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Diversity and community structure of insect pests developing in stored sorghum in the Northern-Sudan ecological zone of Burkina Faso
Journal of Stored Products Research 63 (2015) 6e14
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Diversity and community structure of insect pests developing in stored sorghum in the Northern-Sudan ecological zone of Burkina Faso -Binso a, A. Sanon a, c A. Waongo a, c, *, N.M. Ba a, b, L.C. Dabire Laboratoire Central d'Entomologie Agricole de Kamboins e, Institut de l'Environnement et de Recherches Agricoles (INERA), Burkina Faso International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Niger c Laboratoire d'Entomologie Fondamentale et Appliqu ee, UFR/SVT, Universit e de Ouagadougou, Burkina Faso a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 February 2015 Received in revised form 16 April 2015 Accepted 5 May 2015 Available online xxx
Stored insect pests often create major problems for farmers worldwide. Comprehensive data of insect pests of stored sorghum in Burkina Faso are scarce. Understanding the population structure of insect fauna infesting stored sorghum is important for development of management strategy. Sorghum panicles were collected from January to September 2011 in farmers' granaries in the Northern-Sudanian ecological zone of Burkina Faso to determine the diversity of insect pests and their importance in post-harvest losses. A total of 14 species of insect pests were recorded, including twelve coleopteran and two lepidopteran species. Species diversity peaked between May and September. The highest insect diversity was recorded in sorghum stored in straw granaries and on red coloured grains when compared with that of sorghum stored in mud granaries and on white coloured grains. Rhyzopertha dominica (Fabricius) appears to be the primary insect pest followed by secondary pests including Oryzaephilus mercator (Fauvel), Cryptolestes ferrugineus (Stephens) and Sitophilus zeamais (Motschulsky). The distribution pattern of the pests in granaries corresponds to the Mandelbrot model in which colonization of species in an environment depends on the physical conditions of that environment and on the species currently present, which suggest a progressive colonization occurs in waves with stocks of grain. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Insect pests Population structure Sorghum Species richness
1. Introduction Sorghum, Sorghum bicolor (L.) Moench, is one of the most important cereals in the semi-arid tropics providing a major source of dietary energy and protein for nearly a billion people living in semi-arid areas (Belton and Taylor, 2004; Rooney, 2004). In Burkina Faso, sorghum serves as the major staple food crop in terms of production (1,923,805 tons) and acreage (1,788,695 ha; DGPSA, 2013); the country is the third largest African producer of sorghum (FAOSTAT, 2012). Many sub-Saharan Africa (SSA) countries, including Burkina Faso, suffer from chronic food deficits that are caused by several factors such as the persistently low productivity of staple crops.
* Corresponding author. Laboratoire Central d'Entomologie Agricole de , Institut de l'Environnement et de Recherches Agricoles (INERA), BurKamboinse kina Faso, 01 BP 476 Ouagadougou 01, Kadiogo, Burkina Faso. E-mail address: [email protected] (A. Waongo). http://dx.doi.org/10.1016/j.jspr.2015.05.002 0022-474X/© 2015 Elsevier Ltd. All rights reserved.
Post-harvest loss (PHL) is an often-forgotten factor that also contributes to chronic food deficits. A joint report of the World Bank, Natural Resources Institute in the United Kingdom and Food and Agriculture Organization of the United Nations states the value of PHL for grains in SSA could potentially reach nearly US$4 billion yr1 out of an estimated US$27 billion yr1 of value in grain production (Anonymous, 2011). Storage insect pests cause much of this PHL for grains. Insect pests can not only directly cause grain weight loss for stored sorghum but can also alter the physicochemical properties of the grain (Park et al., 2008). Insects that develop within storage facilities for grains may also favour the development of poisonous aflatoxins produced by the fungus Aspergillus flavus (Lamboni and Hell, 2009). Comprehensive data related to insect pests infesting high value stored commodities, such as cassava, maize and cowpea, are available (Caswell, 1961; Ratnadass and Sauphanor, 1989; Nukenine, 2010); however, to date very little work has been conducted on the insect fauna of stored sorghum (Ratnadass et al.,
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1994; FAO, 1998). Thus, in 2009, an inventory of insect pests affecting stored sorghum in the South-Sudanian ecological zone within Burkina Faso led to the identification of nine species of Coleoptera and Lepidoptera in the storage facilities (Waongo et al., 2013). The present article reports on the population structure of insect fauna infesting stored sorghum in the North-Sudanian ecological zone of Burkina Faso. The objectives were to: (1) determine the temporal variability and diversity of insect pest communities within on-farm stored sorghum (2) identify the effects of sorghum grain colour on the abundance and diversity of insect pest species and (3) determine the effects of various types of storage structures on insect pest fauna.
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October) to 76% (July to September; Fig. 2). 2.2. Sampling of villages and producers
2. Methods
Within each province, local agricultural services aided researchers in compiling a list of all villages with high sorghum production during the 2010 cropping season. Those villages were likely to have sufficient stocks of sorghum to cover the sampling period. From that list, five villages were randomly selected in each of the four provinces covered by the study. In each of these villages focus group discussions were carried out with sorghum farmers; this allowed the selection of three farmers in each village with the highest stocks of grain who all voluntarily participated in the study. A total of 20 villages and 60 granaries were selected for analysis in this study.
2.1. Study area
2.3. Storage of sorghum grain
This study was conducted from January to September 2011 in ga, Ganzourgou Boulkiemde and Kourwe ogo provinces, BurBaze kina Faso, all located in the North-Sudanian ecological zone (Fig. 1). Burkina Faso experiences a unimodal rainfall pattern, with a rainy season lasting from June to October. The four provinces received 675 mme700 mm of rainfall in 2011. During the sampling period, mean temperatures ranged from 24.6 C to 34.1 C across the study area while the average relative humidity varied from 25% (June and
Farmers usually harvest sorghum in late October in this part of Burkina Faso, and store it in granaries in November; consumption of the grain is expected to last until the next harvest. However, following poor growing seasons the stocks are often depleted before the following harvest. In the selected villages, sorghum was stored as panicles in two types of structures and our sample included both types: 20 mud granaries with straw roofs and 40 woven straw granaries. We identified two types of sorghum based
Fig. 1. Map of Burkina Faso showing the four provinces and locations.
