Asian Journal of Agricultural Sciences 3(6): 469-474, 2011
ISSN:2041-3890
© Maxwell Scientific Organization, 2011
Submitted: August 05, 2011
Accepted: October 15, 2011
Published: November 15, 2011
Comparison of Bee Pollinators of Coffee in Organic and Conventional Farms
1
Rebecca H.N. Karanja, 2Mary W. Gikungu, 1Grace N. Njoroge,
3
L.E. Newton and 1John M. Kihoro
1
Jomo Kenyatta University of Agriculture and Technology,
P.O. BOX 43844-00100, Nairobi, Kenya
2
National Museums of Kenya, P.O BOX 40658-00100, Nairobi
3
Kenyatta University, P.O BOX 16443, Nairobi
Abstract: Kenyan Coffea arabica L. is globally recognised for its high quality and it is used to blend other
coffees in the world market. No previous studies in Kenya have identified pollinators of coffee and this
necessitated the study. Coffea arabica was thought to be self-pollinated but recent studies have given an
indication that it is amphicarpic thus needing pollinator services. This is especially for the self sterile flowers
while in self fertile flowers pollination success rate is enhanced. This study assessed the diversity of bee
pollinators of coffee in organic and conventional farming system in Kiambu Kenya. Sampling of bees found
to evidently carry pollen and interact with anthers was done and these bees were recorded. Sixty three bee
species were sampled with organic farm having 60 species and conventional farm 24 species. Bee abundance
and diversity between organic and conventional farms differed significantly (t = -2.1227, df = 61, p<0.05).
Andrena (sp) possibly a new species was collected. Findings from this study revealed that wild bees other than
Apis mellifera are important pollinators of coffee. The wild bees were few in numbers and ways of enhancing
their populations should be devised.
Key words: Abundance, coffee, conventional, organic, pollinators, richness
INTRODUCTION
In East Africa there is paucity of data on pollination
by bees since very few studies have been done and there
is lack of adequate referenced collections as well as bee
taxonomists (Gikungu, 2006). However, a few studies
have been conducted on economic importance of
pollinators to food crop production (Kasina, 2007); bee
populations and bee diversity (Gikungu, 2002, 2006) and
pollination biology of Citrullus lanatus (Njoroge, 2005).
This study focused on the following research questions:
Pollination biology is of great ecological and
conservation relevance as changes in plant populations;
growth rates, population size and density, and community
composition involve reproduction and are an indication of
pollination success (Lennartson, 2002). Pollinators are a
key to agricultural productivity when all the other factors
of production are optimal. There has been a world wide
decline of bee populations in the recent past. Factors
leading to this population decline include natural
phenomena like severe rainy seasons, droughts as well as
human-generated hazards such as deforestation and
insecticides and pesticides application (Freitas et al.,
2004).
Organic farming promotes use of natural means to
control pests and weeds. A study by Roschewitz et al.
(2005), found that organic farming converts fields into
insecticide-free and richer foraging habitats while
herbicides reduce the insects’ diversity and diversity of
flowering weed species in conventional fields. In
homogenous landscapes such as coffee farms, differences
in biodiversity between organic and convectional fields
may be larger because organic fields compensate for the
missing non crop habitats (Bengtsson et al., 2005).
C
C
What are the pollinators of coffee in Kenya?
Is there a difference in abundance and diversity of
bee pollinators in the organic and conventional coffee
farms?
MATERIALS AND METHODS
Study area: This study was carried out from October
2005 to April 2008 in Kiambu District which lies
between latitudes 0°75! and 1°20! South of Equator and
longitudes 36°54! and 36°85! East close to Karura forest
(G.O.K., 1994; Muchena et al., 2004). The area has
privately owned and well managed coffee plantations.
Two contrasting farms were selected for the study. They
included Paradise Lost which carries out organic farming
and Evergreen Farm which is a conventional farm.
Corresponding Author: Rebecca HN Karanja, Jomo Kenyatta University of Agriculture and Technology, P.O. BOX 62000-00200,
Nairobi, Kenya, Tel.: +254722601849
469
Asian J. Agric. Sci., 3(6):469-474 , 2011
Quantification and diversity of bees visiting coffee
flower: Documentation of flower visitors paid special
attention to discriminate between pollinators and mere
flower visitors. Those insects that were found to evidently
carry pollen and make contacts with the anthers and the
stigma were recorded as pollinators while all the others
were recorded as flower visitors (Fausto et al., 2001;
Njoroge, 2005).
