Assessing Storage Insect Pests and Faecal dropping of Rodent in Stored Grains in two districts of Southwestern Ethiopia

This study was designed to assess major insects and occurrence of rodent infestation in stored grain in two districts of south western Ethiopia. Omo Neda and Bako Tibe districts were purposively selected supported their potential growing of maize and sorghum grain, and high postharvest losses in these selected areas. A total of 160 farmers’ stores from both districts were randomly selected. The grain samples used in the present study were stored for 5 different time periods, ranging from 1 to 5 months and from the same farmers’ stores, to identify storage insect pest and to determine grain weight loss and insect damage. The results showed that the dominant insect species in maize and sorghum grains were weevils (Sitophilus spp.) followed by the Angoumois gelechiid (Sitotroga cerealella Olivier) and our beetles (Tribolium spp.). High numbers of insects were recorded from both plastered and un-plastered gombisa and polypropylene bags. Additionally, the amount of every insect pest in each storage container recorded per 100 g grain increased because the duration of grain storage increased. There have been 0.33–1.29 and 0.44-1g droppings per 100-g sample of maize and sorghum grain, respectively. Grain damage showed signicant differences over the storage periods across the study districts. A similar trend was observed for weight loss for each of the grains in all districts. These results indicated that farmers are incurring a substantial grain loss to insects and rodent pests. Hence, there is an urgent need to devise appropriate tactics for protecting the losses in farm-stored maize and sorghum in Ethiopia.


Introduction
Grains are the most source of nutrition for one-third of the world's poorest population in Sub-Saharan Africa and South-East Asia. Among the grain crops rice, wheat and maize represent about 85% of total global production (So et al., 2009). In Ethiopia, Cereals constituted 87.3% of the grain production of the country, with 26.8% contribution from maize, 16.1% from sorghum and 15.7% from wheat (CSA, 2015).
However, production of cereals and grains are constrained by various biotic and abiotic factors. Postharvest losses are one among the most constraints affecting food and nutrition security of smallholder farmers within the country (Tefera, 2012;Tesfaye and Tirivayi, 2018). Poor storage systems make grains susceptible to attacks from insect and rodent pests, which cause a substantial amount of losses in quantity and quality of grains.
Losses resulting from poor post-harvest management of grains are among the key constraints to improving food and nutritional security in Africa that results in grain weight losses of 20-30 % (Tefera, 2012). Consistent with Kumar and Kalita (2017), an approximately 50-60% losses of cereal grains occurred during storage thanks to technical ine ciency. In Ethiopia, the typical grain losses thanks to storage insect pests estimated to be 10-30% (Tadesse, 2005;MoARD, 2010). Among many storage insect pests, grain weevils, Sitophilus spp. (Coleoptera: Curculionidae), and therefore the Angoumois gelechiid, angoumois moth (Olivier) (Lepidoptera: Gelechiidae), are major pests of cereal crops in Ethiopia (Tadesse, 1996;Demisse et al., 2008;Tefera, 2016). Consistent with Sori and Ayana (2012), S. zeamais can cause heavy infestation on maize and sorghum grain stored under traditional storage facilities and resulted in weight losses up to 41-80%.
Farmers in Ethiopia, almost like those in other African countries, use traditional storage facilities such are gotera, gumbi, and polypropylene and jute bags. Gotera is an outside storage structure made up of mud or trash plastered basket work covered with thatched roo ng and raised off the bottom with stones or wooden platform; Gumbi is an inside grain storage bin made from mud plaster mixed with teff straw (Hengsdijk and De Boer, 2017). Such storage structures often fail to guard the stored grains from insect pests and damage by rodents. Traditional storage structures provide ideal conditions for the multiplication of storage insect pests and rodents. Although most smallholder farmers keep grain for a comparatively shorter period, substantial losses occur to stored grains.
Rodents also are a serious postharvest pest, causing a big amount of losses and contamination of stored grains during storage that affect food security and income of small-holder farmers (Brown et al., 2013;Ognakossan et al., 2016). To style effective postharvest pest management methods, knowledge of major pests and their relative abundances in reference to storage facilities is important. However, little information is out there about storage insect pest infestations in reference to storage facilities. Therefore, the aim of this study was to assess storage insects of stored maize and sorghum and their associated losses of quantity in south western Ethiopia.