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Fig. 2. Average monthly temperature and average relative humidity of the study area from January to September 2011.
on grains colour; our sample included red and white coloured sorghum grains from 38 to 22 granaries, respectively. All selected granaries were free of any pesticide application (synthetic or plant insecticide). 2.4. Sampling of sorghum panicles and collection of insects Four panicles of sorghum were randomly sampled every eight weeks from January to September 2011 in each of the 60 granaries in the 20 villages. The panicles were placed in cloth bags and any infestation of insect fauna was determined after sieving samples through a 3 mm mesh sieve in the laboratory. The collected insects were placed into plastic vials containing 70% ethanol. The panicles were then placed in 3-L glass jars until adult insects emerged from the hidden immature stages of insects. The panicles were kept in the lab for eight weeks under average temperature of 29 C ± 3 and relative humidity of 49% ± 19 and samples were sieved weekly to collect emerging adults (Park et al., 2008; Waongo et al., 2013). Emerging insects were identified to the species level using the morphological criteria described by Weidner and Rack (1984), Bousquet (1990), Delobel and Tran (1993), Farrell and Haines (2002) and Koehler et al. (2006). 2.5. Statistical analysis Data on the number of insects per species were log transformed using the formula log10 (x þ 1), where x is the number of individuals observed (Chijindu et al., 2008; Herve, 2011). The “Chao and Boot” and the Jacknife 1 indices were used to estimate species composition and abundance (Longino, 1994). Both indices assess the expected species richness. In addition, taxonomic richness (mean number of taxa per habitat) was calculated using the Shannon diversity Index (H0 ) to estimate the degree of organization of the insect population. A greater value indicates a more diverse insect population (Dajoz, 2000); H0 was calculated using Equation (1): 0
H ¼
s X ðPi log2 Pi Þ;
(1)
i¼1
where Pi is the proportion of each species in the stand and S is the
total number of species. The Pielou Equitability Index (E), which reflects the quality of the organization of the insect population (Dajoz, 2000; Magurran, 2004), is close to 1 when all species tend to have the same abundance, and close to 0 when one or a few species dominate the insect population. E was calculated using Equation (2):
E¼
H0 ; log2 ðSÞ
(2)
where H0 is the Shannon diversity Index calculated above and S is species number. Finally, an Index of Occurrence (IC) was calculated to assess temporal variations in species prevalence (rare to common; Dajoz, 2000). This index categorized the species into three types: constant, secondary and accidental pest species (found in more than 50%, 25e50%, or less than 25% of all samples, respectively) and was calculated using Equation (3):
IC ¼
ni 100 N
(3)
where N is the total number of samples and ni is the number of samples containing species i. All statistical analyses were performed with the software R version 2.15.1 using the ade4 (Dray and Dufour, 2007), vegan (Oksanen et al., 2012), gclus (Hurley, 2012), cluster (Maechler et al., 2012), rcolorbrewer (Neuwirth, 2011), labdsv (Roberts, 2012), mvpart (De'ath, 2012) and BiodiversityR (Kindt and Coe, 2005) software packages. After testing for normality using the ShapiroeWilk Test, analysis of variance was performed for species abundance, richness, equitability and diversity. Separation of means by either grain colour or type of granary or sampling period was performed using the ManneWhitneyeWilcoxon Test or the KruskaleWallis Test, respectively. A 5% significance level was used for all tests. A Hierarchical Classification Analysis (HCA) was used to classify pest species according to their occurrence. The HCA focused on the matrix-based presence or absence of pests in different localities using the Euclidean distance and Ward's method. The “fusion level” method was used to choose the optimal number of groups (Borcard et al., 2011).
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A model of insect abundance and distribution was tested using a rankefrequency diagram. The Akaike Information Criterion (AIC) value was computed using different models (Null, Preemption, logNormal, Zipf and Mandelbrot models; Sakamoto et al., 1986). The model with the lowest AIC value is the most representative of the pattern of insect pest distribution (Sakamoto et al., 1986).
diversity (c2 ¼ 67.9418, df ¼ 4, P 0.001; Fig. 5). However, the E index did not differ significantly (c2 ¼ 11.9985, df ¼ 4, P > 0.05) over time (Fig. 5).
3. Results
Insect pest species were significantly abundant (W ¼ 7151.5, P ¼ 0.046), rich (W ¼ 7028.5, P ¼ 0.024) and diverse (W ¼ 6953.5, P ¼ 0.019) on red coloured sorghum grains (Fig. 6). However the colour of sorghum grain did not significantly affect species homogeneity (W ¼ 7574, P ¼ 0.181; Fig. 6). Insect pest species richness (W ¼ 6379, P ¼ 0.003), diversity (W ¼ 0.9125, P 0.001), and homogeneity (W ¼ 6835, P ¼ 0.033) were significantly higher on sorghum grains stored in straw granaries than those in mud granaries (Fig. 7). However, the type of granary did not significantly affect species abundance (W ¼ 7297, P ¼ 0.1744; Fig. 7).
3.1. Species diversity Fourteen species from ten coleopteran and lepidopteran families were recorded on the stored sorghum; the percentage of individuals representing a single species compared with the total number of individuals collected ranged from 0.19% to 39.53% (Table 1). The three Dermestidae and the 12 coleopteran species found in the grain made them the most diverse family and order, respectively (Table 1). The Family Gelechiidae dominated the Order Lepidoptera (Table 1). The Bostrichidae and Silvanidae were the most important families and the Nitidulidae and Bruchidae the least important. 3.2. Analysis of the sampling effort The rarefaction curve, based on the accumulated data in the study area, showed a richness of 14 species (Fig. 3). Indeed, both the Jacknife 1 and “Chao and Boot” indices give 14 as the expected species richness. This indicates that the probable number of species that could be expected to be identified in these areas was achieved. 3.3. Occurrence index and temporal fluctuations in insect pest communities The occurrence index of the different pest species increased over the storage period from January to the late season storage period in September (Fig. 4). In January, Rhyzopertha dominica was the only constant pest species, and the only secondary pest species was Oryzaephilus mercator while other pests were accidental (Fig. 4). In September, in addition to R. dominica, O. mercator became a constant pest species, while Cryptolestes ferrugineus and Sitophilus zeamais became accidental pest species. Two coleopteran species, R. dominica and O. mercator, had the highest occurrence indices for both observation periods. S. cerellela had the highest occurrence index for the lepidopteran species (Fig. 4). From May to September, insect pest species significantly increased in terms of abundance (c2 ¼ 97.6669, df ¼ 4, P 0.001), species richness (c2 ¼ 76.6125, df ¼ 4, P 0.001) and species
3.4. Effects of grain colour and storage type on insect pest communities
3.5. Community structure of pest insects in sorghum storage The storage pests were split into two groups based on a hierarchical classification (Fig. 8). The first group included four coleopteran species. The second group include ten coleopteran and lepidopteran species (Fig. 8). When the five distribution models, were run the lowest AIC value was recorded from the Mandelbrot model; this model is the most representative of the distribution of insect pests infesting stored sorghum (Fig. 9). 4. Discussion In the part of Burkina Faso that lies within the North-Sudanian ecological zone, 14 species of Coleoptera and Lepidoptera colonized stored sorghum and developed over the normal storage period. Species richness was higher in this zone than the 6e12 species previously reported in other locations in Africa (Ratnadass, 1990; Lavigne, 1991; Tamgno and Ngamo, 2013; Waongo et al., 2013). Apart from location specificity, differences may be the result of sampling intensity or methods that were used in the present study. The results reported by previous authors (Tamgno and Ngamo, 2013; Waongo et al., 2013) included only one to a maximum of 40 samples collected only once to over a maximum period of four months, whereas our study covered ten months of data with 300 samples. Moreover, our study included a much higher number of locations when compared with that of Ratnadass et al. (1994). This is accordance with previous findings highlighting
Table 1 Overview of common insect pests and their abundance in sorghum stocks in Burkina. Order
Family
Proportion of families (%)
Species
Proportion of individuals (%)
Coleoptera
Bostrichidae
40,60
Silvanidae Cucujidae Tenebrionidae
23,79 9,25 7,43
Curculionidae Dermestidae
6,74 3,99
Nitidulidae Bruchidae Gelechiidae Pyralidae
0,50 0,27 6,09 1,34
Rhyzopertha dominica (Fabricius) Prostephanus truncatus (Horn) Oryzaephilus mercator (Fauvel) Cryptolestes ferrugineus (Stephens) Tribolium castaneum (Herbst) Tribolium confusum (Jacquelin du Val) Sitophilus zeamais (Motschulsky) Attagenus fasciatus (Thunberg) ) Anthrenus verbasci (Linne Trogoderma granarium (Everts) Carpophilus dimidiatus (Fabricius) Callosobruchus maculatus (Fabricius) Sitotroga cerealella (Olivier) Corcyra cephalonica (Stainton)
39,53 1,07 23,79 9,25 3,60 3,83 6,74 1,20 0,19 2,60 0,50 0,27 6,09 1,34
Lepidoptera
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Fig. 3. Total stored sorghum insect pests species richness in North-Sudanian Burkina Faso.
