PICS bags for post-harvest storage of maize grain in West Africa
Introduction
Annual maize production in West Africa is estimated to be 16 million tons (FAOSTAT, 2011). Nigeria, Ghana, Benin and Burkina Faso account for 87% of this total. Maize makes a substantial contribution to the diets of rural and urban populations. Its cultivation in the region has gradually increased over the years (FAOSTAT, 2011, Smale et al., 2011) thanks to adoption of better production technologies and improved varieties (Manyong et al., 2003).
A recent USAID study (Boone et al., 2008) highlighted the constraints of the maize sector in West Africa, one of which is post-harvest storage. Several storage insect pests of maize are present: Sitrotoga cerealella (Olivier), Plodia interpunctella (Hübner, [1813]), Sitophilus zeamais (Motschulsky), Rhyzopertha dominica (F.) and larger grain borer, Prostephanus truncatus (Horn) (Ortega, 1987, Boxall, 2002, Throne, 1994, Markham et al., 1994.).
Prostephanus truncatus Horn, one of the most feared, was introduced into Africa in the 1970s and reported for the first time in Togo in West Africa in the 1980s (Dunstan and Magazini, 1981, Golob and Hodges, 1982, Harnisch and Krall, 1984). Development of this species requires a temperature of 30 °C, ambient relative humidity of at least 70% and 13% moisture level of the seeds. Under favorable conditions adults can live for 7–8 months to two years. The development cycle is completed in less than 4 weeks and P. truncatus can produce from 12 to 13 generations per year.
Sitophilus zeamais, a cosmopolitan species, is also recognized as a major postharvest pest of maize (Jacobs and Calvin, 2001, Arannilewa et al., 2002, Demissie et al., 2008). Its development cycle lasts 4 weeks, with the female laying 300–400 eggs (Longstaff, 1981, OzAnimals, 2009). Rhyzopertha dominica is a major pest of several cereals, including maize. The female lays up to 500 eggs and the developmental cycle can be completed in 30 days at 34 °C (Cotton and Wilbur, 1982).
Losses due to post-harvest pests of maize are estimated to average between 20 and 30% after 3 months of storage (Boxall, 2002). For P. truncatus, losses are estimated at 30% in Togo after 6 months of storage (Pantenius, 1988) and between 17.9 and 41.9% in Tanzania after 6–8 months of storage (Keil, 1988). For S. zeamais, losses of 17.5% in Tanzania after 6 months of storage (Mulungu et al., 2007) have been reported. Laboratory studies with wheat showed that R. dominica can cause losses of 25% after 3 months of storage (Patel et al., 1993).
In the African context, the loss of stored grain has several negative impacts at the farmer level (Boxall, 2002), including: 1) deterioration in the nutritional quality of maize grain; 2) reduced food availability for families; 3) resultant need to purchase food products at high prices during the lean season; 4) disruption of the planned family food supply; 5) financial and profitability losses, 6) reduced local maize processing industry and cross-border trade. Long-term pest pressure on stored grain can discourage farmers and even lead them to abandon maize cultivation.
According to the model presented by Compton et al. (1997) the value of maize depreciates from 0.6 to 1% for each percent of insect damaged grain.
Hermetic methods for maize storage in Africa have been considered in part because of the high cost and limited availability of good quality pesticides. Metal silos are being promoted in the sub-Saharan zone (Tefera et al., 2011, Yusuf and He, 2011), but their use by farmers is hindered by the high initial investment and limited availability of the technology. The Super Grain Bag produced by GrainPro is a bag made of high-tech oxygen-impermeable plastic films that represents an alternative to metal silos (Villers et al., 2008). Recent surveys in Kenya and Benin concluded that the GrainPro technology is inadequate for the long-term storage of maize infested by P. truncatus due to perforations of the bag caused by the insect (De Groote et al., 2013; Edoh Ognakossan et al., 2013).
The Purdue Improved Crop Storage (PICS) bag is an alternative hermetic technology extended in West Africa for the storage of cowpea beginning in 2007 (Baributsa et al., 2010). Its effectiveness in the control of Callosobruchus maculatus (F.) is well studied (Murdock et al., 2012, Baoua et al., 2012, Baoua et al., 2013). The PICS technology has the advantage of having an established local distribution network, simplicity, durability, and low cost. Local production is also key: six African factories employing African workers have produced and sold more than 2.5 million bags thus far (PICS unpublished report 2013).
The present study was undertaken in response to requests by farmers, traders and private seed companies that we determine the effectiveness of PICS bags for storage of maize grain and seed. Accordingly, experiments were set up in numerous rural areas in West Africa where maize is produced.
Section snippets
Materials and methods
Trials of the technology were conducted in twelve localities in the maize production zones of Benin, Bukina Faso and Ghana (Fig. 1). In Benin, the experimental units were set up in collaboration with traders and maize marketing cooperatives. Infested maize was purchased locally and used for assessing the performance of PICS bag in preserving grain quality. In Burkina Faso and Ghana, the experiments were conducted with private seed and food processing companies supported by the AGRA program.
Results
Thirteen experimental units testing PICS and woven polypropylene bags were set up using locally-purchased maize grain, five in Benin, six in Burkina Faso, and two in northern Ghana. The degree and nature of the initial infestation varied from location to location. Nine of the test units started with highly infested grain while four were initiated with lightly-infested grain. Two separate trials were set up in each of Ndali in Benin and Po in Burkina Faso.
Discussion
The PICS bag tests described here were conducted in the real-world environment of West African farms, villages and small towns where harvested grain is aggregated and stored. The difficulties of such a research environment where so many factors are not controlled are obvious. At play are uncontrolled, varying and often extreme temperatures and humidity, varying levels of initial infestation, different maize grain types, and uncontrolled and varying initial levels of mold/aflatoxin. Despite the
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