Diversity And Abundance Of Bees And Their Effect On Yield Of French Beans, Adjacent Mt Kenya Forest In Laikipia County

ABSTRACT

French bean (Phaseolus vulgaris L.) is an important crop with high impact on rural

employment and livelihood. In Kenya, the crop is grown for export by small scale

farmers in high potential areas of Central, Rift valley and Western regions. These

regions are densely populated leading to intensive farming and land fragmentation,

which research has reported to be among the major threats of bee pollinators.

However, amongst the known constraints, pollination has not featured amidst many

farmers, a fact associated with lack of knowledge on the same. The crop benefits from

bee pollination through improved pod set and pod quality. The objectives of this study

were to assess the taxonomic composition and diversity of bees visiting flowers of

French beans, assess the abundance of bees visiting flowers of French beans,

investigate the effect of diversity and abundance of bees on the yield of French beans,

determine the effect of time of the day on the trends of the most common bee genera

visiting flowers of French beans. Field surveys were conducted on Julie cultivar of

French beans in Kaitheri and Kangaika locations of Timau division (Likipia

County).The study design was based on a protocol developed and agreed upon by

global partners for testing pollination deficit in crops. Ten farms were selected along a

3 km transect, where five farms were located at 0.2 km from the edge the forest and

other five were at 1 km distance. Sampling was done on a plot measuring 760 m2,

once a week, between 8.00 to 10.00 h and 11.00 to 2.00 h, three times a season at a

weekly interval, in the years 2011 and 2012. Sampling was done on 6 rows each

measuring 25 m x 2 m for 30 minutes. Sampling of bees to assess taxonomic

composition and diversity was done using sweep net. Sampling of bees to assess

abundance was done using two scanners, where one scanner counted newly opened

flowers and another one counted bees in the flowers. Effect of diversity and

abundance of bees on yields of French beans was done by daily weighing and

recording of production inputs and outputs of French beans. Observation of bees to

determine the effect of time of the day on the trends of the bees was done on six

farms, where, each group of two farms was at 0.2 km, 0.8 km and 1 km from the edge

of the forest. Bees were observed from 06.00 h to18.00 h and recorded on hourly

basis. Results on diversity of bees revealed five families, nine genera and twelve

species of bees during the study period of two years. Total diversity of bees sampled

on farm located at 0.2 km and 1 km were not significantly different (P=0.161). Mean

numbers of bees sampled on farms located at 0.2 km and 1 km were not significantly

different (P=0.821). The mean number of Apis mellifera was higher than those of all

other bee species. The mean number of Apis spp was higher than those of Xylocopa

spp and Megachile spp. The total diversity and abundance of bees did not

significantly affect the total yield of French beans. Yield of French beans only

correlated significantly with the abundance of Xylocopa spp. Bees of Apis spp foraged

on flowers of French beans between 08.20 h and 17.00 h, with a peak activity between

10.30 h to 11.00 h. Bees of Xylocopa spp foraged on flowers of French beans between

08.20 h and 15.00 h, with the peak activity at 14.00 h. Bees of Megachile spp foraged

on flowers of French beans between 09.00 h and 16.00 h, with the peak activity at 13.

00 h. Thus, this study recommends implementation of bee friendly practices and measures to enhance pollination of crops.