Public sector storage of wheat in Pakistan and the associated problem of insect pests

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By Hafiz Ahmed, Mubarik Ahmed, Mohammad

Sardar Alam and Siraj Uddin Ahmed**

INTRODUCTION

With its population fast reaching the 100 million mark, Pakistan is still predominantly an agricultural country. It has a total land area of 79.61 million hectares out of which 20.3 million hectare is cultivated. Of the cultivated area, about 70 per cent is irrigated and the balance is mainly rainfed. Agriculture accounts for approximately 30 per cent of the country's Gross Domestic Product and employs a little over 50 per cent of total labour force to earn about 70 per cent of the country's export revenue. The Punjab and Sind provinces are relatively densely populated and are also the main grain producing areas. Surplus grain produced in these provinces is procured and stored by public sector agencies (Table-l) to provide the deficit areas. The main foodgrain crops are wheat, rice, maize and pulses. Wheat is the staple food of the people of Pakistan and is therefore, the most important foodgrain crop. Of the total production of about 19 million tonnes of foodgrains this yesr (1985-86), wheat contributed a record portion of 14 million tonnes. The country has reached a self-sufficiency level for the present in this vital commodity but our needs for wheat are likely to keep growing with our fast growing population. It is projected that despite some limitations, wheat production will increase to about 18 million tonnes by the year 1992-93. Rice is the second important foodgrain crop of Pakistan but its production is nearly static for the last few years varying between 3.0 to 3.5 million tonnes annually of which about 1.0 million tonnes is exported.

PROCUREMENT, STORAGE AND LOSSES:

1. Agencies involved:

From early 50s, government is involved in the procurement, storage and distribution of foodgrains. For this purpose various agencies have been created. The Federal Ministry of Food, Agriculture and Cooperatives (MINFA) formulates policy and sets the minimum prices and procurement targets for public sector agencies. In case of shortfalls in production, MINFA also decides about imports. Other public sector dagencies involved are:

a) Four provincial Food Departments (FDs) having the following functions:

• to purchase wheat of specified qualities from producers and other suppliers;
• to maintain stocks of wheat for market intervention to stabilize prices at a level determined by Government of Pakistan and to supply wheat to government controlled mills to sevice the rationing systems;
• to procure wheat for supplying deficit areas and other agencies;
• to handle imported wheat within the system;
• to procure rice on behalf of the Rice Export Corporation of Pakistan (RECP) in Sind and Punjab.

b) The Pakistan Agricultural Storage and Services Corporation Ltd. (PASSCO), a joint stocks company established in 1973, entered in operation of cereal grain procurement like wheat, paddy, pulses and other agricultural commodities like onion and potatoes on required basis under the direction of the Federal Government.

c) Rice Export Corporation of Pakistan (RECP), is a public sector limited corporation established in 1974. The corporation works on monopoly basis for exporting rice from Pakistan and undertakes all operations connected with the procurement, milling, cleaning, storage, packing and sales of rice for export.

d) National Logistics Cell (NLC), operates a road transport fleet which carries some of the public sector grain stocks. It also undertakes the construction of storage facilities.

Table-II gives the extent of grain storage facilities available with these agencies in the four provinces of the country.

2. Types of storage facilities:

Grain storage facilities in the country are of many types but are mostly horizontal sheds called house type godowns. There are also binishells, hexagonal bins and some silos. These types account for roughly 70, 9, 6 and 6 per cents respectively of the total under cover grain storage capacity in the country. Some details of these storage structures are as under:

i) House type godowns vary in design and capacity form 500 to 16000 tonnes, constructed in different parts of the country to suit local climatic and other requirements. The size of a 500 tonne unit measures 30.48 m x 12.19 m whereas the 16000 tonnes measures 239.6 m x 36.3 m. The size of a standard unit of PASSCO type constructed under IDA aided programme is 30.48 m x 18.90 m with a unit capacity for storage of 1100 tonnes of bagged commodities. The height of units varies between 6.1 7.6 m. The godowns are built on plinths of a height to range between 0.76 - 1.07 m. Wheat is stored in these godowns in bags but in some parts of Punjab bulk-cumbag operational system is also undertaken to increase the storage capacity of the unit.

