PICS hermetic storage bags ineffective in controlling ...

Journal of Stored Products Research xxx (2014) 1e6

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PICS hermetic storage bags ineffective in controlling infestations of Prostephanus truncatus and Dinoderus spp. in traditional cassava chips K. Hell*, K. Edoh Ognakossan, Y. Lamboni International Institute of Tropical Agriculture (IITA), B.P. 08-0932 Tri Postal Cotonou, Benin

a r t i c l e i n f o

a b s t r a c t

Article history: Accepted 6 March 2014

Cassava chips were stored for 8 months in PICS bags, with half of the bags having a natural initial insect infestation, and the other half having this initial natural infestation augmented with 50 Prostephanus truncatus adults. Chips stored in traditional woven polypropylene bags served as controls. Oxygen levels varied during storage from 19.98 to 17.56%, 20.4 to 18.40%, and 20.24 to 19.92%, respectively, in PICS bags with augmented infestation (PICS-A), PICS bags under natural infestation levels (PICS-N) and polypropylene bags (WPP). Carbon dioxide levels varied from 0.73 to 3.90%, 0.65e3.56%, and 0.20e0.61%, respectively, in the three types of bags. P. truncatus populations were significantly higher in PICS-A reaching 98.66 7.21 individuals/kg at the end of storage, compared to 92.66 4.71 in PICS-N and 100.55 3.56 in WPP. Dinoderus spp. density was significantly higher in WPP with 270.55 20.59 individuals/kg after 8 months. The number of holes on chips and weight losses also increased with storage duration in all three treatments, but were significantly higher in WPP. Holes created by insects were noticed in PICS bags and were more important in the inner HDPE (high-density polyethylene) layer than in the outer HDPE layer. Up to 1913.00 114.13 holes were observed on the inner HDPE layer of PICS bags and 1039.00 29.40 in the outer HDPE layer. Hermetic storage bags prolong the storability of chips by approximately 1 month. PICS efficacy was probably affected by the large size of traditional cassava chips with large airspaces between individual chips, leading to a large oxygen store for insects which could not be used up through biotic activity, so that bags were not hermetic. In conclusion, PICS bags cannot be recommended for the storage of large sized traditional cassava chips. Ó 2014 Elsevier Ltd. All rights reserved.

Keywords: Cassava chips Hermetic storage Prostephanus truncatus Dinoderus spp.

1. Introduction Cassava (Manihot esculenta Crantz) is the most important tropical root crop in most parts of Africa and the third most important tropical carbohydrate crop worldwide (http://www.fao.org/ag/agp/ agpc/gcds/). It is primarily grown for its starchy tuberous roots providing more dietary energy per hectare and working hours than any other staple crop (Fregene et al., 2000; Nassar, 2004), but cassava is relatively deficient in protein. Harvested cassava roots need to be processed rapidly to stop spoilage and to reduce the levels of naturally occurring toxins, in particular cyanide compounds. Odoemenem and Otanwa (2011) revealed that about 42% of harvested cassava roots in West and East Africa are processed into dried chips and then milled into flour for consumption or incorporation into divers’ food products. These authors stated that

* Corresponding author. þ229 97077566. E-mail address: [email protected] (K. Hell).

in Africa, dried chips are mainly for human consumption, unlike other countries where they are mainly consumed by animals. Cassava chips are easily infested by insects resulting in high losses. One of the most damaging pests of cassava chips is Prostephanus truncatus Horn (Coleoptera: Bostrichidae) (Larger Grain Borer; LGB) followed by Dinoderus minutus Fabricius (Coleoptera: Bostrichidae) and Tribolium spp. Herbst (Coleoptera: Tenebrionidae) (Schäfer et al., 2000; Hell et al., 2006; Gnonlonfin et al., 2008a). Losses due to P. truncatus increase with storage time and can reach up to 50% for unfermented and 70% of fermented chips after a storage period of only 4 months (Hodges et al., 1985). Losses of 40e50% in stored cassava chips were recorded after 3 months of storage (Hell et al., 2006). In this study, the release of Teretrius nigrescens Lewis (Coleoptera: Histeridae), a predator of P. truncatus, into traditional granaries filled with cassava chips reduced losses by 11%, resulting in a calculated profit of 2.69$/100 kg of chips. Farmers mostly resort to chemical insecticides to reduce post-harvest losses caused by insects (Meikle et al., 1999). The most prevalent insecticides in West African countries are those used to treat insect

http://dx.doi.org/10.1016/j.jspr.2014.03.003 0022-474X/Ó 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Hell, K., et al., PICS hermetic storage bags ineffective in controlling infestations of Prostephanus truncatus and Dinoderus spp. in traditional cassava chips, Journal of Stored Products Research (2014), http://dx.doi.org/10.1016/j.jspr.2014.03.003