Study areas and sample collection methods
Study areas were including the selected zones, woredas and kebele's depend on their potential in maize and sorghum production and selection of farmers was made together with woreda agricultural experts.
Its coverers two major maize and sorghum producing zone of south western Oromia, Ethiopia; namely, Jimma and West shawa. A total of 600 g of grain sample of each storage structure were collected. The grain samples taken from the top, middle and bottom of a storage structure were then bulked together to make a composite sample. Samples were collected at monthly intervals for up to ve months from the same stores for storage insect pest studies, faecal dropping of rodent studies and grain damage and weight loss assessment. Sample collection was carried out after the grain was stored for one month and samples were enclosed in plastic bags and brought to the Postharvest Management Laboratory of Jimma University, College of Agriculture and Veterinary Medicine (JUCAVM) for laboratory analysis.
2.3. Data to be collected 2.3.1. Identification of major insect pest 100g. of sample was taken from each of the storage for the laboratory insect identification. The grain was sieved through 2 mm mesh sieve (to remove dead and alive insects from the sample taken and to left the grain on the sieve) as method used by (Abraham, 1995). Both live and dead insects removed from each sample were counted, placed individually in a veil containing a 70% ethanol solution and identi ed using the procedures described by Borror et al. (2005). The collected insects were identi ed through their morphological characteristics using a dissecting microscope (at magni cation x 25-60) for species identi cation.

Faecal dropping of rodent
100g. of sample was taken from each of the storage for the rodent faecal dropping identi cation. The sample was spread out on a plastic sheet to separate rodent faecal dropping. Faecal drooping removed from each sample were weighed and the weight of faecal dropping of rodent present in grain was computed (Brown et al., 2013).

Grain damage and weight loss assessment
Assessment of grain damaged: Insect damage was recorded by the count and weighing method. Each hundred (100g) grains were taken from initial to last storage periods and from each of the storage types and the number of insect damaged and un-damaged grain were obtained using a hand lens by searching for the presence of hole on the seeds. The percentage of insect damaged grains was calculated according to the methods used by (Wambugu et al., 2009) as follows Grain weight loss: For the assessment of grain weight loss, 100-grain samples were taken from initial to last storage periods and from each of the storage types and the number of insect damaged and undamaged grain were identi ed and tallied using a hand lens to inspect for the presence of a hole or burrow. Grain in each portion were then counted and weighed using a digital balance. The percentage of weight loss was then calculated (Gwinner et al., 1996).
In the above formula, Wu is the weight of undamaged seeds, Nu is the number of undamaged seeds, Wd is the weight of damaged seeds and Nd is the number of damaged seeds.

Data analysis
A 2 x 3 factorial design was used for the analysis of damaged grain, weight loss of maize and sorghum kernels stored in the farmers' traditional storage structures with two storage types (Gombisa/Gotera and polypropylene sack) and three storage duration levels (1 st , 3 rd and 5 th ) months. The data on the insect count, percent grain damage and weight loss were analysed using one-way analysis of variance (ANOVA) with a generalized linear model. Then the data were arcsine transformed to normalize the variances. Signi cance level was set at 0.05, and the means were separated by Tukey's Honestly Signi cant Difference test. All statistical analyses were conducted using MINITAB 16 statistical software 3. Results And Discussion 3.1. Identi cation of storage insect pests Maize weevils (Sitophilus spp.), Angoumois grain moth (Sitotroga cerealella), and our beetle (Tribolium spp.) were the insect species identi ed from both samples (Table 1). In Omo Nada district, there were signi cant differences in the number of maize weevil recorded during storage periods of stored maize (P = 0.05), but the storage type did not affect the number of insects. However, in Bako Tibe district, the number of maize weevil showed highly signi cant (P = 0.005) differences, with interaction effects of storage duration and storage types. Whereas, in stored sorghum grain there were signi cant differences in the number of maize weevil recorded during storage periods both in Omo Nada (P = 0.014) and Bako Tibe (P = 0.020) districts. In both districts the number of Angoumois grain moth and our beetle recorded in stored maize and sorghum were signi cantly (P < 0.05) affected by storage durations with the exception of our beetle recorded in stored maize in Bako Tibe district.  Figure 1 shows result of faecal dropping in maize and sorghum grain stored in gombisa during ve consecutive months of storage period. In Omo Nada faecal dropping collected from maize ranged from 0.33-1.29 g droppings/100 g of sample, while in Bako Tibe it was ranged from 0.58-1.13g droppings/100 g of maize. In Omo Nada it was ranged from 0.44-0.92g droppings/100 g of sorghum, while in Bako Tibe it was ranged from 0.58-1g droppings/100 g of sorghum.

