CHAPTER III Vertebrate Pests: Damage on stored foods

1.1. Magnitude of the Problem

1.2. Losses by Crop Type due to Rodents

1.3. Stored Food Losses at Farm Level

1.4. Disease Implications

1. Introduction

General information on stored food losses at the farm and village level in developing countries is sparse and poorly documented. While it is known that millions of people throughout developing countries share their meagre households and foods with rats, mice, and pest birds, these problems mainly have escaped documentation by scientists and agriculturists. Farm families, living in or near poverty and nutritional catastrophe, suffer a double loss - a portion of their crop both before as well as after harvest.

While field crops are usually vulnerable to vertebrate pest damage during a short portion of the growing season, stored foods are vulnerable for as long as they are held in storage, sometimes for 6-12 months. Most storage of harvested crops occurs in farm household structures; these structures in the tropics and subtropics invariably are infested by one or more species of commensal and/or indigenous rodents and possibly depredatious birds. Stored foods are regularly lost due to the consumption, contamination, wastage, and spoilage by vertebrate pests. Most serious of all is the loss of seed for the next crop.

This chapter will attempt to show the extent of the problem, describe the vertebrate pest species responsible for stored food damage, and suggest some methods of managing and preventing damage by rodent and bird pests.

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* USDA/APHIS/WS/National Wildlife Research Center, Fort Collins, CO 80524 USA

1.1. Magnitude of the Problem

The first attempt to document the world-wide problems of stored food losses due to rodents was the mail survey by Hopf et al. (1976). The responses from a questionnaire about stored food losses included estimates made by stored food managers and agriculturists (Table 1). Almost all responses were guesses as to the actual amounts of stored foods lost due to rodents. The authors state: "The one single fact which emerges from the survey is the widespread ignorance of the magnitude of the rodent problem, and of means to control it."

The following year, Jackson (1977) reviewed stored food losses due to rodents on a world-wide scale, using published sources; however, he was faced with the same lack of precise data. Subsequently, the US National Academy of Sciences (1978) published its review of post-harvest food losses throughout the food pipeline in developing countries. It concluded "Although the methods of loss estimation are frequently suspect and the supporting data rough, there are, as we have noted, sufficient data to show that substantial amounts of food are being lost annually in the post-harvest system."

During the ensuing two decades since these reports were issued, very little new information on stored food losses at the farm and village level was added. Several conferences and books on rodents since 1980 have only touched on the subject of stored food losses (Dubock,ed., 1982; Meehan, 1984; and Richards and Ku, 1986). Rodent Pest Management (1988), Prakash's book, didn't include a separate chapter on post-harvest problems; however, stored food losses are mentioned briefly in three chapters summarising rodent problems in South America, Asia, and Africa. Similarly, Buckle and Smith (1994) included a chapter on rodent control in food stores, but new information was absent.

Table 1. Stored food losses at farm and village level as reported on the mail survey of Hopf et al.
(1976).
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Area	Type of storage	Commodities	Percent damage or loss
Asia:
Bangladesh	Bamboo bins	Rice, wheat	5
India	Village stores	Rice, wheat	1.7
India	Village, bags	Rice, wheat, millet, sorghum	3.5-5
India	bins, bags	Mud and bamboo Rice, wheat, pulses, sorghum	2-5
Korea	Sacks	Rice, barley	20
Laos	Cribs, mud and bamboo bins	Rice	3
Malaysia	Cribs in roof	Rice	2-5
Nepal	Sacks	Maize	3-5
Philippines	Cribs, sacks	Rice, maize	2-3
Thailand	Sacks in roof, maize in cribs	Maize, rice	5
Turkey	Farm houses, underground pits	Wheat, rice, maize	5
Africa:
Egypt	Houses and stores	Maize, wheat, rice, cottonseed	50
Ethiopia	Huts on stilts, underground, bags	Grains	5-15
Ghana		Grains, maize, rice	2-3
Malawi	Woven cane bins, grass baskets	Maize, groundnuts, sorghum, millet	0.5-1.5
Malawi	Cribs	Cob maize	15
Sierra Leone	Cane baskets	Rice	1-10
Sierra Leone	Sacks	Rice	10-100
Sierra Leone	Roof and cribs	Rice, maize	2-3
Zaire	Bags in roof	Rice, maize	3
Zambia	Farm cribs	Cob maize, sorghum, millet	10
Latin America:
Mexico	Cribs, sacks in roofs	Rice, maize	5-10
Brazil	Stacks, sacks, cribs	Rice, maize, beans	4-8

1.2. Losses by Crop Type due to Rodents

Losses occur due to various causes along the entire post-harvest pipeline. In this review, however, we are concerned mainly with losses caused by rodents and birds occurring in farm and village storage. Further, we will focus on cereal grains and legumes, since these two food groups together account for more than half of the world's food production.

