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Bioscience Methods 2014, Vol.5, No.3, 1-11
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4
that were prone to mouldiness. Under drier conditions,
large containers were filled with water and placed
around the corners of the rearing room to help
maintain a relatively high humidity.
1.3 Insect monitoring
Each incubation unit was checked daily for the
presence of puparia, which were picked up using a
pair of soft forceps or by gently sifting. The puparia
recovered were handled based on the procedure of
Mwatawala et al. (2009) for adult fly emergence.
These were counted before being placed in petri
dishes with moistened filter paper. The petri dishes
containing the puparia were placed in small ventilated
transparent rectangular plexiglas (perpex) used as
rearing cages. These were held at 26-28 ºC and
60-70% RH, a condition adequate for preventing
pupal water loss while minimizing development of
moulds. The puparia were held in the cages for 5 to 7
days for the emergence of adult flies. Emerged adults
were monitored following the procedure described by
White and Elson-Harris (1992) and N’diaye et al.
(2012). Emerging flies were maintained for 3 days
during which full adult development and body
coloration were attained to enhance identification. The
flies were killed (by freezing) and the number from
each fruit species recorded in a data sheet.
1.4 Meteorological data
Meteorological data on mean monthly precipitation,
air temperature and relative humidity for the study
period were obtained from the various Meteorological
Units under the Savanna Agricultural Research
Institute (SARI), Ghana. The meteorological stations
for the Guinea savanna, Sudan savanna and Sahel
savanna zones were located in Nyankpala (Northern
Region), Wa (Upper West Region) and Manga (Upper
East Region), respectively.
1.5 Data analysis
Fruit infestation data were processed using Microsoft
Excel and XL Stat for the analysis of variance and
mean comparisons. Infestation level (number of flies
per unit weight of fruit) was determined according to
the procedures given by Copeland et al. (2002). The
ANOVAs for fruit species in relation to emergence of
B. invadens
and
C. cosyra
took particular account of
various sampling seasons (months) and the weather
parameters (precipitation, air temperature and
relative humidity). Relationship between fly
emergence and weather variables was tested using
multiple linear regression analysis following the
procedure of Yonow et al. (2004) to look at the
changes in fruit fly abundance across host fruits,
seasons and climatic factors.
2 Results
2.1 Host infestations
The infestation data for the 12 main host reservoirs
of
B. invadens
and
C. cosyra
indicated that
infestation level varied significantly with type of
fruit (P < 0.001). Mean number of
B. invadens
per kg
fruit was highest in sheanut, followed by African
peach, tropical almond, persimmon, icacina and
mango. Albarillo and jujube recorded the lowest
infestation for
B. invadens
while the rest of the fruit
species recorded moderate infestations with
significant variations among them. On the other hand,
mean number of
C. cosyra
was highest in African
peach, followed by albarillo, jujube and icacina with
significant differences among them. Mango and sour
sop recorded the lowest number of
C. cosyra
per unit
weight of fruit. It general, fruit species that suffered
heavy infestation by
C. cosyra
were slightly infested
by
B. invadens
, and vice versa (Table 3).
Table 3 Infestation data for the main hosts of
B. invadens
and
C. cosyra
in northern Ghana
Fruit species
Avg. no. fruits /sample No.
B. invadens
/kg fruit
*
No.
C. cosyra
/kg fruit
*
Mango
4.0
60.1 ±3.0 d
11.5 ±1.7 a
Marula plum
25.5
51.3 ±2.8 c
47.7 ±3.0 d
Soursop
19.8
45.2 ±3.1 b
24.2 ±2.6 b
Tropical almond
30.6
65.5 ±4.4 e
85.4 ±10.0 f
Persimmon
59.4
65.0 ±6.8 e
36.3 ±2.9.1 c
Syncomore fig
35.0
42.5 ±1.4 b
72.4 ±7.2 e
Jujube
177.5
37.4 ±2.0 a
122.0 ±11.1 h
African peach
18.5
70.7 ±9.6 f
143.0 ±19.0 i
Shea nut
23.7
80.1±11.0 g
90.6 ±12.1 f
Green pepper
20.7
47.8 ±2.4 bc
32.4 ±2.7 c
Icacina
35.5
64.4 ±4.4 e
111.7 ±15.8 g
Albarillo
167.0
35.6 ±2.0 a
128.8 ±12.0 h
Note:
*
Mean number ±standard error. Means with same letters within columns are not significantly different at p = 0.05