ii) Binishells are the dome shaped structures made of reinforced concrete, built recently to increase covered storage capacity on an emergency basis. The height of the dome in the centre is about 10 m while floor area has a diameter of about 32 m. Each binishell has a storage capacity of 1500 tonnes of bagged grain.

iii) Hexagonal bins are structures of bee-hive shape with pre bin capacity of 35.7 tonnes and the total single site capacity ranging between 500 and 3000 tonnes. The bins are supported on columns 2.6 m above ground level. Each bin teas a conical hopper at the bottom made of reinforced cement concrete to facilitate the flow of grains through a 15 cm diameter spout, fitted with locking arrangements. The upper access of each bin is by a centrally positioned manhole in the common roof which is about 9 m above floor level. Each site is provided with a 1.2 m wide stairs for carriage of grains to the top in bags for emptying into the bins.

iv) Silos. Previously there were only metallic silos constructed in early 1960s for 42000 tonnes storage at Multan. Recently some concrete silos have also been constructed with each complex of about 50,000 tonnes capacity. These are constructed in double rows of 7 bins in each case. Each bin has a flat base about 0.6 m above ground level. Bagged grain is tipped into the intake pit and fed to the individual silo via a chain and flight conveyer.

3. Extent of losses:

Storage losses in public sector godowns occur mainly due to inadequate covered storage space as well as shortage of trained manpower to manage proper procurement, warehousing and the pest control operations during storage. Basic quality parameters affecting storage such as moisture content of grains, segregation of lots according to the age of the stocks and biological cleanliness of the warehouse etc. are given little credence in the practices being followed. The result is that serious losses take place quite often.

Published estimates about wheat storage losses vary widely and there is even controversy about any weight loss taking place at all. Agencies responsible for warehousing of wheat do not show any losses in their books. They accept such losses only on occasional basis occurring due to exceptional circumstances. However, entomologists visiting public sector godowns firmly believe that losses in quality as well as in quantity of the stored wheat have to be there in view of the heavy insect pest populations. As such, occurrence of losses should be accepted so that the need for loss reduction programmes could be duly stressed with the policy makers.

GRAIN STORAGE RESEARCH:

1. research on extent of losses:

Only recently, MINFA provided funds to PARC for a coordinated research programme to determine storage losses in all the four provinces of Pakistan. A year long study based on actual sample analyses undertaken at Karachi has confirmed heavy losses particularly in quality as well as quantity losses. Country may be different because the climate of Karachi is particularly suitable for the development of insect pests. The study at Karachi has also shown that a part of the weight loss get obscured due to moisture gain by the grain during monsoon season which follow the hot and dry wheat harvest season. Some results of this study on the over all Pakistan situation are presented in Tables lll and IV. On an average wheat was stored for a period of 5.4 months in that year (1984-85) in the various public sector godowns during the course of which it suffered weight loss to the extent of 3.5 per cent (Table-El). The public sector agencies thus suffered a cumulative loss of about 141,600 tonnes of wheat due mainly to the insect activity (TablelV). The most dominant insect species contributing to these losses were the Rhizopertha dominica, Trogoderma granarium, Sitophilus oryzae and Tribolium castaneum.

2 Research on the development of loss reducing technology:

The Grain Storage Research Laboratory (GSRL) of PARC at Karachi are engaged in the development of technology for reducing losses in the public sector grain warehouses as well as for farm level storage of grains. One of the important findings of this laboratory concerning public sector storage of wheat is the discovery that whole godown phosphine fumigations, as being practiced by the Sind Food Department as well as RECP to control insect infestation, are only partially successful. Few live insects were detected in wheat and rice samples taken immediately after phosphine fumigation operations in the godowns at Karachi. The present practice is that doors, windows and ventilators of godowns are closed and mud plastered to make the structures gaslight for phosphine fumigation. Using locally made 0.2 mm thick polyethylene sheets for comparison, it was demonstrated that sufficient phosphine gas was not being retained in such whole godown fumigation operations even for three days compared to the essential five day's exposure requirement. Under sheet fumigation was therefore recommended in 1984 as a substitute to the whole godown fumigating.

Under sheet fumigations only of individual stacks would however, lead to the problem of reinfestation as soon as the sheet was removed for use elsewhere. This fear led us to the testing of under sheet storage of bagged commodities.

