STORED GRAIN AND STORED PRODUCT

Mites from Pakistan and Azad Kashmir

By DR. MUHAMMAD SARWAR
Nuclear Institute of Agriculture, Tandojam, Pakistan

Mar 08 - 14, 2004

Mites are microscopic creatures. These are widely distributed throughout the globe. They are found in all types of habitats normally comfortable to mankind. They compete in rivalry to the insects for the control of their habitations. Heavy population of these mites are also found on stored grain and stored products. They cause heavy losses to these commodities annually.

The stored grain and stored products mites infest and damage cereals, seeds of all kinds, bulbs, tubers, decaying materials fresh, cultivated stored mushrooms and dried fruits of all kinds. Food products, especially cereals, are liable to become infested directly and be contaminated by these mites after a definitive period of storage. The mites penetrate the seeds through cracks and rages in the outer covering at the embryo and consume the food materials forming cavities, in which they carry on their development and multiplication. The number of mites in the seeds increase rapidly and the cavity is enlarged until the embryo is completely eaten away. Consequently, the germination of the seed is adversely affected. As a result of the destructive activities of stored grain mites, the capacity of wheat to germinate was lowered upto 54 percent. Similar infestation in rye lowered the germination capacity by 51 percent, finally the weight of mite infested grain was also reduced. Concludingly, seed viability test is suggested at farmers level prior to sowing, at least in wheat crop, to overcome the invisible loss of seed viability. The increase in the seed rate, accordingly, is suggested to have an ideal crop stand. It is hoped that just because of this recommendation, we can multiply our wheat production at least to a single-fold without having any additional input or area under wheat cultivation.

The mites also cause indirect damage to stored grain and their products by raising their moisture contents, generating sufficient heat for the growth of infectious bacteria and fungi. They contaminate the space between the grain with their dead bodies, cast skins and with excrement, thereby, hindering in the circulation of air in the stock. Mites also act as vectors of fungal and bacterial diseases and spread them throughout the whole mass of infested and decaying grain. The damage inflicted by these mites activates the respiratory and fermentation processes within the grain.

Biologically speaking, a majority of the stored grain and stored products mites are restricted in activity and can move only within their adopted micro-climate and for this reason, the hypopial stage is considered to have evolved in this group. Hypopial stage is capable of withstanding adverse environmental and climatic conditions and can, thus, be regarded as a transitory quiescent stage. The suckers on ventral side of the hypopus, a distinctive characteristic of these mites, facilitate its attachment to the phoretic hosts including insects, mites, animals and other materials useful to human beings. Thus, they can reach almost always a favourable environment for further development and breeding.

Lot of research work has been done in different parts of the world on stored grain and stored products mites. Similarly in Pakistan, a little attempt has been made to explore and describe mite fauna of this group. It has been reported from Pakistan about 25 new species belonging to 5 genera of the family Acaridae and 11 new species belonging to 3 genera in case of family Histiostomatidae have already been collected, identified and described from different localities of Punjab, Sindh and NWFP by worthy supervisor Dr. M. Ashfaq of Faisalabad, Agricultural University.

Therefore, keeping in view the enormous amount of damage to agricultural products caused by the stored grain and stored products mites and, the precise identification of the pasts and suspected pests in food industry, need was felt to explore, hitherto, comprehensively the unexplored fauna of the families Acaridae Ewing and Nesbitt and Histiostomatidae Berlese to bridge the gap in our knowledge about the taxonomy of these mites.

For this purpose the collection of stored grain and stored products mites samples were carried out by conducting extensive survey of more than 70 different localities in all the four provinces of Pakistan and including Azad Kashmir.

The present research investigations include, in all, a total of 39 species belonging to 8 genera viz., Forcellinia, Lackerbaueria, Acotyledon, Caloglyphus and Troupeauia of the family Acaridae; Copronomoia, Histiostoma and Glyphanaetus of the family Histiostomatidae have been dealt with. Out of these, 36 species are new additions to Acarology, whereas 3 already known and described species have been provided with new distribution and hosts record.

Identification keys for the 8 genera recorded from Pakistan and Azad Kashmir have been prepared. Identification keys to 72 world species, in genera where complete identification characters were available, and 36 new species as well as differentiation remarks have also been prepared and included in the manuscript. Tables showing comparison of characters and similarity matrices of 36 new species alongwith 48 alien species belonging to families Acaridae and Histiostomatidae have been prepared. Phenograms have been constructed to study the level of phenetic affinity among the various species of different genera and the results emerging from phenetic comparisons have been discussed. Geographical maps of Pakistan including Azad Kashmir showing the distributional areas of the included species in each genus have been prepared.

