1. Effect of larval and adult diet on desiccation resistance of marula
fruit fly, Ceratitis cosyra (Walker) (Diptera: Tephritidae)
Sandiso Mnguni
10358626
BSc Honours in Entomology
2014
Supervisors: Dr. Christopher Weldon and Prof. Sue Nicolson
Department of Zoology and Entomology
University of Pretoria
Pretoria
South Africa

2. Abstract
The availability of water affects survival, distribution, fitness and evolutionary trajectories. In insects, water is gained by
consumption of food, drinking, absorption of atmospheric water, and as a by-product of metabolic processes while it is
lost via elimination of nitrogenous waste (urine), faecal matter, cuticular transpiration, respiratory transpiration and body
secretion. Ceratitis cosyra (Walker) (Diptera: Tephritidae) is a major pest found to be destructive in many host fruits
across sub-Saharan Africa. Ceratitis cosyra larvae were grown in high protein larval diet (standard diet, comprising 8%
torula yeast on wet mass basis) as well as low protein larval diet (1% torula yeast). For 10 days after eclosion, adults from
high protein larval diet as well as low protein larval diet were then fed sugar only (low protein adult diet) and sugar with
hydrolysed yeast (high protein adult diet). Newly-eclosed, unfed adult flies as well as fed adult flies were assayed for
initial mass, water content, and desiccation and starvation resistance. After eclosion, adult flies from the high protein
larval diet (compared to those from the low protein larval diet) had high initial mass, high initial body water content, low
initial dry mass, low water remaining at death and low survival rate (both desiccation and starvation resistance). When
fed for 10 days, these flies (those reared in high protein larval diet), compared to newly emerged flies, especially when
fed in high protein adult diet, had higher initial mass, higher water remaining at death and lower survival rate (desiccation
resistance only), even when compared to low adult protein diet. Sex-specific differences were also seen whereby in
newly-eclosed, unfed adult flies, females had greater initial mass and shorter desiccation and starvation resistance
compared to males. Furthermore, in fed adult flies, females had more initial mass, less water remaining at death and
greater desiccation resistance but not starvation resistance (especially when reared in low protein larval diet). Desiccation
resistance of adult flies is enhanced when flies have more food resources, thus more metabolites, and more water. The
results have rather shown that greater body size does not always mean more body water since males assayed for 10 days
after eclosion had more water remaining at death. We then conclude that larval diet is correlated with adult diet in that
adults feed to supplement the larval diet thus enhancing the desiccation resistance further. However, the exposure of
larvae to stressful conditions could also assist adult flies in coping with harsh environments, thus larvae play a huge role in
desiccation resistance of adult flies.

3. Introduction
The availability of water affects the survival, distribution, fitness and evolutionary trajectories of all living organisms
(Hoffman and Parsons, 1991). Due to their small size, insects are particularly sensitive to water availability because their
high surface area to volume ratio has the potential to lead to high rates of water loss (Gefen et al., 2006). This means that
there is a particular need for insects to regulate water to increase their chances of survival (Folk, et al., 2001). Water
intake is one obvious way in which insects can avoid water stress (Gibbs, 2002; Edney, 1977). Insects can obtain water
through the consumption of food, drinking, absorption of atmospheric water, and as a by-product of metabolic processes
(Hadley, 1994; Folk et al., 2001). However, the terrestrial lifestyle of most free-living insects means that free water is
limiting, meaning that other mechanisms must be used to avoid water stress.
There are three general ways in which insects can reduce the likelihood of water stress: reduced water loss rates,
increased water storage, and enhanced dehydration tolerance (Hadley, 1994; Gibbs, 2002; Gefen et al., 2006; Gibbs et al.,
1997; Bradley et al., 1999; Gibbs and Matzkin, 2001). Reduced water loss rates have been achieved by the evolution of
cuticular traits such as body melanisation and the quantity and composition of epicuticular lipids that are known to affect
cuticular transpiration (Hadley, 1994; Gibbs et al., 1998; Parkash et al., 2008a, b, 2010). Factors that increase the melting
point of lipids (such as longer hydrocarbon chain lengths, reduced saturation, or methyl branching) are proposed to
reduce cuticular water loss (Gibbs, 1998; Rourke & Gibbs, 1999). Changes in metabolic rate and the need for oxygen are
believed to modify respiratory water loss rate (Gibbs, 2002).
Body water content can be increased by increased body size and hemolymph volume (Bradley & Folk, 2003). Insect
hemolymph is known as a reservoir that buffers insect tissues during periods of water stress (Mellanby, 1939). Supporting
evidence in this regard is the striking increase in hemolymph volume (~330 nl, a >6-fold increase in hemolymph volume
relative to the control populations) seen in laboratory-selected, desiccation-resistant Drosophila populations (Folk &
Bradley, 2003). Body water content, however, apart from drinking, can also be increased by increased food intake, due to
free water but also the potential for the release of metabolic water from the breakdown of nutrients. Metabolic reserves
are thought to play a large role in adaptation to desiccation resistance (Djawdan et al., 1997). The breaking down of
glucose leads to the production of water and CO₂ as by-products, whereby water is retained and CO₂ is excreted into the
environment (Graves et al., 1992; Djawdan et al, 1998; Folk et al., 2001). Carbohydrates are known to play a big role in
osmoregulation by keeping the body fluids from being too diluted or concentrated (Marron et al., 2003; Gefen et al.,
2006; Djawdan et al., 1998; Chippindale et al., 1998). Lipids also play a part in desiccation as they assist in energy storage,
but an insect also obtains water when lipids are broken down (Service, 1987; Chippindale et al., 1996, 1998; Djawdan et
al., 1998). Recent studies show that proteins help insects during desiccation whereby heat shock proteins act as a cellular