Grain damage and weight loss
The percent damage of stored maize grain was signi cantly affected by storage type (F 1, 12 = 8.92; P < 0.01) and storage duration (F 2, 12 = 417.16; P < 0.001) with the highest percent damage (60.5 ± 0.6) was observed in grain stored in Gombisa/Gotera at fth month of storage duration ( Table 2). The percent damage of stored sorghum showed signi cant differences with storage duration (F 2, 12 = 335.73; P < 0.001) ( Table 2). In all grain type, damage increased with increase in storage duration (Table 2). Values are mean ± SE.
The percent weight loss (WL) of stored maize grain was signi cantly affected by storage duration (F 2, 12 = 310.82; P < 0.001). Similarly, the WL of stored sorghum varied signi cantly among storage durations (F 2, 12 = 198.54; P < 0.001). In all grain type, WL increased with increase in storage duration (Table 3).

Discussion
In the present study, Sitophilus spp., S.cerealella, and Tribolium spp. were recorded in maize and sorghum grains stored in gombisa and polypropylene bags storage containers. These species are reported as the main storage insect pests of cereal grains in several parts of Ethiopia (e.g., Mendesil et al. 2007;Demissieet al., 2008;Tadesse et al., 2008;Tefera, 2016) and other African countries (e.g., Tefera, 2012;Midega et al., 2016;Abass et al., 2018). in both study districts and storage types, Sitophilus spp. were the foremost abundant species, which is corroborated by the ndings of varied studies, like Mlambo et al. (2017). Angoumois moth was also cosmopolitan and therefore the dominant species attacking different cereal crops in Africa (Mlambo et al., 2017). Consistent with Golob (2002), S. cerealella is especially related to unshelled maize and sorghum soon after harvest. As demonstrated during this study, the amount of every storage insect pest recorded increased because the duration of grain storage increased, leading to considerable losses. The presence of faecal dropping in sample grain may be a sign of rodent infestation and it affects the standard attribute of stored grain (Brown et al., 2013). Faecal dropping per 100 g grain increased because the duration of grain storage increased this might ow from to the very fact that gombisa a standard storage structures cannot protect rodent attack. Similar results were reported by Be kadu (2014), that onfarm storage structures like gombisa make grain vulnerable to rodent infestation within the south western a part of the country due to the recent and humid climate, and these structures aren't highly protective generally. Rodents are one among the main postharvest pests causing a substantial amount of losses.
During this study, most farmers considered rodents a signi cant problem that causes estimated grain losses of 26-50%. A study conducted in Kenya showed that farmers perceived rodents causing up to 43% and 30% of losses of maize stored on cobs and shelled grain, respectively (Ognakossan et al., 2016).
The results presented above show that postharvest insect pests cause severe losses in stored grains for small-holding growers in southwestern Ethiopia. Over 50% and 35% of damaged maize and sorghum grain, respectively, were observed by the fth month of storage in Gombisa and polypropylene sack, which are the most common traditional storage structures in the study areas. Consistent with FAO (2010), an estimated loss of 20-30% occurred in Africa thanks to poor postharvest management practices. For instance, in Ethiopia, the typical grain loss thanks to storage insect pests is estimated to be 10-30% (Tadesse, 2005;MoARD, 2010).
In Ethiopia, Sori and Ayana (2012) reported approximately 64.5% of grain damage in traditional farm stores within three to 6 months. Several factors like storage duration, storage type and management practice may have contributed to high grain damage by storage insect pests (Bounechada et al., 2011;Tefera, 2012). Grain weight loss starting from 10-15% in maize and sorghum were recorded during the fth month of storage. Hell et al. (2012) observed a 10 to 12% loss of grains stored in traditional storage structures thanks to insect pests in Tanzania. Gonzalez (2013) noted that grain weight loss was found to be hooked in to storage duration, where a rise in storage time results in a big loss in grain weights. Furthermore, Tefera (2012) also reported that storage losses depend on temperature and humidity, which favour the expansion of mould and bug infestation.
In conclusion, no matter storage type, and therefore the traditional storage systems adopted by the farmers within the study areas couldn't effectively protect against storage losses caused by insect and rodent pests. As a result, grains damage consistently increased from the primary to the fth months of storage. Similarly, grains weight loss increased because the duration of storage increased. This nding indicates the necessity for the development of existing traditional storage facilities and therefore the adoption of improved storage facilities, like hermetic metal silos and PICS bags, which are proven to guard stored grain from insect pest infestation.

Availability of Data
The data used to support the results of this study is available upon request from the corresponding author.

Con icts of Interest
The authors declare that they know the work reported in this paper is not in con ict with nancial interests or personal relationships & also no con icts of interest between the authors. Rodent droppings per 100-g sample (mean ± SE) from maize (A) and sorghum (B) grain sampled over ve months in Omo Neda and Bako Tibe district, southwestern Ethiopia.