Biology of Ixodes Rubicundus Ticks under Laboratory Conditions: Observations on Oviposition and Egg Development

Observations on oviposition and egg development of Ixodes rubicundus were made under laboratory conditions. Engorged females were exposed to temperatures in the range 10–25°C and relative humidities (RHs) of 33 and 93%. The pre-oviposition period, oviposition period, incubation period, conversion efficiency index (CEI) values and fecundity were determined. The mean pre-oviposition period varied from 13.3 days (temperature 25°C and RH 33%) to 68.3 days (temperature 10°C and RH 93%). Oviposition extended from a mean of 39 days (temperature 25°C and RH 93%) to 201.7 days (temperature 10°C and RH 93%). The developmental zero temperature for the pre-oviposition period was 9.2°C. The mean total number of eggs produced by engorged I. rubicundus females varied from 2045.7 (temperature 10°C and RH 93%) to 3777.7 (temperature 20°C and RH 93%). Both female mass and RH significantly (p < 0.01) influenced the number of eggs produced. CEI values varied between 43.1–54.4% (RH 93%) and 34.1–42.5% (RH 33%). At 93% RH females produced between 14.2 and 17.7 eggs per mg body mass compared to the 13.2–14.6 eggs per mg body mass at 33% RH. The shortest mean incubation period recorded was 164.3 days (temperature 25°C and RH 93%). The developmental zero temperature for incubation was 6.5°C. Both the pre-oviposition and oviposition periods of I. rubicundus are more extended compared to other species of the genus. Ixodes rubicundus produces a large number of small eggs compared to other prostriate ticks.     

Reproductive bionomics of the soft tick, Ornithodoros turicata (Acari: Argasidae)

The effects of different temperatures and relative humidities (RHs) were tested on various reproductive parameters of Ornithodoros turicata, an argasid tick that inhabits gopher tortoise burrows in Florida, USA. The pre-oviposition, oviposition and incubation periods of the ticks decreased as temperature increased. These periods were also affected by the RH. The number of eggs oviposited was affected significantly by the combined effect of temperature and RH. Fewer eggs were laid by ticks in the 24°C regimes and the 27°C/95%RH regime compared to those in the other temperature/RH groups. There was an inverse relationship between the number of eggs oviposited and the percentage of hatched larvae that was correlated with the temperature and RH. Ticks reared at 27°C/90%RH and 30°C/90%RH laid more eggs than those reared in the other combinations of temperature and humidity but fewer larvae hatched from these eggs. The reproductive fitness index (RFI) values were highest in females held in the 24°C groups and the 30°C/95%RH group, although significantly more larvae hatched at the lower temperatures. The optimum reproductive conditions for O. turicata under laboratory conditions appear to be 24°C and 90–95%RH. While mating occurred at all temperatures, none of the females laid eggs at 22°C. The ticks may move preferentially to low temperatures when not feeding to remain above the critical equilibrium humidity and/or below the critical metabolic level necessary for prolonged survival. However, most female ticks oviposited after 45 days when moved to 27°C/95%RH. Ornithodoros turicata females may have a limited capability to delay oviposition until an optimal microenvironment for egg deposition can be located in the burrow.     

The life cycle of Amblyomma neumanni Ribaga, 1902 (Acari: Ixodidae) in the laboratory

A colony of Amblyomma neumanni was started with engorged females collected from cattle in the province of Salta (24° 51S, 65° 33W), Argentina. The larvae and nymphs were fed on rabbits and the adults on calves. The non-parasitic stages were maintained in darkness at 27 ± 1°C and 83–86% RH. The life cycle (pre-feeding period not tested) had a mean duration of 205.7 days. The mean time (days) for the different phases of the cycle were as follows: feeding of females 8.8, pre-oviposition 23.8, oviposition 41.4, minimum egg incubation 76.1, feeding of larvae 8.5, pre-moult to nymphs 16.4, feeding of nymphs 7.9 and pre-moult to adults 22.8. The mean recovery rates of larvae, nymphs and females were 83.8, 85.6 and 89.3%, respectively. The nymphs moulting to females were heavier (8.1 ± 2.34 mg) than those moulting to males (6.0 ± 2.34 mg; p < 0.01), but their range of engorgement weight showed overlap (2.3–16.2 versus 2.2–12.8 mg, respectively). Two gynandromorphs were detected between the nymphs. A comparison of biological parameters of A. neumanni with other American Amblyomma species from mammals is presented. © Rapid Science Ltd. 1998     