It is hoped that such approach will serve to stimulate future workers to adopt this objective, method of taxonomic interpretations and their utility will of course lead towards a sound, stable and solid classification of stored grain and stored products mites around the globe as well as in the country.

These studies shall lay basis for further research in ecology, biology and physiology of stored grain and stored products mites, and thus, facilitate to determine and assess meaningfully their potential status in agriculture with regard to the significance of post-harvest losses in the handling and storage of agricultural produces.

Regardless of that what has been presented here in this dissertation, there remains a series of ecological, physiological, behavioural and genetics problems in stored grain and stored products mites for further analysis. As such, further work is needed to verify or modify the views developed here in this presentation.

PREVENTION AND CONTROL OF STORED GRAIN MITES

Not only for the farmers, but to every consumer, the prevention and control of grain and grain products mites is of paramount importance, because, once grain has become infested, it has lost much of its economic value. For this purpose, the attention should be concentrated on the control measures in the field. Prior to harvesting the fresh crops, it is important to prepare the fields depots of the farmers by destroying the mites in their natural habitat, like, the old grain wastes collected near threshing floors. These grain wastes should be destroyed as early as possible, before harvesting and threshing. Prior to harvesting, the threshing floors should be burnt by straws. Storage mites can also live and develop in other field conditions, like, various plant residues, stacks of hay and straw, dead organic matter, stubbles, soil, burrows and plant residues for considerable time. Such field infestations can be eliminated by destroying all these sources of infestation in the proximity or in the vicinity of fields. The transporting and harvesting machineries should be thoroughly cleaned by removing the dust and dirt. Equipments meant for grain collection, where large colonies of over-wintering mites may be present, should be thoroughly cleaned.

It is important to note that all mites prefer dirty and moist grain, therefore, carefully cleaned, dry grain should be kept in the granaries. To preserve newly harvested grain, the danger of infestation must be reduced to the minimum. All grains should be stored in a dry condition as possible, because dry grain is unfavourable for mites development, while, damp grain attracts the large population of mites and accelerates their development tremendously. Preferably, grain should be stored with a moisture content of 10-12 percent. Godowns receiving grain should be carefully prepared before receiving newly harvested grain. Godowns and their surroundings, grain cleaning and transporting equipments should be carefully cleaned. The areas of maximum mite infestation should be treated with a suitable miticide as an emulsion or suspension. Insects, birds and rodents which directly damage the grain are also the vectors of certain storage mites, particularly the hypopial stage from infested storage to healthy one such transporting agents should be destroyed. All these preventive measures are important in the protection of stored grain and stored products. Therefore, it is essential that clean, mite free and weather proof storage be provided, and all the nearly sources of mites infestation be eliminated properly.

Stored grain should be regularly inspected to detect any mite infestation. If they appear, then they should be destroyed immediately. Fumigation of storage at the right time will do more to prevent damage throughout the year. Fumigants, if properly applied will destroy mite infestations, and their should be refumigation whenever infestations are found. To fumigate the storage, to create and maintain a uniform distribution of poisonous gas in grain mass is necessary for appropriate mortality. All the cracks, orifices and other openings in the floor, sidewalls and roof, should be caulked. It is important to note that the use of certain fumigants to fumigate the mites infested grain is not viable due to the reason that the doses recommended for disinfestations do not destroy the eggs and hypopus of the storage mites. To overcome these constraints, cleaning and thermal dehydration are the most suitable methods. Recently, some mites emulsions have been used to disinfest the grain infested by mites.

By using protective covering of dust, wood ashes or similar finely divided materials like silica gel, rock phosphates, precipitated chalk, magnesium oxide, aluminum oxide or the mixing of other local materials with grain to prevent pest damage were found to be satisfactory. The philosophy behind such treatments is that these chemically inert dusts when mixed with grain, they promote the rapid loss of body moisture of pest infesting the grain and cause their death by desiccation. Some pyrethrum powders impregnated with the synergist have been recommended for mixing with grain to protect it from pest attack. These formulations show promise as preventives of infestation and afford excellent protection to stored grain. Such protective dusts or sprays have certain advantages over fumigants; as they prevent infestations from becoming established, do not affect germination and easily applied without hazards. Disinfestations of storage should necessarily be done by the integrated methods. Broadly speaking, these methods include, legislation, cultural practices, physical or mechanical control, biological control, chemical control and the use of resistant varieties.