piroplasmida: Theileriidae) and other tick-borne diseases is needed in southern Zambia, compared to the one adopted in eastern Zambia.     

Further evidence for geographic differentiation in R. appendiculatus (Acari: Ixodidae) from Eastern and Southern provinces of Zambia

Studies in the biology, ecology and behaviour of R. appendiculatus in Zambia have shown considerable variation within and between populations often associated with their geographical origin. We studied variation in the mitochondrial COI (mtCOI) gene of adult R. appendiculatus ticks originating from the Eastern and Southern provinces of Zambia. Rhipicephalus appendiculatus ticks from the two provinces were placed into two groups on the mtCOI sequence data tree. One group comprised all haplotypes of specimens from the Eastern province plateau districts of Chipata and Petauke. The second group consisted of a single haplotype of specimens from the Southern province districts and Nyimba, an Eastern province district on the fringes of the valley. This variation provides additional evidence to the earlier observations in the 12S rDNA and ITS2 data for the geographic subdivision of R. appendiculatus from Southern province and Eastern province plateau. The geographic subdivision further corresponds with differences in body size and diapause between R. appendiculatus from these geographic areas. The possible implications of these findings on the epidemiology of East Coast fever (ECF) the disease for which R. appendiculatus is one of the vectors are discussed. Nucleotide sequence data reported in this paper are available in the GenBank^TM under the Accession Numbers DQ859259–DQ859266     

Abiotic and biotic determinants of the seasonal dynamics of the tick Rhipicephalus appendiculatus in South Africa

Abstract. The creation of a generic population model for the tick Rhipicephalus appendiculatus requires a detailed, quantified understanding of the interactions of these ticks with their biotic and abiotic environment in the different parts of their range, from the tropical regions of East Africa to the temperate regions of South Africa. The much greater seasonal variation in climatic conditions, particularly temperature, further from the equator introduces variable development rates and diapause into the life cycle. Estimates of natural temperature-dependent interstadial development periods, derived from a combination of published laboratory and field data, were applied to published data on the seasonal abundance of R.appendiculatus on three farms in the Eastern Cape Province of South Africa. This enabled an assessment of which ticks of one stage give rise to which ticks of the next stage, from which (a) the onset and duration of diapause in unfed adults, and (b) seasonal interstadial mortality indices in the form of fc-values, could be estimated. The contribution of biotic (tick density) and abiotic (climatic) factors as predictors of mortality at each life stage was investigated by step-wise multiple regression. Density-independent mortality at the female-to-larval stage is correlated with geographically variable climatic factors, minimum temperature at two farms and minimum relative humidity at the third. The other two stages are governed by density-dependent mortality, which, it is argued, may be caused largely by the hosts' acquired resistance to ticks. As expected on theoretical grounds, this density dependence is weaker nearer to the edge of the tick's range and for the more vulnerable immature stages.     

Ecology and phenology of cattle ticks in Zambia: Development and survival of free-living stages

A study on development and survival of free-living stages of three important cattle ticks in Zambia,Amblyomma variegatum Fabricus,Boophilus decoloratus Koch, andRhipicephalus appendiculatus Neumann, was carried out to complement studies on seasonal dynamics of parasitic stages.Different instars of engorged ticks were exposed under quasi-natural conditions according to the season in which they occur naturally. Generally, development rates of all stages of the three species were related to temperature, whilst the duration of survival was influenced mainly by rainfall and consequent relative humidity.Observations on the effect of age and climate on the behaviour of ticks on pastures were also made. BothA. variegatum andR. appendiculatus completed only one generation per year. InA. variegatum, engorged females detaching early in the adult season (August to October) undergo morphogenetic diapause. Adults ofR. appendiculatus emerging between August and October enter a period of behavioural diapause before becoming active in December. These mechanisms effectively synchronize the life-cycles of these two univoltine species. The one-host tick,B. decoloratus, is able to complete three to five generations each year with no indication of seasonal synchronization.     