4. stress response by being expressed in response to a number of stressors, including dehydration (Feder and Hoffman,
1999; Sorensen et al., 2003).
Nutrition plays an essential role in enhancing resistance to many forms of stress (Djawdan et al., 1997). Animals need to
constantly feed in order to be able to grow and reproduce. Many, however, struggle to meet their minimum nutritional
requirements (Raubenheimer and Simpson, 1999), which can lead to nutrient deficiency or imbalance. This detrimental
effect hinders the fitness, well-being and everyday activities of insects (Anderson et al., 2010). This is largely due to the
fact that body tissues require a specific amount of nutrients in order to function adequately (Bauerfeind and Fisher,
2005). In response to nutritional stress, insects extend their growth periods by changing their energy allocation to growth,
thus prolonging or extending the time through which they reach maturity to reproduce by reducing body size (Reichling
and German, 2000; Lobe et al., 2006; Gefen et al., 2006). It has been well established that adult insects do not grow, thus
their body size depends on the size of the last instar larva when it commences metamorphosis (Nijhout, 2003). A critical
developmental stage, characterised by a small pulse of ecdysteroid secretion, is responsible for the timing of
metamorphosis (Nijhout, 1981). Once the critical developmental stage has been attained, resource availability has no role
to play in the completion of metamorphosis (Bakker, 1959).
Despite the large number of studies that have assessed insect tolerance of environmental extremes, or the influence of
nutrition on insect fitness, few have attempted to link nutrient intake to variation in tolerance traits. Larval nutrition
determines how adult flies of Drosophila melanogaster cope with stress (Anderson et al., 2010). This is because the larval
stage is thought to influence metabolic reserves in adults. When reared on a protein-rich larval medium, D. melanogaster
adults exhibited increased desiccation resistance and heat tolerance compared to those reared on a carbohydrate-
enriched medium (Anderson et al., 2010). It has also been shown that increased resistance to starvation stress is strongly
associated with lipid storage (Djawdan et al., 1998). In some insects, adults also feed to obtain nutrients used for
maintenance, survival and sexual development, and this could also affect resistance traits through changes in adult
metabolic reserves (Nestel et al., 2005).
The aim of this study was to determine the effect of the interaction between larval and adult diet with respect to
desiccation resistance and water balance of the marula fruit fly, Ceratitis cosyra (Walker) (Diptera: Tephritidae). This
species was chosen because of its close phylogenetic relationship to other species that have been the subject of water
balance and nutritional studies (Weldon and Taylor, 2010; Weldon et al., unpublished data). Ceratitis cosyra is a serious
pest across sub-Saharan Africa, and it is acknowledged to be more destructive than the Mediterranean fruit fly, C.
capitata (Wiedemann) or the Natal fruit fly, C. rosa (Karsch) (Malio, 1979; Labuschagne et al., 1996; Javaid, 1966; Javaid,
1979; Rendell et al., 1995; Lux et al., 1998) in certain parts of its range and on host fruits from the plant families
Anacardiaceae, Lauraceae, Myrtaceae, Rosaceae, Rubiaceae and Rutaceae (White and Elson, 1992; De Meyer, 1998; Lux,
1998). An increased understanding of how the desiccation resistance and water balance traits of C. cosyra vary according

5. to diet will contribute to predicting its distribution in a changing climate using physiological models that account for flows
of energy and conservation of mass (Kearney et al., 2010). More specifically, the objectives of this study were to establish
whether the interaction between larval and adult diet enhanced desiccation resistance in adults by: (1) increasing body
size which may then increase water storage, (2) increasing dehydration tolerance, which may result from higher levels of
protective molecules from a better quality diet. Starvation resistance was also determined to verify that patterns of
survival under dry conditions were due to water loss rather than nutrient limitations.
Methods and materials
Flies and colony maintenance
Ceratitis cosyra flies were maintained in the Department of Zoology and Entomology, University of Pretoria, South Africa.
The culture had been kept in the lab for approximately 12 generations with 300 adults in each generation. Insect netted-
cages were used to store the flies and each cage had several Petri dishes, each Petri dish having either sugar or
hydrolysed yeast (HG000BX6.500; Merck; Wadesville; Gauteng). Each cage was also supplied with water-soaked cotton
wool as a water source. Flies laid their eggs into oviposition dishes. These oviposition dishes were 100 mL plastic cups
with moist tissue paper and 3 mL of Nectar guava concentrate (Halls; Tiger Consumer Limited, Bryanston, South Africa).
These were covered with a double layer of Parafilm (Neenah; WI 54956; Bemis Flexible Packaging; Gauteng) that was
pierced multiple times with an insect pin. Eggs were eventually washed off the Parafilm with distilled water into a glass
dish where they were permitted to settle. Eggs were then taken up by a 3 mL disposable plastic Pasteur pipette and again
allowed to settle at the tip of the pipette. It has been determined that one drop of densely-packed eggs from such a
Pasteur pipette contains approximately 300 eggs. Eggs were transferred to the larval diet in this way. The cultures and all
experiments described below were kept at a constant temperature of 25 ± 1°C.
Choice of larval diets
Before being able to determine the effect of larval diet quality on adult water balance traits, it was first necessary to
identify larval diets that contained high and low protein, but still permitted sufficient development and survival to obtain
adults for testing. The standard larval diet used to rear C. cosyra is comprised of an undisclosed blend of carrot powder,
sucrose, torula yeast, and sodium benzoate as a preservative. This standard diet, plus a range of diets with different
proportions of sucrose and torula yeast (a source of protein and other nutrients) were screened for development time,
pupal production, and adult eclosion. The diets, which were prepared by Dr Aruna Manrakhan from Citrus Research
International, Nelspruit, South Africa, included 8% (standard), 4%, 1% and 0% torula yeast by wet mass. The proportion of
yeast in the trial diets was selected based on available literature on the protein content of known fruit hosts for C. cosyra:
the protein content of marula fruit, Sclerocarya birrea Hochst. is 0.5% (Wehmeyer, 1966). To 100 g of the dry mix of each
diet, 250 mL of boiling water was added and combined to form a smooth paste. A quantity of 100 g of the wet mix of
each diet was transferred to plastic cups with a volume of 100 mL. There were 5 replicates of each diet.