An experiment was undertaken in the year 198485 where 2000 tonnes of bagged wheat was stored for 9 months in a godown of the Sind Food Department at Landhi (Karachi) under transparent low density polyethylene sheets. The four stacks of 500 tonnes each were fumigated right from the start of the storage period and the sheets were left on the four stacks to act as physical barriers preventing insect reinfestation. Doors and ventilators of the experimental godown were kept closed throughout the storage period to prevent winds blowing out phosphine from underneath the sheets and also to prevent entry of birds etc. A second fumigation was also undertaken at a later stage when some insects were sighted under the sheet. For both fumigations, half the dose of phosphine was used compared to the dosage generally applied by the Food Department (0.5 gram phosphine gas/cubic meter of under sheet space as against 1.13 gram phosphine/cubie meter internal space of the godown). The cost effectiveness of the technology is shown is Table-V. It will be seen that considerable amount (2.81%) of weight loss took place under the traditional practice of whole godown fumigation despite two fumigations as compared to the very little weight loss under polyethylene sheets. A saving of about 54 tonnes of wheat over a period of 9 months storage was thus demonstrated without incurring any additional expenditure for the under sheet storage and fumigation technology.

In the experiment discussed above, polyethylene sheet was sealed with floor of the godown using sand snakes and entry of insects in the head space of the godown was kept under check by repeated fogging. Spraying with insecticides of the floor area between the stacks was also undertaken to prevent insects from creeping into the covered stacks. To simplify the technique further, large scale replication of the experiment was undertaken in year 1985-86 with modifications of laying polyethylene sheet underneath individual stacks. Another modification was that a polyethylene cap made to size of the stack was used instead of using a sheet to cover it. The sides of the cap were sealed with the under laid sheet thus reducing or even eliminating the need of sand snakes. The use of caps also resulted in saving of polyethylene. After such gaslight polyethylene enclosure, fogging and spraying operations were also not needed. Taking advantage of the rodent proof design of the godown buildings, rat control operations were also eliminated. Simple polyethylene enclosure and phosphine fumigation (PEPF) technique was tested and achieved excellent results. No heating of the grain took place in any of the experimental stacks because the grain was quite dry and was fumigated at the start of storage which had eliminated possible (although very low) resident insect population. No aeration of stocks was thus needed. Phosphine gas also ultimately leaks out of the enclosure in about two weeks time thus making fumigation fully successful even at reasonably low dose rate of 0.5 gram phosphine per tonne of the bagged wheat (A dose rate of 1.0 gram phosphine per tonne of stored grain is however, recommended to ensure control of resistant Rhizopertha dominaca and Tribolium castaneum and the diapausing Trogoderma granarium larvae). The cost per tonne of the treatment is related to the size of the stack as shown in Table-VI.

The polyethylene enclosure and phosphine fumigation technology or PEPF technology, as we call it, is based on the assumption that wheat grain in Pakistan always carry some insect infestation even if it is coming into the godowns straight from the threshing floors. It must be emphasized that very low infestation levels may not be easily detectable at the beginning of storage stage. If such resident low infestation is eliminated with phosphine fumigation and the entry of fresh insects is prevented by the physical barrier provided by the gaslight polyethylene enclosure, the grain shall remain free of insects and heat/mould damage provided wheat moisture content is below 11.0 per cent (average) and the stack is made in-doors to save phosphine gas from blowing out of the enclosures through wind action. PEPF technology is particularly suitable for public sector storage of wheat in Pakistan because:

It eliminates the need for spraying of storage building or grain fabric of the wheat stacks which could be misused to add un-necessary amount of moisture into our otherwise dry wheat grain in Pakistan.

• It eliminates the possibility of toxic residues in wheat.
• It ensures complete control of insect pests, even resistant and diapausing species, at a reasonably low dose rate of phosphine gas.
• It eliminates the chances of grain getting reinfested (provision of a second fumigation is subject to actual detection of insects from under the transparent polyethylene sheet which could be from the build up of the pupulation possibly surviving initial fumigation)
• It compares well cost-wise with the traditional pest control practice in public sector godowns.
• It makes long storage of wheat possible in a developing country like Pakistan.
• Grain preserved using PEPF technology remain fully viable for use as seed in the following season.