Effects of temperature on development and growth in the tick,Haemaphysalis longicornis

As a part of ecological studies onHaemaphysalis longicornis, the effects of controlled temperatures (12, 15, 20, 25 and 30°C; 100% RH) on development and growth of the tick were investigated and the critical low temperature for each stage in the life cycle was estimated. As the temperature became low, the periods of preoviposition, oviposition, egg hatching (incubation) and moulting were prolonged. At 12°C, however, oviposition, egg hatching and moulting of the larva and nymph did not occur. The critical low temperatures for oviposition, egg hatching (developmental zero) and larval and nymphal moulting which were calculated theoretically from the regression equations, were 11.1, 12.2, 10.2 and 11.8°C, respectively. The temperature also affected the egg productivity and hatch-ratio. The number of deposited eggs per mg of body weight decreased markedly at 15°C, and the hatch-ratio was lowered with dropped temperatures.     

Biology of <Emphasis Type="Italic">Dermacentor silvarum</Emphasis> (Acari: Ixodidae) under laboratory conditions

The minimum life cycle of Dermacentor silvarum Olenev had a mean duration of 87.5 days (range 74–102 days) under laboratory conditions [(27±1 °C), 70% RH, 6 L: 18 D]. The mean time in (days) for the different stages of its cycle was as follows: incubation period of eggs was 15.3 days; prefeeding, feeding and premoulting periods of larvae and nymphs averaged 5.5, 4.0 and 7.3 days, and 5.2, 5.0 and 14.6 days, respectively; prefeeding, feeding, preoviposition and oviposition periods of female adults lasted for 7.8, 4.5, 4.3 and 14.0 days, respectively. There existed a highly significant correlation between engorged body weight of females and egg masses laid (r = 0.9877, p<0.001). The reproductive efficiency index (REI) and reproductive fitness index (RFI) in females were 11.09 and 9.58, respectively. No relationship between nymphal engorged body weight and resultant sexes was observed. Delayed feeding and non-oviposition (in June and July) existed in females, and low temperature (−10 °C) treatment for 45 days could terminate oviposition diapause. However, the egg masses laid by post-diapause females were significantly smaller than those laid by females engorged in March, April and May.     

Environmental influences on fecundity, egg viability and egg cannibalism in the scale insect predator, Chilocorus nigritus

The effects of temperature on age-specific fecundity, egg viability and egg cannibalism were examined in the coccidophagous coccinellid, Chilocorus nigritus being fed on the cyanophyllum scale, Abgrallaspis cyanophylli. There were no significant differences in lifetime fecundity or oviposition rate at constant temperatures in the range of 20 to 30°C although there was a trend for both parameters to increase with increasing temperatures. Total fecundity ranged from five to 1890 eggs per female whilst the oviposition rate varied from 0.2–12.1 eggs day^-1. Egg viability was significantly greater at 26 and 30°C (63 and 74%, respectively) than at lower temperatures (18 to 30%) whilst egg cannibalism was highest at 24 and 26°C (being the mid range of the temperatures tested). Mean pre-oviposition periods varied from 54 days at 20°C to 8.2 days at 30°C. The effect of relative humidities in the range of 33% to 75% on oviposition rate, egg viability and egg cannibalism was measured and found to have no significant effect on either parameter.     

Cold-hardiness of Dermacentor marginatus (Acari: Ixodidae)

The cold-hardiness of Dermacentor marginatus using laboratory-reared offspring of ticks collected in Germany was characterized. Investigations of unfed stages revealed that adult ticks suffered 50% mortality at –10°C after 4–5 months, but larvae and nymphs suffered mortality within few days, whereas –15°C was lethal for all stages within a very short period. Larval hatch and moulting of engorged larvae and nymphs did not occur at 10°C. Embryonic development of eggs with larval hatch was considerably reduced by exposure of eggs to 10°C. Engorged females did not lay eggs at 10°C, the oviposition capability, however, persisted over 6 months at 10°C, 5 months at 5°C, 3 months at 0°C and 2 months at –10°C without substantial decrease of the oviposition capacity or reduction of viable eggs. These results present evidence that unfed adult ticks are the ecoepidemiologically most effective stages, which are capable to tolerate long and extremely cold winters without substantial impairment of the population density. It is also considered that engorged females interrupt their oviposition at low and subzero temperatures delaying it for months and so contribute in bypassing winter conditions. None of the stages survived supercooling indicating that D. marginatus is freeze intolerant. Mean supercooling point (SCP) ranged between –26°C in eggs and –12, 6°C in engorged females. Compared with eggs, the SCP of the other stages was significantly higher. In conclusion, the SCP is considered to have no predictive value in the context with cold-hardiness.     

