storage All stages of producing peanuts to trade this product 11
Post-harvest losses during storage are among the major problems of the tropical environment, where high relative humidity and temperature are prevalent. As a consequence, mould growth in groundnut seed contributes considerable to bio-deterioration. Groundnut being an oilseed crop is more prone to mould attack than starchy seeds. Lipid peroxidation results in the formation of aldehydes, ketones and other low molecular weight compounds, which may cause off-flavours and odours in stored groundnut seed. Further, these react with proteins, amino acids and vitamins to decrease the seed quality.
Maintenance of seed quality increases with increasing impermeability of packaging and storage material. Seed stored in-shells resulted in 50 percent greater viability than storage as kernel. In estimating the losses caused by insect pests to a consignment of any stored commodity, it is not practical to examine every grain. Measurement of the loss to the commodity as a whole has to be based on the losses recorded from a number of samples. These samples cannot simply be removed from the commodity where it is most accessible,
e.g. from the top of sacks or from the surface of a large heap. Insect infestations are seldom uniformly or even randomly distributed within a stock of stored grain. Thus, to obtain samples that give a true indication of loss, methods must be used which ensure that every grain has an equal chance of selection. The theoretical principles of representative sampling should be applied to all types of groundnut storage regardless of the scale of the storage operation. However, the practical problems involved will differ with the storage situation. For the benefit of the readers following methods for calculating the yield losses due to storage pests as mentioned in the ICRISAT Technical Bulletin no. 22 are given below (Dick, 1987).
3.7.1 Sack storage
Sampling from grain stored in sacks usually involves numbering all the sacks in a stack or warehouse and using random number to decide which of the sacks are to be sampled on any one occasion. With large consignments, the conditions of storage may very markedly between the sacks, e.g., the temperature at the centre of a sack may be different from that at the surface. These differences should be taken into account by using a “stratified” sampling procedure. At its simplest, this involves the division of a single stack into a number of layers, each containing the same number of sacks. A given number of sacks in each layer are then chosen at random for sampling.
As a practical guide, the optimum number of sacks to be sampled from consignments of differing size is as follow:
- 10 sacks or less, sample each sack,
- between 11 and 100 sacks, sample 10 sacks,
- more than 100 sacks, the number to be sampled equals the square root of the total. Ideally, the sacks can be numbered and the first samples removed, when the consignment is being placed in storage. This provides a baseline measure against which the losses recorded in subsequent samples can be compared. One the sacks have been stacked many of them are inaccessible. To obtain representative samples, the sack must be dismantled and this will inevitably involve some expenditure on labour and disruption of normal stock movements with in the store. When sacks are broken down for sampling, the sacks should be replaced in their original positions so that the distribution of insects within the stacks is affected as little as possible. It is stressed that if samples are taken only from the most accessible sacks then the loss measurements obtained only represents that part of the total bulk from which they are collected. Similarly, if stocks are removed during the survey then loss levels in subsequent samples must be applied only to that part of the original material still in store.
Just as each sack to be sampled must be selected without bias, every grain within a sack must have an equal chance of inclusion in the final sample. Specialized equipment is available for removing representative samples from sacks of groundnut, e.g. the TDRI Produce Flow Sampler or for reducing the size of large samples without bias in the laboratory, e.g. Boerner or Gamet dividers. Representative samples can be obtained by “coning and quartering” if no suitable equipment is available. This involves emptying a sack onto a smooth surface, thoroughly mixing the pods or kernels by hand and forming a cone shaped heap, which is then divided into quarters using a flat board. Two opposite quarters are returned to the sack. The remaining two are recombined and the process is repeated until a sample of the appropriate size is obtained.
3.7.2 Bulk storage
Representative samples can be taken accurately from groundnut in sacks, because the consignment to be examined can be divided into easily identical units. These can then be numbered and sampled at random. This can also be done with bulk storage, when the storage is being filled. The containers used to transport the crop to the storage can be designated as the sampling units; these can be numbered and then selected at random for sampling.
3.7.3 Quantitative loss determination
Sampling at monthly intervals is generally recommended. When a delay between sample collection and analysis is expected the samples should be placed in plastic bags with a drop of liquid fumigant such as carbon tetra chloride in order to prevent further development of the insect population in the sample.