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K. Hell et al. / Journal of Stored Products Research xxx (2014) 1e6

pests on cash crops like cotton, cocoa or coffee. Use of these types of insecticides, including their use for the preservation of stored products, exposes populations to health risks which are rarely known and acknowledged by them (Williamson, 2011). One of the non-chemical options for controlling post-harvest quality is triple bagging in hermetically sealed bags, which was first tested for the control of cowpea insects in Cameroon (Murdock et al., 2003) and is now in widespread testing in sub-Saharan Africa as part of the Bill and Melinda Gates PICS Project for storage of cowpea (Baoua et al., 2012a; b). Similar to drum storage, triple bagging is a type of hermetic storage. The principal of hermetic storage is that oxygen levels in a sealed bag decrease with the respiration of the feeding insects, leading to an increase in carbon dioxide and desiccation of the pest (Murdock et al., 2012). Insects will cease to feed, grow, and reproduce in this environment and consequently, populations remain small, inactive and eventually die, resulting in little damage to the stored grains. PICS (Purdue Improved Crop Storage) bags have two inner high-density polyethylene (HDPE) plastic bags of approximately 80 mM thickness and an outer woven polypropylene bag. This technology has been quickly adopted by small-scale farmers and other organizations (Coulibaly et al., 2012) with more than 2.5 million of these bags sold. Presently researchers are testing if the PICS technology can be used to store and protect other commodities such as maize (Hell et al., 2010). In the present study we tested the efficacy of PICS triple bagging for the storage of cassava chips and control of associated cassava pests. 2. Materials and methods 2.1. Purchasing of cassava chips Cassava chips were purchased from two villages, Badjoudé (9 71.440 N, 141.170 E) and Danogou (9 52.380 N, 193.750 E), in the Northern Savanna Zone of Benin. These chips had been stored in traditional clay stores for 3 months prior to purchase. A short questionnaire was administrated to 10 farmers (4 at Badjoudé and 6 at Danogou) to gather information regarding processing and storage practices of cassava chips. Levels of pest infestation, moisture content and losses were evaluated at purchase in 6 replicates on a subsample of cassava chips. 2.2. Trial installation A total of 36 bags (12 woven polypropylene (WPP) bags as control and 24 PICS bags) were filled with 30 kg of cassava chips each and stored from 11th June, 2010 to 20th February, 2011 in a storage room at International Institute of Tropical Agriculture (IITA) e Cotonou, Benin station in the Southern Guinea Savanna (Hell et al., 2000). Half of the PICS bags were augmented with 50 unsexed adults of P. truncatus (PICS-A) and the other half left under natural infestation (PICS-N) in 4 replicates and stored for 8 months; no Dinoderus spp. were added. All bags were placed on pallets in the storage room and tightly sealed (https://ag.purdue.edu/ipia/pics/ documents/4_ghana_english.pdf) and monitored through destructive sampling at 2, 4, 6 and 8 months. 2.3. Moisture content Moisture content was measured according to the ISO 712:1979 routine method. Briefly, from each treatment, a 1 kg sample was milled and three sub-samples were transferred to a metal container, weighed, dried in an oven for 2 h at 130 C and then reweighed. The moisture content was determined with the following formula mc ¼ 100 [(Wi Wd)/Wi], where mc ¼ moisture content, Wi ¼ initial weight and Wd ¼ dry weight.

