Flowering is important to cotton yields because pollinated flowers form cotton bolls. The blooming process takes several days, and the bloom age can be estimated by the bloom colour and characteristics. On the day a flower opens it is white in color. Pollination of that flower usually occurs within a few hours after the white flower opens, and must be done within a day. (4)
Bee foraging on and pollinating a cotton flower in Brazil (3)
Cross section of a cotton flower (4)
Scanning Electron Microscope image of pollen on the stigma of a cotton flower, after pollination has occurred. Plant Imaging Center, University of Wisconsin, USA
After pollination occurs the cotton boll begins to develop. The flower petals wither and fall off to expose a small green immature cotton boll (a segmented pod containing many immature seeds from which the cotton fibres will grow). This ball is considered a ‘fruit’ because it contains seeds. As the fibres continue to grow and thicken within the segmented boll, it enlarges until it becomes approximately the size of a small fig. The cotton fibres have become mature and thickened with cellulose. A mature boll can contain 500,000 fibres of cotton and each plant may bear up to 100 bolls. Under optimum conditions it requires approximately 50 days for a boll to “open” after pollination occurs.
Many bee species have been observed visiting cotton flowers including honeybees (A. mellifera, A. cerana, A dorsata. A. florea), bumblebees, carpenter bees, and melissodes bees. Several authors such as Rhodes (6) have regarded honeybees as effective pollinators of cotton… Caged plots with honey bees had significantly greater total boll mass; total seed mass; and average single-seed weight than caged plots without honey bees.
It is quite evident (2) (3) (6) therefore that in a crop such as cotton where a great many flowers need to be pollinated in a short time period, to gain good yields it would be distinctly advantageous to have a high number of honeybees and other bees available in the pollinator environment.
This advice for cotton growers comes from a respected USA Agriculture College (2) …
Flowers of many varieties are self-fertile and self-pollinating; however, some varieties respond well to cross-pollination. The pollen is not wind-borne, and insects are good pollinators. With some varieties, bee pollination increases seed set per boll (‘Pima S-1’), cotton yield (‘Ashmouni’, ‘Pima S-1’), and earliness of seed set (‘A-33’, ‘A-44’). In practice, few, if any, growers manage bees for pollinating cotton. The crop is attractive to bees, and if insecticide pressure is low honey bees may store surplus cotton honey. Limit insecticide applications to evening to reduce bee kill.
The International Cotton Advisory Committee (1) makes the following ‘Country Statement’ about the Cotton Industry in the Philippines …
The cotton industry is one of the sectors of the government of the Philippines that is geared towards alleviating poverty and attaining food security. While the industry’s contribution to Philippine economy for the last 10 years (1991-2000) is only 0.07% of the Gross Value Added in Agriculture (GVAA), its significance to rural employment cannot be denied. A great number of Filipino farmers depend on it for their living, particularly in areas where no other high value crop could be cultivated. Unfortunately, the industry has not really advanced even as the crop is technically feasible and economically viable. Thus, up to now, the Philippines is still a net cotton importer.
Figures for Philippine cotton production (7) show a fall in the area planted from 1991 to 2000 and limited area planted since then. The yields thoughout this period has been roughly static at about 1 m.ton per hectare.
Figures for Vietnam cotton production (8) show an increase in the area planted from 2008 to 2010. The yields thoughout this period have been roughly 1.3 m.ton per hectare.
Vietnam shares the same latitude as the Philippines and has similar climatic conditions which affects crops such as cotton, and there are many other factors influencing yields in both countries. However, generally it could be argued that having a good pollinator environment compared to the Philippines would have assisted the cotton farmers in Vietnam to attain reasonable yields.
The Philippine cotton industry (7) has contracted, generating less jobs than it used to, whilst at the same time cotton is imported. (Vietnam is increasing its cotton industry.)
As with many crops (mangos, coffee, coconuts, squash and others) there is clear evidence that considering the ‘pollination environment’ is necessary if optimal yields are wanted, yet the Philippine Department of Agriculture has no mention of this in their websites (7). Since it will take time to build a significant beekeeping sector, it will be important to consider the status of the native pollinators. Thinking now and acting as soon as possible to improve awareness of the issues and to bring about ‘honey gathering’ rather than ‘honey hunting’ in rural communities could then have widespread benefits for the remaining cotton farmers (as well as millions of other farmers dependant on the many other crops associated with bee pollination).
1) International Cotton Advisory Committee
2) Pollination: Crop Pollination Requirements
3) Importance of bee pollination for cotton production in conventional and organic farms in Brazil
4) Cotton Squares to Bloom
5) Plant Imaging Center, University of Wisconsin, USA
6) Cotton pollination by honeybees
Australian Journal of Experimental Agriculture, June 2002, by J Rhodes
7) Cotton Development Administration of the Philippines
8) Vietnam Cotton Annual report 2010