A comparison of photoperiodic control of diapause between aestivation and hibernation in the cabbage butterfly Pieris melete

In the cabbage butterfly, Pieris melete, summer and winter diapause are induced principally by long and short daylengths, respectively; the intermediate daylengths (12-13 h) permit pupae to develop without diapause. In this study, photoperiodic control of summer and winter diapause was systematically investigated in this butterfly by examining the photoperiodic response, the number of days required to induce 50% summer and winter diapause and the duration of diapausing pupae induced under different photoperiods. Photoperiodic response curves at 18 and 20 degrees C showed that all pupae entered winter diapause at short daylengths (8-11 h), the incidence of diapause dropped to 82.3-85.5% at 22 degrees C without showing a significant difference between short daylengths, whereas the incidence of summer diapause induced by different long daylengths (14-18 h) was varied and was obviously affected by temperature. By transferring from various short daylengths (LD 8:16, LD 9:15, LD 10:14 and LD 11:13) to an intermediate daylength (LD 12.5:11.5) at different times after hatching, the number of cycles required to induce 50% winter diapause (7.28 at LD 8:16, 7.16 at LD 9:15, 7.60 at LD 10:14 and 6.94 at LD 11:13) showed no significant difference, whereas by transferring from various long daylengths (LD 14:10, LD 15:9, LD 16:8 and LD 17:7) to an intermediate daylength (LD 12.5:11.5) at different times, the number of cycles required to induce 50% summer diapause (5.95 at LD 14:10, 8.02 at LD 15:9, 6.80 at LD 16:8, 7.64 at LD 17:7) were significantly different. The intensity of winter diapause induced under different short daylengths (LD 8:16, LD 9:15, LD 10:14 and LD 11:13) was not significantly different with an average diapause duration of 87 days at a constant temperature of 20 degrees C and 92 days at a mean daily temperature of 19.0 degrees C, whereas the intensity of summer diapause induced under different long daylengths (LD 14:10, LD 15:9, LD 16:8 and LD 17:7) was significantly different (the diapause duration ranged from 75 to 86 days at a constant temperature of 20 degrees C and from 76 to 88 days at a mean daily temperature of 19.0 degrees C). All results suggested that photoperiodic control of diapause induction and termination is significantly different between aestivation and hibernation.     

Seasonal adaptations of different geographical populations of the sunflower moth, Homoeosoma electellum

A photothermogram constructed for a central Missouri population (ca. 39°N latitude) of the sunflower moth, Homoeosoma electellum (Hulst) predicted that this population has a seasonal life cycle of 2 complete and a partial third generation per year, and that daylengths of less than 13 h 30 min light/day and mean temperatures of less than 20°C induce the mature larval diapause. A test of the predicted life cycle revealed that larvae entered diapause when they were exposed from their first instar onwards to natural conditions in central Missouri beginning September 15, 1982. Sunflower moths obtained from northwest Texas (ca. 35°N latitude) and northeast South Dakota (ca. 45°N latitude) displayed shorter critical photoperiods for diapause induction at 20°C (12 h 30 min light/day and 12 h 15 min light/day, respectively) than did those from Missouri. The population of the sunflower moth obtained from South Dakota does not, therefore, appear to be adapted to local conditions, and moths might disperse from lower latitudes to establish transiet populations each year.     

