Journal of Phytopathology and Pest Management 5(2): 129-142, 2018
pISSN:2356-8577 eISSN: 2356-6507
Journal homepage: http://ppmj.net/
∗
Corresponding author:
Marwa F. K. Aly,
E-mail: dr.mero_83@yahoo.com
129
Copyright © 2018
Laboratory host selection and development
of immature
Drosophila suzukii
(Diptera:
Drosophilidae) on fruits and artificial diets
Marwa F. K. Aly
*
Plant Protection Department, Faculty of Agriculture, Minia University, El-Minya, Egypt
Abstract
Keywords: Drosophila suzukii, free choice assay, no-choice assay, artificial diet, oviposition selection.
The spotted-wing drosophila (SWD), Drosophila suzukii (Matsumura) (Diptera:
Drosophilidae), is an important pest of thin-skinned fruits including blueberries,
raspberries, strawberries, and cherry. In this study, six fruit hosts were chosen
(raspberries, blackberries, strawberries, blueberries, green grapes and red
grapes) and used as fruit and artificial diets to evaluate oviposition selection by D.
suzukii females in free choice assays and no-choice assays. Also, development and
performance of progeny until adult emergence was determined. Overall, D.
suzukii females preferred to lay eggs on raspberries rather than green grapes in
both tested fruit and artificial diet. Also, larvae that developed in raspberries
developed 2-4 days faster than those in red grapes and green grapes, in both no-
choice and choice assays for tested fruit and artificial diets. No significant
differences were found among tested fruits in both free choice assays for pupal
duration. Furthermore, adults complete of the development time 3 days earlier in
raspberries rather than green grapes in both choice and no-choice assays for both
tested fruit and artificial diets. Results also showed that strawberries, raspberries
and blackberries had similar and high proportion of pupal survivorship than
green grapes in choice and no-choice assays on tested fruits. Proportion of adults
was greater in raspberries than green grapes in both fruits and artificial diets. No
significant differences were found among fruits and among artificial diets in
proportion of males and females in choice and no-choice assays. It could be
concluded that raspberries were more favorable and comfortable host for D.
suzukii oviposition and progeny development and performance.
Aly Marwa, 2018
130
Introduction
The spotted -wing drosophila,
Drosophila
suzukii
(Matsumura), is an invasive
economic polyphagous pest from Asia
that occurs in North America and Europe
(Asplen et al., 2015; Cini et al., 2014) and
recently in South America (Depra´ et al.,
2014). This pest infests blackberries,
blueberries, cherry, raspberries,
strawberries, plums, peaches, grapes, figs,
kiwi fruit, pears and sometimes wine
grape (Ioriatti et al., 2015; Bellamy et al.,
2013; Lee et al., 2011; Dreves et al.,
2009). Damage is caused when adult
female flies, using a serrated ovipositor
and easily pierce the fruit skin lay eggs in
ripe and partially ripe fruit before harvest.
Developing larvae cause soft,
unmarketable fruit, leading to increased
risk of secondary rot infections (Walsh et
al., 2011). Economic losses of 80% yield
or 20–37% have been reported (Lee et al.,
2011; Goodhue et al., 2011). Given its
rapid life cycle (Tochen et al., 2014) and
that 90–95 % of the population is
estimated to be at immature life stages
during blueberry harvest (Wiman et al.,
2014), commonly used insecticides that
target adult
D. suzukii
have limited
impact on population trajectories. This
situation necessitates repeated pesticide
sprays to maintain pest control and fruit
marketability. Insecticide dependency can
be reduced by improved knowledge of
fruit susceptibility to
D. suzukii
(Lee et
al., 2015). Host preference studies
examined behaviors associated with host
selection e.g., host location, distribution,
and abundance (Gripenberg & Roslin,
2005; Hassan et al., 2003; Kareiva, 1982)
at individual and population levels
(Cunningham & West, 2008; Apperson et
al., 2004; Singer, 1982). Host suitability
studies evaluated factors affecting the
physiological development/ performance
of the harbored organism and other
features of host quality (Papaj, 2000;
McSorley, 1999; McClure, 1980;
Thompson, 1988). The objectives of the
present work were to use, strawberries,
blackberries, raspberries, blueberries,
green grapes and red grapes fruit and
artificial diets to determine: (1)
oviposition host selection for egg laid by
females; (2) performance of
D. suzukii
progeny that develop in each fruit and
artificial diet; (3) preference of
D. suzukii
for various fruit and /artificial diets. No-
choice tests were used to determine
which fruit and artificial diet are most
susceptible based on the physiological
capabilities of
D. suzukii
, otherwise,
choice tests were used to determine
preferences of
D. suzukii
for the group of
tested fruits and group of tested artificial
diets. These controlled laboratory tests
will provide a baseline for future studies
on fruit preference and
D. suzukii
infestation potential in the field.