Table - I. APPROXIMATE SHARE OF AREA, POPULATION, PRODUCTION OF FOODGRAIN AND STORAGE CAPACITY IN THE FOUR PROVINCES OF PAKISTAN.

Table - II. EXISTING PUBLIC SECTOR GRAIN STORAGE FACILITIES (IN THOUSAND TONNES) IN PAKISTAN.

Table- III. AVERAGE WHEAT STORAGE PERIODS AND RATES OF LOSSES IN PUBLIC SECTOR GODOWNS IN THE PROVINCES OF PAKISTAN DURING 1984-85.

* Wheat received at the site of the study had been stored earlier elsewhere.

Source: Losses in Public Sector Storage in Pakistan. A report of Crop Sciences Division (1986), Pakistan Agricultural Research Council, Islamabad.

Table - IV. STORAGE LOSSES IN WHEAT CALCULATED FROM PROVINCIAL RELEASES DURING 1984-85.

Source: Losses in Public Sector Storage in Pakistan. A report of Crop Sciences Division (1986), Pakistan Agricultural Research Council, Islamabad.

Table-VI. Cost per tonne in relation to the size of stack for Polyethylene Enclosure and Phosphine Fumigation (PEPF) technology for the safe storage of bagged wheat (or other grains) in a rodent proof godown.

* Depreciated value calculated from the actual purchase rate of Rs. 27.00/Kg about 30% of which can be recovered by selling back the used sheets for re-processing.

Table - V. Cost effectiveness of the under sheet storage & fumigation technology using 2000 tonnes of bagged wheat (in four stacks of 500 tonnes each measuring 30.0 m x 6.5 m x 4.0 m) stored for nine months at Sind Government Godowns-ll (Shed No.3 measuring 62.0 m x 14.6 m x 7.0 m), at Landhi (Karachi) during 1984-85.

* The life of the sheets has been taken as one year and only depreciated value for nine (9) months is taken.
** Mean percent weight loss in 9 months in control Shed No.10.

The current storage pest problems and their management in the Philippines

Alexander Joel G. Gibe

Rice and corn have been the major food crops grown in the Philippines. Programs designed for greater production of these commodities have been given priority to meet the growing reguirements of the 56 million Filipinos. Other programs were likewise launched to save foreign exchange by reducing importations. Leguminous and plantation crops such as mungbeans, soybeans, peanuts, sweet potato were gaining more attention from the government because these crops are considered important food supplements.

The production of food has been increased but it is not the main goal of the government. The goal is to preserve what has been produced, in storage.

However, storage pests are continuously causing high losses in stored commodities. Insects have been identified as the most important cause of loss in all types of storage, followed by fungi, rodents and birds. Thus, in order to achieve the goal, further reduction of post-harvest losses should be undertaken.

MAGNITUDE OF LOSSES TO PESTS

Insects

In 1976, losses due to insect infestation in corn stored for eight months in government warehouses withont the appropriate pest control measures were estimated to be 34% of its weight (Caliboso 1977); 11 % in 1984 (Caliboso et al .,1985) and 9% in 1986 can be attributed to chemicals and the appropriate pest control techniques (admixture) and improved storage structures and design.

In milled rice, loss could be about 148 million kg a year valued at US$ 49.6 M if insect infestation is left unchecked. This volume is about 20% of the government requirement of 783 M kg to meet a 45-day consumption requirement. This is based on the average mean loss of 21 % due to insects for a period of 13 months.

On the other hand, paddy stored for 12 months loses 12% of its weight. This is equivalent to about 57,000 MT valued at US$ 9.98 M based on the assumption that NFA stores 457,000 MT in a year.

Rodents

Vertebrate pests like rodents, present a serious problem in the storage of grain. Sayaboc et al. (1984) reported that approximately, there exists on average of 72 rodents in a government-managed warehouse and 171 rodents in a private single warehouse, consuming 2 kg and 4.9 kg of grain respectively in a day and could spill 18 and 27 kg more respectinely, while feeding. Considering that there are 10,223 government and private warehouses in the country, a daily loss between 39,000 to 312,000 kg can be realized.

Birds

The main bird species present in grain storages is the Passer montanus (Phil. weaver). A single bird weighing 20 9 consumes about 5.6 9 of grain and spills 2.5 times more. Estimated daily loss in each store is about 0.28 to 22 kg. enough to sustain 50 to 400 birds.