There are several acceptable methods for estimating the mass (weight) loss stored cereals and pulses. Yet, there is little experience in using these methods with groundnut. The procedure selected depends on factors such as the availability of equipment and the estimated number of samples to be collected. Whichever method is chosen, groundnut samples must be shelled before mass loss can be assessed. As the wet mass of groundnuts will change with the ambient RH it is usually necessary to perform the calculations using the dry mass of each sample. This can be obtained either placing a sub sample of the groundnut kernels in a suitable calibrated moisture metre or by drying a number of sub-samples (5 x 10 g) in an oven at 103±2°C for 16 h.
3.7.4 Standard volume/mass method
The accuracy of this method depends on obtaining an exact standard volume of grain using a simple apparatus called volume of grain using a simple apparatus called a chondrometer that drops an amount of grain from a fixed height into a container of precise volume. The relation between the dry mass and the moisture content of the standard volume of non-damaged grain at the time of storing is plotted on a graph. The dry mass of standard volumes of grain from later samples can then be compared to that of the initial sample and the percentage mass loss calculated as follows:
% dry mass loss= D1 x 100
where: D1= dry mass of the standard volume at the beginning of the experiment (read from the graph using the same moisture content as that obtained for DX) and DX= dry mass on occasion X.
In large-scale surveys, which may include numerous sampling sites and different crop varieties, grain size often varies markedly between samples. A single volume/mass relationship cannot be applied to all the samples. The standard volume/mass method can be adopted to allow for situations where baseline samples could not be collected. Each sample can be divided into damaged and apparently non-damaged portions. The mass loss is the difference in dry mass between the non-damaged and damaged portions. With this ‘adapted’ method relatively large samples (>1 kg) may be required in order to obtain enough damaged or non-damaged grain to measure the mass of the standard volume.
3.7.5 Thousand-grain mass (TGM) method
In this method, a sample taken when the commodity is placed in storage is weighed, the number of grains is counted and their moisture content is determined. The dry mass of 1 000 grains is then obtained using the formula:
TGM= 1 000 x m x (100-H)
N x 100
Where: wet mass of the working sample; H= percentage moisture content of the grain; and N= number of grain in the working sample.
The mass loss to subsequent samples as a result of infestation is calculated by using the formula:
% dry mass= M1 – Mx
Where: M1 = TGM of grain at the beginning of the study; and MX = TGM of the grain on occasion X.
3.7.6 Count-and-weight method
This method involves weighing and counting only and generally requires smaller samples than the standard volume/mass method. Each sample is divided into damaged and nondamaged portions. The grains in each portion are then counted and weighed and the moisture content of sample determined. Mass loss is calculated as:
% dry mass loss= U (Nd + Nu) x100
Where: Nu= number of non-damaged grains; Nd= number of damaged grains; U= dry mass of non-damaged grains; and D= dry mass of damaged grains.
The count-and-weight method was used by The ICRISAT to assess losses to in-shell groundnuts stored in sacks at an oil mill warehouse near Kurnool in Andhra Pradesh, India. The results showed that if hidden infestation was ignored, loss were underestimated by 1 to 2 percent of the initial dry sample mass (Dick, 1987).
Several insects attack groundnuts and groundnut products in storage, sometimes causing severe damage. Approximately 6 to 10 percent of the groundnut insects destroy kernels stored in bags. However, no precise numbers of losses are available. For estimation of losses quantity as well as quality losses should be considered. The standard methodology of collecting samples should be followed.
Groundnuts are stored in shells and as kernels and are highly susceptible to attack by various insect pests. The amount of deterioration caused by these biological factors depends upon the condition of the groundnuts defined by moisture content, how it is stored and its maturity at harvest. Insect infestation causes dry mass loss and increases the level of free fatty acids in the kernels. The result is a reduction in quality.
Due to heavy pest infestation the kernels are completely damaged, losing their germinability. The heat and moisture generated by large insect populations within heaps or stacks of groundnuts may also increase the risk of mould growth. The treatment of groundnuts before storage including harvesting, curing, drying, threshing and handling affects the degree of infestation in storage. Mature pods are less susceptible to deterioration than immature pods. Cracks in the pods developed during drying and handling also boosts the susceptibility to pest attack. The careful and scientific drying of pods prevents the infestation of the fungi and mites.