Materials and methods
This research was implemented in the
laboratory of Entomology Department at
North Carolina State University, NC,
USA.
SWD culture:
Spotted-wing drosophila
(SWD) flies were obtained from SWD
rearing colony maintained at Biological
Resource Facilities (BRF). Insects used
in experiments were from a laboratory
colony established from flies reared from
raspberries and blackberries at the Upper
Mountain Research Station (Allegheny
County, NC). Field collected flies reared
from a variety of host fruit are
periodically added to this colony to
maintain genetic diversity. Flies were
held at 20°C, 65% RH and 12:12 light:
dark conditions, and maintained on a
standard cornmeal
Drososphila
diet
Aly Marwa, 2018
131
(Standard Cornmeal Recipe Online,
2012). All flies used to infest different
fruit hosts for experiments were
reproductively mature between 7-14 days
old.
Fruit source:
Six different host fruits
were evaluated in these experiments,
where fruits were purchased at a local
grocery store; red seedless table grapes
(sweet California grown with a mild
flavor profile), green seedless table
grapes (California grown with a sweet
flavor and firm texture), blueberries
(Patagonia, product of Argentina),
strawberries (San Diego, CA, USA),
raspberries (Driscoll’s, Watsonville, CA,
USA) and blackberries (Los Angeles,
CA, USA).
Diet substrates preparation:
Two-
hundred grams of each tested fruit type
were weighted and blended to get puree,
then added to 200 ml of boiled water and
4.0 g of agar. Propionic acid and
Tegosept were added to the mixture (2.4
ml for each) as a preservation material
against molding. The puree was poured
to 60 mm petri dishes and left to cool at
the room temperature, then kept in the
fridge until use.
Laboratory assays:
Fruit and artificial
diet were presented to drosophila females
to evaluate their host selection,
performance and development of
immature
D. suzukii
in both free choice
and no-choice tests.
Free choice assays:
Fifty flies (25 males
and 25 females) were placed in 0.30m
3
collapsible cages with fine mesh sides
and one clear observation panel (Bioquip
Products, Rancho Dominguez, CA) and
exposed to 15 g of each tested fruit (2
grape fruit, 2-3 blackberries and
raspberries, 1 strawberries fruit and 10-
14 blueberries fruit) for 24 hrs. Each
tested fruit was replicated 5 times.
Number of eggs laid/ replicate/ host was
counted using a stereomicroscope.
Samples were stored in 266 mL plastic
containers (up and up brand; Target,
Raleigh, NC) vented on the bottom with
thrips barrier mesh (Bioquip Products,
Rancho Dominguez, CA) at 26
o
C and
checked daily for pupal emergence for 7
days to calculate the larval development
time. Daily visible pupae were collected
and held in 60 mm petri dishes with a
moistened paper towel square until
emergence (Burrack et al., 2013). Petri
dishes with pupae were held at
22
o
C+61%RH under growth chamber
conditions and checked daily until adult
emergence. Emerged adults were
collected daily to determine the pupal
duration, proportion of eggs that
survived to the adult stage, and the sex
ratio of emerged adults were calculated.
