Section 4 - Principles and theory of integrated pest management

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The concept and components of integrated pest management
Some basic economic principles in pest management
Socio-economic and technical dimensions of integrated pest management

The concept and components of integrated pest management

Belen Morallo-Rejesus
Professor and Chairman, Department of Entomology
College of Agriculture, University
of the Philippines at Los Banos

and

Romeo S. Rejesus
Consultant, Postharvest Reserarch
and Training Center, Dept. of Horticulture
Visiting Professor, Dept. of Entomology, University of the Philippines at Los Banos

INTRODUCTION

The goal of development is to maximize the use of energy, natural resources, capital and scientific information for the welfare of mankind. However, the process of developing agricultural production, water resource management, improvement of health and other activities of mankind, create an environment favorable to the development of organisms competing with man. This organism is designated as a pest but such a designation is not static, since a pest may be damaging and edible at the same time. For example, crickets and grasshoppers are acceptable as food by some people, but can be a curse to rice farmers.

A pest problem exists when an organism interferes with human activities or desire, or otherwise competes with man. To rationally minimize or control pest depredations, an holistic approach to suppression is emphasized. The control strategy that has subsequently evolved is called Integrated Pest Management (IPM).

PHILOSOPHY OF INTEGRATED PEST MANAGEMENT

IPM brings together into a workable combination the best strategies of all control methods that apply to a given problem created by the activities of pests. IPM has been defined in various ways but a more scientific definition describes it as, "the practical manipulation of pest populations using sound ecological principles to keep pest populations below a level causing economic injury". The emphasis here is "practical" and "ecological". There are many ways of controlling insect pests but only a few are practical, and fewer are ecologically sound, such that an undesirable citation is created.

Another term we frequently encounter is "intergrated pest control". It is offer used interchangeably with IPM, though in the strictest sense these terms are not identical. Originally, integrated control simply meant modifying chemical control in such a way as to protect the beneficial insects and mites, or integrating chemical and biological control methods. Subsequently the concept was broadened to include all suitable methods that could be used in complementary ways to reduce pest populations and keep them at levels which did not cause economic damage. This essentially is IPM It includes a variety of options, any one of which may not significantly reduce the Pest population, but the sum total of which will give adequate reduction to prevent economic losses. A modern definition of IPM may be-the use of all available tactics in the design of a program to manage, but not eradicate pest population so that economic damage and harmful environmental side effects are minimized.

IPM is not a static, unyielding system. It is dynamic, ever-changing, as we develop a better understanding of all factors that affect the system. These factors include climate, alternate host plants, beneficial insects and man's activities. In a narrow sense, IPM means the management of the few important pests generally found on our crops, but consciously or not it must include all insect pests, not only the "key" ones but also the secondary pests, which seldom do any harm. If this were not so, we might suddenly find some of these minor insect pests or even non-pests elevated to the status of serious insect pests because of our failure to consider them in the total scheme.

IPM as a concept is not new, but one that is receiving new emphasis as man looks for better methods to grow and store food for an expanding population, and at the same time preserve his environment. The rationale for using IPM is threefold. First, it can cut production costs mainly by reducing energy inputs. Secondly, IPM can reduce environmental contamination through the judicious use or reduced use of pesticides. And finally, an IPM program allows for maximum utilization of cultural practices and natural enemies (for plant pests) and physical methods (for storage pests). IPM can be designed to take advantage of the ecological principles governing pest population abundance. This requires a thorough understanding of the role of all the factors responsible for a pest population reaching certain levels at a particular time of the year, or duration of storage.

ELEMENTS OF IPM

There are four basic elements of IPM: natural control, sampling economic levels, and insect biology and ecology.

The first element of IPM relates to the fullest utilization of naturally occurring suppressive factors, including any practice by man which will make the total ecosystem less favourable for growth of the insect pest population. Obviously, this requires a thorough understanding of the ecosystem.