2.4. Sample monitoring Three sub-samples of 1 kg each were taken at 3 levels in the bag (top, middle and bottom) to constitute a composite sample of a total of 3 kg of chips. The number of holes, number of insects and damage on chips were assessed. The number of holes in the bags was also counted for each layer of the PICS bags. To assess insect populations, sampled chips were mixed and passed through sieves of 4, 2, 1 and 0.85 mm diameter. Damage was assessed with the visual damage scale methods as described by Compton et al. (1993) and Stumpf (1998), where damage is classified on a scale from 1 to 5, with 5 being the worst. 2.5. Storage room temperature and relative humidity Temperature and relative humidity in the storage room were monitored continuously (logged every 30 min) during the trial with a USB-502 data logger (Measurement Computing Corporation of Norton, Massachusetts, USA). 2.6. Gas composition in PICS bag Oxygen (O2) and carbon dioxide (CO2) levels in PICS bags were measured at the beginning of the trial and every 15 days with an O2/CO2 portable analyzer (Pac Check Model 325, Mocon, Minneapolis, MN, USA). The inner HDPE plastic of PICS bags was perforated at 3 levels with the analyzer’s needle and O2/CO2 levels determined; holes were immediately taped after measurement. WPP bags were also perforated with the needle and sealed. Holes made by the analyzers needle were encircled with marker pen to differentiate them from holes made by insects. 2.7. Data analysis Data were analyzed with SPSS version 16.0 (SPSS, 2007) using the General Linear Model (GLM). The number of insects, number of holes were log(x þ 1)-transformed and losses and moisture content arcsin square root (x/100)-transformed to normalize data. Studente NewmaneKeuls (SNK) test was used to separate treatment means. 3. Results 3.1. Information on farming and storage practices of cassava chips The information gathered during the interviews showed that farmers processed cassava chips mostly from a local cassava variety with red petioles (Django also called 14/95, Dr. A. Onzo, IITA-Benin, person. commun.). Chips are produced during the dry season, from December to March, when the harmattan wind1 blows. Chips were made following this diagram. Harvesting / peeling / cutting / sun drying / storage. Chips are sun dried on a bed of grasses in the field for 20e30 days, and usually have a length of 10 cm and width of 5 cm, further information on cassava chip processing can be found in Westby (2002). 3.2. Temperature and relative humidity in the storage room The temperature and relative humidity in the storage room varied between 22.04 C and 30.09 C and 62.16e94.21% (Fig. 1). The lowest weekly temperature was recorded in the 8th week (6e13 August

1 The Harmattan wind is a dry and dusty West African trade wind. It blows south from the Sahara into the Gulf of Guinea between the end of November and the middle of March.



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2010) and the highest in the 36th week (11e18 February 2011). The lowest relative humidity was observed in the 32nd week (14e21 January 2011) and the highest in the 2nd week (17e24 June 2010). 3.3. Moisture content of cassava chips The average moisture content of chips prior to storage was 11.5 0.09% (Fig. 2). Moisture content did not differ between the naturally infested and augmented treatments stored in PICS bags. Moisture content was significantly higher in WPP bags than in PICS bags from 2 months of storage onwards. In PICS-N bags, an increase in moisture content was observed during the first 4 months with no significant differences between treatments and the different storage durations. In PICS-A bags, moisture content of chips differed significantly at 2 months and later in storage. Moisture levels in the WWP bags were significantly higher at 2 months of storage compared to initial levels and after 4 months of storage before stabilizing after 6 months of storage.

Fig. 2. Moisture content of cassava chips stored in PICS bags during 8 months of storage.

3.4. Oxygen and CO2 concentrations in the bags during storage In infested and non-infested PICS bags, O2 concentration decreased slightly during the first 4 months and first 3 months, respectively, reaching values of 17.56% and 18.40% (Fig. 3). Thereafter on oxygen levels increased in both treatments reaching, respectively, 18.69% and 19.12% after 8 months of storage. In the WPP bags, O2 increased during the last 7 months of storage with levels varying between 19.92% and 20.24% (Fig. 3). The CO2 concentration at the beginning of storage was 0.75%, 0.65% and 0.55% respectively in PICS-A, PICS-N and WPP bags (Fig. 4). During the first 3 months of storage, CO2 levels increased, reaching values of 3.90% and 3.56% in PICS-A and PICS-N bags. During the last 5 months of storage, CO2 concentrations decreased to 2.25% in PICS-A bags and to 1.91% in PICS-N bags. In the WPP bags, a slight increase in CO2 concentration was observed during the first 2 months of storage and then a steady decrease. 3.5. Effect of PICS bags on the density of P. truncatus and Dinoderus spp. The density of P. truncatus and Dinoderus spp. increased significantly with storage in all treatments (Figs. 5 and 6). In general, the numbers of P. truncatus were significantly higher in the PICS-A

Fig. 3. O2 concentration in the different storage bags during 8 months of storage measured every 15 days.