温度和光周期对管侧沟茧蜂滞育诱导及滞育茧的低温冷藏

【目的】为明确诱导管侧沟茧蜂Microplitis tuberculifer 滞育的主要因子,在田间和室内研究了不同温度和光周期下管侧沟茧蜂的滞育率和滞育茧的最佳冷藏温度。【方法】田间实验分别从8月31日到9月25日每隔5 d在室外罩笼内释放管侧沟茧蜂寄生的粘虫幼虫,待寄生蜂结茧后统计子代蜂的滞育率。室内实验共设5个不同温度（16℃, 18℃, 20℃, 22℃和24℃）和7个不同光周期（6L:18D, 8L:16D, 10L:14D, 12L:12D, 14L:10D, 16L:8D和18L:6D）,分别统计寄生蜂在各个处理条件下的滞育率。【结果】在河北中部地区秋季自然条件下,8月底当日平均气温为24.4℃,日平均光照时间为12 h 51 min 时,少数蛹（5.08%）开始进入滞育;9月25日,当日平均气温为17.2℃,日平均光照时间为11 h 36 min以下时,几乎所有蛹个体进入滞育,滞育率达到99.70%。在室内人工控制条件下,当温度为22℃以上,无论光周期如何变化,管侧沟茧蜂不能进入滞育,所结茧全部为非滞育茧。温度为22℃以下存在光周期反应,在温度16℃, 18℃和20℃,光周期10L:14D时形成滞育茧数量最多,滞育率分别为100%, 89.75% 和 29.58%。可见温度和光周期二者共同影响管侧沟茧蜂的滞育。滞育茧在0℃左右条件下冷藏 240 d 和5℃左右环境条件下冷藏180 d, 成虫的羽化率和寄生能力与发育茧差异不显著(P>0.05);0℃条件下冷藏300 d,滞育茧仍有79%可以正常羽化。【结论】该寄生蜂在秋季进入滞育主要是低温条件和短光照反应相互作用的结果,滞育茧在0℃和5℃温度下至少可以保存240 d。这些结果对管侧沟茧蜂的大规模繁殖和滞育茧的保存具有重要参考价值。     

Ecological aspects of cattle tick control in central Zambia

In ecological studies in central Zambia, both climate and ecotype affected population dynamics of tick species. Below average rainfall for several years caused a suppression in numbers of Rhipicephalus appendiculatus Neumann adults. Reduction in rainfall leading to changes in grazing patterns is thought to have been responsible for an increase in numbers of Amblyomma variegatum Fabricius adults in a grassland habitat. There were reasonable correlations between numbers of each tick species on individual hosts over 1 year old. However, there were no relationships between numbers of ticks and bovine lymphocyte antigens (BoLA).     

The effects of the brown ear-tick, Rhipicephalus appendiculatus, on milk production of Sanga cattle

Abstract. Lactating Sanga cows of the Mashona breed from Zimbabwe, receiving either a low or a high level of nutritional supplement, were exposed to two levels of infestation of adults of the brown ear-tick, Rhipicephalus appendiculatus in the highveld of Zimbabwe. The effect of the ticks on the milk yield was measured over an 11-week period during the rainy season from January to April 1986. A technique in which calves were weighed before and after suckling was used to estimate milk yield. There were significant treatment effects of ticks (P < 0.05) on milk production but no significant differences in liveweight gain between calves from tick-free and tick-infested dams. The loss in milk production was poorly related to the number of female ticks that engorged, being 9 g (SEM 4) per tick. A Friesian x Hereford (Bos taurus) reference group of cattle carried 50% more ticks than the Mashona cows, illustrating a difference in resistance between the breeds. Thirteen screw-worm (Chrysomya bezziana) strikes were recorded amongst the thirty-two Mashona cows compared with twenty-one amongst the ten Friesian × Hereford animals between January and the end of March.     

Geographic variation in diapause response of adult Rhipicephalus appendiculatus ticks

Diapause in adults of the African brown ear tick Rhipicephalus appendiculatus is dependent on latitude and stock origin. Lower latitude populations, that is, those nearer the equator, show no diapause response to long or short day exposure. Diapause response to short day lengths is found in higher latitude populations, further south, and increases with increasing latitude. Nearly all individuals in the southernmost population, used in this study, enter diapause under short and long day exposure which implies that the onset of diapause in this population is obligatory. Diapause termination in higher latitude populations is induced by increasing photo period, further north, but still south of the equator, diapause is terminated by ageing. The differences in diapausing behaviour of the different populations are discussed in relation to their climatic conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Aestivo-hibernal reproductive diapause in Drosophila moriwakii: flight as a controlling factor

Drosophila moriwakii Okada & Kurokawa (Diptera; Drosophilidae) generally has only one generation per year and enters aestivo-hibernal reproductive diapause in Sapporo, northern Japan, but a small fraction of the population produced a second generation in summer at a place where breeding resources were abundant. In this species, diapause seems to be controlled by flight activity. When flies were cultured in cages in which they were able to fly freely, they entered diapause irrespective of photoperiod, but they did not do so at long daylengths when cultured in small vials in which they were prevented from flying. Furthermore, flies with wings removed did not enter diapause at long daylengths even if they were cultured in the cages.     