The number and variety of insect species found in groundnut warehouses and farmers’ stocks are quite extensive. Groundnut in storage, particularly in farmers’ stock, may contain extraneous plant material. Therefore, the insect species found associated with these groundnuts may actually be attracted to feeding on the extraneous plant materials including fungi, rather than the groundnut crop. These insects are considered contaminants together with the arthropods, parasitoids and predators of the phytophagus pests. An extensive record of these pests has been documented by Pattee and Young (1982). The caryedon serratus is the major pest of groundnut in shell in most of the developing countries.
There are 100 insect species that infest stored groundnuts according to the literature. Only those species considered major cosmopolitan pests are described below.
4.1.1 Caryedon serratus (Oliver) Coleoptera: Bruchidae, Common name: Groundnut borer and groundnut weevil.
This species found in the Gambia, Senegal, West Africa and India, breeds on common tree legumes such as Tamarindus indica L. plus harvested groundnuts. It is the only species that can penetrate intact pods to infest the kernels. Infestation of the harvested groundnuts can occur while the crop is being dried in the field, stored near infested stocks or crop residues.
Adult females attach their eggs to the outside of pods or kernels. When the first instar larva hatches it burrows directly through the pod wall to reach the kernel, where the larva feed and develop. A single larva can make a large excavation in the cotyledons, but no sign of damage is visible externally at this stage. Mature larvae emerge partially or completely from the pod and construct an oval papery cocoon. The egg to adult development period is about 42 days under optimum conditions of 30°C and 70 percent RH. The adult is 4 to 7 mm long, with small black markings on the elytra. It is readily distinguished from the other pests of groundnuts by its very broad hind femur, serrate antennae and elytra that do not completely cover the abdomen. Groundnuts damaged due to bruchidae is shown in Figure 36.
Figure 36. Damage due to the storage insects and pests, mainly by Caryedon serratus Bruchidae.
4.1.2. Tribolium castaneum (Herbst) Coleoptera: Tenebrionidae, Common name: rust-red flour beetle.
This species is found throughout the tropics and is regarded major pest of shelled groundnuts. Female lay about 450 eggs at random in the produce. These eggs hatch into cylindrical larvae, which, like the adult, feed on the kernels. Pupation takes place inside the food without a cocoon and the adult beetles may live for 18 months. The developmental period from egg to adult is about 20 days under optimum conditions at 35°C and 70 percent RH. The role of the red flour beetle in the deterioration of shelled groundnuts has been assessed as loss in weight (4.5 percent) and loss in germination (73 percent). The free fatty acid content of the groundnut oil increases manifold, resulting in additional deterioration of quality.
4.1.3. Oryzaephilus mercator (Fauvel) Coloeptera: Silvanidae, Common name: merchant grain beetle.
This species is cosmopolitan in distribution. The adults are 2.5 to 3.5 mm long with a distinctive ridged prothorax bearing six large teeth on either side. Each female lays about 300 eggs loosely in the groundnuts over a 10-week period. The eggs hatch into cream coloured larvae, which move freely until fully grown. Both adult and larvae feed on produce and the adult may live as long as 3 years. The life cycle is completed in 4 to 5 weeks under optimum conditions at 30°C and 70 percent RH. The adult and larva burrow into the groundnut seed causing “warm-cut” groundnut and an increased percentage of split seed. Losses occur through contamination of product by live and dead insects, cast skins, frass and excrement.
4.1.4. Trogoderma granarium (Coleoptera: Dermestidae), common name: Khapra beetle This species is more tolerant of hotter, drier conditions than many other storage pests and is commonly found in semi-arid areas of Africa, West Asia and Northern India. The female lays about 50 to 80 eggs that develop into adults with in 25 days under optimum conditions (35°C and 25 percent RH). When nearly mature, the pre-diapauses larvae often leave the stored commodity to enter crevices in the storage structure where they can remain without feeding for many months. The adult beetle is small, 1.5 to 3.0 mm long, densely covered with hair and the larvae are straw coloured with numerous tufts of hair. The adult lives about 14 days.
Consequently, complete disinfestations are difficult and for this reason many countries reject consignments of a commodity infested by this species.
4.1.5. Elasmolomus sordidus: (Fabricius), Hemipetera: Lygaeidae
This bug is widespread in tropical Africa and India, occurring on pods left for drying in the field and in store. The adult is dark brown, approximately 2mm wide. In the field females lay their eggs in the soil or on groundnut haulms but in store, eggs are laid loosely among the groundnuts or in sacking. The first instar nymphs have a bright red abdomen; later instars become progressively darker. All stages feed on kernels, perforating the pods with their rostrum. This causes the kernels to shrivel and increases the free fatty acid content of the oil, producing a rancid flavour.