Fig. 4. Occurrence index of stored sorghum insect pests at the beginning and end of storage season in North-Sudanian Burkina Faso.
that longer sampling duration, and greater number of samples led to higher likelihood of recording more insect species (Fargo et al., 1989; Elmouttie et al., 2010). When the structure and the organization of the insect populations found in the present study was analysed, two groups were distinguished: i) the minor pests which included ten species, and ii) the group of most abundant species including R. dominica, O. mercator, S. zeamais and C. ferrugineus. Three species found here, R. dominica, S. zeamais and O. mercator occur worldwide and have been described as major pests of stored grains (Loschiavo and Smith, 1970; Hoppe, 1986; Jood et al., 1996; Belda and Riudavets, 2010; Carvalho et al., 2013). R. dominica, the most frequent and most abundant species on stored sorghum in Burkina Faso, is also a primary insect pest of stored sorghum and has been identified as such in several regions across Africa (Seifelnasr, 1992; Ratnadass et al., 1994; Mvumi et al., 2002). O. mercator and C. ferrugineus ranked 2nd and 3rd in abundance, respectively; and over the season, their occurrence index increased when the occurrence index of R. dominica increased. This suggests that R. dominica promotes the establishment of O. mercator and C. ferrugineus in stored sorghum
stock. This is typical of secondary pests (Delobel and Tran, 1993; Mukherjee and Nandi, 1993; Nansen et al., 2009). The ability of a secondary pest to become established in stocks depends on damage caused by primary pests that attack the seed coat, enabling the secondary pests to get inside the grain. The Mandelbrot distribution model of the pest community supports the hypothesis that the colonization of stocks occurs in successive waves and is highlighted in this study. According to Mandelbrot distribution theory (Bastow, 1991), the colonization of a given habitat by a species of the population is based on the earlier presence of another species (pioneer species) and the conditions created by that species. Pioneer species such as R. dominica are therefore primary pests because of the severity of the damage they cause, which leads to the establishment of secondary pests such as O. mercator and C. ferrugineus. This successive colonization of stocks could explain the significant increase in the diversity parameters (abundance, species richness and Shannon index) and could be explained by the homogeneity of the environment from the beginning (January) to the end of the study period (September). Indeed, according to Nansen et al. (2009), when a silo filled of grain is compared with other habitats, natural
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Fig. 5. Temporal variation in stored sorghum insect pests species abundance, richness, diversity and equitability from January to September 2011 in North-Sudanian Burkina Faso. (For each month, means were compared by a KruskaleWallis test at the 5% level, with different alphabetic letters indicating significant differences).
Fig. 6. Insect pest species abundance, richness, equitability and diversity of red and white coloured stored sorghum grains in North-Sudanian Burkina Faso. (For each type of grains, means were compared by a Mann-Whitney-Wilcoxon test at the 5% level, with different alphabetic letters indicating significant differences).
or artificial, a silo constitutes an isolated and homogeneous habitat in which the availability of food for many pest insects is essentially unlimited. In addition to the successive colonization of stocks by different insect pests, the climatic conditions could explain the significant increase in diversity we observed from May until the end of the study period in September. May and September are respectively preceded by a peak of temperature in April (34.1 C) and a relative peak of humidity in August (76%). According to several authors temperature and relative humidity are the most important factors in the developmental cycle of an insect (Fields, 1992; Delobel and Tran, 1993; Ouedraogo et al., 1996; Throne and Weaver, 2013).
The variety of sorghum used influenced the diversity of insect pests infesting farmers' granaries. Thus the red coloured variety of sorghum grain attracted a significantly higher number of insect species than white coloured grains. Several authors have reported on the varietal preferences of insect pests on stored sorghum ndez (Krishnamurthy et al., 1978; Adetunji, 1988; Chuck-Herna et al., 2013; Shehzad et al., 2014). The physical properties and chemical composition of the grain may cause these preferences (Russell, 1966; Ratnadass et al., 1994; Chandrashekar and Satyanarayana, 2006; Ramputh et al., 1999). Barro-Kondombo et al. (2008) reported that the red coloured sorghum grain are generally soft. In Mali, Ratnadass et al. (1994) also reported that
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Fig. 7. Insect pest species abundance, richness, equitability and diversity of sorghum grains stored in straw granaries and mud granaries in North-Sudanian Burkina Faso. (For each storage structure, means were compared by a Mann-Whitney-Wilcoxon test at the 5% level, with different alphabetic letters indicating significant differences).
