Flight intensity of honeybees (Apis mellifera) and its relationship with temperature, sunshine hours, cloudiness and relative humidity

Haftom Gebremedhn, Alemayehu Tadesse* and Tesfay Belay

Tigray Agricultural Research Institute,
Mekelle Agricultural Research Center. P.O.Box 492, Mekelle, Tigray, Ethiopia
haftush@yahoo.com
* Department of Apiculture and Sericulture, Mekelle University, Tigray, Ethiopia

Abstract

Information on flight intensity of honeybees is important in pollinator management programs. However, the flight intensity of local bees ( Apis mellifera) is poorly known. Investigations into the pattern of activity of various races of A. mellifera, in different parts of the world, reveal a lot of variation. Hence, this study was designed to determine the effect of hours of the day and climatic factors on the flight intensity of local honeybees. The study was conducted at Mekelle Agricultural Research Center and the flight intensity of bees was determined by counting the number of bees leaving and returning to their hive. Counting was done in four colonies which had similar strengths. It was done five times per day at 7:00a.m., 9:30a.m., 12:00a.m., 14:30p.m. and 17:00p.m. Each observation time was considered as a treatment. The collected data were analyzed using GLM repeated measurement analysis procedure. 

 The peak in the number of bees that exited and returned was recorded at 9:30a.m, while the smallest number of bees that exited and returned was recorded at 7:00a.m. The number of bees that exited and returned had a positive relationship with air temperature and sunshine hours, and a negative association with relative humidity and cloudiness.  Hence it is advisable to save honeybees by not applying insecticide to crops at times of day when their flight intensity is highest.

Key words: climatic factors, insecticides, managment, pesticides, pollination

Introduction

Information on the flight intensity of honeybees is important, because it provides data that can be used in pollinator management programs (Souza et al 2006). Moreover such information can help to save the pollinators by providing advice to farmers to restrict the application of insecticides to their crops to times of day when the flight activity of honeybees is lowest (Dukku et al 2013; Souza et al 2006). Pollinators can be protected by such rational pest management strategy (Mahfouz et al 2012).

Flight activities of bees can be shaped by environmental factors, such as quality and quantity of food, and competition and behavior of nest mates (Hilario et al 2000). Several authors also pointed out that flight activity of bees is strongly influenced by meteorological conditions like temperature, hour of the day and light intensity (Junior et al 2010; Puškadija et al 2007). However, the flight intensity of local honeybees has been poorly known. Moreover investigations into the flight activity of various races of A. mellifera in different parts of the world reveal a lot of variation (Dukku et al 2013).

Despite local knowledge on the  pattern of movement and flight intensity of  honeybees, it is common  to see insecticide application when honeybees are at high traffic. The use of chemicals and pesticides to control crop pests, weeds, Tsetse fly, mosquitoes and household pests is a real constraint for the beekeeping sector through damaging honeybee colonies and contaminating hive products (Ejigu et al 2009). Yearly in Ethiopia, about 541,467 liters of pesticides are aerially sprayed on 514,923 ha to control migratory pests (Amssalu 2012). Tessega (2009) also reported thaat pesticide and herbicide application were the reason for decreases in availability of hive products. It has been estimated that almost half of the pesticide applications in Ethiopia are carried out in regions with high beekeeping potential (Amsalu 2012). In Burie district , 97.5% of the bee poisoning occurred due to agro chemicals mainly insecticides and herbicides (Tessega 2009). This is mainly due to a failure to synchronize application of insecticides and herbicides with the flight intensity and activities of the bees.

For the above reasons, this study was designed to determine the flight intensity pattern of local honeybees (A. mellifera) so as to provide information that could be used to synchronize their activity with the local application of pesticidess and herbicides.  The influence of climatic factors (air temperature, cloudiness, sunshine hours and relative humidity) on the flight intensity of bees was also determined. It is considered that this information would be of paramount importance for people who work with bees, for them to know the activity of their bees so that they can work with them at the appropriate times.

Materials and methods

Description of study area

The investigation was carried out during the 2013 growing season at Mekelle Agricultural Research Center, Illala site. Illala is located Northeast of Mekelle at an elevation of 2012 m.a.s.l, at N13⁰31’21. 2” latitude and E039⁰30’14. 7” longitude. The site was selected based on the availability of an apiary with indigenous honeybee colonies and access to the meteorological station of Mekelle Agricultural Research Center, Illala. meteorological station.

Counting number of honeybees and weather condition

The flight intensity of honeybees was determined by counting the number of bees leaving and returning to their hive. This was done five times per day (7:00a.m, 9:30a.m., 12:00a.m., 14:30p.m and 17:00p.m.) at three day intervals for a total of 22 days. To see the effect of season, counting of bees was done in two seasons (August for summer and September from spring) of the year 2013. The numbers of bees exiting and returning per hive was counted for three minutes. This was done in four honeybee colonies which had similar strength (in brood coverage and bee population). The mean number of bees leaving and returning for every observation time was obtained by taking the average of the four selected bee colonies. To determine how climatic factors affect the flight intensity of honeybees, data related to air temperature, relative humidity, cloudiness, and sunshine hour were recorded from the Mekelle Agricultural Research Center, Illala meteorological station (around 400 meters away from the colonies' entrance).

Data analysis

Data related to number of bees exiting and returning, air temperature, relative humidity, cloudiness and sunshine hours as a function of time of the day and season, were analyzed using GLM repeated measurement analysis procedure. To compare the number of bees exiting with the number of bees returning per day the Mann-Whitney test was used. Spearman’s correlation was used for relating the flight intensity of bees to climatic factors. The data were analyzed using SPSS 16^th version and Genstat 14^th version statistical software.