Two transects (1.5 km each) per site were selected,
one in the middle of coffee field and the other 6m from
the field edge to minimize edge effect (De Marco and
Coehlo, 2004; Kremen et al., 2004; Holzschuh et al.,
2007). Within these transects four 100 m2 plots were
randomly selected and permanently marked with wooden
sticks and characterized at the same time during this
survey (Kremen et al., 2004). Observations of pollinator
activity throughout the coffee flowering seasons were
done from 07.30 to 17.30 h for 3 days every week.
Foraging bee species in the sampling plots were observed
and captured under similar weather conditions (Gikungu,
2002). A 10 min observation period was set to document
all the pollinators visiting coffee flowers after which they
were captured by sweep nets for 30 min. The bee species
that were caught were put in killing jars having ethyl
acetate to inactivate or kill them (Picker et al., 2004).
After each sampling interval the collected bee species
were pinned in boxes that were later transferred to
laboratory for identification.
To supplement the data of bees caught using sweep
nets, pan traps of different colours namely; Red, blue,
white and yellow (Morandin et al., 2007) were laid
alternately at random points within the 100 m2 plot in
the coffee farms to capture bees that may not have been
collected using sweep nets. Each pan trap was filled with
300 mL water and 500 mL odourless detergent. Insects
caught in pan traps were transferred into vials containing
70% alcohol by use of forceps for later identification
(Gikungu, 2002).
Organjc farm bee families
Organjc farm bee species
Conventional farm bee families
Conventional farm bee species
Percentage of bee families and
representative species
50
40
30
20
10
ae
Me
gac
hil
id
tid
ae
Ha
lic
tid
ae
llec
Co
Ap
ida
e
An
dre
nid
ae
0
Bee families collected from the study area
Fig. 1: Bee families collected in the study area and their
species representation
Organic farm
Conventional farm
Percentage of bees collected
from study farm
50
40
30
20
10
O th
er
na
spp
og
l
spp ossu
m
Pa
t
z on e l la
a li p is
ctu
s1
No
mi
as
pp
He
ria
d es
rat
i
ssi
La
Ce
A. m
e ll
ife
ra
0
Bee species
Fig. 2: Common bee species sampled in the organic and
conventional farms
1
Statistical analysis: Statistical analysis was performed by
use of R 2.6.1/Tree Diversity program (Kindt and Coe,
2005). Bee abundance and richness in the two study areas
was analysed by use of frequencies, percentages, paired
t-test and R nyi’s diversity index measure. Renyi diversity
index combines Shannon Weigner and Simpson’s
diversity measures with the help of a scale parameter and
most importantly, it is extremely sensitive to rare species
when the scale parameter is 0. Therefore, it caters for both
rare and common species (Magurran, 1988; Kindt and
Coe, 2005).
4
Profile value
2
3
2
1
0
1
2
0
0.25 0.5
1
2
4
Species richness
8
Inf
Fig. 3: Renyi profile for the two farms; 1: Organic farm; 2:
Conventional farm
RESULTS
bee specimen from 63 species were collected and are
deposited at National Museums of Kenya. The Organic
farm registered 95.2 % (60 species) and the Conventional
Farm 24 species which is 38.1% of the total number of
Diversity of bee pollinators of coffee flowers in organic
and conventional farms in Kiambu: Sampling was done
for 31 months from October 2005 to April 2008 and 9439
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Asian J. Agric. Sci., 3(6):469-474 , 2011
25
-0.5
-1.0
15
10
5
5
2.5
42
31
-3.5
0
0.25
0.5
1
2
Alpha
4
8
Inf
Fig. 6: Rênyi’s bee species evenness profile across various
seasons
Percentage of bees samples
Fig. 4: Seasonal changes in bee species abundance in coffee
farms in Kiambu coffee farms
1 Short rain
2 Dry and hot1
3 Long rain
-1.5
-2.0
-3.0
Dry and hot 2
Season
Dry and hot 1
Short rains
Long rains
Cold
0
4 Cold
4
3
2
0.06
0.05
0.04
0.03
0.02
0.01
0.00
Pse
u
mi doan
cra th
nth idiu
idi m
um
s
Ep p
eol
Am
us
eg i
Co
lla
llet
sp
es
mi
ma
dv
ena
Hy
Br
lae
au
us
nsa
pis
s
p
Ma
1
cro
ga
An
lea
dre
na
Br
sp
au
2
nsa
pis
sp
2
Pa
site
ss
p
H-alpha
4Cold
0.0
20
H-alpha
Percentage of bees collected
1Short rain
2Dry and hot1
3Long rain
Organic farm
Conventional farm
+
30
1
0
0
0.25 0.5
1
2
Alpha
4
8
Inf
Rate bee species
Fig. 5: Rênyi’s bee richness profile for various seasons across
both study sites for 31 months
Fig. 7: Diversity of rare bees collected from the Organic farm
Conventional Farm (Fig. 1). A. mellifera was the most
abundant bee species in the sample area and it formed
72.6% of the total bee collection from the two farms
(Fig. 2).
