Post-Harvest Insect Management Practices in Ethiopia

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1		Muez Berhe Gebremedhin	--	2660	2022-11-22 10:36:31	\|
2	Format correction	Sirius Huang	Meta information modification	2660	2022-11-28 03:14:30	\|

This entry is adapted from the peer-reviewed paper 10.3390/insects13111068

Ethiopian subsistence farmers traditionally store their grain harvests, leaving them open to storage pests and fungi that can cause contamination of major staple crops. Applying the most effective strategy requires a precise understanding of the insect species, infestation rates, storage losses, and storage conditions in the various types of farmers’ grain stores.

Ethiopia stored commodities post-harvest practices storage pests storage losses pest management options

1. Cultural Practice

While the enormous storage damage caused by a number of storage pests is successfully controlled by the use of improved storage technologies and various insecticides, most farms have also used a variety of conventional or cultural methods since time immemorial to manage pre- and post-harvest insect infestations. Improved varietals, good hygiene and sanitation, appropriate harvesting times, better storage facilities, and efficient drying are all part of this process. To keep their seed grain dry, Ethiopian farmers have stored their grain above the stove in the kitchen. When several cultural techniques were evaluated in Ethiopia, sun heating of maize resulted in a significant mortality (70–100%) of maize weevil under heating conditions of 55–60 °C for two–three hours utilizing solar heat absorption beds ^[1]. Similarly, the heat treatment of C. chinensis for about an hour in an obtuse-base-angle box heater lined with aluminum foil was also reported to completely kill adults of C. chinensis and also cause their failure to lay eggs in chickpea ^[1]. Although there are many different cultural practices used in various regions of Ethiopia, the assessment found that the most popular traditional approaches used by many farmers to reduce post-harvest loss include: drying grains to a safe moisture content before storage to prevent mold infection; avoiding mixing infected and healthy grains; heating at certain temperatures; adding inert powder to prevent damage by pests; cleaning before storage; smoking traditional storage with locally available plant materials; and other indigenous practices (Table 1). Clearly, there were differences in how well these generally accepted traditional methods controlled storage insect pest infestations and mold in both the field and storage settings. Therefore, based on the findings and suggestions from research, farmers and other participants along the value chain of a particular crop might employ a wide range of cultural strategies.

Table 1. Comparison analysis on effectiveness of storage pest control methods in Ethiopia.

Control Methods	Crop/Trait	Treatment	Target Pest	Measurement Scale	Efficiency	Reference
Cultural	Maize	Solar heating (55–60 °C)	S. zeamais	Mortality rate %	70–100%	^[1]
Variety screening	Maize (husk level)	G1	S. zeamais	NWPEAM	59.15 ± 8.13 a	^[2]
		G2			12.78 ± 1.44 c
		G3			15.85 ± 7.76 c
		G4			32.45 ± 8.09 b
		G5			10.55 ± 1.94 c
	Maize (Biochemical level)	Pratap makka-5	S. cerealella	Grain loss %	7.21%	^[3]
	Maize (Biochemical level)	PMH-1	S. cerealella	Grain loss %	31.12%	^[3]
Botanicals	Haricot beans	Orange powder (96 h)	Zabrotes subfasciatus	Mortality rate %	65.9%	^[4]
	Haricot beans	Orange essential oil (hours)		Mortality rate %	67.4%	^[4]
	Sorghum	Neem seed oil	S. zeamais	Mortality rate %	91.25–100%	^[2]
	Sorghum	Citrus seed oil	S. zeamais	Mortality rate %	83–100%	^[2]
	Maize	Cooking oils	S. zeamais	Mortality rate %	54.54%	^[5]
		Triplex			92.66%
		Chemicals			100%
		control			24.2%
Entomopathogenic fungi	Lab	Metarhizium anisopliae & B. bassiana	S. zeamais	Mortality rate %	92–100%	^[6]
Entomopathogenic fungi	Lab	13 isolates of	P. truncatus	Mortality rate %	98–100%	^[6]
Inert dust	Maize	SilicoSec rates (15 days)	S. zeamais	Mortality rate %	100%	^[7]
		Filter cake rates			100%
		Wood ash rates			98.7%

(NWPEAM = number of adult weevils per ear after a month of storage); Source (analyzed by the author). Means in columns with the same letter are not significantly different.