For artificial diet free choice assay; the
same previous steps were implemented,
where one petri dish from each tested
fruit was positioned in the collapsible
cage and (20 males and 20 females) were
released for four hours. Each diet type
was replicated 5 times. Diets were
removed from cages and numbers of laid
eggs were counted for each replicate and
each treatment using stereomicroscope.
Petri dishes which recorded zero after
infestation (females did not oviposit
eggs), 10 eggs were transferred to
measure the larval duration and some
other biological aspects. Other infested
petri dishes, a range of 5-20 eggs were
kept inside each petri dish and held on
the growth chamber at 22
o
C+61%RH
Aly Marwa, 2018
132
until the first appearance for pupae. Then
the same previous steps were carried out
for pupae as mentioned above.
No-choice assays:
In no-choice assays,
groups of (five males and five females)
of
D. suzukii
were exposed to 15 g of
each tested fruit (each host kept
separately) held in a small plastic cup
covered with mesh and tightly closed
with rubber for 24 hrs. Five replicates
were conducted for each tested fruit and
number of eggs laid per replicate per
treatment was counted using a
stereomicroscope. Infested fruits were
held in 266 mL plastic containers and
treated with the same method as
mentioned above. For artificial diet no-
choice assays; each individual petri dish
was confined with a group of (5 males
and 5 females) for four hours. Each
tested fruit type was replicated 5 times.
Extra eggs than 20 eggs were removed
from infested dishes, while zero ones,
about 10 eggs were transferred to
measure the same parameters as
mentioned.
Statistical analysis:
The experiment was
conducted in a randomized complete
block design. Data obtained in the
present study was subjected to an
analysis of variance (ANOVA) with the
honestly significant difference value,
calculated as LSD (Post Hoc Test)
Multiple Comparison Test at 0.05
Probability (IBM SPSS Statistics version
9.0, 1998).
Results
Oviposition in host fruit (free choice
and no-choice assays):
The number of
D. suzukii
eggs laid was counted for both
free choice and no-choice assays and
presented in Figure (1). There were
significant differences among host fruit
in number of eggs for free choice assays
(F=17.85, P<0.01). Raspberries showed
greater number of eggs (101.2 eggs/
female) compared to strawberries, green
grapes and red grapes with a range of
4.4-34.4 eggs, but not significantly differ
from blackberries and blueberries.
While, green grapes had the least number
of eggs (4.4 eggs/ female) than all tested
fruits except red grapes (14.22 eggs). In
no-choice assays, no significant
differences were found among tested
host fruits in number of eggs laid
(F=1.82, P>0.05). Number of eggs was
slight similar for strawberries,
blackberries, raspberries and blueberries
(56.6, 60, 64 and 63.6 eggs,
respectively). Otherwise, green grapes
had the least number of eggs (25.4 eggs)
than all fruits.
Oviposition in artificial diets (free
choice and no-choice assays):
Egg laid
by females showed a significant
difference among tested artificial diets
for both free choice and no-choice assays
(F=3.09, P<0.01 and F=4.89, P<0.01). In
free choice assay, raspberries showed the
greatest number of eggs (15.4 eggs).
While, no eggs were deposited on
strawberries which did not significantly
differ with green grapes, red grapes and
blackberries (0.2, 3.8 and 1.8 eggs)
(Figure 2). In no-choice assay, highest
number of eggs was recorded for
raspberries (27.4 eggs), but not different
with blueberries (16.2 eggs). Otherwise
the least number of eggs was found in
green grapes (1 egg), which was not
Aly Marwa, 2018
133
significantly different with red grapes and strawberries (5.8 eggs and 6.6 eggs).
