| dc.description.abstract | A field experiment was carried out twice in the long rains, 2004 and the short rains, 2005 In
Makueni District, Eastern Kenya to establish the diversity of sunflower pollinators and their
effect on the seed yield. Four treatments were used in a randomized complete block design
with plots sizes of 4 x 4 m replicated four times. The treatments included, bagging at night and
opening during the day for free aecessibity by daytime pollinators, bagging during the day and
opening at night for free accessibility by nocturnal pollinators, bagging throughout the
flowering period to exclude all pollinators, and no bagging for free access by all pollinators.
The pollinators were collected and identified and the honeybees' diurnal behaviour noted.
Head diameter, the number of seeds per head, weight of seeds per head, number of deformed
seeds per head and the % oil content determined.
A total of 14 insects species were observed visiting sunflower floral heads. Other visitors
included, the nOI1- apis bees; Plebeina denoiti, Ceratina sp, Heriades sp, Pseudoantliidium sp,
two (2) species of Diptera namely; Rhynchomydaea sp and Phytomia ill cisa , six (6) species of
Lepidoptera; Danaus chrysippus, Belenois aurota, Junonia oenone, Byblia ilithyia. Junonia
hierta, Cephonodes hylas and one (I) species of coleoptera, Merylis flavipes Apis mellifera
was the most abundant and important sunflower pollinator recording the highest pollination
efficiency index (7606). Peak foraging periods for the honeybees and the non-apis pollinators
was observed between lOam and 12 pm .The length of visitation was not significantly
different with time of the day. Number of seeds per head and seed weight per head increased
by two to three times, and number of deformed seeds reduced by 35 % while the oil content or
seeds per head increased by 66.7 % in the plots exposed to pollinators compared to the plots
bagged to exclude pollinators.
Two insecticides namely dimethoate ( Dimethoate 40 % EC) and L -cyhalothrin (Karate 1.75
% EC) were evaluated for their effect on sunflower pollinators and seed yield. Five treatments
in a randomized complete block design with plot sizes of 4 x 4 m replicated thrice were used.
The treatments were spraying in the morning and evening after flowering for each of the
insecticides and a control (untreated). Numbers of foraging honeybees for five days alter
treatment were noted. The head diameter, number of seeds per head, weight of seeds and the
numbers of deformed seeds were recorded.
Untreated plots gave higher numbers of seeds per head, seed weight per head and lower umber
of deformed seed per head compared to the treated plots. However, the weight of seeds from
Dimethoate and Karate treated plots were not significantly different. Insecticides application
in the morning had higher number of 'deformed seeds per head compared to the evening
applications. On average seed number per head was reduced by 52 %, seed weight per head by
38 % and the number of deformed seeds per head increased by 63 %.
lt was evident that lower yield were attributed to reduced honeybee visits due to pesticide
toxicity. | en |