Bags, when compared to PICS-N bags during the first 6 months of storage (Fig. 5). The density of Dinoderus spp. was significantly higher in WPP bags, as compared to PICS bags (Fig. 6), with higher population densities observed in PICS bags augmented with P. truncatus than in PICS bags under natural infestation after 4 and 6 months of storage (Fig. 6).

Fig. 1. Temperatures and relative humidity recorded in storage room during the trial.


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the PICS bags (Fig. 7). Comparing both treatments, the number of holes observed in PICS-A bags was significantly higher than those seen in PICS-N bags. 3.7. Damage to cassava chips Damage to cassava chips was assessed by counting the number of holes in the chips. The numbers were significantly higher in WPP bags than in chips stored in PICS bags during the 8 months of storage (Table 1). During the first 6 months of storage significantly higher number of holes were observed in cassava chips infested with P. truncatus as compared to non-infested chips, but at 8 months no differences were observed. Fig. 4. CO2 concentration in the different storage bags during 8 months of storage measured every 15 days.

3.8. Weight losses in cassava chips Weight losses were significantly higher in cassava chips stored in the WPP bags as compared to PICS bags (Table 2) and in chips stored in PICS-A bags compared to PICS-N bags at 4 months of storage, with no significant differences prior to this date. In both treatments, losses increased significantly with storage time. 4. Discussion

Fig. 5. Population development of P. truncatus per kg grains stored for 8 months in different storage bags.

3.6. Holes in PICS bags More holes were observed in the inner HDPE layer, directly exposed to the stored cassava chips, than in the outer HDPE layer of

Fig. 6. Population development of Dinoderus spp. per kg grains stored for 8 months in different storage bags.

The collected data showed that chips stored in PICS bags had a moisture content below 13%, levels considered to be safe for storage and sustaining quality of cassava chips (Gnonlonfin et al., 2008b). The spike in moisture obtained in the WPP bags at 2 months could be related to higher ambient relative humidity observed during the first four weeks of the trial. The rainy season was setting in and since these bags are not airtight this would have directly resulted in an increase in moisture levels. Moisture levels of the stored cassava chips were adequate for insect development and could have affected the chips susceptibility to insect damage. Higher moisture content would lead to softness in chip texture facilitating tunneling by pests. Environmental parameters in the storage room were conducive for the development of P. truncatus, with optimal conditions for the development of this species described at 27 C and 70e80% r.h. (Subramanyam and Hagstrum, 1991) similar to the climatic conditions in the storage room. PICS bags are hermetic storage bags and the basic principle of hermetic storage is the reduction of oxygen levels to levels that suppress or deactivate the capacity of insects, pests, and fungi to

Fig. 7. Number of holes on PICS bags.



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Table 1 Number of holes (mean SE) on cassava chips stored in PICS bags and control during 8 months of storage. Treatments

PICS-N PICS-A WPP

Storage duration 0 month

2 months

4 months

6 months

8 months

3.02 0.68 a 3.02 0.68 a 3.02 0.68 a

3.98 0.04 Aa 4.55 0.13 Ba 14.73 0.61 Cb

21.28 1.15 Ab 27.16 0.46 Bb 41.78 1.61 Cc

71.25 3.01 Ac 92.71 4.22 Bc 129.86 3.29 Cd

144.41 3.64 Ad 150.11 2.58 Ad -a

Means within column (row) followed by the same upper case letter (lower case letter) are not significantly different at P < 0.05 (SNK test). PICS-N e natural infestation; PICS-A e augmented infestation; and WPP e control woven polypropylene bags. a Lost due to rat damage.