CURRENT PEST STATUS

Insects

In the Philippines, Sitophilus zeamais is more dominant than Sitophilus oryzae in maize and sorghum, but it appears Sitophilus oryzae has been displaced by Rhyzopertha dominica as the dominant pest species in paddy negating a previous survey by Labadan (1959) which indicated that Sitophilus oryzae was the major pest of paddy.

The shift of dominance can be attributed to several factors i.e. increase in volume of paddy with low moisture content kept in storage (9-11 %), high moisture, temperature (34°C) and sustained selection pressure exerted by the regular and frequent application of malathion. R. dominica is more tolerant to low moistures (9%) and high temperature in store (up to 38°C) (Sabio et al., 1984).

Earlier studies have suspected that the lesser grain borer (R. dominica) has already acquired resistance to malation because of its massive use in storage, thus higher density of this pest was observed. This was confirmed by the findings of Sayaboc et al. (1984) in a resistance test.

The dominance of R. dominica over S. oryzae was further validated by an insect trapping study conducted by the same author on the same commodity (paddy) (ACIAR Project 8307, Progress Report 1987).

Another primary pest observed in the trapping study is Sitotroga cereallela while the secondary pests identified are Cryptolestes sp.. Oryzaephilus sp., Latheticus oryzae, T castaneum and Liposcellis sp.

In milled rice, the most abundant species are the T. castaneum and Corcyra cephalonica while Callosobruchus maculatus and C. chinensis were proven to be the major pests attacking soybeans and mungbean with the former pest as the dominant species.

In copra, Alpuerto (1979) made a survey in the provinces of Batangas and Quezon and found Nicrobia rufipes, Oryazophilus surinamensis, Dermestes ater (Degeer), C. dimidiatus (Fab.) and Carpophilus pilosellus Motsch as the most dominant species infesting the commodity.

The occurrence of Thorictodes heydeni Reitter in local storages presented a new record in the Philippines. This pest was found to be abundant in mungbean, corn, sorghum and paddy.

Rodents

The major species affecting food in storage in the Philippines are Rattus norvegicus, the Norway rat; Rattus rattus mindanensis, the common ricefield rat; and the Mus musculus the house mouse. These species differ in their habits. R. norvegicus is expected to have dominance over other species because of its size (Caliboso 1982b; 1983, Sayaboc et al., 1984).

Mites and Birds

The species of mites found to be dominant and widely distributed was Suidasia pontifica. It is a primary consumer and was found to be frequently present in paddy, milled rice, rice bran and corn (Sabio et al. 1984).

Fifteen other species of mites have been recorded from the survey.

The survey of Genito et al. (1982) recorded only one bird species, Passer montanus. Being seed eaters, its diet comprises 91-97% grains which is 30% of its body weight.

PEST CONTROL METHODS

The National Food Authority (NFA), a government agency responsible for the procurement and maintenance of an adequate supply of food stocks does most of the stored product pest control. Pesticides are not commonly used by farmers against stored product pests except for seed treatment.

At present, the NFA utilizes a ready to use formulation of bioresmethrin for space treatments using sprayers consisting of a reservoir, high speed blower and buffled nozzles mounted on a movable trolley. The air turbulence physically breaks the insecticides into small droplets of more uniform particle size and in essence is an Ultra - Low-Volume (ULV) or Controlled Drop Application (CDA) system. if properly adjusted, the size of the droplets will tend to fall into 1-30 micronrange with a greater percentage being in the 20-30 micron range, which is considered ideal for impinging on the setae of insects, agglomerating and being absorbed in lethal quantities.

Aluminum phosphide is the common fumigant used while malathion, chlorpyrifos-methyl, tetrachlorvinphos, pirimiphos-methyl, diazinon and fenitrothion are used for residual sprays of facilities. The first four residual compounds are also recommended for sack and seed treatments. The insecticides used for spraying piled bag stacks are malathion, pirimiphos-methyl and permethrin (see Table 1).

Private companies such as flour mills and feed miller, seed producers and other processors that store their raw materials hire private Pest Control Operators (PCO) to fumigate their stocks and storage facilities.