Fig. 8. Hierarchical classification of stored sorghum insect pests in Burkina Faso.
sorghum cultivars with soft grains were more susceptible to insect damage than cultivars with hard grain. The hardness of grains and resistance to stored insect pests was reported for different commodities (Arnason et al., 1994; Odeyemi and Daramola, 2000; Nawrot et al., 2006). In addition to the effect of sorghum variety, several researchers have shown that the type of storage structure used to store grain
also influenced insect diversity (Shazali et al., 1996; Shazali and Ahmed, 1998). In the present study, the number of insect species recorded on sorghum grains stored in woven straw granaries was higher than that stored in mud granaries. Compared with mud granaries, which are a confined environment, woven straw allows airflow. The continuous renewal of ambient air in woven straw may have led to the more rapid development of insect pests. In addition,
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Fig. 9. Adjustment the sorghum insect pest distribution to a few models of distribution.
the woven straw creates passages for insects to make their way into the structure. Controlling the infestations of grains by pioneer pest species is critical to the prosper storage of sorghum. Therefore, particular emphasis must be placed on the management of R. dominica, O. mercator and C. ferrugineus for sustainable and effective conservation of sorghum stocks in Burkina Faso. Acknowledgements This study was supported by a PhD research grant from the re des Enseignements Secondaire et Supe rieur of Burkina Ministe Faso and also by the Project CORUS-6072 contract funded by the re de la cooperation Française. We are also thankful to Ministe farmers who graciously gave their sorghum for the experiments and to our collaborators. References Adetunji, J.F., 1988. A study of the resistance of some sorghum seed cultivars to Sitophilus oryzae (L.) (Coleoptera: Curculionidae). J. Stored Prod. Res. 24 (2), 67e71. Anonymous, 2011. Missing Food: the Postharvest Grain Losses in Sub-saharan Africa. The World Bank, NRI and FAO. Arnason, J.T., Conilh de Beyssac, B., Philogene, B.J.R., Bergvinson, D., Serratos, J.A., Mihm, J.A., 1994. Mechanisms of resistance in maize grain to the maize weevil and the larger grain borer. In: Insect Resistant Maize Recent Advances and Utilization, Proceedings of an International Symposium Held at the International Maize and Wheat Improvement Center, pp. 91e95. Barro-Kondombo, C.P., Vom Brocke, K., Chantereau, J., Sagnard, F., Zongo, J.-D., 2008. phe notypique des sorghos locaux de deux re gions du Burkina Faso: Variabilite la Boucle du Mouhoun et le Centre-Ouest. Cah. Agric. 17 (2), 107e113. Bastow, J.W., 1991. Methods for fitting dominance/diversity curves. J. Veg. Sci. 2, 35e46. Belda, C., Riudavets, J., 2010. Distribution of insect pests and their natural enemies in a barley pile. In: Carvalho, M.O., Fields, P.G., Adler, C.S., Arthur, F.H., et al. (Eds.), Proceedings of the 10th International Working Conference on Stored Product Protection, 27 Junee2 July 2010, Estoril, Portugal, pp. 741e745. Belton, P.S., Taylor, J.R.N., 2004. Sorghum and millets: protein sources for Africa. Trends Food Sci. Technol. 15, 94e98. Borcard, D., Gillet, F., Legendre, P., 2011. Numerical Ecology in R. Springer, New York, p. 306. Bousquet, Y., 1990. Beetles Associated with Stored Products in Canada. Annual Agricultural Canadian Publication. 1837, 224pp. Carvalho, M.O., Faro, A., Subramanyam, B., 2013. Insect population distribution and
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Lamboni, Y., Hell, K., 2009. Propagation of mycotoxigenic fungi in maize stores by post-harvest insects. Int. J. Trop. Insect Sci. 29 (1), 31e39. Lavigne, R.J., 1991. Stored grain insects in underground storage pits in Somalia and their control. Insect Sci. Appl. 12 (5e6), 571e578. Longino, J., 1994. How to measure arthropod diversity in a tropical rainforest. Biol. Int. 28, 3e13. Loschiavo, S.R., Smith, L.B., 1970. Distribution of the merchant grain beetle, Oryzaephilus mercator (Silvanidae: Coleoptera) in Canada. Can. Entomol. 102 (08), 1041e1047. Maechler, M., Rousseeuw, P., Struyf, A., Hubert, M., Hornik, K., 2012. Cluster: Cluster Analysis Basics and Extensions. R Package Version 1.14.2. Magurran, A.E., 2004. Measuring Biological Diversity. Blackwell Publishing, Malden, Oxford and Victoria, p. 256. Mukherjee, P.S., Nandi, B., 1993. Insectefungus associations influencing seed deterioration in storage. J. Mycopathol. Res. 31, 87e92. Mvumi, B.M., Golob, P., Stathers, T.E., Giga, D.P., 2002. Insect population dynamics and grain damage in small-farm stores in Zimbabwe, with particular reference to Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae). In: Credland, P.F., Armitage, D.M., Bell, C.H., Cogan, P.M., Highley, E. (Eds.), Proceedings of the 8th International Working Conference on Stored Product Protection, pp. 151e168. York, UK. Nansen, C., Flinn, P., Hagstrum, D., Toews, M.l.D., Meikle, W.G., 2009. Interspecific associations among stored-grain beetles. J. Stored Prod. Res. 45, 254e260. Nawrot, J., Warchalewski, J.R., Piasecka-Kwiatkowska, D., Niewiada, A., Gawlak, M., Grundas, S.T., Fornal, J., 2006. The effect of some biochemical and technological properties of wheat grain on granary weevil (Sitophilus granarius L.) (Coleoptera: Curculionidae) development. In: Proceedings of the 9th International Working Conference on Stored Product Protection, 15 to 18 October 2006, ~o Paulo, Brazil. Brazilian Post-harvest Association e ABRAPOS, Campinas, Sa Passo Fundo, RS, Brazil, pp. 400e407 (ISBN 8560234004). Neuwirth, E., 2011. RColorBrewer: ColorBrewer Palettes. R Package Version 1.0-5. http://CRAN.R-project.org/package¼RColorBrewer. Nukenine, E.N., 2010. Stored product protection in Africa: past, present and future. In: Carvalho, M.O., Fields, P.G., Adler, C.S., Arthur, F.H., et al. (Eds.), Proceedings of the 10th International Working Conference on Stored Product Protection, 27 Junee2 July 2010, Estoril, Portugal, pp. 26e41. Odeyemi, O.O., Daramola, A.M., 2000. Storage Practices in the Tropics: Food Storage and Pest Problems, , First ed.vol. 1. Dave Collins Publication, Nigeria, p. 235. Oksanen, J., Blanchet, G.F., Kindt, R., Legendre, P., Minchin, P.R., O'Hara, R.B., Simpson, G.L., Solymos, P., Stevens, M.H.H., Wagner, H., 2012. Vegan: Community Ecology Package. R Package Version 2.0-4. http://CRAN.R-project.org/ package¼vegan. Ouedraogo, A.P., Sou, S., Sanon, A., Monge, J.P., Huignard, J., Tran, M.D., Credland, P.F., 1996. Influence of temperature and humidity on populations of Callosobruchus maculatus (Coleoptera: Bruchidae) and its parasitoid Dinarmus basalis (Pteromalidae) in two zones of Burkina Faso. Bull. Entomol. Res. 86, 695e702. Park, S.H., Arthur, F.H., Bean, S.R., Schober, T.J., 2008. Impact of differing population