Biology of Dermacentor silvarum (Acari: Ixodidae) under laboratory conditions

The minimum life cycle of Dermacentor silvarum Olenev had a mean duration of 87.5 days (range 74–102 days) under laboratory conditions [(27±1 °C), 70% RH, 6 L: 18 D]. The mean time in (days) for the different stages of its cycle was as follows: incubation period of eggs was 15.3 days; prefeeding, feeding and premoulting periods of larvae and nymphs averaged 5.5, 4.0 and 7.3 days, and 5.2, 5.0 and 14.6 days, respectively; prefeeding, feeding, preoviposition and oviposition periods of female adults lasted for 7.8, 4.5, 4.3 and 14.0 days, respectively. There existed a highly significant correlation between engorged body weight of females and egg masses laid (r = 0.9877, p<0.001). the=" reproductive=" efficiency=" index=" (rei)=" and=" reproductive=" fitness=" index=" (rfi)=" in=" females=" were=" 11.09=" and=" 9.58,=" respectively.=" no=" relationship=" between=" nymphal=" engorged=" body=" weight=" and=" resultant=" sexes=" was=" observed.=" delayed=" feeding=" and=" non-oviposition=" (in=" june=" and=" july)=" existed=" in=" females,=" and=" low=" temperature=" (−10 °c)=" treatment=" for=" 45 days=" could=" terminate=" oviposition=" diapause.=" however,=" the=" egg=" masses=" laid=" by=" post-diapause=" females=" were=" significantly=" smaller=" than=" those=" laid=" by=" females=" engorged=" in=" march,=" april=" and=">     

Influences of daylength and temperature on the period of diapause and its ending process in dormant larvae of burnet moths (Lepidoptera,Zygaenidae)

The onset of larval diapause in the burnet moth Zygaena trifolii is clearly characterized by the larva molting into a specialized dormant morph. In a potentially bivoltine Mediterranean population (Marseille) two types of diapause can occur within 1 year: firstly, a facultative summer diapause of 3–10 weeks, and secondly, an obligate winter diapause, which can be lengthened by a period of thermal quiescence to several months in temperatures of 5°C. For the first time, three successive physiological periods have been experimentally distinguished within an insect dormancy (between onset of diapause and molting to the next non-diapause stage), using chilling periods of 30–180 days at 5°C, and varying conditions of photoperiod and temperature. These stages are: (1) a continuous Diapause-ending process (DEP); (2) thermal quiescence (Q); and finally, (3) a period of postdiapause development (PDD) before molting to the next larval instar. The result of transferring dormant larvae from chilling at 5°C to 20°C depended on the length of the chilling period. After chilling for 120–180 days, molting to the next instar occurred after 6–10 days, independent of daylength. This period corresponds with the duration of PDD. After shorter chilling periods (90, 60, 30 days and the control, 0 days) the period to eclosion increased exponentially, and included both the latter part of the previous diapause process and the 6–10 day period of PDD. However, photoperiod also influences the time to eclosion after chilling. Short daylength (8 h light / 16 h dark: LD 8/16) lengthened the diapause in comparison to long daylength (16 h light / 8 h dark: LD 16/8). Short daylength had a similar effect during chilling at 5°C, as measured by the longer time to eclosion after transfer. The shorter time to eclosion resulting from longer chilling periods (30–90 days) demonstrates that the state of diapause is continuously shortened at 5°C, and corresponds to the neuroendocrine controlled DEP. Presumably the DEP has already started after the onset of diapause. When chilling was continued after the end of the DEP, which ranged between 90 and 120 days, thermal quiescence (Q) followed (observed maximum 395 days). Different photoperiodic conditions during the pre-diapause inductive period modified diapause intensity (measured as the duration of diapause), in that a photoperiodic signal just below the critical photoperiod for diapause induction (LD 15/9) intensified diapause. Experiments simulating the summer diapause showed that PDD occurred in the range of 10–25°C. Higher temperatures (15 and 20°C) shortened the DEP at LD 16/8, so that at 20°C many individuals had already terminated diapause after 10–40 days and had molted after the 6–10 days of PDD. A temperature of 25°C unexpectedly lengthened the DEP to 110 days in several individuals. The ecological consequences and the adaptive significance of variation in the duration of the diapause are discussed in relation to the persistence of local populations predictably variable and rare climatic extremes throughout the year.     