6. After preparing the diets, C. cosyra eggs were obtained from the lab culture. Approximately 2700 eggs (3 Petri dishes,
each having 3 drops of eggs) were allowed to hatch on moist filter paper in covered Petri dishes. Using a dissecting
microscope, 100 freshly-hatched larvae were transferred with a moist, very fine paint brush to each replicate of the four
diets (i.e., a total of 2000 freshly-hatched larvae). The inoculated diets were then placed on top of a 2 cm layer of dry sand
in individual ventilated containers (with a volume of 2 L). After 18 days, the sand was sifted from each container to count
the number of pupae that were produced from each replicate of each diet. The pupae were returned to the ventilated
containers and covered with a 2 cm layer of dry sand. The containers were observed on a daily basis to record the date of
first adult emergence and main emergence. The adults were left to starve until death, after which, the number and sex of
adults was determined by counting them manually.
Diet manipulation
Based on the results of the trials described above, the standard larval diet (8% torula yeast) and the larval diet containing
1% torula yeast were used for subsequent diet manipulations. These larval diets are referred to as ‘high protein’ and ‘low
protein’ throughout the remainder of this thesis, respectively.
Approximately 2400 eggs were obtained from lab culture, as mentioned described above. A droplet having approximately
300 eggs was inoculated in three 100 mL of high larval diet and five 100 mL of low larval diet. Rates of adult emergence
from the pilot study were used to estimate the number of eggs needed to obtain the number of adults needed for
planned desiccation and starvation resistance assays. These were placed on a 2 cm layer of dry sand in 2 L plastic
containers with ventilated lid. Larvae emerged out of the larval diets at the end of the third instar and entered the pupal
stage. The sand was sifted after 18 days to obtain pupae. Pupae were then placed in an empty cage to emerge as adults.
Upon emergence, the adults from each larval diet were allocated to assays for initial mass, water content, and desiccation
and starvation resistance (described below) or transferred to one of two cages where they were allocated to one of two
adult diet treatments: sucrose and hydrolysed yeast, or sucrose only. Hydrolysed yeast is a rich source of amino acids,
lipids and micronutrients (Taylor et al., 2013). Each cage was also supplied with water-soaked cotton wool as a water
source. Flies provided with food as adults were assayed for initial mass, water content, and desiccation and starvation
resistance at 10 days after adult emergence.
Initial mass and water content
At 0 days and 10 days after adult emergence, 20 flies (10 females and 10 males) were placed in centrifuge tubes of known
weight and weighed on a microbalance (to 0.001 mg; CPA2P, Sartorius AG, Germany). Initial mass of each fly was
obtained by subtracting tube weight from tube + fly weight. These adult insects were then frozen and stored at -20 °C for
several days. At a later date, adult flies were freeze-dried using an automated freeze-drier (ISO 9001; VIRTIS & SP

7. Industries Company; United Scientific (PTY) LTD; Gauteng) for approximately 48 hours before being weighed again on a
microbalance to determine dry mass. Water content was determined by subtracting dry mass from body mass.
Desiccation and starvation resistance
At 0 days and 10 days, 30 female and 30 male flies were placed into individual, numbered, 2 mL micro-centrifuge tubes
that had been pierced with 12 holes (approximately diameter = 1 mm) and then pre-weighed. Flies in tubes were then
weighed (to 0.001 mg) and initial body mass of each fly was calculated by subtracting tube mass. Half of the tubes were
then placed onto racks in airtight containers over anhydrous silica gel to maintain relative humidity below 5%. The other
half were placed onto racks in airtight containers over distilled water to maintain relative humidity close to 100%. All
airtight boxes were maintained at 25°C for the duration of the experiment. All tubes were checked for mortality every 3-
hours by viewing them through the clear plastic top of the airtight containers. Dead flies were removed from the tubes
and weighed to record body mass at death (to 0.001 mg). These were then placed in new, intact, labelled tubes for
storage in a freezer at -20°C. Later, all flies were freeze-dried and weighed as described above to determine dry mass at
death and body water at death (expressed as percentage of initial water content, this is referred to as dehydration
tolerance (Gibbs et al., 1997).
Data analysis
An analysis of variance (ANOVA) was used to analyse the data obtained from the preliminary determination of suitable
larval diets. The independent variable was diet (8%, 4%, 1% and 0% torula yeast of wet mass) development time (from
set-up to main adult emergence), number of pupae, and adult emergence (expressed as a percentage of the number of
pupae) as dependent variables. The sex ratio was established by manually counting the number of females vs. males and
it was found to be 1:1. A contingency analysis was used to determine if the number of females and males obtained
depended on the diet and it was established that larval diet had no significant effect on the sex ratio of C. cosyra (X2
=
3.13, df= 2, p= 0.209). By excluding the 0% torula yeast treatment from all analyses (after yielding 0 pupae and thus 0
adults), data met the assumptions of parametric tests. A post-hoc Tukey’s HSD multiple comparisons test was used to
identify where differences existed between the diets.
General linear models were used to determine the effects of larval diet only on initial mass of newly emerged-flies (at 0
days). The independent variables were larval diet, the sex and diet by sex interaction. Similar models used to determine
the effects of larval diet and sex on dry mass and water content of newly-emerged flies, but initial mass was also included
in the model to account for potential size effects. Linear models were also used to determine the effects of larval and
adult diet on initial mass, dry mass and water content of the flies (at 10 days after emergence) that had fed as adults. In
this case, the independent variables were larval diet, adult diet and sex, and their full factorial interactions, and initial
mass was a covariate in models for dry mass and water content.