levels of Rhyzopertha dominica (F.) on milling and physicochemical properties of sorghum kernel and flour. J. Stored Prod. Res. 44, 322e327. Ramputh, A., Teshome, A., Bergvinson, D.J., Nozzolillo, C., Arnason, J.T., 1999. Soluble phenolic content as an indicator of sorghum grain resistance to Sitophilus oryzae (Coleoptera: Curculionidae). J. Stored Prod. Res. 35, 57e64. Ratnadass, A., Berte, S., Diarra, D., Cisse, B., 1994. Insect losses on sorghum stored in selected Malian villages, with particular emphasis on varietal differences in grain resistance. In: Highley, E., Wright, E.J., Banks, H.J., Champ, B.R. (Eds.), Proceeding of the 6th International Working Conference on Stored Product Protection, vol. 2, pp. 953e959. Canberra, Australia. Ratnadass, A., 1990. Losses caused by insects in stored sorghum in the villages of and Ouham (Central African Republic). Agron. Trop. 45 (1), Ouham-Pende 31e41. Ratnadass, A., Sauphanor, B., 1989. Les pertes dues aux insectes sur les stocks re ales en Co ^ te d'ivoire. Cereales en regions chaudes AUPELF-UREF, paysans de ce EdsJohnLibheyEurotext, pp. 47e56. Roberts, D.W., 2012. Labdsv: Ordination and Multivariate Analysis for Ecology. R Package Version 1.5-0. http://CRAN.R-project.org/package¼labdsv. Rooney, L.W., 2004. Sorghum improvement-Integrating traditional and new technology to produce improved genotypes. Adv. Agron. 83, 37e109. Russell, M.P., 1966. Effects of four sorghum varieties on the longevity of the lesser rice weevil, Sitophilus oryzae (L.). J. Stored Prod. Res. 2 (1), 75e79. Sakamoto, Y., Ishiguro, M., Kitagawa, G., 1986. Akaike Information Criterion Statistics. D. Reidel Publishing Company. Seifelnasr, Y.E., 1992. Stored grain insects found in sorghum stored in the central production belt of Sudan and losses caused. Trop. Sci. 32 (3), 223e230. Shazali, M.E.H., Ahmed, M.A., 1998. Assessment and reduction of losses in sorghum stored in traditional mud bins in Sudan. Trop. Sci. 38, 155e160. Shazali, M.E.H., El Hadi, A.R., Khalifa, A.M., 1996. Storability of Sorghum grain in traditional and improved matmoras (storage pits) in Sudan. Trop. Sci. 36, 182e192. Shehzad, H., Munir, A., Muhammad, A., 2014. Assessment of Sitotroga cerealella losses in different sorghum varieties under controlled conditions. Arch. Phytopathol. Plant Prot. 47 (8), 993e999. Tamgno, B.R., Ngamo, T.S.L., 2013. Diversity of stored grain insect pests in the Logone Valley, from northern Cameroon to Western Chad Republic in Central Africa. J. Agric. Sci. Technol. A3, 724e731. Throne, J.E., Weaver, D.K., 2013. Impact of temperature and relative humidity on life history parameters of adult Sitotroga cerealella (Lepidoptera: Gelechiidae). J. Stored Prod. Res. 55, 128e133. -Binso, C.L., Ba, M.N., Sanon, A., 2013. ConserWaongo, A., Yamkoulga, M., Dabire colte des ce re ales en zone sud-soudanienne du Burkina Faso: vation post re valuation des stocks. Int. J. Biol. Chem. Sci. 7 (3), perception paysanne et e 1157e1167. termination des principaux ravageurs des Weidner, H., Rack, G., 1984. Tables de de es entrepose es dans les pays chauds. Eschborn, Allemagne, Gesellschaft denre für Technische Zusammenarbeit (GTZ), p. 157.
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Diversity and community structure of insect pests developing in stored sorghum in the Northern-Sudan ecological zone of Burkina Faso -Binso a, A. Sanon a, c A. Waongo a, c, *, N.M. Ba a, b, L.C. Dabire Laboratoire Central d'Entomologie Agricole de Kamboins e, Institut de l'Environnement et de Recherches Agricoles (INERA), Burkina Faso International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Niger c Laboratoire d'Entomologie Fondamentale et Appliqu ee, UFR/SVT, Universit e de Ouagadougou, Burkina Faso a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 February 2015 Received in revised form 16 April 2015 Accepted 5 May 2015 Available online xxx
Stored insect pests often create major problems for farmers worldwide. Comprehensive data of insect pests of stored sorghum in Burkina Faso are scarce. Understanding the population structure of insect fauna infesting stored sorghum is important for development of management strategy. Sorghum panicles were collected from January to September 2011 in farmers' granaries in the Northern-Sudanian ecological zone of Burkina Faso to determine the diversity of insect pests and their importance in post-harvest losses. A total of 14 species of insect pests were recorded, including twelve coleopteran and two lepidopteran species. Species diversity peaked between May and September. The highest insect diversity was recorded in sorghum stored in straw granaries and on red coloured grains when compared with that of sorghum stored in mud granaries and on white coloured grains. Rhyzopertha dominica (Fabricius) appears to be the primary insect pest followed by secondary pests including Oryzaephilus mercator (Fauvel), Cryptolestes ferrugineus (Stephens) and Sitophilus zeamais (Motschulsky). The distribution pattern of the pests in granaries corresponds to the Mandelbrot model in which colonization of species in an environment depends on the physical conditions of that environment and on the species currently present, which suggest a progressive colonization occurs in waves with stocks of grain. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Insect pests Population structure Sorghum Species richness
1. Introduction Sorghum, Sorghum bicolor (L.) Moench, is one of the most important cereals in the semi-arid tropics providing a major source of dietary energy and protein for nearly a billion people living in semi-arid areas (Belton and Taylor, 2004; Rooney, 2004). In Burkina Faso, sorghum serves as the major staple food crop in terms of production (1,923,805 tons) and acreage (1,788,695 ha; DGPSA, 2013); the country is the third largest African producer of sorghum (FAOSTAT, 2012). Many sub-Saharan Africa (SSA) countries, including Burkina Faso, suffer from chronic food deficits that are caused by several factors such as the persistently low productivity of staple crops.
* Corresponding author. Laboratoire Central d'Entomologie Agricole de , Institut de l'Environnement et de Recherches Agricoles (INERA), BurKamboinse kina Faso, 01 BP 476 Ouagadougou 01, Kadiogo, Burkina Faso. E-mail address: [email protected] (A. Waongo). http://dx.doi.org/10.1016/j.jspr.2015.05.002 0022-474X/© 2015 Elsevier Ltd. All rights reserved.
