Assessment of quantitative and qualitative losses of stored grains due to insect infestation in Ethiopia

Highlights

• The traditional storages are ineffective to protect grains from storage pests.

• High quantitative losses of stored grains occurred due to storage pests.

• Losses of protein and fat contents of grains occurred along the storage periods.

• Fibre and ash contents of stored grains increased along the storage periods.

• High post-harvest losses of grains contribute to food insecurity.

Abstract

This study was designed to determine the quantitative and qualitative losses of stored grains that arise from insect infestation in three districts of southwestern Ethiopia. One district was selected from each zone based on the production potential of the target crops (maize, sorghum, wheat and fababean). A total of 240 farmers’ stores from all 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 determine grain weight loss, insect damage, and nutritional losses. Grain damage showed significant 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. The moisture content of the grains decreased along the storage duration. Crude protein and crude fat contents significantly decreased as the storage duration increased in all traditional storage types. Furthermore, the crude fibre and ash contents of the different grain types significantly increased as the storage duration increased in all storage types. These results demonstrated that traditional storage structures have a substantial effect on quantitative and qualitative losses of stored grains. This finding has great implications for food security and hidden nutritional deficits in society. Thus, there is a need to develop and disseminate storage technologies that minimize losses and that are affordable for small farm holders.

Introduction

Grains are the main source of nutrition for one-third of the world’s poorest population living in Sub-Saharan Africa and South-East Asia. Among the grain crops, rice, wheat and maize are the most important cereals, which contribute more than half of all calories consumed by humans (Awika, 2011). In Ethiopia, grain crops are grown annually on approximately 12.5 million hectares of land; of these, 1.5 million hectares are covered by pulses, of which 443,074.68 ha are dedicated to fababean, with an annual production of approximately 8.4 million quintals (CSA, 2014). Cereals constituted 87.3% of the grain production of the country: 26.8% from maize, 16.1% from sorghum, and 15.7% from wheat (CSA, 2015).

Poor postharvest management, resulting in grain losses, is one of the key constraints to improving food and nutritional security in Africa, including Ethiopia (Midega et al., 2016). In Ethiopia, grain is often stored for less than eight months due to poor storage techniques and inadequate pest management systems (Demissie et al., 2008; Tadesse et al., 2008). Stored grains are damaged by a number of insect pests, leading to qualitative and quantitative losses during storage. Farmers’ grain storage losses are further aggravated by poor postharvest handling, inefficient storage facilities and inadequate pest management systems (Demissie et al., 2008; Tefera et al., 2016).

The FAO (2010) estimated a 20–30% loss of grains, with an estimated monetary value of more than US$ 4 billion annually. In Ethiopia, the average grain loss due to storage insect pests is estimated to be 10–30% (Tadesse, 2005; MoARD, 2010). The major postharvest pests of cereal grains in Ethiopia include the maize weevil (Sitophilus zeamais), the Angoumois grain moth (Sitotroga cerealella), the lesser grain weevil (Sitophilus oryzae), and Callosobruchus spp. in grain legumes (Demissie et al., 2008; Tefera, 2016). According to Sori and Ayana (2012), S. zeamais can cause heavy infestation of maize and sorghum grain stored in traditional storage facilities and result in weight losses of up to 41–80%.

Despite the severe losses incurred by insect pests in poor storage facilities, many farmers in Ethiopia continue to use traditional storage structures to store their grains, thereby providing an abundant food source for the pests, and aggravating damage. In most cases, farmers store grain in traditional storage facilities such as Gotera and Gombisa (Haile-Gabriel and Hundie, 2006; Tadesse et al., 2008; Dubale et al., 2012). According to these authors, on-farm storage structures such as Gombisa make maize susceptible to bio-deterioration, especially in hot and humid climates. In some instances, farmers are forced to sell their produce immediately after harvest and therefore receive low market prices for any surplus grain produced (Kimenju et al., 2009). Gotera (above-ground bin), is a common traditional storage structure in Ethiopia. It is located outdoors and usually cylindrical structure, flat or conical at the base, placed on a raised platform or stones, and covered with a conical thatched roof. The gombisa is usually an unplastered structure mostly made from bamboo and its roof is covered with thatched grass. Gumbi is smaller than Gotera which has got sections fitted together made from mud reinforced with tef straw, sundried and placed in the house (Tadesse et al., 2008).

Despite the importance of grain storage for food security, the potential impact of insect pests on stored grain quality and quantity have not been well investigated. As described by FAO (2014), Kader (2005), Nega and Semeon (2006) and Haile-Gabriel and Hundie (2006), qualitative and quantitative loss studies are generally sporadic in Africa. The current study was therefore designed to quantify the types and magnitudes of postharvest losses from insects in selected grains (maize, sorghum, wheat and fababean) in different storage structures and over different storage periods in several agro-ecological zones of southwestern Ethiopia. The objectives of the study were to quantify the extent of grain damage and weight loss, and to assess the nutritional value losses caused by insect damage.