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Bioscience Methods 2014, Vol.5, No.3, 1-11
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2
because the seasonal pattern of the insect may not
coincide with the plant susceptible stage or period of
occurrence (Messina and Jones, 1990). Knowledge
about fruit fly species and their respective seasons of
occurrence in relation to host plant phenology is
crucial to understanding the population dynamics of
these economically important insects (Souza-Filho et
al
.,
2009). According to Messina and Jones (1990),
fruit infestation by tephritid pests is influenced by its
degree of maturation during the fruit fly oviposition
period. Foraging differences can be observed as fruit
flies make incursions into fruits of certain devel-
opmental stage. According to Dias and Vásquez
(1993), such information can be obtained by collecting
and incubating host fruits throughout their develop-
ment or maturation periods. Papadopoulos et al
.
(2001)
noted that in the tropics, the phenology and abundance
of fruit flies is determined by environmental
temperature, rainfall, relative humidity, and host fruit
availability. These environmental variables show
annual fluctuations within optimum levels and are
therefore, much of limiting factors in population
establishment and persistence of tephritid species (Lv
et al., 2008).
The African invader fly,
B.
invadens
and the mango
fruit fly,
C. cosyra
have been considered the most
economically important fruit fly pests in sub-saharan
Africa (Lux et al., 2003) owing to their quarantine
status and losses recorded in fruit and vegetable crops
(STDF, 2009). The seasonal occurrence of these pests
in relation to host phenology and abiotic factors in the
sub-region is yet to be fully optimized. In fact, only
few studies in Africa have examined the effect of host
fruit and weather variability on population
fluctuations of
B. invadens
and
C. cosyra
(Mwatawala
et al
.,
2009; Vayssieres et al
.
, 2009; N’diaye et al.,
2012). N’diaye et al
.
(2012) found that the dynamics
of emergence of tephritid species in mango orchards
in the Niayes and the Thies Plateau of Senegal
fluctuated in response to the occurrence and ripening
periods of the main host plants. Fruit fly populations
outside mango season was sustained at various levels
by the diversity of fruit trees, changes in weather
factors, lack of pest control and poor orchard care.
Vayssieres et al. (2009) in a correlation study of fruit
fly infestation of major mango cultivars reported that
temperature, relative humidity and rainfall were the
major factors influencing fruit fly populations in
northern Benin. Mwatawala et al
.
(2009) observed that
widespread variability and abundance of fruit species
in certain localities of central Tanzania ensured
year-round breeding of fruit fly pests.
At present, no known studies have been conducted in
Ghana to monitor the seasonal occurrence and
phonological patterns of these species
through the host
fruit collection and incubation approach. Preliminary
trapping by Billah et al. (2006) in the forest ecology of
Ghana revealed the presence of high populations of
B.
invadens
and
C. cosyra
in mango orchards. Updated
reports by Billah (2012) and Nboyine et al. (2012) in
the savanna ecology of Ghana have confirmed that
B
.
invadens
and
C
.
cosyra
still remain the most dominant
and damaging fruit fly species in northern Ghana. It
was imperative to obtain baseline data on the seasonal
occurrence pattern of fruit flies and the influence of
host phenology and abiotic factors on the activity of
these pests in the ecology. This would be helpful in
developing
and
implementing
management
programmes for tephritid pests in the country. The
present study determined the seasonal pattern of
occurrence of
B
.
invadens
and
C
.
cosyra
as affected
by availability of major hosts and abiotic parameters
in the northern savanna ecology of Ghana. The
primary goals were to monitor the seasonality of the
pests, and establish the importance of the different
host fruits for population development in relation to
temperature, rainfall and relative humidity.
1 Materials and Methods
1.1 Fruit collection
To determine the seasonal phenology of
B. invadens
and
C. cosyra
in the savanna ecology of Ghana, fruit
samples were collected from predetermined host
plants in the area. Collections were made from
multiple sites in the Northern, Upper West and Upper
East regions of the country between October, 2011
and September, 2013. A total of five sampling
localities were selected in each region for the
collection programme (Table 1). Fruit species
included in the study were those that proved to be the
main hosts of
B. invadens
and
C. cosyra
based on
previous survey records in the area (Nboyine et al.,
2012). Details of the selected fruit species sampled for
the study are shown in Table 2. Ripe, semi-ripe and
mature fruits as well as fruits from underground as
windfalls or senescence were collected.