8. Cox proportional hazards survival models were used to determine the effects of diet, sex an initial mass of adult C. cosyra
on time to death in desiccation and starvation resistance assays. Data from desiccation and starvation resistance assays
were analysed separately. For flies tested as newly-emerged flies, the model included the main effects of larval diet and
sex, their interaction, and initial mass as a covariate. The model for flies that were fed for 10 days before being tested
included the main effects of larval diet, adult diet and sex, their full factorial interactions, and initial mass as a covariate.
General linear models were used to determine the effect of larval and adult diet on water content at death of desiccated
flies that were tested when newly-emerged or fed, 10-day-old adults. The models for newly-emerged flies included the
main effects of larval diet and sex, and their interaction. The model for fed, 10-day-old flies included the effects of larval
diet, adult diet, sex, and their full factorial interactions. In all models, estimated water content was entered as a covariate
to account for body water available to be lost. This is more appropriate than analysing percentages in parametric models
(Warton and Hui, 2011). Estimated water content was calculated using the results of the linear regression of initial mass
and water content of flies that were not subjected to desiccation or starvation was performed. A separate regression was
performed for each larval diet, adult diet and sex combination for recently-emerged and fed, 10-day-old flies (Table A1).
All data analyses were performed using Statistica for Windows software (version 11).
Results
Choice of larval diets
No pupae were obtained from the 0% torula yeast larval diet. There was a significant difference between the numbers of
pupae obtained from the remaining three larval diets (F3, 16= 265.42, p< 0.0001). The number of pupae was highest in the
4% and 8% torula yeast larval diets, and differed significantly from the 1% torula yeast diet (Figure 1a). Larval diet also
had a significant effect on adult emergence expressed as a percentage of pupae obtained from each diet (F3, 16= 70. 39, p<
0.0001). The highest adult emergence was obtained from the diets containing 4% and 8% torula yeast, which did not
differ from each other. Adult emergence from the 1% torula yeast larval diet was significantly lower than the other two
diets (Figure 1b). There was a significant effect of larval diet on development time (F3,16= 7374.60, p< 0.0001), with the
adult stage reached in a shorter period of time by individuals reared on the 4% and 8% torula yeast in comparison with
those reared on the 1% torula yeast diet (Figure 1c). Based on these results, the 8% torula yeast larval diet was selected
as the high protein larval diet, and the 1% torula yeast larval diet was selected as the low protein larval diet

9. Figure 1. Effect of larval diet on the development and survival of C. cosyra. (a) Mean number of Ceratitis cosyra pupae.
Each replicate began with 100 newly-emerged larvae. (b) Mean percentage of adult emergence of C cosyra. Percentages
calculated using the number of pupae obtained from each replicate as the denominator. (c) Mean development time
(from set-up to main adult emergence) of C cosyra. In all diet treatments, n=5. Error bars indicate ± 1 s.e..
Meanadultemergence(%)
B
Developmenttime(days)
Torula yeast (% of wet mass)
C

10. Newly-eclosed, unfed adults: effects of larval diet
There was a significant effect of larval diet on the initial mass of flies that were weighed immediately after adult
emergence (F1, 36= 17.128, p< 0.0001). Flies that were reared on the high protein larval diet were significantly heavier than
the flies that had been reared on the low protein larval diet (Figure 2a). There was also a significant effect of sex on the
initial mass of these flies (F1, 36= 29.302, p< 0.0001), with females being heavier than males (Figure 2a). There was no
interaction between larval diet and sex on initial mass of the flies at adult emergence (F1, 36= 2.096, p= 0.16).
Dry mass of flies on emergence was significantly affected by larval diet (F1, 35= 12. 560, p< 0.05). The dry mass of flies that
were grown on the high protein larval diet was less than that of flies that were grown on the low protein larval diet
(Figure 2b). Sex had no effect on the dry mass of the flies (F1, 35= 0.008, p= 0.927). The interaction of larval diet and sex
had no effect on the dry mass of the flies (F1, 35= 0.003, p= 0.954). The covariate of initial mass had a significant effect on
dry mass of the flies on emergence (F1, 35= 92.706, p< 0.0001), with dry mass being positively associated with initial mass.
Water content of newly-emerged adult C. cosyra was also significantly affected by larval diet (F1, 35= 12. 560, p< 0.005).
Flies that were reared on the high protein larval diet had significantly greater water content than those reared on the low
protein larval diet (Figure 2c). There was also a significant effect of initial mass on water content of the flies (F1, 35=
646.634, p< 0.0001), with water content being positively associated with initial mass. Neither the effect of sex (F1, 35=
0.008, p=0.927), nor the interaction of larval diet and sex (F1, 35= 0.003, p= 0.954) had an effect on water content of flies
on emergence.

11. SEX
female
SEX
male
high yeast low yeast
LARVAL DIET
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
10.5
11.0INITIALMASS(mg)
SEX
female
SEX
male
high yeast low yeast
LARVAL DIET
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
DRYMASS(mg)
A
SEX
female
SEX
male
high yeast low yeast
LARVAL DIET
5.4
5.5
5.6
5.7
5.8
5.9
6.0
WATERCONTENT(mg)
B

12. SEX
female
SEX
male
high yeast low yeast
LARVAL DIET
5.4
5.5
5.6
5.7
5.8
5.9
6.0WATERCONTENT(mg)
Figure 2. Effect of larval diet on initial mass, dry mass and water content of newly-emerged adult female and male C.
cosyra. (a) Initial mass; (b) least squares mean dry mass; (c) least squares mean water content. Mean dry mass and water
content are estimated relative to a mean initial mass of 8.338 mg.
There was a significant effect of larval diet on the desiccation resistance of adult C. cosyra (X2
= 32.539, p< 0.0001). The
longevity of flies reared on the high protein larval diet was shorter than that of those reared on the low protein larval diet
(Figure 3a). Sex (X2
= 0.076, p= 0.783), the interaction of larval diet and sex (X2
= 1.425, p= 0.233) and initial mass (X2
=
14.585, p> 0.0001) had no effect on the desiccation resistance of newly-emerged flies (Figure 3a).
There was a significant effect of larval diet on water remaining at death of the flies (F1, 115= 7.684, p< 0.0001). The water
remaining at death of flies reared on the high protein larval diet was significantly higher than those reared on the low
protein larval diet (Figure 3b). There was also a significant effect of the estimated water content on water remaining at
death of the flies (F1, 115= 52.418, p< 0.0001). Flies reared in low protein larval diet had significantly more water remaining
at death (Figure 3b). There was a no effect of sex on water remaining at death of the flies (F1, 115= 3.063, p= 0.08). The
larval diet by sex interaction showed no effect on water loss before death of newly-emerged flies (F1, 15= 0.459, p= 0.499).
C

