Proceedings of 6th International Fruit Fly Symposium
6–10 May 2002, Stellenbosch, South Africa
pp. 91–95
Demographic parameters and biotic factors of two Dacini species,
Bactrocera cucurbitae and Dacus ciliatus, on Réunion Island
Jean-François Vayssières*, Yannick Carel & Mathieu Coubes
Laboratoire d’Entomologie de Kourou – CIRAD-FLHOR, B.P. 701-97387, Kourou, Cedex, France
Réunion Island is characterized by a particular orography and a variable distribution of host
plants for Dacini species. A complex of 3 Dacini species infests 16 host plant species belonging
to the family Cucurbitaceae. These three species of vegetable fruit flies represent the primary
pests of this plant family and are the main insect problem for cucurbit crops. We included in
this study the two species B. cucurbitae (melon fly) and D. ciliatus (Ethiopian fruit fly). Adults of
B. cucurbitae are classified as ‘R-strategists’, spending more energy than D. ciliatus in effectively
using environmental resources. Adults of D. ciliatus can be classified as ‘K-strategists’. B. cucurbitae is the species best adapted to exploit short-lived host plants. This adaptation explains its predominance over D. ciliatus under larval interspecific competition on Réunion Island.
INTRODUCTION
Réunion Island is characterized by a particularly
diverse topography and variable distribution of
host-plants for Dacini fruit fly species. A complex of three Dacini species infests 16 host plant
species belonging to the Cucurbitaceae family.
These represent the primary pests of this plant
family and are the main insect problem for cucurbit crops.
The present study focuses on two species,
Bactrocera cucurbitae (melon fly) and Dacus ciliatus
(Ethiopian fruit fly), both of which were introduced to Réunion Island and have different
bio-ecological characteristics.
The objectives of this study were: 1) to compare
the main demographic parameters of two Dacini
species living on Réunion island; 2) to compare
the main biotic factors of these two Dacini species.
MATERIALS AND METHODS
Rearings of adults (wild strains). For both species,
30 male–female pairs were randomly isolated in
30 individual cages – 10 pairs were isolated on each
of three cucurbits, squash (Cucurbita pepo), pumpkin (C. pepo), and cucumber (Cucumis sativus) at
25 ± 1°C and 75 ± 10% relative humidity. Adults
were fed with protein hydrolysate and sugar.
Adults could also feed on three slices of cucurbit
laid on the wire mesh top of the cage. Females
could also oviposit within these three slices.
Rearing of larval instars. Eggs were collected,
placed in Petri dishes in cohorts of 100 eggs,
and then observed until eclosion. Four different
incubator temperatures, 15 ± 0.2°C, 20 ± 0.5°C, 25 ±
1°C and 30 ± 1°C, were used for larval rearing in
Petri dishes. Nine Petri dishes of each species
and for each temperature were observed.
*To whom correspondence should be addressed.
E-mail: [email protected]
Statistical analysis was performed using the life
test procedure (SAS 1997) for life span, with
variance analysis, followed by the Newmann-Keuls
test, P = 0.05, for the other parameters. [The life
test procedure gives the point estimate (in days)
of the survival distribution of each quantile
(e.g. 50% of surviving flies) for each Dacini
species with 95% confidence interval (lower,
upper) for each host-species.]
RESULTS AND DISCUSSION
Pre-oviposition period
Table 1 shows that the mean pre-ovipositional
period was 10.9 days for B. cucurbitae and 11.2
for D. ciliatus (Table 2) at 25°C. No significant differences were observed for the pre-oviposition
period (in days) between the two fruit fly species
and the three host-plants.
Oviposition period
Table 1 shows that the mean oviposition period
was 112.4 days for B. cucurbitae and 82.9 days
for D. ciliatus (Table 2) at 25°C. Significant differences were observed between the two fruit fly
species and between squash and cucumberpumpkin for melon fly.
Life span
For B. cucurbitae, 50% of the flies were still alive
after five months on cucumber and 60% after six
months on pumpkin at 25°C.
For D. ciliatus, 50% of the flies were still alive
after four months on pumpkin, and 50% after 105
days on squash at 25°C.
Gross fecundity
Table 3 shows that gross fecundity was significantly different for B. cucurbitae between the three
92
Proceedings of the 6th International Fruit Fly Symposium
Table 1. Oviposition period and life span (in days) of the melon fly, Bactrocera cucurbitae, at 25°C in three host
plants.