2. Storage Structure

In Ethiopia, traditional grain stores, such as “gotera” bags (made of polyethylene, sisal, or goatskin), “gumbi” earthen pots, and others, are the principal methods used to store grain. In a majority of the country, “gotera” (an above-ground bin) is the most widely utilized storage container. This above-ground bin is made of bamboo, which is plastered internally and externally with mud and cow dung and mostly placed outdoors ^[8]. “Gumbi”, on the other hand, is a tiered construction of rings placed one on top of the other and is made of mud, cow dung, and straw from crop leftovers such as teff and eragrostis tef ^[8]. Teff was also kept in various regions of the nation in traditional storage structures such as baskets, pots, gusgusha, barrels, and goggo ^[8]. According to research done in Southeast Ethiopia, 81% of the farmers stored their sorghum in “gotera”, whereas 17% used clay pots, and 1% used “gumbi” to preserve their sorghum after harvest ^[9]. Similar dried maize cobs were also kept in “gotera”, while farmers kept their harvested grain in polypropylene or jute bags after shelling and winnowing ^[10].

According to a comparison study of various storage structures, most farmers preferred to keep their cereals in bags within their homes (46%) and traditional “gotera” (39%) rather than use more modern storage such as metal silos (1%); this could be attributed to their lower cost and ease of access (Table 3). In Eastern Ethiopia, Harar, or cone-shaped subterranean pits with an average depth of 165.8 cm, a mouth diameter of 62.1 cm, and a bottom diameter of 152.0 cm, were also utilized for storing sorghum and corn (Figure 1) ^[9]^[10]. According to a survey performed in Harar, 70% of farmers kept their sorghum in the customary underground storage pits until they were used or sold ^[1]. Due to mycotoxin contamination, however, storing sorghum in subterranean pits proved less successful for preserving the quality ^[8]. Similar studies carried out in Ethiopia’s main food crop producing regions found traditional stores such as gotera (grain pits), bags (made of polyethylene, sisal, or goat leather), earthen pots, and others ^[11]. According to this study, more than 70% of the respondents stored their crop products in polyethylene bags and sacks, followed by the traditional gotera (67.8%), which is mostly preferred to store large quantities for a longer period of time (Table 2).

Figure 1. Large traditional underground pit for sorghum in Fedis, Ethiopia. Source; taken from FAO, 2017 ^[11].

Table 2. Post-harvest storage methods in Ethiopia expressed as % of the total number of storage methods used for each cereal type.

Survey No.	Type of Structure	Respondents (%)	Grains Stored (%)	References
1	Bags	70.5	46	^[11]^[12]
2	Gotera	67.8	39	^[11]^[12]
3	Pots	9.4	NA	^[13]
4	Underground pits	0.3	NA	^[11]
5	Metallic silo	NA	<1	^[12]
6	Others	19.1	14	^[11]^[12]

NA = data not available; Source (analyzed by the author).

In conclusion, even though there are many storage technologies available for various grains, the choice of technology may depend on a variety of factors, such as the volume of production, the type of crop, the current weather conditions, the crop storage duration, the farmers’ ability and willingness to store the crop, as well as the cost-effectiveness of purchasing or implementing the storage structure for a given amount of crop produced. The post-harvest management strategy for a given crop under particular storage conditions could therefore be improved by extensive research to improve the capacity and efficiency of widely used traditional storage structures, as well as provide improved technologies to the community. This is due to the fact that these and other factors may potentially affect the capacity of safe storage.

In conclusion, although there are many storage technologies available for various grains, the choice of the specific technology depends on a variety of factors, such as the volume of production, the type of crop, the current weather conditions, the storage duration, the farmers’ ability and willingness to store the crop, as well as the cost-effectiveness of purchasing or using the storage structure for a given amount of crop produced. The post-harvest management strategy for a given crop under particular storage conditions could therefore be improved by extensive research to improve the capacity and efficiency of widely used traditional storage structures as well as provide improved technologies to the community.

3. Botanical Control

Plant products are seen to be effective and suitable for smallholder farmers to protect stored grain from insect damage. Treatment with the leaves of Eucalyptus globulus, Schinese molle, Datura stramonium, Phytolacca dodecandra, Lycopersicum esculentum, Milletia ferruginea, Mexican tea powder, triplex, filter cake, and neem seed were observed to cause high adult weevil mortality, reduced progeny emergence, and low grain damage of S. zeamais ^[5]^[7]^[14]^[15]. In a study on the management of the Adzuki bean beetle (Callosobruchus chinensis) using botanicals, inert materials, and edible oils in stored chickpeas, it was found that Chenopodium ambrosioides caused a high adult mortality, while the use of Brassica juncea, Linum usitatissimum, and Guizotia abyssinica seed oils caused a reduction in progeny emergence ^[14]. A study conducted to determine the effective concentrations of neem seed powder, citrus peel powder, and their oil extracts for effectiveness against maize weevil on sorghum varieties found that neem seed oil (NSO) and citrus seed oil (CSO) caused adult mortality in the range of 91.3–100% and a seed protection of 83–100% (Table 3). For the same botanicals, the study also revealed that weevil emergence, seed damage, and weight losses were statistically on par with the synthetic insecticide (Table 1). Similarly, beans treated with sun-dried powder of orange peel and an essential oil killed 65% and 67% of Z. subfaciatus after 96 h, respectively ^[4].

