Pollen Collection and Pollen Foraging Behaviour of Honeybees (Apis mellifera) during Different Time Intervals from Brassica campestris L.

The experiment was conducted in the Brassica crop grown at National Agricultural Research Centre, Islamabad during March 2015. Twenty five honeybee (Apis mellifera) colonies, all equalized to have similar number of worker bees, brood combs and stored food (i.e. honey) were transported to the experimental site on the onset of flowering and kept there for 2 months over the period of the experiment. The experimental area had a natural water source nearby, enough for fulfilling the water requirement of the apiary.

In order to study the pollen collection and foraging activity of honeybees, the pollen traps were installed at the entrance of each hive. The number of pollen foragers returning to the hive entrance was recorded for 10 min duration on hourly basis between 0800 – 1000 hours (early morning foraging activity), 1000-1200 hours (late morning foraging activity), 1200-1400 hours (early noon foraging activity) and 1400-1600 hours (afternoon foraging activity).

The observations included three steps i.e. installing pollen traps at the entrance of the hive, recording number of pollen carrier bees returning to the hive, calculating quantity of bee pollen collected in the pollen trap trays and weighing the total weight of bee pollen collected by each hive. These observations were recorded in the experimental site under good weather conditions for foraging bees: temperature ≥ 15°C, low wind, no rain, and dry vegetation as followed by Cartin et al., (2008). Foraging efficiency of a honeybee colony was calculated in terms of number of bees with pollen load entering the hives were counted for a specific period during the four time intervals. The pollen collected in the trays were collected at regular intervals for a period of one month using pollen traps fitted at the entrance of the hives and left for a period of 8 hours. The pollen loads were weighed fresh by using standard electronic scale and preserved in the compact / air tight containers in the refrigerator. Collected pollen were cleaned and preserved separately for each duration of time. The pollen foraging ratio (PFR) was calculated according to Wilde et al. (2003) as:

The comparison of pollen collected in traps by several honeybee colonies placed at one location were found less problematical as they were carried out using the same trap type and identical experimental procedures.

Furthermore, the pollen influx into the honeybee colonies at the apiary was calculated by computing the ‘r’ value, the mean rate of pollen harvested by the pollen traps on the colonies: (O’Neal and Waller, 1984). The influx is calculated by computing the pollen harvest from pollen traps.

The data was subjected to statistical analysis using Analysis of variance (ANOVA). The differences of means were tested for significance using the Duncan test.

Foraging bees can be classified as bees which move out of the hive and perform different foraging activities such as nectar, pollen, water and resin collection (Maria and Thrasyvoulou, 2007). Table I shows the starting and ending of Apis mellifera foraging time. The mean timing of all the four groups differed significantly with each other. The highest foraging ratio was observed during the time between 1000-1200 hours showing the mean value 59.88 ± 2.89 followed by 1200-1400 hours showing the mean value 58.24±3.03. The starting and ending time periods i.e. 0800-1000 and 1400-1600 hours showed lower mean values of 48.36±2.84 and 44.36±3.36, respectively. Similarly the pollen collected through pollen traps during different time periods was in correlation with the foraging ratio i.e. the highest pollen was collected during 1000-12000 hours showing mean value 145.8±8.79 followed by the mean value 134.4±5.49 for the hours 1200-0200. The pollen collection during the hours from 0800-1000 were significantly low showing mean value of 121.8±6.73 followed by the least pollen collected during the timings between 1400-1600 which showed mean values of 117±3.77. Thus the best foraging time and peak activity for foraging bees was 1000-1200 hours followed by 0200-0400 hours (Table I).

These results are in agreement with earlier results of Stephen and Currie (2001) showing maximum foraging rate during the afternoon period than the morning period depicting values of 36.02 foragers/min and 17.66 foragers/min, respectively. Similarly these results are in confirmation with the observations that foraging bees visited onion flowers between the periods from 0815 to 1630 hours with 1100 to 1200 hours was the peak foraging time (Banu and Duman, 2005). Hari et al. (1994) reported maximum foraging activity of A. mellifera on Brassica juncea during 1300 hours. The findings are also in accordance with Domagala-Lipinska (1962) and Grabowski et al. (2000) that foraging rate starts increasing early in the morning, reaches its peak in the midday and later on declines in the afternoon. It can be concluded that best time for pollen collection and foraging time for honeybee is 1000-1200 hours.

We acknowledge Mr. Qurban Ali, Senior Scientific Assistant and Mr. Zafar Iqbal, Aman Ullah Bee Attendants for collecting pollen and placement of pollen trap.

We declare that we have no conflict of interest.