Figure 1: Number of D. suzukii eggs fruit/female (mean ± SE) in different host fruits in free choice and no-
choice bioassays. Different letters indicate significant differences within each group of bars representing
egg number for each tested host fruit and bioassay type, according to the LSD test (P < 0.05).
Figure 2: Number of D. suzukii eggs fruit/female (mean ± SE) in different artificial diets in free choice and
no-choice bioassays. Different letters indicate significant differences within each group of bars
representing egg number for each tested host fruit and bioassay type, according to the LSD test (P < 0.05).
Larval development time, pupal
duration and adult development time
in fruit:
Larval development time (days
from egg to pupation), pupal duration and
adult development time were recorded
for each tested fruit and presented in
Figure (3).
Larval development time:
D. suzukii
larval development time showed
significant differences among fruit in
choice assay (F=35.62, P<0.01) and no-
choice assay (F=50.47, P<0.01). In
choice assay, raspberries had shorter
larval development (5.8 days) than other
Aly Marwa, 2018
134
tested fruits except blackberries and
strawberries (6.2 days and 6.3 days).
Otherwise, longer larval development
time was observed on red grapes and
green grapes (9.2 days and 9.1 days) than
other tested fruits except blueberries (8.5
days). In no-choice assay, similar results
were recorded for raspberries which had
shorter larval development time (5.7
days) than other tested fruits but not
different with strawberries and
blackberries (6.3 days). While, red grapes
showed longer larval development time
(9.1 days) which not differ from
blueberries and green grapes (8.5 days
and 8.8 days).
Pupal duration:
Pupal duration was
recorded daily for each pupa/ tested fruit
and presented in (Figure 3). No
significant differences were found
among tested fruits in both free choice
assay (F=0.75, P>0.05) and no-choice
assay (F=0.71, P>0.05). Where pupal
duration ranged between 6.17-6.5 days
on fruits in both assays.
Figure 3: Larval development time, pupal duration and adult development time measured for D. suzukii in
six host fruit. Different letters indicate significant differences within each group of the same colored bars
separate for each parameter and each assay according to the LSD test (P < 0.05).
Adult development time:
Adult
development time was recorded daily for
each pupa/ tested fruit and showed in
(Figure 3). Significant differences were
found among tested fruits in adult
development time in free choice assay
(F=57.6, P<0.01) and no-choice assay
(F=99.5, P<0.01). In choice assay, adult
development time took shorter time in
raspberries fruit (11.08 days) than other
tested fruits, but not significant different
with blackberries and strawberries
(11.31 and 11.57 days). On the other
hand, adult development time elongated
3 days in green grapes, blueberries and
red grapes (14, 14.10 and 14.29 days,
respectively). In no-choice assay, similar
shorter adult development was recorded
for raspberries, strawberries and
blackberries (11.13, 11.42 and 11.64
days, respectively) than the rest of tested
fruits. While, longer adult development
Aly Marwa, 2018
135
time was recorded for green grapes (14.5
days) as compared with all fruits except
red grapes (14.38 days).
Larval development time in artificial
diets:
Significant differences were found
among diets in larval development time
in choice assay (F=8.97, P<0.01), and
no-choice assay (F=4.12, P<0.01). For
choice assay, in raspberries, the larval
development time took 8.1 days which
significantly was shorter than all diets
except strawberries and red grapes (9.2
days and 9.4 days). Otherwise, the
longest larval development time was
recorded for green grapes 11.97 days as
compared with all diets except
blackberries (11.33 days). In no-choice
assay, the shortest larval development
time was recorded for raspberries (9.13
days as compared with all diets except
red grapes (9.33 days). While, longer
larval development time was in green
grapes (10.9 days), but with no
difference for strawberries, blackberries
and blueberries (10.5, 10.7 and 10.7
days, respectively) (Figure 4).