Table 3. Effect of NSO and CSO on weight loss, damage, and germination.

Treatment	Rate (mL or g/0.1 kg)	Weight Loss %	Damage %	Germination %
CSO	1.50 mL	0.3 f	1.1 f	70.3 bc
	1.00 mL	1.6 e	4.7 e	73.3 b
	0.75 mL	1.9 e	5.6 e	62.5 bc
	0.50 mL	3.1	8.5 d	64.8 bc
	0.25 mL	5.9 c	14.6 c	65.8 bc
NSO	1.50 mL	0.0 f	0.0 g	59.8 bc
	1.00 mL	0.0 f	0.0 g	73.8 b
	0.75 mL	0.3 f	0.9 f	77.0 b
	0.50 mL	7.6 b	20.6 b	55.8 bc
	0.25 mL	9.6 a	25.5 b	56.0 cd
Malathion5% dust	0.05 g	0.0 f	0.0 g	92.3 a
Acetone treated	2.00 mL	10.7 a	31.9 a	47.8 c

Means in columns with the same letter are not significantly different at α = 0.01. Mean separation was analyzed by the Student–Newman–Keuls test; CSO = Citrus Seed Oil; NSO = Neem Seed Oil; Source; Kifle et al. ^[4].

In general, this assessment revealed that insecticidal plant parts that are readily available locally play a crucial role in preventing pest damage in storage under various circumstances. In order to combat the significant infestation of storage pests, small-scale farmers might be encouraged to employ these readily available, affordable, and biodegradable plant products. It is critical to provide the target group with adequate knowledge on the formulation and application techniques, potential residual effects, toxicity to non-target species, and the ease of accessibility of those selected plant botanicals for practical use against target storage pests.

4. Use of Inert Dusts

Grain and seed storage have long been done using inert materials like wood ash, lime powder, sand, and other mineral dust. According to studies on the effectiveness of various insert dusts, using SilicoSec at 0.1% w/w, filter cake at 1% w/w, wood ash at 2.5 to 10% w/w, and sand at 30–70% was suggested as a substitute for reducing maize weevil damage under storage circumstances (Table 4). Similarly, coffee husk and wood ash at different rates also showed a good effect against the maize weevil ^[16]. An experiment done on grain wheat treated with ash and sand showed less grain and weight loss by S. cerealella and Tribolium spp. than the untreated grains ^[9]. A test conducted in the Gambella region also indicated that wood ash had a significant effect on managing bruchids on cowpea and a 90% reduction in F1 progeny of C. chinensis ^[17]. Similarly, cotton and Ethiopian mustard seed oils exhibit strong toxic activity against the Angoumois grain moth under laboratory experimental conditions ^[18]. In conclusion, the development of secure repellents against product pests is required due to the growing adverse effects linked with the usage of synthetic insecticides against stored product insects. Although different inert dusts, such as wood ash and other admixed grains, provide efficient protection against insect pests in storage, using inert dust in large amounts has several drawbacks. Alternative materials that could be effective at acceptable lower costs should therefore be given consideration.

Table 4. Main effects (±SE) of inert dust (SilicoSec, filter cake, and wood ash) and their rates on the percent of the mortality of adult maize weevil 3, 7, and 15 days after exposure.

Main Effect	Inert Dust/Rate (% w/w of Grain)
	SilicoSec Rate			Filter Cake Rate			Wood Ash Rates
	0.05	0.1	0.2	1.0	2.5	5.0	2.5	5.0	10
3-day after exposure
	98.8 ± 1.3 a	99.1 ± 0.4 a	99.5 ± 0.9 a	87.4 ± 2.4 cd	92.3 ± 7.8 bc	97.8 ± 7.5 ab	65.0 ± 6.9 f	73.2 ± 12.7 ef	79.6 ± 5.5 de
Inert dust		99.1 ± 0.43 a			92.5 ± 1.58 b			72.6 ± 3.29 c
7-day after exposure
	99.4 a	100 a	100 a	95.8 ± 0.67 ab	98.5 ± 1.33 ab	99.6 ± 4.22 a	84.7 ± 6.57 c	89.0 ± 8.04 c	93.7 ± 5.22 c
Inert dust		99.8 a			97.9 ± 0.64 b			89.1 ± 1.61 c
15-day after exposure
	100 a	-	-	100 a	100 a	100 a	97.6 ± 1.11 b	99.3 ± 2.0 ab	99.3 ± 0.67 ab
Inert dust		100 a			100 a			98.7 ± 0.37 b

Means with the same letter in a row are not statistically significant at α = 0.05. “-” Data not available as all treated insects died. Source: Girma et al. ^[19].