Pre-oviposition
Cucumber
Pumpkin
Squash
Oviposition
10.0 a
12.0 a
10.6 a
Life span
121.8 a
133.1 a
82.2 b
143 a
211 b
142 a
Means followed by the same letter in a column do not differ significantly by the Newmann-Keuls test (P = 0.05).
Table 2. Oviposition period and life span (in days) of the Ethiopian fruit fly, Dacus ciliatus, at 25°C in three host
plants.
Pre-oviposition
Oviposition
9.8 a
12.5 a
11.2 a
84.0 b
85.2 b
79.4 b
Cucumber
Pumpkin
Squash
Life span
110 a
107 a
116 a
Means followed by the same letter in a column do not differ significantly by the Newmann-Keuls test (P = 0.05).
host-plants, with 1111 eggs for cucumber compared with 521 for pumpkin and 343 for squash at
25°C. The gross fecundity is the measure of the
number of eggs a hypothetical cohort of females
would lay if all lived to the last possible age. The
net fecundity is the actual number of eggs laid by
females observed in this study over their life.
Table 4 shows that gross fecundity was also
significantly different for D. ciliatus between the
three host-plants, with 375 eggs for cucumber
compared with 423 for pumpkin and 571 for
squash at 25°C.
Gross daily fecundity
Table 3 shows that gross daily fecundity by
host-plant is significantly different for B.cucurbitae:
8.6 eggs per day for cucumber versus 3.8 for pumpkin and 4.3 for squash at 25°C.
Table 4 shows that gross daily fecundity by
host-plant for D.ciliatus is also significantly different,
Table 3. Fecundity, fertility and egg hatching success of Bactrocera cucurbitae at 25°C in three host plants.
Number of eggs
Cucumber
Pumpkin
Squash
Gross
fecundity
Net
fecundity
Gross
fecundity/day
Net
fecundity/day
Gross
fertility/day
1111 a
521 b
343 c
1015 a
435 b
313 c
8.6 a
3.8 b
4.3 b
8.1 a
3.6 b
4.2 b
7.4 a
3.0 b
3.8 b
Net
fertility/day
Gross hatch
(%)
6.7 a
2.5 b
3.5 b
91
83
91
Means followed by the same letter in a column do not differ significantly by the Newmann-Keuls test (P = 0.05).
Table 4. Fecundity, fertility and egg hatching success of Dacus ciliatus at 25°C in three hosts-plants.
Number of eggs
Cucumber
Pumpkin
Squash
Gross
fecundity
Net
fecundity
Gross
fecundity/day
Net
fecundity/day
Gross
fertility/day
375 c
423 b
571 a
333 b
357 b
533 a
2.7 c
3.5 b
6.6 a
2.3 c
3.1 b
6.1 a
2.2 c
2.8 b
5.8 a
Net
fertility/day
1.9 b
2.3 b
5.4 a
Means followed by the same letter in a column do not differ significantly by the Newmann-Keuls test (P = 0.05).
Gross hatch
(%)
89
84
93
Table 5. Egg incubation period and developmental rate of larval instars of Bactrocera cucurbitae and Dacus ciliatus at 30°C in three host plants. L1 = first larval instar;
L2 = second larval instar; L3 = third larval instar.
Pumpkin
Squash
B. cucurbitae
D. ciliatus
B. cucurbitae
D. ciliatus
B. cucurbitae
D. ciliatus
L1 in hours
L2 in hours
L3 in hours
23.67 ± 0.58 a
30.67 ± 1.15 b
24.33 ± 0.58 a
31.67 ± 0.58 b
23.67 ± 0.58 a
29.67 ± 0.58 b
8±1a
15.67 ± 0.58 b
7.67 ± 1.15 a
15 ± 1.73 b
10 ± 0 a
15.67 ± 2.08 b
12.33 ± 0.58 a
14.67 ± 8.14 a
14 ± 1 a
14.33 ±1.53 a
12.33 ± 1.15 a
14.33 ± 8.50 a
65 ± 7.00 a
92 ± 17.78 b
84 ± 3.46 a
86 ± 14 a
65 ± 7.21 a
81.33 ± 7.77 b
Pupae in days
8.67 ± 0.58 a
10 ± 0.58 b
9±0a
11 ± 0 b
9.00 ± 0 a
10 ± 1 b
Total eggs → adults
(hours)
317 ± 23.01
385 ± 41.5
346 ± 6.20
407 ± 17.8
327 ± 8.94
381 ± 42.9
Total eggs → adults
(days)
13.2 ± 0.96 a
16 ± 1.73 b
14.4 ± 0.26 a
17 ± 0.74 b
13.6 ± 0.37 a
15.9 ± 1.79 b
Means ± S.E. for each host-plant followed by the same letter are not significantly different (intraspecifically) by the Newmann-Keuls test (P = 0.05).