4.1.6. Corcyra cephalonica: (Stainton) Lepidoptera: Pyralidae, common name: rice moth
This species has the ability to develop at low humidity (<20 percent RH). The adult is brown and 12 to 15 mm long with its wing folded. The head bears a projecting tuft of scales. The female lies up to 150 eggs within a few days of emergence from the cocoon. The larvae are mobile and feed upon and within the kernels. Infestation causes aggregation of kernels by the presence of webbing. The development period at optimum temperature (range: 28 to 30°C) is 4 to 5 weeks. The larvae are capable of damaging intact kernels and feed both on the surface and within seed. They spin a tough silky fibre, webbing together kernels, frass and cast larval skins.
4.1.7. Ephestia cautella (Walker) Lpidoptera: Pyralidae, common name: tropical warehouse moth, almond moth
This pest is common throughout the tropics but is less prevalent in arid areas. It commonly infests shelled groundnut in store. It is a dull greyish brown moth. The forewings have obscure markings, with an outer pale band and broad dark band with a broad pale band on the inner edge. The adult avoids strong light and rests in dark places during daylight. Female lays up to 300 eggs in the groundnut produce often by simply dropping the eggs through holes between the fibres in jute bags or by laying eggs liberally on the surface of the kernels. The larvae move freely through the produce contaminating it with webbing and frass. They feed on the kernels until they are mature. In optimum conditions at 28°C and 70 percent RH, the eggs hatch in three days, develop from egg to adult in about 24 days and complete the life cycle within 40 to 50 days.
4.1.8. Plodia interpunctella (Hubner), Lpidoptera: Pyralidae, common name: Indian meal moth.
This species is more frequently found in cooler areas of the tropics, e.g. highland regions. The basal third of the forewing of this moth is a pale yellowish buff colour. The reminder is reddish brown. The larvae feed on and within kernels and spin a silken thread on which the larval droppings accumulate. Females lay about 500 eggs at a time and development from egg to adult takes about 26 days. The life cycle of this moth may be prolonged by the diapause under certain temperature conditions. During diapause the metabolic activities are very low and normal application rates of control chemicals, especially use of fumigation may not prove effective.
4.1.9. Alphitobius spp. (Coleoptera: Tenebrionidae), Common name: Black fungus beetle.
These species (Alphitobius diaperinus ans A. laevigatus) are 5 to 7 mm long. They feed upon damp kernels, groundnut cake plus other grain residues and their presence in groundnut stores and oil extraction mills is indicative of poor storage conditions involving spillage and dampness.
4.1.10. Cryptolestes ferrugineus: (Coleoptera: Cucujidae), common name: Flat grain beetle.
These beetles are small, 1.5 to 4 mm long, flat-bodied and light brown in colour, with long antennae which can be more than half the length of the body. They are mainly scavengers and tend to breed in broken or dusty produce with high moisture content. They are not normally a primary pest of groundnut or groundnut products, but may frequently be found in association with other species.
Records list over 100 insect species that infest stored groundnuts. In India the major pests of groundnut in store are: rust-red flour-beetle, Tribolium castaneum Herbst; the saw-toothed beetle, Oryzaephilis surinamensis Linn., the almond moth, Cadra cautella (Walker) and the rice moth, Corcyra cephalonica (Stainton). The first two species cause damage both in adult and larval stages while the other species harm the crop only in the larval sage. The other minor pests in storage are: Necrobia rufipes (Degeer); corn-sap beetle, Carpophilus dimidatus Fabr.; the khapra beetle, Trogoderma granarium Everts; caddle beetle, Tenebroides mauritanicus Linn.; and the lesser grain-borer, Rhizopertha dominica Fabr. Bruchid Beetle (Caryedon serratus) is the major storage pest of groundnut found in many parts of tropical Asia and Africa. It breeds on common tree legumes such as Terminalia indica L. as well as on harvested groundnuts. It is generally regarded as the only species that can penetrate intact pods to infest the kernels. The insect infestation causes considerable losses to the stored groundnuts either stored in-shell for the seed purpose or shelled for milling. Estimated losses due to this pest in India are about 19 to 60 percent when stored for more than 5 months (Pal et al., 2000).
