Diversity of sunflower pollinators and their effect on seed yield in Makueni District, Eastern Kenya

Abstract

A field experiment was carried out in 2004 and 2005 to identify the diversity of sunflower (Helianthus annuus L.) pollinators and their influence on seed yield in Makueni district, a semi-arid area in Eastern Kenya. Insect flower visitors were recorded, pollen counted from their body and pollination efficiency index for each visitor determined. Seed yield from plots where insect visitors had access to and where they were denied access was compared. The proportional difference of yield from this pollination scenario was used to estimate monetary net-gain by farmers that could be attributed to insect pollination. In total, individuals belonging to 14 insect species were observed visiting sunflower floral heads. These included six Lepidopteran species, five Hymenopteran species, two Dipteran species, and one Coleopteran species. Apis mellifera L. was the most frequent visitor and had the highest pollination efficiency index. Plots where insect visitors had access produced on average 53% more seed yield compared with plots where insect visitors were excluded. This translates to a net monetary benefit of 51% of the total annual market value of sunflower, accruing to farmers in Makueni district in 2005 due to insect pollination.Additional key words: Apis mellifera, non-Apis bees, pollination efficiency index, pollination value. Resumen Diversidad de polinizadores de girasol y sus efectos en el rendimiento de semillas en el Distrito Makueni, este de KeniaSe condujo un experimento de campo entre 2004 y 2005 para determinar la diversidad de polinizadores de girasol (Helianthus annuus L.) y su influencia en el rendimiento de semillas en el distrito Makueni, una región semi-árida del Este de Kenia. Se identificaron los insectos vectores de polinización y se contó el polen adherido a sus cuerpos, a fin de determinar el índice de eficiencia de polinización de cada especie. Se comparó el rendimiento de semillas entre las parcelas visitadas y no visitadas por los vectores de polinización. Se estimó la ganancia monetaria neta de los campesinos atribuida a la polinización por insectos. En total, se observaron 14 especies de insectos visitando girasoles, que incluyeron 6 especies de Lepidópteros, 5 de Himenópteros, 2 de Dípteros y un Coleóptero. Apis mellifera L. fue la especie visitante más frecuente y obtuvo el mayor índice de eficiencia de polinización. Las parcelas a las que los insectos tuvieron acceso produjeron como promedio un 53% más semillas que las parcelas de las que los insectos fueron excluidos. Esto implica un beneficio monetario neto del 51% del valor total del mercado anual de girasol, debido a polinización por insectos, para los campesinos del distrito Makueni en 2005.Palabras clave adicionales: abejas no Apis, Apis mellifera, índice de eficiencia de polinización, valor de la polinización.

Honey bee visitation to sunflower: effects on pollination and plant genotype

“…These results corroborate those found by Du Toit (1990), Nderitu et al (2008) and Oz et al (2009), who observed increasing on production of sunflower's seed in area with introduction of Africanized bees of 38 %, 53 % and 206 %, respectively, related areas without bees.…”

Growth and yield of three sunflower hybrids cultivated for two years under Mediterranean conditions

“…In our study, the high concentration of elaic acid in Oleko is rather anticipated (Skoric, 1992), however, the high concentration in 63A90 was probably due to cross pollination and the insects previously visited the high oleic hybrid (Table 4). Genotype is considered as the main factor that determines the oleic acid concentration as previously suggested by Fernandez et al (1989) and Izquierdo et al (2002), however, cross pollination by honeybees can affect the grain yield and oil content (Nderitu et al, 2008). Moreover, the high temperatures during grain filling until maturity may have also played an important role to the high values observed (Robertson et al, 1971;Anderson et al, 1978;Hazel et al, 1978).…”

Chemical composition of the ‘low quality’ pollen of sunflower (Helianthus annuus, Asteraceae)

“…Here we present a comparable analysis of the pollen of sunflower, Helianthus annuus (Asteraceae). This species, native to North America (Neff and Simpson, 1990), is a major annual oilseed crop worldwide, and pollination by honeybees improves seed production, seed mass and oil content (Krause and Wilson, 1981;Nderitu et al, 2008;Carvalheiro et al, 2011). In his study of honeybee behaviour on sunflowers, Free (1964) suggested that bees visit the florets mainly for nectar and discard excess pollen because it is less attractive than other pollens.…”