Comparative activity of three repellents against the ticks Rhipicephalus sanguineus and Argas persicus

The residual repellent activity of N,N-diethylphenyl-acetamide (DEPA), N,N-diethyl-3-methyl benzamide (DEET) and dimethylphthalate (DMP) against the hard tick Rhipicephalus sanguineus (Latreille) and the soft tick Argas persicus (Oken) from topical application on rabbits and hens respectively in the laboratory have been studied. It was found that a 25% concentration of DEET gave strong repellency (greater than 90%) against larvae and nymphs of R. sanguineus for 15 and 7 days respectively and against A. persicus larvae and nymphs greater than 90% for 11 and 5 days respectively. Strong repellency (greater than 90%) against adults of the hard and soft ticks was observed for 9 and 7 days respectively with 40% DEET. DEPA at 25% concentration showed strong repellency (greater than 90%) against larvae and nymphs of R. sanguineus and A. persicus for 11 and 5 days respectively. Adults of hard and soft ticks were strongly repelled (greater than 90%) for 9 and 5 days respectively by 40% DEPA. DMP was found to be the least effective against all stages of both species of tick.     

Life history of Galerucella nymphaeae and implications of reproductive diapause for rearing univoltine chrysomelids

Abstract. Galerucella nymphaeae L. , a chrysomelid that feeds on Lythrum spp., water lily and water chestnut, is closely related to two European species that were recently introduced into North America for biological control of L.salicaria , purple loosestrife. To develop a paradigm for continuously rearing these and other univoltine chrysomelids, we conducted field and laboratory studies on G. nymphaeae's development , reproduction and diapause.
A high incidence of reproduction without diapause occurred when fourth instars, pupae, and adults (held as pairs) experienced very long daylengths (LD18:6 h), i.e. longer than those G.nymphaeae encounters in nature. Under similar photoperiodic conditions, adults maintained in groups showed a significantly higher rate of reproductive diapause than those held as pairs. Females laid three to seven egg masses/week, and the size of egg masses varied between nine and nineteen eggs. During their reproductive lifetimes, individual females showed a highly significant propensity to lay a consistent number of eggs/egg mass.
After diapausing under short daylengths and low temperature (LD 10:14h, 5C), adults transferred to long days (LD 18:6h at 21C) had high rates of diapause termination and postdiapause oviposition. In contrast, those transferred to short daylengths (LD 10:14h at 21C) had low rates of reproduction.
Laboratory-derived heat-degree models accurately predicted egg and pupal, but not larval, development in the field. In nature, most females in the summer generation entered reproductive diapause without ovipositing; a small proportion of females that emerged relatively early (by mid June) oviposited before entering diapause. The overwintering population consists of adults from the first-generation and a small number from the second generation.     

Environmental and genetic control of the larval diapause of the Southwestern corn borer, Diatraea grandiosella

ABSTRACT. The interaction of photoperiod and temperature in the regulation of the induction and termination of the larval diapause of the Southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera), was examined. A population originating from south-eastern Missouri had critical daylengths for diapause induction of about 15h 5min (ecological threshold) and llh (physiological threshold). The ecological threshold was more stable than was the physiological threshold at temperatures lower than 25°C. Above 25°C the diapause response was suppressed. The insect appears to measure photoperiods in a stationary manner since a stepwise increase or decrease in photoperiod did not affect the incidence of diapause. In the critical region of the photoperiodic response curve, a higher incidence of diapause was found among females than among males. Females entered diapause later than did males, but resumed active development earlier than males. The rate of diapause development was more temperature dependent than was the rate of diapause induction, yet it was also clearly under photoperiodic control. The temperature coefficient (Q₁₀) for this process was about 4. Several other factors including sex-linkage, age, and geographic adaptations are involved in controlling the rate of diapause development, even more so than they are in controlling diapause induction. In the laboratory, the intensity of diapause declined gradually without larvae being exposed to non-diapause inducing conditions. Incubation of field-collected larvae revealed that their sensitivity to diapause maintaining photoperiods had ended by January. Three generations of selection of a Mississippi population of D. grandiosella at 30°C and LD 12:12 led to the production of an essentially diapause-free strain and a diapause strain.     