reproduce and/or develop (Villers et al., 2010). However, in our trial hermetic storage was probably not achieved, since measured O2 levels of 17% and 4% of CO2. In hermetic storage, insects die when the O2 content in the air is reduced to 3% or less (Moreno et al., 2000), feeding will cease when O2 drops below 4% (Murdock et al., 2012). This was elucidated in studies by Oxley and Wickenden (1963) who determined that stored grain insects will perish if O2 level reach approximately 2%. In this trial oxygen levels in the PICS bags did not drop below 17%. One of the potential factors for the lack of hermetic conditions in the storage bags are the large size of traditional cassava chips with a maximum length of 20 cm and a circumference of 10 cm (K. Hell, personal observation). If cassava chips are poured into bags for storage similar to the farmers’ practices they would not fall in a regular pattern and leave large air spaces which could not be consumed through biotic activity. Cassava chips after drying have little observed biotic activity (Gnonlonfin et al., 2008b), so that the only biotic activity on the chips was from insects and microorganisms probably their activity was not enough to reduce O2 levels to hermetic conditions. Grains and pulse seeds have a higher level of biotic activity so that they will consume higher levels of O2, making these products more favorable to hermetic storage. Probably holes in PICS bags favored leakage of O2 and CO2 during storage and thus there was potential oxygen exchange between the environment and the interior of the bags causing the hermetic storage system to fail. Holes made by post-harvest pests in PICS bags have been reported already in the studies on storage of cowpea in PICS bags in Niger by Baoua et al. (2010) and when storing maize in PICS bags in Benin (Hell et al., 2010). In Niger the number of holes in 100 kg bags varied between 44.8 and 132.8 holes, without specifying the length of storage period (Baoua et al., 2010), in the trials reported here these numbers were far exceeded after already 4 months of storage resulting in less airtight bags. Inspection of PICS bags showed that more holes were found in the inner plastic layers than on the outer layers. This would suggest that insects emigrated from the bag rather than immigrating into them, similar to observations of Baoua et al. (2010). A higher percentage of holes were found in maize in treatments where P. truncatus had been added prior to storage than in maize held under natural insect infestation, naturally number of holes were lower in bags where initial infestation levels were lower. Baoua et al. (2010) and Hell et al. (2010) reported that holes did not seem to have a major impact on efficiency of PICS bags some

of the holes in those trials might have been blocked by grains closing air entry. Maize and cowpea grain are a great deal smaller than cassava chips, so that in the trial reported here blocking of holes would have been rare. Insect behavior should be taken into account when conceiving storage technologies. P. truncatus and Dinoderus spp., the main species attacking cassava chips, belong to the family of Bostrychidea which have a remarkable ability to tunnel through hard materials. An adult of P. truncatus was able to penetrate plastic of 35 mm thickness (Li, 1988). The number of P. truncatus adults observed on the stored chips was less than 50 per kg at 4 months of storage rising to 100 per kg at 8 months of storage. The observed densities were very low when compared to those observed by Chijindu and Boateng (2008) on sundried cassava chips. These authors detected 550 P. truncatus per 300 g of chips after already 69 days; with an initial infestation of thirty adults. Higher number of Dinoderus spp. than P. truncatus were observed on the stored chips in this trial, suggesting that cassava chips are more susceptible to infestation by this species. Borgemeister et al. (1999) observed that Dinoderus bifoveolatus was the predominant insect species in the cassava chips collected from the principal market in Cotonou, Benin. Similarly D. minutus accounted for 74% of all insects sampled on cassava chips collected from farmers’ stores in northern Ghana (Stumpf, 1998). The number of holes in the cassava chips and the losses recorded during the storage period in the trial presented here are the result of the intensity of the insect infestation. Observed weight losses during storage were much lower than levels observed by Hell et al. (2006) with 40e50% after 3 months of storage. Similarly, Hodges et al. (1985) observed mean weight losses (SD) of 73.6 25.9% in fermented roots to 52.3 12.0% in unfermented roots after 4 months of storage, much higher levels than those found in this study. In conclusion, storage of conventional, farmer produced cassava chips in PICS Bags was not successful and losses were beyond acceptable economic levels, even though results showed that storage of cassava chips in PICS bags for periods of less than 4 months might protect against insect damage. When using PICS bags for storage of cassava for periods beyond that, probably the size of the cassava chips did not allow sufficient reduction of O2 in the bags, so that insect growth and reproduction were little affected. One of the potential ways of reducing the airspace between

Table 2 Weight losses (%) (mean SE) in cassava chips stored in PICS bags and control during 8 months of storage. Treatments

Storage duration 0 month

2 months

4 months

6 months

8 months

PICS-N PICS-A WPP

1.11 0.10 a 1.11 0.10 a 1.11 0.10 a

1.48 0.06 Aa 1.68 0.01 Ab 3.03 0.09 Bb

5.29 0.13 Ab 6.57 0.31 Bc 8.31 0.25 Cc

9.92 0.14 Ac 10.28 0.31 Ad 12.50 0.34 Bd

13.45 0.40 Ad 13.83 0.10 Ae 16.55 0.05 Be

Means within column (row) followed by the same upper case letter (lower case letter) are not significantly different at P < 0.05 (SNK test). PICS-N e natural infestation; PICS-A e augmented infestation; and WPP e control woven polypropylene bags.