1.2.1. Rice:

The data for rice losses from several causes in Asia probably approach the level of accuracy with which it is possible to assess losses on a large, nonexperimental scale. These are summarised for the Philippines by De Padua (1974), for Bangladesh by Greeley (1982), and forIndonesia by Winaro (1984). The losses in storage are primarily due to insects, rodents, and fungi. These range from 2-6 percentage in the three studies.

Table 2. Rice losses from harvest to milling in Asain countries (% weight loss)

	Philippines	Bangladesh	Indonesia (season)
			Wet	Dry
Harvesting	1-3	1.45	0.89	0.63
Handling	2-7	1.03	--	--
Threshing	2-6	1.79	0.99	0.99
Drying	1-5	--	3.16	2.65
Storing	2-6	2.60	2.25	2.45
Milling	2-10	--	4.50	2.46

Post-harvest rice losses in developing countries are summarised in Table 3. The loss criteria were not given in the NAS (1978) report. In general, reported storage losses in rice are least in Asia, more in Africa, and most severe in Latin America. This may be because where research and documentation are done thoroughly, the loss estimates tend to be lower.

1.2.2. Maize:

Maize losses appear to be moderately serious in African countries and severe in the Latin American region (Table 4). There are few reports from Asia; consequently no

Table 3. Reported post-harvest losses of rice world-wide (US NAS, 1978, based upon FAO data, 1977 unless otherwise indicated).

Region/Country	Total Percent Weight Loss	Remarks
Africa:
Sierra Leone	10
Uganda	11
Rwanda	9
Egypt	2.5	(Quoted in NAS, 1978)
Asia:
Bangladesh	7
India	3-5.5	Improved traditional storage Boxall and Greeley,1978)
Indonesia	2-5
Malaysia	5	On-farm storage (Quoted in NAS, 1978)
Nepal	3-4	On farm storage
Sri Lanka	2-6	On-farm storage (Quoted in NAS, 1978)
Thailand	1.5-3.5	On-farm storage
		On-farm storage (Quoted in NAS, 1978)
Latin America:
Belize	20-30	On-farm storage (Quoted in NAS, 1978)
Bolivia	16	On-farm storage
Dominican Republic	6.5	On-farm storage

conclusions can be drawn on losses from this region. FAO (1977) reported the losses in maize as averaging from 9.6 to 20.2 percent, mainly in storage and due primarily to insect damage, followed by fungus and rodent damage. However, the data are markedly inadequate. Maize presents considerable problems of loss estimation because it can be stored either on the cob or shelled. In South America the ears are bent down on the stalk and are left in the field to dry. This may lead to some rodent and bird damage before harvest.

Table 4. Reported post-harvest losses of maize world-wide (US NAS, 1978, based upon FAO, 1977 data unless otherwise indicated).

Region/Country	Total Percent Weight Loss	Remarks
Africa:
Benin	8-9	Traditional on-farm storage (Harris and Lindblad, 1978)
Malawi	8	On-farm storage (TPI, 1977; Schulten, 1975)
Nigeria	1-5	On-farm storage
Rwanda	10-20	On-farm storage
Zambia	9-21	On-farm storage (Adams and Harman, 1977)
Asia:
Pakistan	2-7
Latin America:
Belize	10-20	On-farm storage (Quoted in NAS, 1978)
Brazil	15-40
Dominican Republic	19	Farm storage
Honduras	20-50	Traditional storage, poor facilities (Quoted in NAS, 1978)
Mexico	10-25
Nicaragua	15-30
Paraguay	25	(Quoted in NAS, 1978)
Venezuela	10-25

1.2.3. Wheat:

Farm losses of wheat reported from several countries indicate that this crop is lost in about the same percentage as rice (Table 5). The loss reports for wheat average 10 percentage, with the combined major causes being insects, rodents, and mould during storage. Rodents are a major problem of stored wheat in India, but are only partly responsible for the estimated 10 percentage losses there.