13. SEX
female
SEX
male
high yeast low yeast
LARVAL DIET
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
WATERATDEATH
Figure 3. (a) Least squares mean longevity (desiccation resistance) of Ceratitis cosyra females and males. (b) Least squares
mean water remaining at death of C. cosyra females and males. These were all obtained from marula fruit flies reared on
high and low protein larval diets but unfed as adults. Mean water loss before death is estimated relative to a mean
estimated water content of 5.448 for all figures shown.
LARVAL DIET
LONGEVITY(hours)
SEX: female
SEX: male
high yeast low yeast
50
60
70
80
90
100
110
120
A
B

14. Larval diet had a significant effect on starvation resistance of the newly-emerged C. cosyra (X2
= 18.896, p< 0.0001). The
longevity of flies grown in high protein larval diet was shorter than to those grown in low protein larval diet (Figure 4).
There was no significant effect of sex (X2
= 0.295, p= 0.587), the interaction of larval diet and sex (X2
= 1.526, p= 0.217) or
initial mass (X2
= 1.257, p= 0.262) on the starvation resistance of adult C. cosyra when newly-emergence (Figure 4).
Figure 4. Least squares mean longevity (starvation resistance) of Ceratitis cosyra females and males reared on high and
low protein larval diets but unfed as adults. Mean water loss before death is estimated relative to a mean estimated
water content of 5.448.
Fed adults: effects of both larval and adult diet
There was a significant effect of the larval diet on the initial mass of the fed flies (F1, 72= 40.522, p< 0.0001). The initial
mass of flies grown in high protein larval diet was greater compared to those grown in low protein larval diet (Figure 5a).
There was also a significant effect of the adult diet on the initial mass of the fed flies (F1, 72= 11.567, p< 0.0001). The initial
mass of flies grown in high protein adult diet (sugar + YH) was greater than those grown in low protein adult diet (sugar
only), whether the flies were from high or low protein larval diets. There was a significant effect of sex on the initial mass
of the fed flies (F1, 72= 52.316, p< 0.0001). Females grown in high protein adult diet had significantly higher initial mass
than those grown in low protein adult diet, whether from high or low protein larval diets (Figure 5a). Lastly, the
interaction between larval diet and sex showed a significant effect on the initial mass of the fed flies (F1, 72= 4.014, p<
LARVAL DIET
LONGEVITY(hours)
SEX: female
SEX: male
high yeast low yeast
50
60
70
80
90
100
110
120

15. 0.05). Flies grown in high protein larval diet had significantly higher initial mass than flies grown in low protein larval diet
(Figure 5a). The larval diet and adult diet interaction (F1, 72= 3.111, p= 0.082), adult diet and sex interaction (F1, 72= 0.021,
p= 0.886), larval diet, adult diet and sex interactions (F1, 72= 0.001, p= 0.977) all had no effect on the initial mass of the
flies (Figure 5a).
There was a significant effect of the initial mass on the dry mass of the flies (F1, 71= 154.795, p< 0.0001). The larval diet (F1,
71=2.747, p= 0.102), adult diet (F1, 71= 0.733, p= 0.395), sex (F1, 71= 0.576, p= 0.450), larval diet and adult diet interaction
(F1, 71= 0.567, p= 0.454), larval diet and sex interaction (F1, 71= 0.782, p= 0.380), adult diet and sex interaction (F1, 71= 0.151,
p= 0.699) and lastly, larval diet, adult diet and sex interaction (F1, 71= 0.425, p= 0.517) all did not show any effect on the
dry mass of the flies.
There was a significant effect of the initial mass on the water content of the flies (F1, 71= 639.003, p< 0.0001). The larval
diet (F1, 71= 2.747, p= 0.102), adult diet (F1, 71= 0.733, p= 0.395), sex (F1, 71= 0.576, p= 0.450), larval diet and adult diet
interaction (F1, 71= 0.567, p= 0.454), larval diet and sex interaction (F1, 71= 0.782, p= 0.380), adult diet and sex interaction
(F1, 71= 0.151, p= 0.699) and lastly, larval diet, adult diet and sex interaction (F1, 71= 0.425, p= 0.517) all did not show any
effect on the dry mass of the flies.
A
SEX
female
SEX
maleLARVA DIET: high yeast
ADULT DIET:
sugar
sugar + YH
6
7
8
9
10
11
12
13
INITIALMASS(mg)
LARVA DIET: low yeast
ADULT DIET:
sugar
sugar + YH
A

16. SEX
female
SEX
maleLARVA DIET: high yeast
ADULTDIET:
sugar
sugar+YH
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3DRYMASS(mg)
LARVA DIET: low yeast
ADULTDIET:
sugar
sugar+YH
SEX
female
SEX
maleLARVA DIET: high yeast
ADULTDIET:
sugar
sugar+YH
5.4
5.5
5.6
5.7
5.8
5.9
6.0
6.1
6.2
WATERCONTENT
LARVA DIET: low yeast
ADULTDIET:
sugar
sugar+YH
Figure 5. (a) Initial mass of Ceratitis cosyra females and males. (b) Least squares mean dry mass of C. cosyra females and
males. (c) Least squares mean water content of C. cosyra females and males. These were obtained from marula fruit flies
reared on high and low protein larval diets then fed as adults for 10 days on either sugar only or sugar and hydrolysed
yeast. Mean water content is estimated relative to a mean initial mass of 8.695 mg for dry mass and body water content.
Mean initial mass had no effect on mean dry mass and body water content of the flies at 10-day post-eclosion.
B
C