In Gujarat the only primary pest of stored pods Caryodon serratus was reported in 1969 but remained a pest of tamarind and only a minor pest of groundnut. However, this pest became a major problem in 1990s. In this part earlier farmers use to store their rainy season produce for the summer planting and next rainy season (about 8 to 10 months storage). Now, due to Bruchid, farmers are unable to store their produce. Storage of the seed by the seed cooperative agencies is being managed by fumigation of Clphos®. In a study of the development of pest populations on stored groundnuts in warehouse in Andhra Pradesh, India, serious losses by groundnut Bruchid were recorded. Reports of damage to groundnuts by this species had previously been confined to West Africa (Dick, 1987). A good post harvest pest management based on good storage practices is the most vital solution. The need for alternatives to chemical measures for the protection of stored products is also strongly felt. In particular, the discovery of insect resistance to methyl bromide and phosphine, the most common fumigants, has intensified the pressure to minimize the use of conventional insecticides against post-harvest pests.
Though various approaches like dissemination of insect pathogen of stored product moths,
e.g. the bacterium Bacillus thuringiensis or Nuclear Polyhedrosis and Granulosis virus are in use, either by directs application onto the stored commodity or by applying formulated products (Pal et al., 2000). Looking for the possible source(s) of resistance of Bruchid beetle in germplasm pool and following the IPM approach may be helpful in the control of the Bruchid.
In West Africa, the extent of post-harvest losses has prompted several studies in insect population development on groundnuts stored as pods and kernels. Still, few attempts have been made to measure the extent of losses caused by insects either in farmers` stores or in large commercial storage. Various methods of estimating the extent of storage losses are outlined in Information Bulletin No. 22 published by ICRISAT (Dick, 1987). The most important storage pest in Nigeria is also Bruchid.
As most post-harvest groundnut pests except Bruchid are unable to penetrate intact pods, leaving the crop in the shell for as long as possible during storage is an effective method of limiting damage. Infestation of clean stock usually begins in the surface layers of a stack or bulk of groundnuts; the application of an insecticide spray or dust will provide some measure of protection against Bruchid. In sack stores, the sacks on the surface of each stack can be sprayed with any of the insecticides recommended for residual application on store walls etc.
although at a lower rate of application (Table 23 and 24). The decision on when to shell groundnut stocks is often based on factors apart from good storage practices, e.g., the economics of transporting a crop destined for export. Groundnut destined for confectionery use or for seed are often shelled soon after harvest so that imperfect or damaged kernels can be discarded. This increases their susceptibility to attack by a number of insect pests. The direct application of insecticides to shelled groundnut is not recommended as this can result in the presence of unacceptable high level of toxic residues. Yet, kernels in sacks can be protected in the same way as groundnuts in-shell, by applying one of the recommended insecticides as a spray or dust to the outside surface of the sacks.
In most of the developing countries where, Caryedon serratus is most common storage pest, it is advantageous to store groundnuts unshelled. It is important to detect low-level infestation of storage pests if control measures are to be implemented in sufficient time to prevent losses. The use of traps for this purpose often requires less time and efforts than more conventional methods of inspection, such as ‘spear’ sampling. Traps cause less damage to the commodity and often provide the first evidence of an infestation that has developed between store inspections. A variety of traps are available differing in cost, sophistication and in the range of insects attracted to them. In the developing countries the high cost of insecticides, the frequent nonavailability of suitable formulation and packaging along with the increasing incidence of insecticide resistance necessitate an approach to post harvest pest management based on sound storage practices. When determining the need for insecticide application, the economically acceptable level of insect infestation must be considered. This will depend on whether the groundnuts are destined for oil production, local consumption, resale as seed or export.
Insecticide-resistant strains of stored-product pests are known therefore the need for alternatives to chemical control methods for the protection of stored products is now seen as increasingly urgent.
- Control of temperature, humidity and atmospheric gases in storage facilities to create conditions unsuitable for insect development.
- Admixture of abrasive materials such as fine sand, kaolin or wood-ash to protect grain in farmer’s level storage.
- Use of plant material such as crushed neem seed, neem leaves or neem oil, which has an antifeedant or repellent effect on storage pest.
- Dissemination of insect pathogens of stored product moths e.g., the bacterium Bacillus thuringiensis, Berliner or nuclear polyhedrosis and granulosis viruses, either by direct application onto the stored commodity or by attracting insects to traps containing a source of the disease.
- Control of pest by natural enemies.
Use of genotypes resistant to attack by the main post-harvest pests.