Table 6. Egg incubation period and developmental rate of larval instars of Bactrocera cucurbitae and Dacus ciliatus at 25°C in three host plants. L1 = first larval instar;
L2 = second larval instar; L3 = third larval instar.
Cucumber
Pumpkin
Squash
B. cucurbitae
D. ciliatus
B. cucurbitae
D. ciliatus
B. cucurbitae
D. ciliatus
Incubation
in hours
L1 in hours
L2 in hours
L3 in hours
Pupae in days
30 ± 1 a
40.33 ± 0.58 b
30.67 ± 1.53 a
41.67 ± 1.53 b
31 ± 0 a
43 ± 1 b
23.33 ± 0.58 a
23.33 ± 0.58 a
19 ± 3.61 a
23.67 ± 2.08 a
18.33 ± 2.31 a
22.67 ± 1.15 b
24 ± 0 a
24 ± 0 b
24 ± 0 a
24.33 ± 0.58 a
22.67 ± 2.31 a
24.67 ± 1.15 b
64.67 ± 12.70 a
71.33 ± 1.15 a
64.67 ± 12.70 a
79 ± 9.64 a
72 ± 0 a
71.33 ± 1.15 b
11.33 ± 0.58 a
14 ± 0.58 b
12.67 ± 0.58 a
15.67 ± 0.58 b
11 ± 0 a
14.33 ± 0.58 b
Total eggs → adults
(hours)
414 ± 28.1
503 ± 16.2
442 ± 31.7
545 ± 27.7
408 ± 4.62 a
506 ± 18.3
Total eggs → adults
(days)
17.2 ± 1.17 a
21 ± 0.67 b
18.4 ± 1.32 a
22.7 ± 1.15 b
17 ± 0.19 a
21 ± 0.76 b
Means ± S.E. for each host-plant followed by the same letter are not significantly different (intraspecifically) by the Newmann-Keuls test (P = 0.05).
Table 7. Egg incubation period and developmental rate of larval instars of Bactrocera cucurbitae and Dacus ciliatus at 20°C in three host plants. L1 = first larval instar; L2 =
second larval instar; L3 = third larval instar.
Cucumber
Pumpkin
Squash
B. cucurbitae
D. ciliatus
B. cucurbitae
D. ciliatus
B. cucurbitae
D. ciliatus
Incubation
in hours
L1 in hours
L2 in hours
L3 in hours
Pupae in days
Total eggs → adults
(hours)
49.67 ± 3.21 a
72.33 ± 1.53 b
49.67 ± 3.21 a
75.33 ± 1.15 b
49.33 ± 2.08 a
71.66 ± 1.15 b
17.33 ± 2.31 a
21 ± 2 a
17 ± 1.73 a
24 ± 5.29 b
19.33 ± 1.53 a
23 ± 1 b
46.33 ± 0.58 a
49.67 ± 1.15 b
46.67 ± 1.53 a
46 ± 4 a
48 ± 0 a
46.33 ± 2.31 b
96 ± 1 a
179 ± 11.79 b
110.33 ± 12.42 a
185 ± 8.19 b
112.33 ± 14.36 a
168.33 ± 3.06 b
16.33 ± 1.15 a
21.67 ± 0.58 b
16.33 ± 1.15 a
21 ± 0 b
16.33 ± 1.15 a
20.66 ± 0.58 b
601
842
616
834
621
826
25.1 ± 1.45 a
35.1 ± 1.26 b
25.6 ± 1.94 a
34.8 ± 0.77 b
25.8 ± 1.90 a
33.5 ± 0.89 b
93
Means ± S.E. for each host-plant followed by the same letter are not significantly different (intraspecifically) by the Newmann-Keuls test (P = 0.05).