Effects of pre-storage conditions on storage of in vitro cultures of Nephrolepis exaltata (L.) Schott and Cordyline fruticosa (L.) A. Chev.

In vitro cultures of Nephrolepis exaltata and Cordyline fruticosa were stored at 5°, 9° or 13°C, at a low irradiance (3–5 mol m^–2 s^–1) or in darkness. Prior to storage the cultures were subjected to 18°, 21°, 24° or 27°C and 15, 30 or 45 mol m^–2 s^–1 in a factorial combination.The optimal storage conditions for Nephrolepis were 9°C in complete darkness. These cultures were still transferable to a peat/perlite mixture at the end of the experimental period of 36 months.The optimal storage conditions for Cordyline were 13°C and a low light level (±3–5 mol m^-2 s^-1). When the pre-storage conditions were normal growth room conditions (24°C and 30 mol m^-2 s^-1), in vitro cultures could be stored for 18 months. With the most favourable pre-storage treatment (18°C and 15 mol m^-2 s^-1) some cultures still had green shoots after 36 months of storage, but did not survive transfer to peat/perlite.Pre-conditioning before storage was most favourable for Nephrolepis, and not that important, but still favourable, for Cordyline. There was an interaction between pre-storage temperature and pre-storage irradiance. For both species a high irradiance level was less favourable than a low irradiance level when combined with high growth room temperatures.Abbreviations BA 6-benzyladenine - IAA indole-3-acetic acid - NOA 2-naphthoxyacetic acid     

Influence of temperature, photoperiod and humidity on oviposition and egg hatch of the root-feeding flea beetle Longitarsus bethae (Chrysomelidae: Alticinae), a natural enemy of the weed Lantana camara (Verbenaceae)

The root-feeding flea beetle Longitarsus bethae Savini & Escalona, was introduced into South Africa as a candidate biological control agent for the noxious and invasive weed, Lantana camara L. As part of the study to predict the beetles' survival in its new range, the influence of climatic conditions on its egg development and reproductive performance were investigated in the laboratory. The threshold temperature (T degrees) and degree-days (DD) required for egg hatch were determined after exposing the eggs to various constant temperatures (12, 17, 22, 27 and 32 degrees C) in separate growth chambers. The DD required for egg hatch was 178.6, and the temperature threshold required for egg hatch was 11.3 degrees C. Survival of eggs varied from 27 to 56% at 32 and 17 degrees C, respectively, and was optimum between 17 and 25 degrees C. Oviposition was examined under high and low relative humidity (RH) regimes while egg hatch was determined at six RH levels, each maintained in a separate controlled growth chamber set at a constant temperature (25 degrees C). Whilst RH had no influence on oviposition, eggs were highly susceptible to aridity, and continuous exposure to relative humidity below 63% for more than three days was wholly lethal at 25 degrees C. Optimum egg hatch occurred at RH between 85 and 95% for up to 12 days. The effect of day length on oviposition and subsequent egg hatch was investigated under two photoperiod regimes. Neither oviposition nor subsequent egg hatch was influenced by photoperiod. The knowledge obtained will be useful for mass rearing as well as field release programmes for L. bethae.     