Post-harvest loss (PHL) is an often-forgotten factor that also contributes to chronic food deficits. A joint report of the World Bank, Natural Resources Institute in the United Kingdom and Food and Agriculture Organization of the United Nations states the value of PHL for grains in SSA could potentially reach nearly US$4 billion yr1 out of an estimated US$27 billion yr1 of value in grain production (Anonymous, 2011). Storage insect pests cause much of this PHL for grains. Insect pests can not only directly cause grain weight loss for stored sorghum but can also alter the physicochemical properties of the grain (Park et al., 2008). Insects that develop within storage facilities for grains may also favour the development of poisonous aflatoxins produced by the fungus Aspergillus flavus (Lamboni and Hell, 2009). Comprehensive data related to insect pests infesting high value stored commodities, such as cassava, maize and cowpea, are available (Caswell, 1961; Ratnadass and Sauphanor, 1989; Nukenine, 2010); however, to date very little work has been conducted on the insect fauna of stored sorghum (Ratnadass et al.,
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1994; FAO, 1998). Thus, in 2009, an inventory of insect pests affecting stored sorghum in the South-Sudanian ecological zone within Burkina Faso led to the identification of nine species of Coleoptera and Lepidoptera in the storage facilities (Waongo et al., 2013). The present article reports on the population structure of insect fauna infesting stored sorghum in the North-Sudanian ecological zone of Burkina Faso. The objectives were to: (1) determine the temporal variability and diversity of insect pest communities within on-farm stored sorghum (2) identify the effects of sorghum grain colour on the abundance and diversity of insect pest species and (3) determine the effects of various types of storage structures on insect pest fauna.
7
October) to 76% (July to September; Fig. 2). 2.2. Sampling of villages and producers
2. Methods
Within each province, local agricultural services aided researchers in compiling a list of all villages with high sorghum production during the 2010 cropping season. Those villages were likely to have sufficient stocks of sorghum to cover the sampling period. From that list, five villages were randomly selected in each of the four provinces covered by the study. In each of these villages focus group discussions were carried out with sorghum farmers; this allowed the selection of three farmers in each village with the highest stocks of grain who all voluntarily participated in the study. A total of 20 villages and 60 granaries were selected for analysis in this study.
2.1. Study area
2.3. Storage of sorghum grain
This study was conducted from January to September 2011 in ga, Ganzourgou Boulkiemde and Kourwe ogo provinces, BurBaze kina Faso, all located in the North-Sudanian ecological zone (Fig. 1). Burkina Faso experiences a unimodal rainfall pattern, with a rainy season lasting from June to October. The four provinces received 675 mme700 mm of rainfall in 2011. During the sampling period, mean temperatures ranged from 24.6 C to 34.1 C across the study area while the average relative humidity varied from 25% (June and
Farmers usually harvest sorghum in late October in this part of Burkina Faso, and store it in granaries in November; consumption of the grain is expected to last until the next harvest. However, following poor growing seasons the stocks are often depleted before the following harvest. In the selected villages, sorghum was stored as panicles in two types of structures and our sample included both types: 20 mud granaries with straw roofs and 40 woven straw granaries. We identified two types of sorghum based
Fig. 1. Map of Burkina Faso showing the four provinces and locations.
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A. Waongo et al. / Journal of Stored Products Research 63 (2015) 6e14
Fig. 2. Average monthly temperature and average relative humidity of the study area from January to September 2011.
on grains colour; our sample included red and white coloured sorghum grains from 38 to 22 granaries, respectively. All selected granaries were free of any pesticide application (synthetic or plant insecticide). 2.4. Sampling of sorghum panicles and collection of insects Four panicles of sorghum were randomly sampled every eight weeks from January to September 2011 in each of the 60 granaries in the 20 villages. The panicles were placed in cloth bags and any infestation of insect fauna was determined after sieving samples through a 3 mm mesh sieve in the laboratory. The collected insects were placed into plastic vials containing 70% ethanol. The panicles were then placed in 3-L glass jars until adult insects emerged from the hidden immature stages of insects. The panicles were kept in the lab for eight weeks under average temperature of 29 C ± 3 and relative humidity of 49% ± 19 and samples were sieved weekly to collect emerging adults (Park et al., 2008; Waongo et al., 2013). Emerging insects were identified to the species level using the morphological criteria described by Weidner and Rack (1984), Bousquet (1990), Delobel and Tran (1993), Farrell and Haines (2002) and Koehler et al. (2006). 2.5. Statistical analysis Data on the number of insects per species were log transformed using the formula log10 (x þ 1), where x is the number of individuals observed (Chijindu et al., 2008; Herve, 2011). The “Chao and Boot” and the Jacknife 1 indices were used to estimate species composition and abundance (Longino, 1994). Both indices assess the expected species richness. In addition, taxonomic richness (mean number of taxa per habitat) was calculated using the Shannon diversity Index (H0 ) to estimate the degree of organization of the insect population. A greater value indicates a more diverse insect population (Dajoz, 2000); H0 was calculated using Equation (1): 0
H ¼
s X ðPi log2 Pi Þ;
(1)
i¼1
where Pi is the proportion of each species in the stand and S is the
total number of species. The Pielou Equitability Index (E), which reflects the quality of the organization of the insect population (Dajoz, 2000; Magurran, 2004), is close to 1 when all species tend to have the same abundance, and close to 0 when one or a few species dominate the insect population. E was calculated using Equation (2):
E¼
H0 ; log2 ðSÞ
(2)
where H0 is the Shannon diversity Index calculated above and S is species number. Finally, an Index of Occurrence (IC) was calculated to assess temporal variations in species prevalence (rare to common; Dajoz, 2000). This index categorized the species into three types: constant, secondary and accidental pest species (found in more than 50%, 25e50%, or less than 25% of all samples, respectively) and was calculated using Equation (3):
IC ¼
ni 100 N
(3)
where N is the total number of samples and ni is the number of samples containing species i. All statistical analyses were performed with the software R version 2.15.1 using the ade4 (Dray and Dufour, 2007), vegan (Oksanen et al., 2012), gclus (Hurley, 2012), cluster (Maechler et al., 2012), rcolorbrewer (Neuwirth, 2011), labdsv (Roberts, 2012), mvpart (De'ath, 2012) and BiodiversityR (Kindt and Coe, 2005) software packages. After testing for normality using the ShapiroeWilk Test, analysis of variance was performed for species abundance, richness, equitability and diversity. Separation of means by either grain colour or type of granary or sampling period was performed using the ManneWhitneyeWilcoxon Test or the KruskaleWallis Test, respectively. A 5% significance level was used for all tests. A Hierarchical Classification Analysis (HCA) was used to classify pest species according to their occurrence. The HCA focused on the matrix-based presence or absence of pests in different localities using the Euclidean distance and Ward's method. The “fusion level” method was used to choose the optimal number of groups (Borcard et al., 2011).