Variation in body size in the tick complex Rhipicephalus appendiculatus/Rhipicephalus zambeziensis.

We examined the relationship between body size and the phenology of the tick complex Rhipicephalus appendiculatus/Rhipicephalus zambeziensis. These ticks transmit Theileria parva in cattle. In Africa, the body size of R. appendiculatus increases with latitude while the body size of the morphologically similar Rhipicephalus zambeziensis is constant at two different latitudes. A larger body size is necessary once survival becomes a constraint. The most plausible explanation for the smaller R. appendiculatus in equatorial Africa is the cost to produce a larger egg. The consequences of these findings for the introduction of R. appendiculatus in new environments are discussed. New field observations from southern Zambia indicate that R. appendiculatus body size does not vary seasonally as compared to eastern Zambia. This is an additional indication of the presence of a single diapausing population of larger ticks.     

Summer and winter diapause in pupae of the cabbage butterfly,Pieris melete Ménétriés

The cabbage butterfly, Pieris melete is multivoltine with a pupal summer and winter diapause. Summer and winter diapause are induced principally by relatively long and short daylengths, respectively. The intermediate to relatively short daylengths of autumn permitted some pupae to develop without diapause in the field. A short daylength had a stronger diapause inducing effect than a relatively long one under higher temperatures. The principal sensitive phase for photoperiodic response occurred before the late 3rd larval instar. The critical daylength for wild autumnal populations was between 12h 30min and 12h 40min at an average temperature of 20.5 degrees C. A night interruption by 2h of light averted diapause most effectively when it was placed 10 to 12h after lights-off. High temperatures and long days during summer inhibited the incidence of diapause, suggesting that the occurrence of summer diapause is due to the specific climatic conditions occurring in April and early May, rather than to the high temperatures in summer. This indicates that the butterfly has a cryptic ability to reproduce in summer. High temperatures delayed diapause development, whereas low temperatures enhanced it, indicating that the optimum temperature of diapause development is lower. The diapause regulating mechanisms thus ensure that the species synchronises its development and reproduction with the growth seasons of the host plants and provide the species with a high degree of flexibility in its life cycle.     

Resistance and cross-resistance in guinea-pigs and rabbits to immature stages of ixodid ticks

Infestation of guinea-pigs and rabbits with larvae of any one of five species of ticks, Rhipicephalus appendiculatus Neumann, Rhipicephalus evertsi evertsi Neumann, Amblyomma hebrauem Koch, Amblyomma variegatum Fabricius and Ixodes ricinus L., conferred resistance in the animals when exposed to subsequent infestations with the same tick species. Resistance to infestations by other tick species was not observed.     

Questing activity of Rhipicephalus appendiculatus (Acari: Ixodidae) nymphs: a random process?

Abstract.  In Zambia, an experiment under quasi-natural conditions indicated that Rhipicephalus appendiculatus nymphs react to prevailing climatic conditions. Higher temperatures and higher vapour pressure deficits lead to decreased activity. The majority of nymphs (>75%) were recorded at ground level. Simulations showed that larval phenology and temperature during the nymphal premoulting period largely explain the seasonal abundance patterns of nymphs, as observed on cattle, given the absence of a behavioural diapause. Consequently, the effect of climate, as observed in our studies, is masked. However, the results of the present study indicate that daily climatic conditions probably have a much larger effect on the transmission dynamics of Theileria parva . The vertical distribution of questing instars is a function of temperature and humidity. In years of unfavourable conditions, nymphs might feed mainly on hosts other than cattle, and this could govern the infection prevalence in the adult population. This suggestion is supported by previous epidemiological studies.