Pupal duration in artificial diets:
Significant differences were found
among diets in pupal duration in choice
assay (F=5.23, P<0.01) and no-choice
assay (F=7.00, P<0.01). For choice
assay, shorter pupal durations were
similarly recorded on blackberries and
red grapes (6.3 days), and strawberries
(6.6 days) as compared to the rest of
diets. Otherwise, the longest pupal
duration was observed on green grapes
as compared with the other tested diets
(6.79 days). In no-choice assay,
blackberries showed the shortest pupal
duration (6.25 days) than all fruit. Green
grapes had the longest pupal duration (7
days) followed by blueberries and
strawberries (6.8 days and 6.8 days).
Figure 4: Larval development time, pupal duration and adult development time measured for D. suzukii in
six artificial diets. Different letters indicate significant differences within each group of the same colored
bars separate for each parameter and each assay according to the LSD test (P < 0.05).
Aly Marwa, 2018
136
Adult development time in artificial
diets:
A significant difference in adult
development time were found among
diets in choice assay (F=12.01, P<0.01),
but not significant for no-choice assay
(F=1.78, P>0.05). Adults had faster
development time in raspberries in
choice assay (13.4 days) than other tested
diets except for red grapes and
strawberries (13.9 days and 14.4 days).
While longer adult development time
was observed on green grapes and
blackberries (16.9 days and 16.8 days).
In no-choice assay,
raspberries had
significantly shorter adult development
time (14.5 days) than strawberries (16.7
days), but not different with the rest of
diets. While, strawberries had the
longest adult development time than
raspberries only.
Table 1: Proportion of pupal survivorship, adults, males and females for D. suzukii assayed for six host fruits in free
choice and no-choice laboratory tests.
Fruit host
Proportion (Mean ± SE)
Free choice assay
No-choice assay
Pupal
survivorship
Adults
Females
Males
Pupal
survivorship
Adults
Females
Males
Strawberries
0.913± 0.03a
0.357±0.09ac
0.867±0.07abc
0.133±0.07abc
0.933±0.21a
0.438±0.02ac
0.768±0.08ab
0.232±0.08ab
Blackberries
0.961±0.01a
0.402±0.02a
0.781±0.04abc
0.219±0.04abc
0.950±0.01a
0.515±0.02ac
0.792±0.02ab
0.208±0.02ab
Raspberries
0.957±0.01a
0.619±0.07b
0.731±0.05b
0.269±0.05b
0.905±0.03ad
0.541±0.12c
0.703±0.02a
0.297±0.02a
Blueberries
0.579±0.02bc
0.275±0.05ac
0.850±0.02abc
0.150±0.02abc
0.659±0.08b
0.365±0.04a
0.787±0.02ab
0.213±0.02ab
Green grapes
0.633±0.19ac
0.167±0.11c
1.000±0.00c
0.000±0.00c
0.158±0.04c
0.046±0.03b
0.833±0.17ab
0.167±0.17ab
Red grapes
0.498±0.16bc
0.128±0.06c
0.783±0.16abc
0.217±0.16abc
0.716±0.16bd
0.114±0.04b
0.931±0.04b
0.069±0.04b
Means within columns followed by the same letters are non-significantly different at 0.05 probability.
Proportion of pupal survivorship in
fruits:
Results showed that there is a
significant difference among fruit in
proportion of pupal survivorship in
choice assay (F=4.26, P<0.01) and no-
choice assay (F=16.54, P<0.01). In
choice assay, strawberries, raspberries
and blackberries had similar and high
proportion of pupal survivorship (0.913,
0.957 and 0.961). While, red grapes had
significantly the least value for
proportion of pupal survivorship (0.498)
compared with the tested fruits except
blueberries and green grapes (0.579 and
0.633). For no-choice assay, highly
similar proportions of pupal survivorship
were observed for raspberries,
strawberries and blackberries with no
significant difference (0.905, 0.933 and
0.950, respectively). Otherwise, green
grapes showed the least proportion for
pupal survivorship (0.158) (Table 1).
