| dc.description.abstract | The effects of temperature and relative humidity on
the development and bloodmeal utilization by the tick,
ornithodoros porcious porcinus have been investigated
during this study. Four temperature regimes
(25, 30
34 and 37 C) were tested at a constant
relative humidity of 85%; and the effects of nine
relative humidities (10 to 96%) were also investigate
d at a constant temperature, OoC. The ticks
were fed on the ears and abdomen of rabbits of
chinchilla breed, Studies on the effects of
exposure of ticks, for 24 hours, to the various
conditions of temperature and relative humidities
on their subsquent feeding performance sho~ed definite
individual variations. However, differences in
the quantity of bloodmeal ingested at the various
treat-lents were non-significant; relationship between
unfed body weight and the quantity of bloodmeal
ingested was established.
Studies of egg production was compounded
through :understanding of precoviposition neriods
rhythm of egg producticn, duration of oviposition, ,
the numtrer' and eight of eggs and the efficiency of
nutrient conversion into eggs. Thus the mean preoviposition
periods were significantly lower at
o 0 30 C than at 25 C, and at higher05-96%) than lower
(10 - o 55% RHs.
At 34 C, only one female oviposited
at 37 C, no female oviposited and all of them died
within two weeks. Based on the rhythm of oviposition,
majority of eggs were laid during the earlier
portion of oviposition cycle, with peak egg output
occuring on the second aay of the cycle, thereafter
the egg yield gradually declined more females
oviposited each time at 30oC and higher RHs than
at 25
C and lower RHs. However, the mean duration
of oviposition was not affected by variations of
temperatures and relative humidities, although a
tendency of heavier ticks taking lohger time to
complete oviposition than the light ones existed.
Great individual variability of reproductivr pot ential
was noticed, Signficantly more eggs were
Besides 10, 45 and
85%, R"II.,s, the egg production within other relative
humidities were comparable. Relationships were
found between the quantity of bloodmeal ingested and
egg yield. The weight of eggs laid under various
conditions generally corresponded to egg yield.
However within the
the weights of eggs
first 4 days of oviposition cycle,
w e r e greater than at ,
and t hes-at mp sp h er e of greater evaporative water loss
criated by 30 C was thought to be responsible for this.
Based on the extent of concentration and
utilization of ingested bloodmeal, the efficiency
of nutrient conversion into eggs was found a useful
parameter in .assessing the reproductive potential
of ticks. The number of eggs laid/eggs blood, egg
production and nutrient iridices were significantly
greater at 30 o C than a.t 25 0C, but the values 0 f
ingested bl~odm~dj inGex were no~-significant.
Clear correlation was iound between ~utrient index
and egg yield. Significantly higher values of
number of eggs laid/rug blood were recorded at higher
than lower relative humidities; but the vilues of
ingested bloodmeal, Egg production" and Nutrient
indices were non-significant. At higher relative
humidities, inverse relationships between Nutrient
index and pre-oviposition periods, were established
signifyin~ that ticks with superior nutrient
copv"lr.s,ion mechanism took shorter time to commence
egg-laying.
The viability of eggs was assessed from
percentage hatphability values. The incubation
period~
than at
eggs were significantly
250
C; the few eggs laid by
shorter at 30°C
one female
exposed to 34 C. did not hatch at all, suggesting
t~at this temperature is too high for embryonic
development. The e~s exposed to 10 - 35% RHs
did not also hatch and the differences in incubation
periods of eggs exposed to relative humidities above
55% were non-signifisant. Although the majority
of eggs were laid during the early portion of oviposition
cycle; their viability were comparable
throughout the cycle: Relat{onships were found
betweeL pertentage hatchability, engorged female
we igh t and egg y ie 1d . Significantly higher perceno
tage hatchability of eggs occured at 30 C than at
Similarly, significantly higher percentage
hatchability was recorded at 75 and 85% RHs as
compared to 55, 65 and 96% RHs, -Temperature and
relative humidity limitations in egg production and
their viability have therefore, been demonstrated.
