Antonio José Manrique and Rafael Ernesto Thimann

Antonio José Manrique. Zootechnician, Universidad Ezequiel Zamora (UNELLEZ), Venezuela. Doctor in Genetics, Universidade de São Paulo, Riberão Preto, Brazil. Researcher, Instituto Nacional de Investigaciones Agrícolas (INIA), Caracas, Venezuela. Address: INIA, Parque Central, Torre Este, Piso 11, Caracas, Venezuela. e-mail: tonyman77@terra.com

Rafael Ernesto Thimann Ramírez. Zootechnician, Universidad de Oriente (UDO), Venezuela. M.Sc. in Animal Production, University of Edinburgh, Scotland. Associated Professor in Apiculture, UNELLEZ. Address: UNELLEZ, 3323, Guanare, Edo. Portuguesa, Venezuela. e-mail:  rafael_ernesto_t@hotmail.com

In order to evaluate the pollination potential of Africanized honeybees, 10 hives were placed between rows of a coffee (Coffea arabica L.) plantation at "El Laurel" Experimental Station, of the Central University of Venezuela, Miranda State, Venezuela. Secondary branches were selected randomly from 60 adult plants. Yields from uncovered (T1) and mesh covered (T2) branches, as well as from uncovered branches located 1km away from the hives (T3) were compared. Number of flowers blooming per branch, mature grains per branch and weight of the wet/dry grains harvested were recorded. The numbers of mature grains relative to flowers showed differences (p<0.05) with percentages of 91.6 (T1), 82.6 (T2) and 86.9 (T3). Differences (p<0.05) were found in wet weight (g/grain) with values of 2.05 (T1), 1.71 (T2) and 1.83 (T3). Highly significant differences (p<0.01) were found for dry weight (g/grain) with values of 0.45 (T1), 0.37 (T2) and 0.41 (T3). The results suggest that the use of honeybees as coffee plant pollinators increases the percentage of mature grains/ branches; thus increasing yields.

Con la finalidad de estudiar el efecto de la abeja africanizada como agente polinizador en la producción de café, se realizó un ensayo en la Estación Experimental "El Laurel" de la Universidad Central de Venezuela, Estado Miranda, Venezuela, en un cafetal de 14 hectáreas de superficie, donde se seleccionaron 60 plantas adultas de café (Coffea arabica L.) al azar y de cada una se seleccionó una rama secundaria. En los callejones del plantío fueron colocadas 10 colmenas de abejas africanizadas, tres días antes de la floración. Se comparó el producto de ramas sin (T1) y con (T2) cobertura con una malla fina, así como de ramas sin cobertura en plantas ubicadas a más de 1km de distancia de las colmenas (T3). Se determinó el número de botones florales por rama, número de granos maduros por rama, y peso húmedo y peso seco de los granos cosechados. Los tratamientos T1, T2 y T3 arrojaron resultados estadísticamente diferentes (p<0,05) en peso húmedo (g/grano) con valores medios de 2,05, 1,71 e 1,83, respectivamente. En peso seco (g/grano) hubo diferencia altamente significativa (p<0,01) entre T1, T2 y T3, con valores de 0,45, 0,37 y 0,41, respectivamente. El porcentaje de granos formados relativos a flores también mostró diferencias significativas (T1= 91,6%, T2= 82,6% y T3= 86,9%). Los resultados obtenidos muestran que la polinización con abejas africanizadas promueve un incremento en el peso y la cantidad de grano formados, aumentando la productividad.

Received: 02/28/2002. Modified: 06/10/2002. Accepted: 07/02/2002

In Venezuela, coffee and cocoa have been the most important cash crops for trading and exports since the 18th century until oil was exploited, providing giving jobs for more than 60000 families in the highlands and their slopes, which constitute more than 35% of the land, where no other cash crop can be harvested without causing erosion. National coffee yields of 7.5 quintals (1q=100 pounds) per hectare are considered low (MAT, 2002) and for this reason research has been carried out to rationally and economically increase crop yields. This can be done by integrating the coffee crops with (e.g.) sheep to control weeds and supply organic matter to the soil, diverse fruit plant species (trees) for shade, small production of minor or secondary crops used for the everyday meals (cassava, squash, yams and others) and by the use of honey bees to increase entomophily pollination efficiency.

Coffee (Coffea arabica) is defined as an autogamous plant with some degree of cross-pollination with insect intervention. The great majority of coffee varieties have very aromatic flowers that produce abundant nectar and pollen that attracts insects (Henao, 1991). Non-attractive flowers and a short blooming period are cited as limiting factors in the use of honeybees for coffee crops (Couto, 1995). However, even though the blooming period is short, there are two sequences in it, one period of dense flower populations that bloom simultaneously followed by another short period of blooming where the honey bees can get nectar from the extra-floral nectaries located on the edge of the leaves (Sánchez, 1995). In spite of being considered by beekeepers in Venezuela as an excellent plant for honey production, preliminary work by Manrique (1996) has not led to this conclusion. While beekeepers agree on the use of honeybees to pollinate coffee crops, Badilla and Ramírez (1991) indicated that cross-pollination of coffee is still un-explained. On the other hand, Gómez (1986) pointed out that C. arabica species are self pollinated, but the use of honeybees would increase yields. An adult coffee plant has from 10000 to 50000 flowers, but almost 90% of them fall due to pollen incompatibility, defects of the embryonal sac or no pollination at all. Amaral (1972) suggested that a coffee plant can have different types of flowers in the same blooming period, and Badilla and Ramírez (1991) add that the loss of unmatured grains can be caused by a hormonal stimuli produced by cross-pollination with other plants of the same species that promotes the phenomenon.