5. Resistant Varieties

Different storage pest species react differently to different crop varieties for feeding and reproducing. Experiments conducted with hybrid maize varieties showed different levels of resistance to maize weevil and large grain borer ^[20]. In this case, maize genotypes such as AW8047, INT-A, Pob-62TLWF-QPM, TUXEPENO C6, USB, and Golden Valley were reported as comparatively resistant to the maize weevil, and these technologies can be used by resource-poor farmers ^[20]. Maize varieties with a tight and complete husk cover were selected by most farmers for its advantage of protecting against field infestation of the grain better than those with bare-tipped ears ^[2]. Similarly, significant differences in the storage resistance of haricot bean varieties to insect pests were also reported ^[21]. Likewise, 21 maize varieties were recently tested for resistance to maize weevil in the Bako Agricultural Research Center and the results of this study indicated that, based on the selection index, 6 were classified as resistant, 5 were rated as moderately resistant, and 8 were rated as moderately susceptible ^[13]. Currently, one weevil-resistant maize variety has been released by the National Maize Research Center ^[13]. In this approach, it is important to note that, for the effective use of resistant varieties against storage pests, the use of Marker Assisted Selection (MAS) methods can enhance the speed of resistant cultivar development. As a result, these new resistant types could be used as an affordable and environmentally responsible strategy to lessen post-harvest loss during storage. The resistant variants might also be a crucial part of an integrated pest control plan against pests that invade storage facilities.

6. Use of Entomopathogenic Fungi

Currently, many farmers and growers in developed countries are familiar with the use of predators and parasitoids for the biological control of arthropod (insect and mite) pests. However, it is also feasible to use specific microorganisms that kill arthropods. These include entomopathogenic fungi, nematodes, bacteria, and viruses. There are over 750 different types of fungi that can attack many insect and mite species simultaneously; although, some species and fungal strains have very specific targets ^[22]^[23]. Different experimental results in Ethiopia indicated that isolates of the two most common entomopathogenic fungi, Beauveria bassiana and Metarhizium anisopliae, showed a significant difference in mortality and the survival time for pests including the sesame seed bug and maize weevil (Table 4). The efficacy of 13 isolates of entomopathogenic fungi (Beauveria, Metarhizium, or Paecilomyces sp.) was assessed against S. zeamais and P. truncatus using a total immersion bioassay technique in the laboratory ^[6]. The result obtained indicated that all isolates tested were virulent to P. truncatus (98–100% mortality), while M. anisopliae and B. bassiana were virulent to S. zeamais (92–100% mortality); the isolate of Paecilomyces spp. was found to be the least virulent against S. zeamais (26.3–64.3% mortality). However, the pathogenicity and virulence level varied with the concentration and strain of the isolates ^[6]. According to this study, P. truncatus proved to be more susceptible to the entomopathogenic fungi tested than S. zeamais under Ethiopian conditions.

In general, there is a lot of pressure on farmers and growers to use fewer chemical pesticides. In order to combat storage pests, various control strategies must be sought out. The research to date suggests that utilizing entomopathogenic fungi may be a promising alternative strategy to manage the pests of stored products under particular storage conditions. Additionally, this technique could be used in Integrated Pest Management (IPM) programs.

7. Integrated Pest Management (IPM)

Integrated pest management emphasizes the integration of disciplines and control measures, such as varietal resistance, cultural methods, physical control, insecticidal plants, natural enemies, and pesticides, into a total management system to prevent pests from reaching damaging levels. However, only some reports on integrated management of post-harvest pests in Ethiopia have been available so far. In Ethiopia, the integrated use of the varieties, chenopodium plant powder, botanical triplex, SilicoSec, and filter cake against maize weevil was reported ^[14]. Generally, due to the costs and feasibility implications of using specific control methods, none of the various methods listed above can ensure safe storage. Therefore, it is crucial to combine all of the current pest control techniques, including biological control, cultural approaches, resistant genotypes, and other non-polluting techniques, in order to develop a post-harvest loss management strategy that is both affordable and long-term.

References

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Muez Berhe

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