Proportion of adult in fruits:
Proportion of adults showed a significant
difference among fruit in choice assay
(F=6.37, P<0.01) and no-choice assay
(F=13.76, P<0.01). Raspberries had
greatly the highest proportion of adults
in choice assay (0.619) than all fruit.
Otherwise, lower proportion of adults
was detected on red grapes (0.128)
compared to other tested fruits, except
green grapes and blueberries (0.167 and
0.275, respectively). In no-choice assay,
raspberries had significantly the highest
Aly Marwa, 2018
137
proportion of adults (0.541) than all
tested fruits except strawberries and
blackberries (0.438 and 0.515). Lowest
proportion of adults was occurred on
green grapes (0.046), but no difference
with red grapes (0.114).
Proportion of females in fruits:
No
significant difference was found among
fruits in proportion of females in choice
assay (F=1.44, P>0.05) and no-choice
assay (F=1.75, P>0.05). Highest
proportion of females was observed on
green grapes (1.000) as compared with
raspberries (0.731) which had the lowest
proportion of females in choice assay.
Results for no-choice assay showed that
red grapes had significantly the highest
proportion of females (0.931) as
compared with the raspberries which had
the lowest proportion of females (0.703).
Proportion of males in fruits:
No
significant difference was found among
fruits in proportion of males in choice
assay (F=1.44, P>0.05) and no-choice
assay (F=1.75, P>0.05). High proportion
of males was detected on raspberries
(0.269) in choice assay, while no males
were found in green grapes.. In no-
choice assay, proportion of males was
high on raspberries (0.297) than on red
grapes, which had the lowest proportion
of males (0.069).
Table 2: Proportion of pupal survivorship, adults, males and females for D. suzukii assayed for six fruit artificial diets in
free choice and no-choice laboratory tests.
Fruit host
Proportion (Mean ± SE)
Free choice assay
No-choice assay
Pupal
survivorship
Adults
Females
Males
Pupal
survivorship
Adults
Females
Males
Strawberries
0.460±0.09a
0.380±0.09a
0.800±0.08ab
0.200±0.08ab
0.480±0.28a
0.426±0.25ab
0.849±0.08ab
0.151±0.08ab
Blackberries
0.340±0.14a
0.060±0.04c
1.000±0.00b
0.000±0.00b
0.540±0.19a
0.060±0.40a
0.750±0.14ab
0.250±0.14ab
Raspberries
0.840±0.10b
0.740±0.14b
0.706±0.06a
0.294±0.06a
0.703±0.04a
0.595±0.09b
0.776±0.07ab
0.224±0.07ab
Blueberries
0.800±0.09b
0.780±0.10b
0.779±0.07ab
0.221±0.07ab
0.540±0.29a
0.488±0.27ab
0.843±0.06ab
0.157±0.06ab
Green grapes
0.243±0.21b
0.243±0.09ac
0.854±0.09ab
0.146±0.09ab
0.186±2.83b
0.186±0.48ab
1.000±0.00a
0.000±0.00a
Red grapes
0.795±0.03b
0.795±0.09b
0.849±0.08ab
0.151±0.08ab
0.525±0.26a
0.500±0.23ab
0.704±0.04b
0.296±0.04b
Means within columns followed by the same letters are non-significantly different at 0.05 probability.
Proportion of pupal survivorship in
artificial diets:
Results for proportion of
pupal survivorship showed that, there is a
significant difference among tested diets
in choice assay (F=3.92, P<0.01) and no-
choice assay (F=4.93, P<0.01). In choice
assay, raspberries, blueberries and red
grapes had significantly higher
proportion of pupal survivorship (0.840,
0.800 and 0.795, respectively) than
blackberries and strawberries (0.340 and
0.460) (Table 2). While, blackberries
had the lowest proportion of pupal
survivorship as compared with all diets
except strawberries. For no choice assay,
significantly highest proportion of pupal
survivorship was observed on
raspberries (0.703) compared to the
tested diets. Otherwise, greatly lowest
proportion of pupal survivorship was
Aly Marwa, 2018
138
recorded on green grapes (0.186) than all
tested diets.