The Organic farm had higher species richness than
the Conventional farm. Bee diversity of both the rare and
common bee species was consistently higher in Organic
than Conventional Farm and it was comparable as shown
in the H-alpha of Rênyi profile (Fig. 3).
species. The organic farm had 59% of the total specimens
collected. Bee abundance and diversity between the two
farms were significantly different (t = 2.1227, df = 61,
p<0.05).
Specimens collected in the two study sites
represented five out of six world’s documented bee
families namely Apidae, Halictidae, Megachilidae,
Andrenidae and Colletidae. The only bee family not
sampled in this study was Mellitidae. Family Apidae was
the most abundant with 79.1% (45.5% from the Organic
Farm and 33.6% from the Conventional Farm) of total
bees collected, Halictidae followed with 17.4% (11%
from Organic Farm and 6.4% from Conventional Farm of
the total while Colletidae which was sampled from the
Organic Farm only had the lowest representation with
0.1% of the total bees sampled. In terms of bee species
richness per family, Halictidae had the highest number of
species (39%) followed by Apidae (33%). The lowest
number of species was from Family Andrenidae and
Colletidae each with 3% of the total number of species.
Both Colletidae and Andrenidae were absent in the
Bee abundance and richness in various seasons: The
highest number of bees 46.5% of the total (26.8% Organic
Farm, 19.7% Conventional Farm) were collected during
the short rain seasons: October, November and December,
followed by long rain seasons: March, April and May
(37.1%), with the lowest numbers in the cold season
(3.6%): July and August and dry and hot season 2 in
September (1.4%) of total bees collected (Fig. 4).
According to Renyi diversity profiles, the highest
diversity was recorded during the short rains followed by
long rains with the lowest profiles during the dry and hot
seasons (Fig. 5). The species richness for the rare species
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Asian J. Agric. Sci., 3(6):469-474 , 2011
and Tropical America found that, A. mellifera was the
most dominant pollinator species in all coffee
management systems in terms of abundance accounting
for more than 80% of total pollinator assemblages
(Roubik, 2002b; Vergara and Badano, 2008).
The short rain season had moderate rain and warm
conditions which led to sparse flowering and this
encouraged the presence of a diverse number of solitary
bee communities (Roubik, 2002b) possibly because they
lacked competition from A. mellifera which dominate
during mass flowering. Members of the species are floral
density-dependent and tend to abandon sparsely
distributed flowers (Heard, 1994). The results of this
study imply that solitary bees could be the main
pollinators of coffee during sparse flowering.
During long rains mass flowering led to increased
A. mellifera which are aggressive bees that lead to a
decrease in the solitary bees which are out competed by
honeybees due to their aggression (Roubik, 2002a, b).
Coffee has been documented to flower after a shower of
rain falls following a dry season (Coste, 1992; Roubik,
2002b). The bees collected during the cold season were
the least diverse since they were dominated by
A. mellifera.
Organic farming was found to favour bee abundance
and diversity. Conventional farming system may impact
on bee diversity due to poisoning by agro-chemicals and
lack of other plants that can serve as alternative floral
resources and source of refuge when the main crop has
been sprayed with agro-chemicals. Other studies have
shown that the most serious threat to pollinators in agroecosystems is poisoning from pesticides (Tew, 1998;
Marshall et al., 2006). Sub-lethal effects of pesticides may
have significant impacts on bees and pollination in
addition to the more easily observable mortality,
disrupting foraging and causing decreased pollination
and/or bee reproduction (Morandin et al., 2005).