INSECTICIDE EVALUATION AND RESIDUE

Various insecticides are being utilized for application to grains for food and feed and for seed in the Philippines.

Grain admixture on corn and paddy have been tested using single and combinations of insecticides as grain protectant by Sayaboc et al. (1987). This technology (grain admixture) appears to be very promising in the eradication of important storage pests specifically T. granarium as it was proven to be economically viable and workable under Philippine conditions.

Among the insecticides tested, deltamethrin was the best treatment while methacrifos was the least effective treatment in controlling Rhyzopertha dominica.

The same study revealed that combination treatments (chlorpyrifos - methyl + permethrin + piperonyl butoxide (PB); fenitrothion + fenvalerate + PB and pirimiphos-methyl + carbaryl) were better than single treatments against corn weevil, S. zeamais.

Losses incurred during storage of grains can be reduced by 60% if grain admixture using these recommended treatments are adopted.

Residue analysis of grain protectants showed that fenitrothion deteriorated faster than the other protectants tested while fenvalerate was proven to be the most persistent (Bautista, 1987).

INSECT RESISTANCE

Research made by Sayaboc and Acda, (1986) on stored insect resistance indicated that malathion specific resistance is widespread in Tribolium castaneum (75.5%), while the remaining 24.5% of populations tested were malathion non-specific resistant in addition to being resistant to pirimiphosmethyl.

All populations of Sitophilus zeamais were still susceptible to both malathion and pirimiphosmenthyl. Eighty percent (80%) of populations of R. dominica were malathion resistant and nearly 20% were resistant to pirimiphos-methyl, but the number of populations evaluated at this stage were too low to indicate any permanent trend.

Other surveys of insecticide resistance indicated that Sitophilus spp. and R. dominica, the first insects found to acquire resistance to insecticides in the Philippines (Champ and Dyte, 1976) are resistant to DDT, lindane, carbaryl, but are usceptibie to malathion. (Moralio-Rejesus 1973b; Morallo-Rejesus and Javier, 1978d; Morallo-Rejesus and Virrey, 1978a, b).

OTHER CONTROL METHODS

Sabio et al. (1984) established that fumigation with phosphine-generating formulations in both maize and paddy, and maintenance of maximum levels of warehouse sanitation will realize potential benefits in terms of reducing losses by insect pests above the cost of implementing the control Technique. Similarly, Sayaboc et a/.(1984) have demonstrated the cost effectiveness of a pest control regimen consisting of chronic poison baiting, warehouse trapping and the maintenance of maximum levels of warehouse sanitation both internally and the immediate surroundings, which reduce losses due to rodents by as much as 87%.

Non-chemical control using CO2, a sealed enclosure technique and a residue-free method for long term storage, has been evaluated in the Philippines. The use of CO2 for control of insects was proven to be effective.

BOTANICAL MATERIALS

Botanical insecticides are being explored. Studies evaluated lagundi leaves both in whole dried leaves and powdered form against S. zeamais. The result showed that whole dried leaves checked S. zeamais population for 90 days (Bhulyah, 1988). Five percent (5%) lagundi leaf powder reduced fecundity of adult female weevils.

Javier and Morallo Rejesus (1982) evaluated ground black pepper against weevils. It was found to be as effective as malathion and residually toxic for 2 to 4 months against O. surinamensis, R. dominca and T. castaneum.

PREDATOR AND RARASITOIDS

Several biological agents such as pseudoscorpions, parasitic wasps, predatory bugs and spiders were observed in survey studies but their potential economic importance has not been evaluated. Recently, a predatory bug (probably Xylocoris spp.) has been observed to be prevalent in paddy and milled rice (Acda et a/., 1988 Progress Report, Integrated Use of Pesticides), (Sia and Morallo-Rejesus, 1987).

CONCLUSION

High priority has been always given on the use of pesticides to disinfest produce coming from the field till it reaches the consumer. But pesticide use leads to the development of pesticide resistant pests and its indiscriminate use likewise leads to the presence of unwanted toxic residues in treated commodities.

Magnitude of losses to pests has been reduced to a certain extent. However, the government should be more committed to further reducing post harvest losses through an effective plan of action. There is a need to intensify our research in storage pests of existing commodities. This can be done through the use of natural controls, non-chemical methods and checks, and integrating these with the minimum use of chemicals commensurate with adequate control and reasonable cost. The development of an integrated pest management system will ultimately result in greater pest control efficiency.