1.2.4. Millets and Sorghums:

Millets and sorghums are the main staple in drier regions of Africa, the Middle East, India, Pakistan, and China. Post-harvest technology is relatively unimproved for millets and sorghums as compared to that for the major cereal grains. Sorghum commonly stands in the field, or in piles, in Africa. This results in serious losses due to field rodents. The few reports on post-harvest losses in farm storage available are given in Table 5; these are relatively severe.

Table 5. Reported world-wide post-harvest losses from all causes of wheat, millets, and sorghum (US NAS, 1978, based on FAO, 1977 data unless otherwise indicated).

Region/Country	Total Percent Weight Loss	Remarks
Wheat:
Pakistan	5-10	On-farm storage (Quoted in NAS,
India	8-25	(Quoted in NAS, 1978)
Rhodesia	10	On-farm storage (Quoted in NAS, 1978)
Sudan	10
Bolivia	7	Stores
Brazil	1-4	Storage
Millets:
India	5	Farm storage (Quoted in NAS, 1978)
Mali	2-4	On-farm storage (Guggenheim, 977)
Nigeria	0.1-0,2	On-farm storage
Zambia	10	On-farm storage
Zimbabwe	10-15	On-farm storage (Quoted in NAS, 1978)
Sorghum:
Nigeria	0-37	On-farm over 26 months (Hall, 1970
Senegal	1-5	On-farm storage (Spencer et al. 1975)
Zimbabwe	25	On-farm storage (Quoted in NAS, 1978)

1.2.5. Grain Legumes:

Rodent damage to grain legumes (beans, peas, lentils, cowpeas, groundnuts) is minimal. Legumes are not preferred foods of rats and mice except for groundnuts. Damage in farm-level storage is given in Table 6. Most damage is due to insects and fungi, not rodents. Experienced observers agree that legume post-harvest losses most often exceed those of cereal grains.

Table 6. Post-harvest losses at farm-level of grain legumes due to all causes (NAS 1978).

Country	Total Percent Weight Loss	Remarks
Kenya	30	On-farm storage (De Lima, 1973)
Zimbabwe	5	On-farm storage (NAS, 1978) (Groundnuts)
Thailand	12-15	Farm stores (NAS, 1978)
Honduras	20-50	On-farm storage (NAS, 1978) (Dry beans)

1.3. Stored Food Losses at Farm Level

There are several studies of stored food losses at farm level carried out since 1980. The losses of stored paddy (rice) from open woven bamboo storage baskets at Bangladesh farm households was indirectly measured by trapping small mammals in farm structures and estimating their populations before and after removal trapping by inked tracking tiles (Mian et al. 1987; Ahmad et al. 1994). These two studies estimated stored food losses based upon the numbers of small mammals found in farm structures and the amounts of stored paddy they potentially could consume, contaminate, or hoard. It was found that this approximated 50 kg of paddy/farm family/year. This amount of paddy represents about 5 percentage of the average 1,000 kg stored by the farm families over a crop season.

1.3.1. Other Losses.

Much grain on smallholder farms is stored in various containers, including woven baskets, earthen jars, metal cans, and in jute bags. Jute bags are frequently damaged by rodents. Often the monetary loss of bag or basket damage is greater than the loss of stored grains.

Rodents also contaminate stored foods with their faeces, urine, and hairs. This contamination often is more serious than the actual food losses because of the public health aspects and the possibility of disease transmission. The foods must be cleaned before being prepared for human consumption.

1.4. Disease Implications

The rodents that frequent food stores and live in close association with humans (commensal) in many parts of the tropics and subtropics in developing countries are also known to be the reservoirs and vectors of several human diseases. Among these are plague, murine typhus, Lassa fever, leptospirosis, several types of haemorrhage fevers , including hantavirus, and salmonella infections. Roof rats, Norway rats, Polynesian rats, multimammate rats, and lesser bandicoot rats spread plague and murine typhus through their fleas. Lassa fever is known to be spread by the urine and faeces of the multimammate rat in parts of west Africa. Leptospires are bacteria present in the urine of roof rats and Norway rats. Hantavirus is spread in the droppings and urine of Norway rats and other rodents (Peromyscus, Sigmodon, Microtus, Oligorzyomys species). Argentine/Bolivian haemorrhage fevers are spread by the Calomys species in parts of

Bolivia and Argentina. Salmonella organisms are spread through the droppings of all the commensal rodents, house mice and rats alike. Prevention, reduction, or elimination of rodents from farm and village structures where these diseases are prevalent can reduce food losses as well as increase human health.