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A model of insect abundance and distribution was tested using a rankefrequency diagram. The Akaike Information Criterion (AIC) value was computed using different models (Null, Preemption, logNormal, Zipf and Mandelbrot models; Sakamoto et al., 1986). The model with the lowest AIC value is the most representative of the pattern of insect pest distribution (Sakamoto et al., 1986).
diversity (c2 ¼ 67.9418, df ¼ 4, P 0.001; Fig. 5). However, the E index did not differ significantly (c2 ¼ 11.9985, df ¼ 4, P > 0.05) over time (Fig. 5).
3. Results
Insect pest species were significantly abundant (W ¼ 7151.5, P ¼ 0.046), rich (W ¼ 7028.5, P ¼ 0.024) and diverse (W ¼ 6953.5, P ¼ 0.019) on red coloured sorghum grains (Fig. 6). However the colour of sorghum grain did not significantly affect species homogeneity (W ¼ 7574, P ¼ 0.181; Fig. 6). Insect pest species richness (W ¼ 6379, P ¼ 0.003), diversity (W ¼ 0.9125, P 0.001), and homogeneity (W ¼ 6835, P ¼ 0.033) were significantly higher on sorghum grains stored in straw granaries than those in mud granaries (Fig. 7). However, the type of granary did not significantly affect species abundance (W ¼ 7297, P ¼ 0.1744; Fig. 7).
3.1. Species diversity Fourteen species from ten coleopteran and lepidopteran families were recorded on the stored sorghum; the percentage of individuals representing a single species compared with the total number of individuals collected ranged from 0.19% to 39.53% (Table 1). The three Dermestidae and the 12 coleopteran species found in the grain made them the most diverse family and order, respectively (Table 1). The Family Gelechiidae dominated the Order Lepidoptera (Table 1). The Bostrichidae and Silvanidae were the most important families and the Nitidulidae and Bruchidae the least important. 3.2. Analysis of the sampling effort The rarefaction curve, based on the accumulated data in the study area, showed a richness of 14 species (Fig. 3). Indeed, both the Jacknife 1 and “Chao and Boot” indices give 14 as the expected species richness. This indicates that the probable number of species that could be expected to be identified in these areas was achieved. 3.3. Occurrence index and temporal fluctuations in insect pest communities The occurrence index of the different pest species increased over the storage period from January to the late season storage period in September (Fig. 4). In January, Rhyzopertha dominica was the only constant pest species, and the only secondary pest species was Oryzaephilus mercator while other pests were accidental (Fig. 4). In September, in addition to R. dominica, O. mercator became a constant pest species, while Cryptolestes ferrugineus and Sitophilus zeamais became accidental pest species. Two coleopteran species, R. dominica and O. mercator, had the highest occurrence indices for both observation periods. S. cerellela had the highest occurrence index for the lepidopteran species (Fig. 4). From May to September, insect pest species significantly increased in terms of abundance (c2 ¼ 97.6669, df ¼ 4, P 0.001), species richness (c2 ¼ 76.6125, df ¼ 4, P 0.001) and species
3.4. Effects of grain colour and storage type on insect pest communities
3.5. Community structure of pest insects in sorghum storage The storage pests were split into two groups based on a hierarchical classification (Fig. 8). The first group included four coleopteran species. The second group include ten coleopteran and lepidopteran species (Fig. 8). When the five distribution models, were run the lowest AIC value was recorded from the Mandelbrot model; this model is the most representative of the distribution of insect pests infesting stored sorghum (Fig. 9). 4. Discussion In the part of Burkina Faso that lies within the North-Sudanian ecological zone, 14 species of Coleoptera and Lepidoptera colonized stored sorghum and developed over the normal storage period. Species richness was higher in this zone than the 6e12 species previously reported in other locations in Africa (Ratnadass, 1990; Lavigne, 1991; Tamgno and Ngamo, 2013; Waongo et al., 2013). Apart from location specificity, differences may be the result of sampling intensity or methods that were used in the present study. The results reported by previous authors (Tamgno and Ngamo, 2013; Waongo et al., 2013) included only one to a maximum of 40 samples collected only once to over a maximum period of four months, whereas our study covered ten months of data with 300 samples. Moreover, our study included a much higher number of locations when compared with that of Ratnadass et al. (1994). This is accordance with previous findings highlighting
Table 1 Overview of common insect pests and their abundance in sorghum stocks in Burkina. Order
Family
Proportion of families (%)
Species
Proportion of individuals (%)
Coleoptera
Bostrichidae
40,60
Silvanidae Cucujidae Tenebrionidae
23,79 9,25 7,43
Curculionidae Dermestidae
6,74 3,99
Nitidulidae Bruchidae Gelechiidae Pyralidae
0,50 0,27 6,09 1,34
Rhyzopertha dominica (Fabricius) Prostephanus truncatus (Horn) Oryzaephilus mercator (Fauvel) Cryptolestes ferrugineus (Stephens) Tribolium castaneum (Herbst) Tribolium confusum (Jacquelin du Val) Sitophilus zeamais (Motschulsky) Attagenus fasciatus (Thunberg) ) Anthrenus verbasci (Linne Trogoderma granarium (Everts) Carpophilus dimidiatus (Fabricius) Callosobruchus maculatus (Fabricius) Sitotroga cerealella (Olivier) Corcyra cephalonica (Stainton)
39,53 1,07 23,79 9,25 3,60 3,83 6,74 1,20 0,19 2,60 0,50 0,27 6,09 1,34
Lepidoptera
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Fig. 3. Total stored sorghum insect pests species richness in North-Sudanian Burkina Faso.
Fig. 4. Occurrence index of stored sorghum insect pests at the beginning and end of storage season in North-Sudanian Burkina Faso.