Result and discussion

Influence of time of the day on flight intensity

 The study noted as time of the day had significant effect in the flight intensity of honeybees (Table 1). The peak in the number of bees exiting and returning was observed at 9:30a.m (Table 1), while the least number of bees exiting and returning was recorded at 7:00a.m. The time of 9:00a.m. to 12:00a.m. was also indicated as the most intense activity time when the highest numbers of bees (in this case Apis cerana) were seen to depart and to arrive at the bee hive (Tripathi 2011). There was a very strong positive association between the number of bees exiting and those  returning (Table 4).

Influence of season on flight intensity

Season had a substantial effect on the flight intensity which varied over the months (Table 1). A greater traffic of entries and exits was observed in September than in August. Junior et al (2010) reported that season had an influence on the flight activity of stingless bees. Another study also showed noticeable differences in the traffic of bees between rainy and dry seasons (Nascimento and Nascimento 2012). The variation in the flight intensity of bees between September and August in this study might be due to the variation of climatic factors, seasonal colony strength and availability of honeybee plants. In August, rains with variable intensity occurred throughout the collection days, and most of the plants were starting to bloom. Whereas, in September, flowering plants are usually available throughout the day from a variety of annuals, including crops and the rain ceases at the end of August. Dukku et al (2013) also indicated that the availability of bee plants influenced the pattern and activity of honeybees. Haftom et al (2013) revealed that there is seasonal variation in the availability of honeybee plants in the study area.

There was an interaction between time of day and season interaction on the bee flight intensity (Table 3). The greatest intensity was recorded at 12:00a.m. in September, while the lowest was recorded at 7:00a.m. in August.

Time of the day and weather conditions

The highest mean air temperature (24.9ºC) was recorded at 12:00am and 14:30pm, while the lowest temperature (13.9⁰C) was recorded at 7:00a.m. Similarly the highest intensity of sunshine (33.4 to 35minutes per hour) was recorded starting from 9:30a.m. to 14:30p.m. during which time the highest temperature was recorded (Table 2). The highest relative humidity was at 7:00a.m., when the temperature was lowest, whereas the lowest humidity was recorded at 14:30p.m. Regarding cloudiness there were no appaarent differences  between the observation times of the day (Table 2).

Season and weather conditions

Highest mean air temperature and relative humidity were recorded in September and August, respectively. Moreover, more cloudiness was indicated in August than in September (Table 2). This might be due to the incidence of rain in the summer season.

Season and time of the day interaction and weather conditions

Time of the day and season interaction had a substantial influence on mean air temperature and relative humidity (Table 3). The highest and the least mean air temperatures were recorded in September at 14:30p.m (27.1ºC) and 9:30a.m (12ºC), respectively. Regarding relative humidity, the highest relative humidity indicated in August at 9:30a.m. whereas the least humidity was recorded in September at 14:30p.m. Interaction of time of the day and season however had no significant influence on mean sunshine intensity and cloudiness (Table 3).

Effect of climatic factors on the flight intensity of honey bees

Climatic conditions had a significant influence on the flight intensity of honey bees (Table 4). The number of bees exiting tended to be positively associated with mean air temperature (r= + 0.46) and sunshine hours (r= +0.55), while there was a negative tendency with relative humidity (r= -0.45) and cloudiness (r= -0.21). Similarly the number of bees returning had positive trend with air temperature (r= + 0.47) and sunshine hours (r= +0.52), and negative relationship with relative humidity (r=-0.450) and tended to be negatively correlated with cloudiness (r= -0.20; P=0.053). The data revealed that flight intensity of honeybees tended to increase concomitantly with air temperature and sunshine hours and to decrease as the relative humidity increased.

 Dukku et al (2013) also reported differences in flight activity of honeybees (Apis mellifera L) due to temperature and light intensity. Other studies indicated that the number of bees exiting their hive had a positive association with temperature and light intensity. Szabo (1980) and Burrill (1981) revealed that increasing air temperatures resulted in increased flight departures of honeybees, while decreasing temperatures was associated with decreasing numbers of departures. In stingless bees and Apis florae,  increases in air temperature resulted in a substantial increase in the number of bees exiting, while there was an increase in the number of bees exiting with a decrease in relative humidity (Kajobe and Echazarreta 2005; Souza et al 2006). Sihag and Abrol (1986) reported that relative humidity directly influenced flight activity of bees. Dukku et al (2013) also reported that thick clouds were associated with reduced foraging of bees.

Conclusions

• Time of the day, climatic factors and season had a significant effect on the flight intensity of honeybees.
  
  
• The observation time of 9:30a.m. had the highest number of honeybees exiting from their hive and number of bees returning, while the observation time of 17:00p.m. had the smallest number of honeybees leaving and returning.
  
  
• Flight intensity of honeybees’ tended to increase concomitantly with air temperature and sunshine hours and decrease as the relative humidity increased.
  
  
• Season also had a significant effect on the flight intensity of honeybees with the greater traffic of entries and exits observed in September than in August.
  
  
• It is recommended crop protection with pesticides should be done when the flight intensity of honeybees is lowest.

Acknowledgements

We are grateful for the financial and material support provided by the Tigray Agricultural Research Institute, Mekelle Agricultural Research Center. We are also very grateful to Kinfe Mezgebe of Mekelle agricultural research center coordinator, Dr. Zelalem Tesfay and Embza Kasa from Mekelle Agricultural Research Center, Teklay Gebrezgabhear and Gebremedhn Girmay and Alemat Embaye for their special support throughout the study.

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Received 8 November 2013; Accepted 10 December 2013; Published 1 January 2014

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