17. There was a significant effect of larval diet on desiccation resistance (X2
= 15.704, p< 0.0001). Flies grown in high protein
larval diet had shorter longevity than those grown in low protein larval diet (Figure 6). There was a significant effect of
adult diet on desiccation resistance of fed flies (X2
= 8.739, p< 0.005). Flies fed in high protein adult diet had shorter
longevity than those grown in low protein adult diet. There was also a significant effect of the adult and sex interaction
(X2
= 12.559, p< 0.0005). Females survived longer when grown in low protein adult diet (sugar only) whereas males
survived longer when grown in high protein adult diet (sugar + YH) (Figure 6). The larval diet and adult diet interaction
(X2
= 0.220, p= 0.639), sex (X2
= 0.591, p= 0.442), larval diet and sex interaction (X2
= 0.012, p= 0.912), initial mass (X2
=
7.789, p= 0.005) as well as larval diet, adult diet and sex interaction (X2
= 1.424, p= 0.233) all did not show any effect
towards the desiccation of the fed flies (Figure 6a).
ADULT DIET
LONGEVITY(hours)
LARVAL DIET: low yeast,
SEX: female
LARVAL DIET: low yeast,
SEX: male
LARVAL DIET: high yeast,
SEX: female
LARVAL DIET: high yeast,
SEX: malesugar sugar + YH
28
30
32
34
36
38
40
42
44
46
48
50
52
54
56
58
Figure 6. Least squares mean longevity (desiccation resistance) of Ceratitis cosyra females and males reared on high and
low protein larval diets then fed as adults for 10 days on either sugar only or sugar and hydrolysed yeast. Mean water
content is estimated relative to a mean initial mass of 6.239 mg.

18. There was a significant effect of adult diet on water remaining at death of the flies (F1, 231= 14.159, p< 0.005). Flies reared
in high protein adult diet (sugar + YH) had significantly more water remaining at death than those reared in low protein
adult diet, irrespective of whether they were grown in high or low protein larval diet (Figure 7). There was a significant
effect of the sex on water loss before death of the fed flies (F1, 231= 71.250, p< 0.0001). Males exhibited greater water
remaining at death than females, with those grown in high protein larval diet having even more water remaining at death
(Figure 7). There was a significant effect of larval diet and sex interaction on water remaining at death of the flies (F1, 231=
16.373, p< 0.0001). Males recorded the highest water remaining at death when grown in high or low protein larval diet
(Figure 7). There was a significant effect of adult sex and sex interaction (F1, 231= 32.557, p< 0.0001). Males grown in high
protein adult diet had significantly more water remaining at death than those grown in low protein adult diet, irrespective
of the larval protein diet they have been exposed to (Figure 7). There was a significant effect of the larval diet, adult diet
and sex interaction on water remaining at death of the flies (F1, 231= 9.168, p< 0.005). Males grown in low protein larval
diet and high protein adult diet recorded the highest water remaining at death (Figure 7). Lastly, there was a significant
effect of estimated water content on the water loss before death of the fed flies (F1, 231= 26.589, p< 0.0001). There was no
effect of larval diet (F1, 231= 0.690, p< 0.407), larval and adult diet interaction (F1, 231= 3.823, p= 0.052) on water remaining
at death of the flies (Figure 7).

19. Figure 7. Least squares mean water remaining at death of Ceratitis cosyra females and males reared on high and low
protein larval diets then fed as adults for 10 days on either sugar only or sugar and hydrolysed yeast. Mean water content
is estimated relative to a mean initial mass of 6.239 mg.
There was a significant effect of the adult and sex interaction on starvation resistance of the fed flies (X2
= 7.664, p<
0.005). Females lasted longer when grown in low protein adult diet (sugar only) whereas males lasted longer when grown
in high protein adult diet (sugar + YH) and this was irrespective of whether they were grown in high or low protein larval
diet (Figure 8). There was a significant effect of initial mass on starvation resistance of fed flies (X2
= 14.028, p< 0.0001).
The flies with higher initial mass had a slightly extended longevity than the latter and this is seen in females and males
(Figure 8). The larval diet (X2
= 0.291, p= 0.589), adult diet (X2
= 0.276, p= 0.599), larval diet and adult diet interaction (X2
=
0.776, p= 0.378), sex (X2
= 4.089, p= 0.043), larval diet and sex interaction (X2
= 0.050, p= 0.824) as well as larval diet, adult
diet and sex interaction (X2
= 1.046, p= 0.306) all did not show any effect on the starvation resistance of the fed flies
(Figure 8).
SEX
female
SEX
maleLARVAL DIET: low yeast
ADULTDIET:
sugar
sugar+YH
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0WATERATDEATH
LARVAL DIET: high yeast
ADULTDIET:
sugar
sugar+YH

