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Bioscience Methods 2014, Vol.5, No.3, 1-11
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8
Table 4 Regression analysis of counts of
B. invadens
and
C. cosyra
with climatic factors
Covariates
Likelihood ratio chi-square (p<0.05)
B. invadens
C. cosyra
Both species
Month (12-lev. factor)
57.34
206.13
63.30
Max. Temp
(+) 11.00
ns
(
-
) 30.06
Min. Temp.
(+) 0.64
(+) 71.06
(
-
) 34.12
Mean-RH
(+) 31.00
(
-
) 46.00
(
-
) 130.00
Rainfall
(+) 601.23
(+) 12.05
(+) 110.68
Month x Max. Temp.
(
-
) 398.50
ns
(
-
) 113.40
Month x Min. Temp.
(
-
) 59.07
ns
(
-
) 245.95
Month x Mean RH
ns
(
-
) 329.90
(+) 143.05
Month x Rainfall
ns
ns
(
-
) 105.25
Max. Temp. x Min. Temp.
ns
ns
(+) 11.20
Max. Temp. x Mean RH
ns
ns
(+) 105.99
Max. Temp. x Rainfall
ns
ns
ns
Min. Temp. x Mean RH
ns
ns
(+) 86.60
Min. Temp. x Rainfall
ns
ns
(
-
) 111.87
Mean RH x Rainfall
(
-
) 540.48
ns
ns
Note: (+) or (
-
) indicates the sign of the regression coefficients. ns = not significant at p = 0.05
3 Discussion
The results of this study have shown that suitable
hosts are available all-year-round for
B. invadens
and
C. cosyra
in the savanna ecology of Ghana. From the
sampling of the major and economically important
fruits species, it was evident that this host range
provided suitable reservoir for the fruit flies
throughout the full year cycle but with fluctuating
importance, depending on the fruit availability.
Non-commercial fruits such as African peach, sheanut,
tropical almond, jujube and albarillo played a key role
in bridging the period between the fruiting season of
mango and other cultivated crops. The mechanisms
behind the decline of incidence and infestation rate of
B. invadens
and
C. cosyra
as the rains subsided could
either be due to the absence of suitable hosts or
unfavourableness of available fruits for oviposition.
Mwatawala et al. (2006) showed that
B. invadens
populations increase from the onset of the short rains
period onwards to reach a maximum at the long rains
period. This observed patterns need to be confirmed
through continuous sampling over successive years
prior to any control programme.
The relationship between the start of the rainy season,
and the increase of
B. invadens
with heavy fruit
infestation, was observed on mango in Benin
(Vayssie`res et al
.,
2005). The period of short rains
was followed by a shorter period of drier conditions
(but with high relative humidity) in February-March,
to be followed by a period of higher rainfall during a
more extended period (long rains season). The average
temperature remained high but gradually decreased
during the long rains. This season was the main
fruiting season for tropical almond, sheanut, marula
plum and albarillo. Populations of
B. invadens
remain
high during this period but seem to infest mainly
sheanut and tropical almond, as well as other
non-commercial fruits that were available around that
time. When temperature and rainfall decrease during
the dry season, the populations of
B. invadens
also
decrease dramatically (Mwatawala et al., 2006), but
viable populations can be maintained in
noncommercial hosts, such as persimmon, jujube and
figs, till the next short rains period. Host availability
for
C. cosyra
seemed a little more ambiguous from the
analysis. It was unclear what the predominant hosts
are for this species in the dry season since only
sporadic records were obtained from icacina and
persimons during that period.
Bactrocera
invadens
is currently considered as one of
the major tephritid pest in Africa. Its polyphagous
nature, predominance in certain hosts and rapid spread
throughout Africa (Drew et al., 2005) makes it a
devastating pest. Local farmers have indicated that
there is a huge impact of this fruit fly on their fruit
production (Yaya Toure´ and Temiognage, 2007).