Malerbo (1996) used chemical attractants in a coffee crop that bloomed simultaneous to an orange plantation and observed that the honeybees preferred foraging for pollen when few flowers were opened and foraging for nectar when a great number of flowers were open.

Amaral (1972) selected a patch of coffee plants where half of the plants were covered with mesh and the other half were uncovered and found a 13.6% increment of mature grains in uncovered plants, noting the benefit of entomophily pollination. Furthermore, the same author found that the closer the hives were to the coffee crop, the higher the number of honey bees that visited them, suggesting distances of 25m rather than 50 to 100m. Raw and Free (1977) obtained increases of 59% in the Caturra coffee production due to honey bee pollination. For this reason, Free (1993) suggested that the coffee growers should place hives among crops during the blooming periods, as a means to achieve higher yields.

The purpose of the present work was to evaluate the pollination effect of Africanized honeybees in coffee (Coffea arabica L.) production at an experimental station.

Research was carried out at the "El Laurel" Experimental Station, Central University of Venezuela, Miranda State, which is located in a pre-mountain forest considered by FONAIAP (1988) to have the best coffee production climatic conditions, such as 80% relative humidity, 1400mm annual rainfall, 17°C average temperature and 1400m altitude.

The experimental area was a 14ha coffee (Coffea arabica L var. Catimor) crop, with seven year plants and a density of 2m between rows and 1m within plants. Shade was provided with adult Inga spp. trees. Sixty adult plants were selected randomly and from each one a secondary branch was marked with a white plastic ring. Three days before the flowers bloomed, 10 hives with strong Africanized honeybee colonies were placed between rows in a 7ha plot, each hive separated by 30m, so as to saturate the surroundings with honeybees. The other 7ha plot, with the same agro-ecological conditions, was located 1km from the first plot. Three different treatment groups were considered: 20 uncovered branches (T1) and 20 branches covered with a fine mesh (T2), both in the hive-containing plot, and 20 uncovered branches from the plot located 1km away from the hives (T3). The bee colonies were fed with sugar syrup (1:1) one month prior to flower blooming.

Secondary branches were selected two days before placing the hives in the experimental area, and floral sprouts counted. Following the sixth day of blooming, the covering mesh and the beehives were retired. Three months later, grains formed were counted so as to compare their numbers with the matured grains harvested later by hand. The mature harvested grains were counted, placed in paper bags to determine wet weight, and then de-pulped and dried for three days at 38°C to determine dry weight. For statistical analysis, the multiple comparison Tukey test was applied to the recorded data.

Coffee flowers standard blooming behavior was closely related to the beginning of the rainy season in the region, where rainfall above 10mm was followed by a reduction of the hydric balance, as mentioned by Benezra (1987). Early in the morning coffee flowers began opening, until the afternoon. The highest numbers of pollinating agents foraged mostly between 7 and 10am and from 4 to 5pm (Figure 1). These specific hours of forage might be related to the moderate solar radiation on the crop, which promotes a rise in temperature and humidity that stimulates nectar and aroma production. On the other side, honeybees were seen foraging mostly for nectar and less for pollen, in accordance with the observation of Badilla and Ramírez (1991). Carvalho and Krug (1950) observed that in days without sunlight the coffee flowers would not open and tend to self-pollinate.

Figure 2. Flowers, sprouts and coffee grains obtained after honeybee and insect pollination for the three experimental groups.

Gómez (1986) pointed out that coffee crops were a good source of nectar for honey production, but in this work results showed low nectar (honey) yields, probably due to sunny days, continuous rain, low night temperatures and the short blooming period (5 days), affecting negatively the storage of nectar, in agreement with the results obtained by Manrique (1996).

Figure 2 summarizes the average number of flower buds, mature flowers and ripe grains during the experimental period. Coffee grain counts were higher (P<0.05) in T1 as compared to T2 and T3. The percentage of ripened grains, relative to flowers was also higher (P<0.05) in T1 (91.6%) when compared to T2 (82.6%) and T3 (86.9%). These results differ somewhat from those of Amaral (1972) and Raw and Free (1977) who obtained increments in ripe grains of Caturra coffee of 13.6 and 59%, respectively, when honey bees were used to pollinate the crops.

The lower yields obtained in T2 and T3, could be due to a greater fall of non-mature grains or to the absence of fruit formation, which would indicate that a greater entomophily pollination is necessary in the formation of the grain, as suggested by Amaral (1972) who states that the smaller formation of coffee fruits in absence of insects indicates that a given plant has some flowers that require cross-pollination and others that are self-fertilized. On the other hand, Badilla and Ramírez (1991) indicate that the fall of non-mature fruits could be due to the fact that bees and other pollinators, when bringing pollen of other plants of the same species, produce a stimulus in the initial growth of the fruit, through a hormonal effect, that remains until the fruit achieves maturity.

Table I shows the average weights for dry and wet ripe grains harvested. T1 resulted in higher yields when comparing the total wet weight (TWW), with values of 27.2 and 15.6% above those from T2 and T3, respectively. When comparing the total dry weight per grain (DW/GRAIN) T1 resulted in yields 21.6 and 9.75% higher than T2 and T3, respectively. Taking into account that T3 did not have a control of natural/feral pollinating agents, the small (~10%) differences between T1 and T3 might give the impression that for higher yields of ripe coffee grains there is a need for honeybees to pollinate the crops.

The results suggest that the use of Africanized honeybees as pollinating agents for coffee crops might increase yields of ripe grains per plant.

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