20. ADULT DIET
LONGEVITY(hours)
LARVAL DIET: low yeast,
SEX: female
LARVAL DIET: low yeast,
SEX: male
LARVAL DIET: high yeast,
SEX: female
LARVAL DIET: high yeast,
SEX: male
sugar sugar + YH
40
45
50
55
60
65
70
75
80
85
Figure 8. Least squares mean longevity (starvation resistance) of Ceratitis cosyra females and males reared on high and
low protein larval diets then fed as adults for 10 days on either sugar only or sugar and hydrolysed yeast. Mean water
content is estimated relative to a mean initial mass of 6.239 mg.
Discussion
Larval and adult diet both affect desiccation resistance in marula fruit flies, Ceratitis cosyra (Walker), as established in this
present study. This is indicated by flies exhibiting greater water remaining at death when fed for 10 days, with males
(smaller in size) having more water remaining at death. This then means that having a larger body size (higher initial
mass) does not always mean that the fly has more water available to lose. This greater water remaining at death is seen in
flies having been grown in both high and low protein larval diets. In females, the effects become even more pronounced
in flies fed in low protein adult diet (sucrose only) whereas in males it becomes more pronounced in flies fed high protein
adult diet (sucrose + YH). These findings concur with that of Andersen et al. (2010) who found that desiccation tolerance
was highest in flies grown in protein-enriched medium in Drosophila melanogaster. This study also related to Parkash &
Ranga (2013) and Parkash and colleagues who found sex differences for adaptation to dehydration stress in Drosophila
kikkawai. This study brings a new dimension to Parkash et al. (2008), who found a positive correlation between
desiccation tolerance and lipid accumulation in tropical Drosophilids. This highlights the role nutrition plays in enhancing
desiccation resistance. Furthermore, the protein-rich medium could be activating several enzymes which are necessary
for water conservation or dietary protein is used to manufacture them. Future studies could investigate this.

21. Recently, Tejeda et al. (2014) found that resistance to stressful environments increases with fly size in the tephritid fruit
fly Anastrepha ludens. However, this varies across environments (access to water and relative humidity). For example, in
Drosophila sp., structural size was positively correlated with desiccation but not starvation resistance (Matzkin et al.,
2009). Conversely, in the tephritid Bactocera tryoni, wing length was not correlated with either desiccation or starvation
resistance (Weldon & Taylor, 2010) while mass was found to be positively correlated with desiccation resistance (Weldon
et al., 2013). This then links to the present study where greater initial mass led to greater water content and thus greater
flies grown in high protein larval diet as well as high protein adult diet (sugar + YH). Our study demonstrated that flies
with greater initial mass survived desiccation and starvation better with females outshining males in desiccation
resistance and males outshining the females in starvation resistance (Figure 6 and Figure 8).
Furthermore, in this study, we have also established that larval and adult diets have a significant role to play in
desiccation resistance because flies grown in low protein larval diet had a greater desiccation resistance than those grown
in high protein larval diet (Figure 3a). However, when grown in low protein adult diet (sugar only), females had greater
desiccation resistance but when grown in high protein adult diet (sugar + YH), males had greater starvation resistance.
This finding, that females adults do better when fed sugar only, may be linked to Taylor et al. (2013), who found that
supplementation with yeast hydrolysate may expose flies to increased starvation thereby shortening their lifespan if food
is limited. Flies are thus faced with a dilemma (a trade-off between survival and reproduction) since it has been reported
that feeding on yeast hydrolysate promotes ovarian development and oogenesis (Meats & Khoo, 1976; Meats & Leighton,
2004; Meats et al., 2004, 2009; Perez-Staples et al., 2008), early mating ages and increased maturity (Perez-Staples et al.,
2007; Prabhu et al., 2008). In comparison with flies fed sugar only, it has been shown that flies fed sugar + YH reach sexual
maturity sooner, have longer copulations and induced better sexual inhibition (Perez-Staples et al., 2007, 2009; Weldon &
Taylor, 2011).
In terms of initial mass, the adult diet ameliorates or improves the larval diet. Thus is seen when the flies grown in high
protein larval diet as well as high protein adult diet had more initial mass than flies grown in low protein larval diet and
low protein adult diet (Figure 5a). In terms of dry mass, and water content, adult diet did not compensate for larval diet.
No pattern was seen when flies fed in either high or low protein adult diet, after the same flies were grown in high
protein larval diet had less dry mass but more water content than those grown in low protein larval diet (Figure 2a, b).
There seems to have been a compensation for low protein larval diet, when flies feed on high protein adult diet. This is
demonstrated by flies having lower initial body mass yet surviving desiccation better than the flies grown in high protein
larval diet. This then highlights the fact that the larval diet is responsible for the initial mass of the adults. This was further
shown when dry mass and water content were not improved by either high or low protein larval diet in adult flies.

22. Explanation of our results could lie on the fact that it has been long suggested that the size of adult insects depends on
the larval developmental time and growth rate (Gefen et al., 2006). Prolonged development time is proposed to result in
increased food consumption and atmospheric water, thereby increasing the resource of the adult flies (Gefen et al.,
2006). It is likely that the observed difference in total development time (Figure 1c) between high larval diet and low
larval diet results from an extended third larval instar stage (Gefen et al., 2006). Larvae of C. cosyra reach a ‘critical age’
early in the third instar whereby they will undergo pupation and eclosion even if prevented from further feeding (Bakker,
1959). Most notably, differences in critical weight in natural populations of D. melanogaster have been shown to occur in
different geographical regions, indicating the existence of genetic variation in this development trait (de Moed et al.,
1999). Gefen et al. (2006) found that larval diet is affected by adult diet, but it is still unclear whether the development
changes lead to greater fitness of adult flies grown in low protein larval diet under desiccation resistance. Most
importantly, their results show that the extended third instar larval development contributes significantly towards the
overall higher desiccation resistance in adult flies grown in low protein larval diet compared to those grown in high
protein larval diet. This pattern is said to be a result of low rates of water loss (Gibbs et al., 1997). This reduced water loss
is further linked to higher carbohydrate content, glycogen and trehalose in the hemolymph (Djawdan et al., 1998;
Chippindale et al., 1998; Folk et al., 2001) (but see Hoffman & Harshman, 1999).
In D. melanogaster, desiccation-selected adults usually have 34% more water volume than control-selected flies (Folk et
al., 2001). Two-thirds of this ‘extra’ water volume is located to the hemolymph, which acts as a reservoir from which
water can be removed and transported to cells to prevent excessive cellular loss (causing irreparable damage of
macromolecules, thus resulting in cell death) (Folk et al., 2001). Removing only water from hemolymph increases the
osmotic pressure since solutes in the hemolymph become more concentrated. When that occurs, osmotically active
solutes have to be removed from the hemolymph to maintain a constant osmotic pressure. In terms of hemolymph
osmolarity, there are three ways in which insects cope with desiccation and these include: (1) toleration of fluctuations in
osmolarity, (2) excretory regulation of osmolarity by excreting solutes during hemolymph reduction and (3) internal
regulation of osmolarity by sequestering solutes when blood volume declines (Wall, 1970; Arlian, 1979; Nicolson, 1980;
Cohen et al., 1986; Naidu, 1998).
Osmoregulation of hemolymph as well as internal storage of osmotically active solutes helps the blood osmotic pressure
to remain relatively constant irrespective of reductions in volume of either water or blood (Folk et al., 2001). Rehydration
only assists in transporting the solutes from storage sites, back into the blood thus the adult flies will not be forced to look
for solute-laden resources (Folk et al., 2001). In conjunction with a study conducted by Folk & Bradley (2003), our results
could be explained by the fact that in comparison with flies grown in high protein larval diet, the low protein larval diet
flies had significantly lower hemolymph volume, because they had lower initial body mass and lower initial body water
content, but surprisingly had more water available at death, meaning they had greater retention of water.