Proportion of adult in artificial diets:
Proportion of adult revealed that, there is
significant difference among tested diets
in choice assay (F=11.22, P<0.01), but
not significant in no-choice assay
(F=0.94, P>0.05). In choice assay, red
grapes had significantly higher
proportion of adults (0.795) than other
tested diets except raspberries and
blueberries (0.740 and 0.780). While,
significant low proportion of adults was
occurred on blackberries (0.060) than all
tested diets, except green grapes (0.243).
For no choice assay, results showed that
raspberries had significantly more
proportion of adults (0.595) than
blackberries, which had the lowest
proportion of adults (0.060).
Proportion of females in artificial
diets:
No significant difference was
found among diets in proportion of
females in choice assay (F=1.70, P>0.05)
and no-choice assay (F=1.22, P>0.05).
Blackberries had higher proportion of
females (1.000) than raspberries (0.706)
in choice assay. While in no-choice
assay, green grapes had significantly
more proportion of females (1.000) than
red grapes, which had the lowest
proportion of females (0.704).
Proportion of males in artificial diets:
No significant difference was found
among diets in proportion of females in
choice assay (F=1.70, P>0.05) and no-
choice assay (F=1.22, P>0.05). Choice
assay results showed that raspberries had
higher proportion of males (0.294) than
blackberries which showed no proportion
of males. Red grapes had the highest
proportion of males (0.296), while no
proportion of males was recorded for
green grapes in no choice assay.
Discussion
Ongoing research study the behavior
oviposition host selection of
D. suzukii
,
host preference and development and
performance of spotted wing drosophila
(SWD) progeny on six tested fruits and
artificial diets. Overall, our results for
choice and no-choice assays on fruit and
artificial diets showed that raspberries
fruit and artificial diet was the most
preferred host for females oviposition,
followed by blackberries, blueberries and
strawberries, while green grapes showed
the least preferred ones to SWD
followed by red grapes. Where the mean
numbers of eggs laid in raspberries fruit
were (101.2 eggs in choice assay and 64
eggs in no-choice assay) and in artificial
diets were (15.4 eggs in choice assay and
27.4 eggs in no-choice assay). While the
mean number of eggs laid in green
grapes fruit were (4.4 eggs in choice
assay and 25.4 eggs in no-choice assay)
and in artificial diets were (0.2 eggs and
1 egg in choice and in no-choice assays,
respectively). Raspberries have the
highest actual preference probability
followed by blackberries, strawberries,
peaches, cherries, blueberries and grapes
(Bellamy et al., 2013). Previous
observations have suggested that, despite
higher egg and larval densities in
raspberries than in other fruit,
D. suzukii
performed the best in raspberries
(Burrack et al., 2013). This suggests that
some attribute of raspberries may make
them a better host than other commonly
Aly Marwa, 2018
139
infested fruit. Revadi et al. (2012)
showed recently that
D. suzukii
flies are
attracted to odors from intact raspberry,
blackberry, blueberry, cherry, and
strawberry fruit, indicating that fruit
volatiles are important in its host
location. Also, Burrack et al. (2013)
reported the highest
D. suzukii
oviposition in raspberry fruit and the
lowest in blueberry fruit, and suggested
that there is a positive relationship among
adult
D. suzukii
attraction, female
oviposition, and offspring performance,
particularly for raspberries. Additionally,
mentioned that raspberries had
significantly lower average surface
penetration force when compared with
the blackberries, strawberries and
blueberries. Also, when flies were given
a choice between blackberries,
blueberries, strawberries or raspberries,
more eggs were always laid in
raspberries. Larvae that developed in
raspberries developed 2-4 days faster
than those in red grapes and green
grapes, in both no-choice and choice
assays for tested fruits and artificial diets.