Effect of hydration,photoperiod and temperature on diapause termination in eggs ofPetrobia (Tetranychina) harti (Acari: Tetranychidae)

Petrobia harti (Ewing) displays a facultative summer diapause in the egg stage. An adult female will lay only either diapause or non-diapause eggs throughout her life. In the laboratory, diapause eggs are laid by females which develop on detachedOxalis articulata leaves under long-day photoperiods and a relatively low temperature of 19±1°C.Diapause occurs in a stage of advanced embryonic development, in which the embryo appears U-shaped when observed from the egg's ventral side. Embryonic development ceased at this stage, and no further growth occurred when the eggs were kept under a relative humidity of about 70% in various photoperiod and temperature conditions. However, when the eggs were hydrated by placing them on wet cotton wool, development in some embryos (apparently in those which had completed their diapause development) proceeded beyond the U-stage at a rate similar to that in non-diapause embryos and the eggs hatched.Under LD 168 and 19±1°C or 26±1°C, the later from oviposition the period of egg hydration started, the higher the percentage of diapause termination. Under LD 168 and 26±1°C, diapause termination occurred mostly during the first week of hydration, while at 19±1°C mostly during the second and third week.At 26±1°C, in eggs hydrated 15 days but not 30 days from oviposition, the percentage of diapause termination was higher under a long-day than under a short-day photoperiod.Under LD 168, when the eggs were hydrated continuously from oviposition or starting 15, 30 and 45 days from it, the percentage of diapause termination was higher at 26±1°C than at 19±1°C.The percentage of diapause-laying adult females and the intensity of egg diapause were higher when the pre-imaginal mites grew at LD 1212 and 19±1°C, than when they grew at LD 168 and 26±1°C. This maternal effect on egg diapause intensity was expressed when the eggs were maintained at LD 1212 and 19±1°C but not at LD 168 and 26±1°C.     

Reproduction of the calanoid copepod Calanus propinquus in the southern Weddell Sea,Antarctica: observations in laboratory

Reproduction of the dominant Antarctic copepod Calanus propinquus was studied in February–April, 1989 aboard the R.V Dmitry Mendeleev during cruise N° 43 to the Weddell Sea. Single females were kept at 0 °C in the laboratory for 56 days with abundant food concentration (above 300 µg C l^–1 of Platymonas viridis). Females released clutches at night at 2–3 day intervals. Most clutches contained from 10 to 40 eggs, mean 37.3 eggs female^–1. Average carbon content of an egg was 0.37 ± 0.05 µg C. The maximum daily egg production rate of 30–50 eggs female^–1 d^–1 was observed for the first 3 days of the laboratory incubation, corresponding to 3.7–6.2% body C. The state of gonadal development of females showed the decline of the reproductive season in late February. The data suggest that egg laying in the region under study starts in December and lasts until March. The state of ovarian maturation, changes in vertical distribution and biochemical body composition of females suggest the possibility of two-year life cycle in C. propinquus in the southern Weddell Sea.     

The life cycle ofAmblyomma parvum Aragao, 1908 (Acari: Ixodidae) under laboratory conditions

A colony ofAmblyomma parvum was started with engorged females collected from cattle in the Province of Salta (25°01 S, 63°56 W), Argentina. The progeny of those ticks were fed on rabbits and the non-parasitic stages maintained at 27±1°C, 83–86% RH in darkness. The life cycle (prefeeding period not evaluated) had a mean duration of 99.6 days. The mean time (days) for the different phases of the cycle were as follows: feeding period of females, 8.0; pre-oviposition period, 5.7; oviposition period, 17.5; minimum incubation period of the eggs, 31.8; feeding period of larvae, 3.2; premoult period to nymphs, 10.9; feeding period of nymphs, 4.7; premoult period to adults, 17.8. The oviposition pattern was typical of an ixodid tick, including a linear relationship between weights of engorged females and the number of eggs laid (r=0.8659). The males increased 18% in weight after feeding on hosts (P<0.01). The mean recovery rates of larvae, nymphs and females were 28.2%, 95.3% and 90.7%, respectively. The nymphs moulting to females were heavier (6.8±0.69 mg) than those moulting to males (3.2±0.29 mg) (P<0.01). A comparison of biological values ofA. parvum with American and non-AmericanAmblyomma species is presented.     

Effect of temperature on the ovipositional biology and egg viability of the cattle tickBoophilus annulatus (Acari: Ixodidae)