23. In newly-eclosed, unfed flies, as well as fed flies, sex differences were commonly seen. The observed sex differences seen
in this study correspond with the findings of Parkash & Ranga (2013) who found higher desiccation resistance in females
in D. kikkawai. This could then mean that the water used for egg production is reabsorbed and made available to enhance
desiccation resistance in females. Further studies are needed to evaluate this conjecture. However, this could also mean
that since females generally have greater initial mass, that then enables them to have more body water content and
ultimately more water loss before death. Perhaps females are then able to store more water and hemolymph content
thus they can afford to lose more water than their male counterparts. This then assisted the females in having greater
desiccation resistance, whether grown in high or low protein larval diet. An explanation to this could be associated to
Parkash & Ranga (2013) who found that desiccation resistance was correlated with cuticular melanisation in females but
with changes in cuticular lipid mass in males, in D. kikkawai. In this study species, it is postulated that storing more body
water leads to more desiccation resistance in females although reduced water loss works best for males. Furthermore,
the increased content of trehalose in females and glycogen in males support the bound-water hypothesis for water
retention in Drosophilids (Parkash et al., 2014), that higher trehalose levels lead to greater dehydration tolerance.
Summary
The study has shown that flies grown in high protein larval diet have higher initial mass compared to those grown in low
protein larval diet. The same flies that have greater initial mass tend to have greater initial body water content. Females
(sex-specific differences) tend to have greater initial mass as well as greater initial body water content than their male
counterparts. However, those same flies then tend to have less initial dry mass (after eclosion). When the same adults
have been fed for a period of 10 days, they tend to have an even greater initial mass (whether grown in high protein
larval diet or low protein larval diet). However, in terms of dry mass and water content, the diet overlapped with each
other thus no pattern could be drawn from that. After eclosion, flies grown in high protein larval diet had greater water
loss before death than those grown in low protein larval diet. Females had an even greater water loss before death than
males. The same pattern was observed when they have been fed for a period of 10 days. After eclosion, the survival
analysis clearly showed that flies grown in high protein larval diet tend to last for a shorter period of time when compared
to those grown in low protein larval diet (shown by lower survival rate). When the flies have been fed for a period of 10
days, flies grown in high protein larval diet survive starvation better whereas flies grown in low protein larval diet survive
desiccation better. Once again, sex-specific differences were found whereby females (grown in low protein larval diet)
survive desiccation even better than males whereas males (grown in high protein larval diet) survive starvation more than
females, highlighting the role played by the hydrolysed yeast in females and males (yeast hinders the longevity of females
by increasing susceptibility to starvation). So in conclusion, greater mass leads to greater body water content, which then
eventually leads to enhanced desiccation resistance, with females (having greater initial mass) having an even more
enhanced desiccation resistance than their male counterparts since they had more water available to lose.

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30. Appendix
Table A1. Results of linear regression of water content on initial mass of C. cosyra that were not subjected to desiccation
or starvation resistance assays. N/A = not applicable; flies were not fed as adults
Age Larval diet Adult diet Sex Equation R2
F(1,8) P
0 days Low protein N/A female y= 0.7546x – 0.7113 0.956 172.481 < 0.001
0 days Low protein N/A male y= 0.6506x + 0.0806 0.943 131.611 < 0.001
0 days High protein N/A female y= 0.7555x – 0.5596 0.958 183.574 < 0.001
0 days High protein N/A male y= 0.7099x – 0.1367 0.939 122.461 < 0.001
10 days Low protein Sugar only female y= 0.7511x – 0.5998 0.959 186.434 < 0.001
10 days Low protein Sugar only male y= 0.6712x – 0.0251 0.961 198.735 < 0.001
10 days Low protein Sugar + YH female y= 0.6990x – 0.2368 0.930 106.958 < 0.001
10 days Low protein Sugar + YH male y= 0.5421x + 1.0489 0.877 57.038 < 0.001
10 days High protein Sugar only female y= 0.7534x – 0.8837 0.874 55.275 < 0.001
10 days High protein Sugar only male y= 0.6007x + 0.5863 0.889 64.019 < 0.001
10 days High protein Sugar + YH female y= 0.5060x + 1.6701 0.924 97.515 < 0.001
10 days High protein Sugar + YH male y= 0.5330x + 1.1731 0.583 11.176 > 0.005
Acknowledgements
Supervisors: Prof. Susan W Nicolson and Dr. Chris W Weldon
Diet preparation: Dr Aruna Manrakhan
Lab Assistants: Ezette duRand and Tshidi Hlalele
Funding: NRF Postgraduate Freestanding Scholarship and University of Pretoria Postgraduate Bursary