基本HTML版本
Bioscience Methods 2014, Vol.5, No.3, 1-11
http://bm.biopublisher.ca
9
Besides being an important pest, it also seems to have
an impact on the indigenous fruit fly fauna in
commercial fruit produce. Although pre-invasion data
are generally lacking, there is some indication that the
pest could have an impact on the presence of major
indigenous pests, such as C
. cosyra
. Duyck et al. (2007)
indicated that K-selected tephritid species could be
better invaders, and through interspecific competition,
decrease the number and niches of pre-established
species.
Bactrocera
species appeared to have
K-selected traits and to dominate representatives of the
genus
Ceratitis
, as in a case study in La Re´union (Lv
et al., 2008). It is not unlikely that similar trends can be
observed on mainland Africa in environments such as
northern Ghana.
The study further demonstrated a distinct seasonal
pattern in the population fluctuations of
C
.
cosyra
in
the ecology. Infestation rate for this pest was relatively
low during the early and mid rains period, increased in
June, reaches high levels in July and peaks in August.
Larval activity becomes low at end of November,
during which period, the fly survives as a larva inside
host fruits which either remain on the trees or fall to
the ground. Though the mortality of larvae and pupae
during winter may be very high, proportion of the
population survives and yields a small number of
adults in spring (Papadopoulos et al. 2000). Although
not detected by fruit sampling or trapping, these adults
appear in December and a proportion of them may
live until the end of February (Papadopoulos et al
.
,
2001). Reproduction is thus, possible during the early
rains when host conditions become favourable giving
rise to the following generation.
The influence of abiotic factors is closely related with
fly abundance (Vera et al., 2002; Duyck et al
.,
2006)
and on their population dynamics (Amice and Sales,
1997). With
B. invadens
, temperature (min–max), RH
and rainfall all had positive relationship with
infestation rate. Among them, daily rainfall was the
factor showing the strongest positive correlation with
B
.
invadens
populations. The population dynamics of
B
.
invadens
in northern Ghana appeared very similar
to those of
B
.
cucurbitae
in Benin (Vayssieres et al
.,
2005) and
B
.
dorsalis
in Asia (Chen et al
.
(2006
).
Han
et al
.
(2011) underlined that the monthly rain days are
the strongest one among all the climatic factors.
Similar studies with abiotic factors were carried out on
B. dorsalis
,
B.
zonata
and
B.
correcta
in India (Sarada
et al., 2001). They showed a positive correlation for
B.
dorsalis
populations captured partly at periods of high
RH, but also with the onset of the rains. Shukla and
Prasad (1985)
however, observed a negative
correlation between the populations of
B. dorsalis
captured and temperature, and maximum RH.
According to Agarwal and Kumar (1999),
B. zonata
populations have positive correlation with temperature
and rainfall in India. With
C. cosyra
in northern
Ghana, minimum temperature and rainfall had
positive relationships with infestation level.
Vayssieres et al. (2009) recorded the similar positive
correlation of
C. cosyra
with minimum temperature
and RH on mango and guava. Positive relationship
with minimum temperatures was also recorded in
India on the
oriental fruit fly,
B. dorsalis
(Kannan
and
Venugopala,
2006) and guava fruit fly,
B.
correcta
(Jalaluddin et al., 2001
)
.
These results suggest that climatic factors such as
temperature, RH and rainfall play an important role in
regulating populations of
B. invadens
and
C
.
cosyra
.
Rainfall makes the soil moist and thus provides some
favourable conditions for eclosion of adults from their
puparia. The first important rains, and increasing
relative humidity are important factors favouring the
sudden outbreak of
B. invadens
especially as it
coincides with the fruiting seasons of the major host
plants. Other reasons could be proposed such as the
quasi-absence of natural enemies and the polyphagous
status of this formidable invasive species. It could be
proposed that the three main factors involved in
population dynamics are the reduced availability of
fruits (due to trees bearing in alternate seasons), the
fruit sampling method, and the impact, albeit to a
lesser extent, of incubating fruits. Further research is
needed to estimate their respective importance. These
findings generally imply that programs that aim at
suppressing of fruit fly populations could focus on the
hosts with high infestation rates with respect to
particular fruit fly species. In export situations, fruits
with a higher incidence of fruit flies become a major
concern because of strong quarantine regulations
imposed by importing countries. Non-commercial
hosts with high incidence and infestation rates, and
found in the vicinity of commercial orchards, should
be removed to reduce the alternative reservoirs of fruit
fly population build up in between crop peaks. In