Faster larval development time, adult
development time and proportion of
adults were observed on raspberries fruit
and this suggests that raspberries are
suitable host for
D. suzukii
larvae
development. Other studies cleared that
suitability for larval development and
attraction can differ widely among fruit
variety, cultivar and ripening stage. Also,
the host suitability of different fruits,
raspberries and blackberries turned out to
be the most preferable (Bellamy et al.,
2013; Burrack et al., 2013). Larvae
developed faster in raspberry, suggesting
that sufficient nutrients were acquired in
raspberries diet, so as not to hinder pupal
development time (Hardin et al., 2015).
Grapes have skins too thick for
D.
suzukii
females to oviposit (Sampson et
al., 2016), also, Bellamy et al. (2013)
mentioned that SWD larvae developed
slowest on the grape-agar medium.
Furthermore,
D. suzukii
will reject a host
if it is too firm (highest brix and the
highest penetration force) and has
implications for determining field host
susceptibility, particularly for firm fruit
such as peaches, apples and grapes
(Burrack et al., 2013). Lee et al. (2011)
and Burrack et al. (2013) mentioned that
both skin thickness and fruit firmness
have been posited as a deterrent to
successful oviposition in fruit crops. The
susceptibility of cold hardy grapes to
D.
suzukii
may depend on variety, the fruit’s
chemical and physical characteristics.
One important chemical characteristic,
which has been posited as a determinant
in
D. suzukii
preference in cane fruits, is
sugar content (Lee et al., 2011; Burrack
et al., 2013).
Also, Ioriatti et al. (2015)
found oviposition increased with sugar
content in intact
Vitis vinifera
grape
varieties. A weak relationship has also
been noted between acid levels (pH) and
infestation in blueberries and cherries
(
Prunus spp.
) (Lee et al., 2011) and
V.
vinifera
varieties (Ioriatti et al., 2015).
Physical characteristics could also
impact susceptibility, especially traits
which impede oviposition in the flesh of
the fruit. In two laboratory studies,
damaged grapes had greater levels of
oviposition in
V. vinifera
varieties
(Atallah et al., 2014; Ioriatti et al., 2015).
In other fruits, peaches with indumenta
(peach fuzz) deter female oviposition,
while damaged areas can have high rates
of oviposition (Stewart et al., 2014) and
cranberries are susceptible only if
damaged (Steffan et al., 2013).
D. suzukii
Aly Marwa, 2018
140
larvae developed significantly slower on
all grape varieties compared to raspberry.
Our result showed that adult development
time took 11 and 14 days in raspberries
fruit and artificial diets, while in green
grapes the adult development time
reached to 14 days and 17 days in fruit
and artificial diets. These results cleared
that adults took 3 days longer to complete
its development time in grapes rather
than raspberries. In concur with our
results; Emiljanowicz et al. (2014)
observed that
D. suzukii
flies reared on
raspberries took 12.9 days from egg to
adult which is comparable to
development time observed on artificial
diet (12.8 days). Comparably, mean
development time on grape ranged from
14.4 to 16.7 days. Despite grapes
relatively higher sugar content (°Brix
value of14.5–19.7), grapes have higher
acid levels than raspberry which may
make grapes suboptimal hosts (Pelton et
al., 2017). However, the trends across the
six fruit types suggests that differences in
susceptibility between fruit types may be
largely influenced by other factors such
as color, odor, texture, firmness and size
of fruit (Lee et al., 2011).
Acknowledgements
I am grateful for Professor Hannah
Burrack Professor and extension
specialist at Department of Entomology
at North Carolina State University, USA
for hosting me at her laboratory and
offering space and materials in the
laboratory. Also, special thanks for
Aurora Toennisson a Research Associate
and Specialty Crops Lab at Department
of Entomology at North Carolina State
University.
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