Bee species that had low populations were sampled
in the Organic farm as opposed to the conventional farm,
which may indicate that these bees are sensitive to the
chemicals used to manage weeds and pests. A study in
Germany (North Rhine) found that a higher bee diversity,
flower cover and diversity of flowering plants were
recorded in organic compared to conventional farms
(Holzschuh et al., 2007). Presence of rare bees in the
organic farm may be further explained by organic farms
being more flora and fauna diversity friendly.
Andrena sp. was collected in the Organic farm and
suspected to be a new species that has not been previous
recorded in Kenya. Some bee species in families
Andrenidae and Colletidae were rare but that does not
imply that they were not pollinators of coffee. Bee
populations as well as diversity are highly variable in time
and space and a species that is an unimportant pollinator
in one year may be important in the following year
(Freitas et al., 2004).
was comparable across seasons with the short rains season
having the highest diversity and dry season in September
having the lowest. However, where the common bee
species A. mellifera predominated, the results were not
comparable since the common bees were abundant across
all seasons (Fig. 5).
The evenness profile (E-alpha) was calculated to try
and separate the diversity across all the seasons. The
highest evenness was during the two dry seasons
(January, February and September) and the cold season
(June to August) an indication that during these seasons,
the bees were not diverse. The evenness was comparable
for the common species but not the rare species. Bees
collected were mainly from the same family with the most
common bee species being the most abundant. The most
diverse seasons were the short rain season (October,
November and December) and long rain season (March,
April and May) with both the rare and common species
being collected (Fig. 6).
Some bee species in this study (0.37%) of total bees
collected were collected in the Organic farm but not in
the Conventional farm. Andrena sp. 2 was collected at
Organic farm and this was the first record of this species
in Kenya (Fig. 7).
DISCUSSION
This study revealed a high diversity of bees visiting
coffee flowers in central Kenya. From literature it is
evident that in tropical and temperate areas, Halictidae are
the most abundant compared to all the other bees except
the honey bees (Michener, 2000). This is an important
finding because Halictidae could be important in coffee
pollination than the more abundant social bees. The
collective role of a species rich bee community is more
important than species abundance for pollination success
(Klein et al., 2003).
The families that were least abundant and diverse in
the study area have also been noted as globally rare.
Family Collectidae has been described as the most
primitive bee family and they are also few in numbers and
most of them are solitary. The family is relatively scarce
in the moist sub tropics areas (Michener, 1974). Family
Andrenidae is not well represented since in sub-Saharan
Africa there are only a few genera and species (Michener,
1974).
Apis dominance in the area is due to the fact that
A. mellifera is a social bee and sociality is often important
in that social bees can communicate the presence of
resources to their colony and recruit in large numbers to
mass flowering crops like coffee (Klein et al., 2008).
A. mellifera is aggressive in nature and takes advantage of
intense nectar flow associated with coffee flowering
(Vergara and Badano, 2008). Klein et al., (2008)
indicated that A. mellifera and solitary bees are the main
pollinators of C. arabica. Studies conducted in Mexico
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Asian J. Agric. Sci., 3(6):469-474 , 2011
Holzschuh, A., I.S. Steffan-Dewenter, D. Klein and
T. Tscharntke, 2007. Diversity of flower-visiting
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Kasina, J.M., 2007. Bee pollinators and economic
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Kindt, R. and R. Coe, 2005. Tree diversity. A manual and
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2003. Fruit set of highland coffee increases with the
diversity of pollinating bees. Proceedings of the
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Klein, A.M., B.E. Vaissiere, J.H. Cane, J.H. Cane,
I. Steffan-Dewenter, S.A. Cunningham, C. Kremen
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CONCLUSION
This study provides evidence that it’s not only A.
mellifera that pollinates coffee but other soil solitary bees
may play pollination role in varying landscapes and
regions. Conventional farming was found to have a
negative impact on bee abundance and diversity. Results
from this study revealed that organic farming should also
be promoted so as to increase the number of pollinators
visiting coffee plants. An integrated approach in pest
control and habitat management is therefore needed in
coffee production systems in order to enhance the
delivery of pollination service.
ACKNOWLEDGMENT
We wish to acknowledge Jomo Kenyatta University
of Agriculture and Technology for the support accorded
during the study period. We are grateful to DAAD and
ANAFE for the financial support during the study period.
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