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individual chips would be to reduce the size of individual chips. Reduction of chip size, with a slicer or chipper would speed up drying, thereby avoiding fermentation and mouldiness (Westby, 2002). Socioeconomic constraints could hinder the acceptance of such a technology, with larger chips being preferred, since farmers and traders sell cassava chips in heaps and not by weight. References Baoua, I.B., Margam, V., Murdock, L.L., 2010. Performance of pics cowpea storage technology in villages in Niger. In: Proceedings of the Fifth World Cowpea Research Conference, 27 September to 1 October 2010, Saly, Senegal. https://ag. purdue.edu/ipia/pics/Documents/Baoua-%20Performance%20of%20PICS% 20Cowpea%20Storage%20Technology%20in%20Villages.pdf. Baoua, I.B., Amadou, L., Margam, V., Murdock, L.L., 2012a. Comparative evaluation of six storage methods for postharvest preservation of cowpea grain. J. Stored Prod. Res. 49, 171e175. Baoua, I.B., Margam, V., Amadou, L., Murdock, L.L., 2012b. Performance of triple bagging hermetic technology for postharvest storage of cowpea grain in Niger. J. Stored Prod. Res. 51, 81e85. Borgemeister, C., Schäfer, K., Goergen, G., Awande, S., Sétamou, M., Poehling, H.M., Scholz, D., 1999. Host-finding behavior of Dinoderus bifoveolatus (Coleoptera: Bostrichidae), an important pest of stored cassava: the role of plant volatiles and odors of conspecifics. Ann. Entomol. Soc. Am. 92, 766e771. Chijindu, E.N., Boateng, B.A., 2008. Effects of nutritional content of processed cassava chips on development of Prostephanus truncatus (Horn). World J. Agric. Sci. 4, 404e408. Compton, J.A.F., Wright, M.A.P., Gay, C., Stabrawa, A., 1993. A Rapid Method for Lossassessment in Stored Maize and Dried Cassava. NRI Report R5103, Chatham, UK. Coulibaly, J.Y., Nouhoheflin, T., Aitchedji, C., Damisa, M., D’Alessandro, S., Baributsa, D., Lowenberg-DeBoer, J., 2012. Purdue Improved Cowpea Storage (PICS) Supply Chain StudyPurdue University, Department of Agricultural Economics. Working Papers. http://ageconsearch.umn.edu/handle/138675. Fregene, M., Bernal, A., Doque, M., Dixon, A., Tohme, J., 2000. AFLP analysis of African cassava (Manihot esculenta Crantz) germplasm resistant to cassava mosaic disease (CMD). Theor. Appl. Genet. 100, 678e685. Gnonlonfin, G.J.B., Hell, K., Siame, A.B., Fandohan, P., 2008a. Infestation and population dynamics of insects on stored cassava and Yams chips in Benin, west africa. J. Econ. Entomol. 101, 1967e1973. Gnonlonfin, G.J.B., Hell, K., Fandohan, P., Siame, A.B., 2008b. Mycoflora and natural occurrence of aflatoxins and fumonisin B1 in cassava and yam chips from Benin. West Afr. Int. J. Food Microbiol. 122, 140e144. Hell, K., Cardwell, K.F., Setamou, M., Schulthess, F., 2000. Influence of insect infestation on aflatoxin contamination of stored maize in four agroecological regions in Benin. Afr. J. Entomol. 8, 169e177. Hell, K., Lamboni, Y., Houndekon, T., Guirguissou, M.A., 2006. Augmented release of Teretruis nigrescens Lewis (Coleoptera: Histeridae) for the control of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) in stored cassava chips. J. Stored Prod. Res. 42, 367e376. Hell, K., Edoh Ognakossan, K., Tounou, A.K., Lamboni, Y., Adabe, K.E., Coulibaly, O., 2010. Maize stored pests control by pics-bags: technological and economic evaluation. In: Proceedings of the Fifth World Cowpea Research Conference, 27