The effect of temperature on the ovipositional biology ofBoophilus annulatus (Say) was determined under laboratory conditions. Engorged females subjected to constant temperatures of 12 and 45°C died without ovipositing, while females held at 15 and 40°C laid eggs which did not hatch. The preoviposition period at 25–40°C was 2–3 days; however, significant increases occurred at 20°C (5.2 days) and at 15°C (16.3 days). The number of eggs laid per female was ca. 2700 at temperatures of 25–35°C, but decreased significantly at 20°C (ca. 2300 eggs/female), 15°C (ca. 1800 eggs/female), and at 40°C (ca. 300 eggs/female). No differences were observed in the Conversion Efficiency Index (CEI) values at temperatures of 20–30°C (ca. 50%), while temperatures of 15 and 40°C produced the lowest CEI values at 35.6 and 4.9%, respectively. Hatch-ability of eggs was ca. 80% at temperatures of 20–35°C. Incubation period of eggs ranged from 52.2 days at 20°C to 16.2 days at 35°C. The thermal threshold for egg development determined by linear regression was 12.9°C. Females subjected to four fluctuating temperature regimes produced no differences in number of eggs/female (ca. 2400), CEI (ca. 50%), or hatchability of eggs (ca. 75%). Preoviposition period and incubation were significantly affected by a change in the thermoperiod, becoming longer in duration as the temperatures were decreased. From studying females exposed for various intervals from 0 to 105 days at 12°C, indications were that the longer the exposure period the more adverse the effects were on oviposition and egg-hatch. Correspondingly, exposure of eggs to a temperature of 15°C for up to 105 days gave indications that the longer the eggs remained at 15°C, the lower the hatch would be after transfer back to a temperature of 25°C.     

The effects of acclimation to alternating environmental temperature on metabolic and endocrine responses in guinea pigs,during acute heat and cold exposure

Male Guinea pigs (n=80) were divided into four groups and maintained in a climatic chamber for three weeks in one of the following environmental conditions: (1) T_a20°C and 55% RH; (2) T_a35°C and 30–35% RH from 08:00 to 20:00 h and 5°C; 60–65% RH, from 20:00 h to 08:00 h; (3) T_a5°C and 60–65% RH; (4) T_a35°C and 30–35% RH. At the end of this period the animals were exposed to either –5°C, 60–65% RH or 45°C, 30–35% RH, for a period of 20 min, following which T_re, plasma 11-OHCS, thyroxin, glucose, and FFA, and body and organ weights were determined. The cold-warm adapted animals seemed to develop a more efficient adaptability to acute heat and cold exposure. It is suggested that on acute exposure to severe environmental conditions the endocrine and the nervous system play a dominant role in maintaining optimal body temperature, while on chronic exposure the metabolic rate of the various organs becomes relatively more important.     

Differences in development time,mortality and water loss between eggs from laboratory and wild populations ofDermatophagoides pteronyssinus (Trouessart, 1897) (Acari: Pyroglyphidae)

A total of four microcultures of adults ofDermatophagoides pteronyssinus, two each from laboratory and wild populations, were fed on separate diets of house dust and yeast granules. A total of 35 eggs of known age from each of the four microcultures were harvested and incubated at 15°C, 60% RH for 16 h/day and 30°C, 75% RH for 8 h/day to simulate diurnal microclimatic fluctuations in a bed. Eggs from females fed on yeast were larger and underwent more rapid rates of water loss, estimated by measurements of reduction in visible surface area (VSA), than eggs from females fed on house dust. There were no significant differences in mean egg development time between the four microcultures (range 6.0–6.88 days). Mortality of the eggs was as follows: from laboratory females fed on yeast, 31.4%; laboratory females fed on house dust, 11.5%; wild females fed on yeast, 2.9%; wild females fed on house dust, 0%. Thus diet and egg size at oviposition had no effect on mortality. Since the microclimates at which eggs from both populations were oviposited and incubated were identical, it is hypothesized that mortality was higer in eggs from laboratory cultures because the mites had become acclimated to the optimal conditions at which they had been kept and were less able to withstand the diurnal fluctuations in microclimate, similar to those imposed upon wild mites in their natural habitats.     

The life cycle ofRhipicephalus lunulatus Neumann, 1907 (Acarina:Ixodidae) under laboratory conditions,with notes on its ecology in Zimbabwe

The durations of the developmental periods ofRhipicephalus lunulatus at 25°C and 87% RH were: preoviposition, 2–9 days; oviposition, 29–34 days; minimum incubation, 11–27 days; nymphal premoult period, 11–23 days; and adult premoult period, 19–30 days. The durations of the feeding periods on a rabbit were: 3–7 days for larvae and 4–11 days for nymphs. Adult feeding was completed on a rabbit and a sheep in 10–22 days in January and 14–64 days in September, and only fertilized females completed engorgement. The mean number of eggs laid by engorged females was 4732, with 95% being laid within the first 16 days. In the southeastern lowveld of Zimbabwe adult ticks were most abundant on cattle between November and December, and their preferred sites of attachment were the legs and tail. Other hosts of adultR. lunulatus were impala (Aepyceros melampus), warthog (Phacochoerus aethiopicus), kudu (Tragelaphus strepsiceros) and eland (Taurotragus oryx).     