Table 1: NFA RECOMMENDED PESTICIDES/FUMIGANTS AND THEIR APPLICATION

REFERENCES

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ALPUERTO, V.V.1979. Survey of insects associated with stored copra. B.S. Thesis. University of the Phils. at Los Banos, Laguna, Phils.

BAUTISTA, M.C. 1987. Progress report on Kinetics of Decay of candidate Pesticide for Integrated Pest Control Program, NAPHIRE, Nueva Ecija, Philippines.

BHUIYAH, I.M. 1988. Evaluation of Leaves of Lagundi (Vitex negundo Lin.) as corn seed protectant against the corn weevil, Sitophilus zeamais Motsch. M.S. Thesis Central Luzon State University, Nueva Ecija, Phils.

CALIBOSO, F.M., P.D. Sayaboc and M.A. Acda. 1985. Pest problems and the use of pesticides in grain storage in the Phils.. Presented at Pesticides and Humid Tropical Grain Storage System Seminar, Manila, Phils.

CALIBOSO, F.M. 1977. Studies on the losses of stored grains due to insect infestation. Presented at the "Action Oriented Field Workshop for Prevention of Post Harvest Rice Losses". Malaysia.

GENITO, A.M. Aquino & W. Arayata. 1982. Bird pests in commercial storages. unpublished Progress Report. National Food Authority, Philippines.

HILARIO, J.M. Storage pests and their control manual. Technical Research and Extension Directorate. National Food Authority. pp 9.

JAVIER, P.A. and B. Morallo-Rejesus.1982. Isolation and bioassay of insecticidal principles from black pepper (Piper nigrum L.) against three stored grain insects. In: Progress in Grain Protection Proc. 5th Annual Workshop in Grains Post Harvest Technology. pp. 45-59.

MORALLO-REJESUS, B. 1981b. Stored grain pest problems and research needs in Southeast Asia. Phil. Entomologist 4151: 361-382.

MORALLO-REJESUS, R.P. Garcia and E. Benigno. 1986. The current pest problems in storage and their management in the Philippines. Presented at Symposium on Pests of Stored Products. Bogor, Indonesia.

MORALLO-REJESUS, B. 1973b. Resistance to insecticides of rice weevil complex. Advances in Food, Agriculture, Forestry and Community Research and Development. Part I, 307-318.

MORALLO-REJESUS, B. and C. Virrey. 1978a. Insecticide resistance of field collected red flour beetle, Tribolium castaneum in Batangas and Laguna, Los Banos, Laguna, U.P. at Los Banos. Unpublished report.

MORALLO-REJESUS, B. and C. Virrey. 1978b. Susceptibility of DDT and lindane resistant field strains of T. castaneum to three organophosphorous insecticides. Los Banos, Laguna. University of the Philippines. Unpublished report.

SABIO, G.C. 1984. Insects and mites associated with stored products. Nueva Ecija, Philippines. National Post Harvest Institute for Research and Extension. Unpublished report.

SABIO, G.C. 1987. Progress Report on Insect Trapping Studies. Nueva Ecija, Philippines. National Post Harvest Institute for Research and Extension.

SAYABOC, P.D., F.M. Caliboso, E.A. Benigno and J. Hilario. 1984. Rodent losses in commercial grain storage. Presented at Grain Post Harvest Workshop. ASEAN Crops, Post Harvest Program. August 1984. Kuala Lumpur.

SAYABOC, P.D., M.A. Acda, F.A. Cano, Jr. and A.J.G. Gibe. 1987. Evaluation of Grain Protectants on Stored Maize: Presented on 10th ASEAN Technical Grains Post Harvest Workshop. Bangkok, Thailand.

SAYABOC, P.D. and M. A. Acda. 1984. Survey of resistance on coleopterous pests in storage. Presented on 9th ACPHT ASEAN Technical Grain Post Harvest Workshop. Singapore.

SIA and Morallo-Rejesus.1987. Toxicity of several insecticides on three major coleopterous pests of stored products and their effectiveness for sack treatment in the warehouse. Masters Thesis. U.P. at Los Banos, College, Laguna, Philippines.

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