September to 1 October 2010, Saly, Senegal. https://ag.purdue.edu/ipia/pics/ documents/presentation-%20hell%20-wcc%202010-%2029%20sept.pdf. Hodges, R.J., Meik, J., Denton, H., 1985. Infestation of dried cassava (Manihot esculenta Grantz) by Prostephanus truncatus (Col.: Bostrichidae). J. Stored Prod. Res. 21, 73e77. Li, L., 1988. Behavioural Ecology and Life History Evolution in the Larger Grain Borer Prostephanus truncatus (Horn). PhD thesisUniversity of Reading, Reading, UK, p. 229. Meikle, W.G., Degbey, P., Oussou, R., Holst, N., Nansen, C., Markham, R.H., 1999. Pesticide use in grain stores: an evaluation based on survey data from Benin. PhAction News 1, 5e9. Moreno, M.E., Jimenez, A.S., Vazquez, M.E., 2000. Effect of Sitophilus zeamais and Aspergillus chevalieri on the oxygen level in maize stored hermetically. J. Stored Prod. Res. 36, 25e36. Murdock, L.L., Seck, D., Ntoukam, G., Kitch, L., Shade, R.E., 2003. Preservation of cowpea grain in sub-Saharan Africa e bean/cowpea CRSP contributions. Field Crops Res. 82, 169e178. Murdock, L.L., Margam, V., Baoua, I.B., Balfe, S., Shade, R.E., 2012. Death by desiccation: effects of hermetic storage on cowpea bruchids. J. Stored Prod. Res. 49, 166e170. Nassar, N.M.A., 2004. Cassava: some ecological and physiological aspects related to plant breeding. Gene Conserve 3, 229e245. http://ww2.geneconserve.pro.br/ artigo024.pdf. Odoemenem, I.U., Otanwa, L.B., 2011. Economic analysis of cassava production in Benue state, Nigeria. Curr. Res. J. Soc. Sci. 3, 406e411. Oxley, T.A., Wickenden, G., 1963. The effect of restricted air supply in some insects which infest grain. Ann. Appl. Biol. 51, 313e324. Schäfer, K., Goergen, G., Borgemeister, C., 2000. An illustrated identification key to four different species of adult Dinoderus (Coleoptera: Bostrichidae), commonly attacking dried cassava chips in West Africa. J. Stored Prod. Res. 36, 245e252. Stumpf, E., 1998. Post-harvest loss due to pests in dried cassava chips and comparative methods for its assessment. In: Case Study Small-scale Farm Households Ghana. GTZ, p. 172. http://www.fao.org/wairdocs/x5426E/ x5426E00.htm. Subramanyam, B., Hagstrum, D.W., 1991. Quantitative analysis of temperature, relative-humidity, and diet influencing development of the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera, Bostrichidae). Trop. Pest Manag. 37, 195e202. Villers, P., Navarro, S., De Bruin, T., 2010. New applications of hermetic storage for grain storage and transport. In: Navarro, S., Riudavets, J. (Eds.), Fumigation, Modified Atmospheres and Hermetic Storage, Proceedings of the 10th International Working Conference on Stored Product Protection, 27 June to 2 July 2010, Estoril, Portugal, Julius-Kühn-Archiv, vol. 425. Bundesforschungsinstitut für Kulturpflanzen, Berlin, pp. 446e452, 1077 pp. Westby, A., 2002. Cassava utilization, storage and small-scale processing. In: Hillocks, R.J., Thresh, J.M., Bellotti, A.C. (Eds.), Cassava, Biology, Production and Utilization. CAB International, Wallingford, UK, pp. 281e300. Williamson, S., 2011. Understanding the full costs of pesticides: experience from the field, with a focus on Africa. In: Stoytcheva, Margarita (Ed.), Pesticides e The Impacts of Pesticides Exposure. InTech, ISBN 978-953-307-531-0. Available from: http://www.intechopen.com/books/pesticides-the-impacts-ofpesticides-exposure/understanding-the-full-costs-of-pesticides-experiencefrom-the-field-with-a-focus-on-africa.