Total eggs → adults
(days)
Vayssières et al.: Demographic parameters and biotic factors of two Dacini species on Réunion Island
Cucumber
Incubation
in hours
44.2 ± 2.52 a
86 ± 12 b
Means ± S.E. for each host-plant followed by the same letter are not significantly different (intraspecifically) by the Newmann-Keuls test (P = 0.05).
1061
2072
26.67 ± 0.58 a
63 ± 1 b
205 ± 41.57 a
224 ± 13.86 a
72 ± 24 a
120 ± 10 b
48 ± 0 a
96 ± 24 b
96 ± 0 a
120 ± 0 b
B. cucurbitae
D. ciliatus
Pumpkin
Total eggs → adults
(hours)
Pupae in days
L3 in hours
Rate of development of larval instars at four
temperatures
At 30°C (Table 5), 25°C (Table 6), 20°C (Table 7)
and 15°C (Table 8), the larval instars of melon fly
developed significantly faster than those of the
Ethiopian fruit fly.
The terms ‘R-selection’ and ‘K-selection’ can be
used to describe extreme strategies of exploitation of host plants (McArthur & Wilson 1967). This
classification considers demographic parameters
in relation to their main biotic factors. ‘R-selection’
corresponds to unpredictable environmental
conditions (short-lived host plants) and ‘K-selection’ to stable ones (long-lived host plants).
Adults of B.cucurbitae are classified as ‘R-strategists’,
are large and have great mobility, high fecundity
(more than 1000 eggs per female on the most
favourable host plant), high daily fecundity (an
average of eight eggs per day per female), a high
fertility (more than 90%), a long life span (more
than five months), and a short egg eclosion
period (24 h at 30°C). Other plants belonging to
the families Solanaceae and Passifloraceae are
occasionally infested by larvae of the melon fly.
B. cucurbitae spend more energy than D. ciliatus
in effectively using environmental resources.
Adults of D. ciliatus are smaller and have a lower
mobility, lower fecundity (~500 eggs per female
on the most favourable host plant), lower daily
fecundity (an average of two eggs per day
per female), lower fertility (83%), a shorter life
span (four months), and a longer egg eclosion
period (31 h at 30°C). Owing to these characteristics, the Ethiopian fruit fly can be classified as a
‘K-strategist’.
Significant differences in demographic parameters
and main biotic factors (egg incubation and
instar development) between the two fruit flies
species explain the predominance of B. cucurbitae
L2 in hours
Egg incubation period at four temperatures
At all temperatures tested, 30°C (Table 5), 25°C
(Table 6), 20°C (Table 7) and 15°C (Table 8), melon
fly had a significantly shorter incubation period
than the Ethiopian fruit fly.
L1 in hours
Egg hatching success
Tables 3 & 4 show that there was no significant
difference in egg hatch between the two fruit fly
species; more than 88% of eggs hatched for both
species at 25°C.
Incubation
in hours
with 2.7 eggs per day for cucumber versus 3.5 for
pumpkin and 6.6 for squash at 25°C.
Total eggs → adults
(days)
Proceedings of the 6th International Fruit Fly Symposium
Table 8. Egg incubation period and speed of development of larval instars of Bactrocera cucurbitae and Dacus ciliatus at 15°C on pumpkin. L1 = first larval instar; L2 = second
larval instar; L3 = third larval instar.
94
Vayssières et al.: Demographic parameters and biotic factors of two Dacini species on Réunion Island
on D. ciliatus on Réunion Island.
Furthermore, the classification of the melon fly
as an ‘R-strategist’ can explain its worldwide
distribution and its ability to colonize new
areas such as in West Africa in 1999 and 2000
( Vayssières 2000), which were then already
occupied by the Ethiopian fruit fly (Mali, northern
Ivory Coast, Guinea, Senegal).
95
REFERENCES
McARTHUR, R.H. & WILSON, E.O. 1967. The Theory of
Island Biogeography. Princeton University Press,
Princeton, N.J.
SAS INSTITUTE 1997. The SAS system for Windows, ver. 6,
4th edn, vol. 2, Lifetest procedure. 1027–1070. SAS
Institute, Cary, NC.
VAYSSIÈRES, J.F. 2000. Rapport de mission au Mali sur le
complexe des mouches des fruits (Diptera Tephritidae) inféodées au manguier. Projet CAE/SEG/USAID.