that longer sampling duration, and greater number of samples led to higher likelihood of recording more insect species (Fargo et al., 1989; Elmouttie et al., 2010). When the structure and the organization of the insect populations found in the present study was analysed, two groups were distinguished: i) the minor pests which included ten species, and ii) the group of most abundant species including R. dominica, O. mercator, S. zeamais and C. ferrugineus. Three species found here, R. dominica, S. zeamais and O. mercator occur worldwide and have been described as major pests of stored grains (Loschiavo and Smith, 1970; Hoppe, 1986; Jood et al., 1996; Belda and Riudavets, 2010; Carvalho et al., 2013). R. dominica, the most frequent and most abundant species on stored sorghum in Burkina Faso, is also a primary insect pest of stored sorghum and has been identified as such in several regions across Africa (Seifelnasr, 1992; Ratnadass et al., 1994; Mvumi et al., 2002). O. mercator and C. ferrugineus ranked 2nd and 3rd in abundance, respectively; and over the season, their occurrence index increased when the occurrence index of R. dominica increased. This suggests that R. dominica promotes the establishment of O. mercator and C. ferrugineus in stored sorghum
stock. This is typical of secondary pests (Delobel and Tran, 1993; Mukherjee and Nandi, 1993; Nansen et al., 2009). The ability of a secondary pest to become established in stocks depends on damage caused by primary pests that attack the seed coat, enabling the secondary pests to get inside the grain. The Mandelbrot distribution model of the pest community supports the hypothesis that the colonization of stocks occurs in successive waves and is highlighted in this study. According to Mandelbrot distribution theory (Bastow, 1991), the colonization of a given habitat by a species of the population is based on the earlier presence of another species (pioneer species) and the conditions created by that species. Pioneer species such as R. dominica are therefore primary pests because of the severity of the damage they cause, which leads to the establishment of secondary pests such as O. mercator and C. ferrugineus. This successive colonization of stocks could explain the significant increase in the diversity parameters (abundance, species richness and Shannon index) and could be explained by the homogeneity of the environment from the beginning (January) to the end of the study period (September). Indeed, according to Nansen et al. (2009), when a silo filled of grain is compared with other habitats, natural
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Fig. 5. Temporal variation in stored sorghum insect pests species abundance, richness, diversity and equitability from January to September 2011 in North-Sudanian Burkina Faso. (For each month, means were compared by a KruskaleWallis test at the 5% level, with different alphabetic letters indicating significant differences).
Fig. 6. Insect pest species abundance, richness, equitability and diversity of red and white coloured stored sorghum grains in North-Sudanian Burkina Faso. (For each type of grains, means were compared by a Mann-Whitney-Wilcoxon test at the 5% level, with different alphabetic letters indicating significant differences).
or artificial, a silo constitutes an isolated and homogeneous habitat in which the availability of food for many pest insects is essentially unlimited. In addition to the successive colonization of stocks by different insect pests, the climatic conditions could explain the significant increase in diversity we observed from May until the end of the study period in September. May and September are respectively preceded by a peak of temperature in April (34.1 C) and a relative peak of humidity in August (76%). According to several authors temperature and relative humidity are the most important factors in the developmental cycle of an insect (Fields, 1992; Delobel and Tran, 1993; Ouedraogo et al., 1996; Throne and Weaver, 2013).
The variety of sorghum used influenced the diversity of insect pests infesting farmers' granaries. Thus the red coloured variety of sorghum grain attracted a significantly higher number of insect species than white coloured grains. Several authors have reported on the varietal preferences of insect pests on stored sorghum ndez (Krishnamurthy et al., 1978; Adetunji, 1988; Chuck-Herna et al., 2013; Shehzad et al., 2014). The physical properties and chemical composition of the grain may cause these preferences (Russell, 1966; Ratnadass et al., 1994; Chandrashekar and Satyanarayana, 2006; Ramputh et al., 1999). Barro-Kondombo et al. (2008) reported that the red coloured sorghum grain are generally soft. In Mali, Ratnadass et al. (1994) also reported that
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Fig. 7. Insect pest species abundance, richness, equitability and diversity of sorghum grains stored in straw granaries and mud granaries in North-Sudanian Burkina Faso. (For each storage structure, means were compared by a Mann-Whitney-Wilcoxon test at the 5% level, with different alphabetic letters indicating significant differences).
Fig. 8. Hierarchical classification of stored sorghum insect pests in Burkina Faso.
sorghum cultivars with soft grains were more susceptible to insect damage than cultivars with hard grain. The hardness of grains and resistance to stored insect pests was reported for different commodities (Arnason et al., 1994; Odeyemi and Daramola, 2000; Nawrot et al., 2006). In addition to the effect of sorghum variety, several researchers have shown that the type of storage structure used to store grain
also influenced insect diversity (Shazali et al., 1996; Shazali and Ahmed, 1998). In the present study, the number of insect species recorded on sorghum grains stored in woven straw granaries was higher than that stored in mud granaries. Compared with mud granaries, which are a confined environment, woven straw allows airflow. The continuous renewal of ambient air in woven straw may have led to the more rapid development of insect pests. In addition,
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Fig. 9. Adjustment the sorghum insect pest distribution to a few models of distribution.
the woven straw creates passages for insects to make their way into the structure. Controlling the infestations of grains by pioneer pest species is critical to the prosper storage of sorghum. Therefore, particular emphasis must be placed on the management of R. dominica, O. mercator and C. ferrugineus for sustainable and effective conservation of sorghum stocks in Burkina Faso. Acknowledgements This study was supported by a PhD research grant from the re des Enseignements Secondaire et Supe rieur of Burkina Ministe Faso and also by the Project CORUS-6072 contract funded by the re de la cooperation Française. We are also thankful to Ministe farmers who graciously gave their sorghum for the experiments and to our collaborators. References Adetunji, J.F., 1988. A study of the resistance of some sorghum seed cultivars to Sitophilus oryzae (L.) (Coleoptera: Curculionidae). J. Stored Prod. Res. 24 (2), 67e71. Anonymous, 2011. Missing Food: the Postharvest Grain Losses in Sub-saharan Africa. The World Bank, NRI and FAO. Arnason, J.T., Conilh de Beyssac, B., Philogene, B.J.R., Bergvinson, D., Serratos, J.A., Mihm, J.A., 1994. Mechanisms of resistance in maize grain to the maize weevil and the larger grain borer. In: Insect Resistant Maize Recent Advances and Utilization, Proceedings of an International Symposium Held at the International Maize and Wheat Improvement Center, pp. 91e95. Barro-Kondombo, C.P., Vom Brocke, K., Chantereau, J., Sagnard, F., Zongo, J.-D., 2008. phe notypique des sorghos locaux de deux re gions du Burkina Faso: Variabilite la Boucle du Mouhoun et le Centre-Ouest. Cah. Agric. 17 (2), 107e113. Bastow, J.W., 1991. Methods for fitting dominance/diversity curves. J. Veg. Sci. 2, 35e46. Belda, C., Riudavets, J., 2010. Distribution of insect pests and their natural enemies in a barley pile. In: Carvalho, M.O., Fields, P.G., Adler, C.S., Arthur, F.H., et al. (Eds.), Proceedings of the 10th International Working Conference on Stored Product Protection, 27 Junee2 July 2010, Estoril, Portugal, pp. 741e745. Belton, P.S., Taylor, J.R.N., 2004. Sorghum and millets: protein sources for Africa. Trends Food Sci. Technol. 15, 94e98. Borcard, D., Gillet, F., Legendre, P., 2011. Numerical Ecology in R. Springer, New York, p. 306. Bousquet, Y., 1990. Beetles Associated with Stored Products in Canada. Annual Agricultural Canadian Publication. 1837, 224pp. Carvalho, M.O., Faro, A., Subramanyam, B., 2013. Insect population distribution and
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