Temperature conditions enhancing resting egg production of the euryhaline rotifer Brachionus plicatilis O. F. Müller (Kamiura strain)

We examined the effect of low temperature treatment(12°C), followed by transfer to highertemperature (25°C), on resting egg formation ofthe rotifer Brachionus plicatilis, Kamiurastrain. This strain has been mass cultured as livefeed at Kamiura Station (Japan Sea FarmingAssociation) for 9 years at 20°C without theappearance of sexual reproductive stages.After preculture in 20 l of 27 seawater at 12°C for 0, 10, 20, and 30 days,rotifers were inoculated into 0.5 l mass cultures andcultured at 25°C for 7–9 days. The inoculationdensities were changed from 20 to 400 ind. ml^–1,depending on mixis rate. Condensed and frozen Nannochloropsis oculata was fed to rotifers at thefeeding rate of 0.14 µg (dry weight)rotifer^–1day^–1. The control was cultured at12°C for the entire 36 day experiment. No mixisappeared and no resting eggs were produced when thelow temperature treatment was 0 or 10 days. However,mixis rates reached 50-60% after 20 or 30 days ofexposure to 12°C. The number of resting eggsproduced in these treatments reached 25,500 about 13 times higher than the control. Our resultssuggest that low temperature stimulated mictic femaleproduction and the transfer to the high temperatureaccelerated resting egg formation. This method may beuseful for producing resting eggs of rotifer strainsthat lack sexual reproduction in the common culturecondition at larval rearing facilities.     

An analysis of diapause and resistance in the egg stage of Floronia bucculenta (Araneida: Linyphiidae)

Summary Floronia bucculenta hibernates in the egg stage; the egg sacs are deposited on the leaves of grass tussocks without any shelter. The morphogenesis of the eggs was divided into 10 arbitrarily chosen stages, in order to test the dependence of embryonic development on temperature in the laboratory. The eggs developed slowly at 23°C, 16°, 12.5°; embryogenesis stopped after 70–45 days, when prosomal appendage rudiments began to form. At 10°, 7.5°, 5°, 0° complete embryogenesis was possible until the emergence of the first complete stage. The eggs developed most rapidly at 5° (mean developmental time 203 days). The egg development was normal at 5° and 0°, when compared with the timetable of the embryogenesis of the linyphiid Bathyphantes gracilis, a species which has no egg diapause. At 7.5° and 10° the embryogenesis was strongly delayed during the median phases of development (elongation of the germ band, formation of prosomal appendages); after reversion the development was accelerated (postdiapause phase). After long exposure to low temperatures (-10° to +10°) the diapause was terminated. A temperature of 0° was optimal (minimal time of exposure 8–9 weeks). The time required for embryonic development of postdiapause eggs decreased hyperbolically with increasing temperature. In the field the median phases of embryogenesis were retarded by low ambient temperatures; diapause was terminated from late December to mid-January. The spread of hatching in spring was 7–15 days.During the diapause phase the O₂-consumption of the eggs at 25° was depressed. It rose from 1.55 (in late diapause) to 4.21 ml/100 eggs·h at the onset of postdiapause, whereas O₂-utilization did not change significantly at 5° (from 0.54 to 0.61 ml/100 eggs·h just after the termination of diapause).The diapause phase was not characterized by higher resistance to cold, drought, or flooding. As compared with single eggs removed from the cocoon, the silken wall of the intact egg sac did not affect the survival of postdiapause eggs exposed to-15° (LD₅₀=28 days); it raised, however, the survival time of eggs exposed to a R.H. of 32% (at 5°) or flooding by distilled water (at 5°): from LD₅₀=37 to 68 days at drought, from LD₅₀=30 to 92 days at flooding.Diapause is important for synchronizing the life-cycle of F. bucculenta with the seasonal fluctuations of environment. The egg stage is highly tolerant to the extreme factors of the winter. Some implications of the relation of the studied spider to its habitat are discussed.