The effect of seasonal flooding situations
during rainy seasons) in warthog burrows on the
viability of eggs of o. p. porcinus ~as investigated
by immersing the eggs in tap water for periods
ranging from 10 minutes to 96 hours. These eggs
showed significant level of resistance to water
immers)0It)and 80% w er e still viable after 20 hours
of rm~e~sion however, from 70 hours onwards,
ne gld g.ib Le pertentage . hatchability w a s recorded and
after 96 hours all eggs failed to hatch.
Under the various ~onditions of temperatures
at a constant relative humidity of 85%, studies on
nymphal development were based on nymphal periods,
changes in unfed body weights, the quantity of
bloodmeal ingested,mortality, the rate of adult
emergence and their. respective weights. The results
show that the nymphal periods ~o~ the first 4
nymphal ins tars were significantly influenced by
temperature; these periods shortened with increase
in temperature from 2SoC to 340
(. How eve r, from
the 5th to 7th instars, nymphal periods at 25
and 300C did not significantly differ.
the 5th nymphal instars died within 3 weeks after
emerg enc e, an d at::'J7I~OC , all the 2nd nymphal instars
died within one week after emergence. Significantly
higher mortalities were recorded during the 3rd
and 4th nymphal instars, and these instars were
thought to be transition phases before adult
emergen<;e. The days on which peak moulting
occured also decreased with increase in temperature
from 25
a
to 34 C. The total quantity of bloodmeal
ingested by nymph-producing adults were generally
greater at 30 C than at 25 C, the largest blodd
intake accuring at the 6th - 7th instars. No
significant differences in- ingested bloodmeal
index was recarded within the first 5 and the 7th ,
nymplraLtinstars : but significantly lower values
occured during the thin stars. Based on the increases
in unfed body weights, the greatest rate nymphal
growth occured within the first 5 instars, with
peak growth being recorded during the 4th - 5th
instars. The slowest rate of growth occured during
the 5th - 6th and 6th - 7th instars. Adult
emergence was accelerated with increase in temperature.
At 25 °C, adult emergence commenced at the 5th
nymphal inster, while at 30 and 34° C, it commenced
at the 4th instars. Generally, higher percentage of
male~ emerged earlier than the females. The weights
of emerging adults were also greater at 30°C than
The extent of bloodmeal utilization by o. p.
porcinus was assessed from the protease activity and
protein degradation in the guts of males, virgin and
m at ed females at various intervals after feeding.
The ticks used in this study had been starved for
about 5 months. The gut homogenates were used as
the source of enzymes, and the suitability of
haemoglobin as substrate for these enzymes as
compared to bovine serum albumin was demonstrated.
Little protease activity occurred within the first
4 days, after which it rose steeply to peak levels
on days 8 (males), 9 (mated females) and 12
(virgin females), respectively. The levels of
protease activity if males were far lower than in
the
mated and vir~in females. After peak activity, the
decline? protease activity were faster in mated I
than in virgin females. The rate of gut protein
degradation a 150 corresponded to the pattern of
protease activity. Based on the pattern of weight
loss by engorged, mated females and protease
activity, three phases of blood digestion were
established. Future areas of research on the
extent of bloodmeal utilization and possible
improvements on techniques have been suggested.
Under the various conditions of temperatures
and relative humidities, the weight changes in
engorged males and mated females were expressed
as percentage of the initial engorged weights. The
weight changes were gradual during pre-oviposition
periods, but increased with the cbmmencements of
oviposition; the ticks which laid more eggs
experienced greater weight loss. Since egg production
was inhibited at 34 and 37°C, the corresponding
weight changes were also very gradual. However,
there were little differences in weight losses at
the various relative'humidities. The,mechanisms
responsible for restricting greater weight
losses in engorged ticks under adverse conditions
of temperatures and relative humidities is not yet
understood | en |