The naturally occurring suppressive factors may act directly or indirectly on pest populations. Indirectly, the ecosystem may be managed or altered in such ways as to make the environment more harmful to the pest and thus limit population growth. More directly, protection and the use of beneficial insects may help keep potentially damaging insect pest populations at subeconomic levels In storage, parameters that can be manipulated to control the buildup of a pest population are temperature, relative humidity, moisture content and composition of gases within the storage atmosphere.

The second element is that of using sound economic threshold (ETL) levels as the basis for applying control measures, especially chemical measures. Establishing and using dynamic ETL's provide a basis for delaying the use of insecticides. This permits the maximum utilization of other control methods, such as the use of beneficial insects.

The use of economic threshold levels implies adequate sampling of all harmful and beneficial insects in the agroecosystem and particularly in any one crop at a given time. The levels found through sampling must then be measured against the economic level established for the crop, the beneficial insects, and the probable population trend of the pest species. The sampler thus becomes a key person in an IPM system.

The fourth element, insect biology and ecology, is essential to the fullest utilization of the other three elements. Little concerning natural control can be understood without detailed knowledge of the biology and ecology of all the species present. This knowledge is also essential in establishing the role of each species in the system and in deermining the amount of damage inflicted by each pest species. Adequate sampling is directly dependent a thorough familiarity of the species involved.

Knowledge of the biology of a certain problem pest will serve as a basis for planning the control strategies and provide operational guidelines for these strategies. In this context, it is important to know the relationship between the pest and the crop (crop life tables) and the mortality factors (pest life tables), both biotic and abiotic (parasites, predators, temperature, relative humidity) which play a major role in the determination of pest population dynamics.

An understanding of the sequential dominance of pests in relation to growth stages could provide the immediate impetus for developing a simple integrated control program based on minimum pesticide application (Rejesus, 1976). By delineating the succession of major pests at different stages of plant growth (or storage time for stored products), the frequency, timing and dosage of insecticide application could be synchronized, hence avoiding pesticide use on a time-wise basis, or the "calender" method. The control program could then be based on expected pest population at any given growth stage of storage duration.

ECONOMIC INJURY LEVELS AN D ECONOMIC THRESHOLD

There is a wide variation in the degree to which pests may be tolerated even for the same species in different areas, in different times of the year on different host plants, and in different stages of crop development. Thus, determination of the Economic Injury Level is critical in defining the ultimate aim of any pest management program, and in delineating the pest population level below which damage is tolerable and above which specific intervention is needed to prevent a pest explosion and to avert significant damage (Fig. 1). Stern et al. (1959) defined Economic Injury Level as "the lowest pest population that will cause economic damage" while economic threshold level (ETL) of more accurately Control Action Threshlod (CAT) as "the density at which control measures should be applied to prevent an increasing pest population level from reaching the economic injury level". Although the damage or losses at the economic threshold can be tolerated of neglected, it is at this level that every effort should be made to reduce the pest population by various methods (i.e. chemical, physical, biological, etc.).

Determining the Economic Injury Level and Control Action Threshold is generally a complex matter based on detailed operations of pest ecology as it relates to bioclimatology, predation diseases, the effect of host plant resistance and the environmental consequences of applied control interventions (Luckman and Metcalf, 1975). Rabb (1972) has suggested the following factors as essential for the determination of the Economic injury Level:

1. Amount of physical damage related to various pest densities.
2. Monetary value and production costs of the crop at various levels of physical damage.
3. Monetary loss associated with various levels of physical damage.
4. Amount of physical damage that can be prevented by the control measure.
5. Monetary value of the portion of the crop that can be saved by the control measure.

From this information, it is possible to determine the level of pest density at which control measures can be applied to save crop equal to, or exceeding the cost of control.

The rise and fall of the Control Action Threshold is determined by the importance of the ecosystem, value of the crop, the pest status, and consumer standards. For example, Heliothis zea feeding on cotton boll, has an economic threshold of four larvae per plant (Stern, 1965) and generally requires insecticidal treatment several times yearly. H. zea feeding on sweet corn, has an economic threshold approaching zero population in the United State since the consumer will reject sweet corn with any damage or one larva on it.

In special cases, where pests serve as vectors of plant, animal and human diseases, the economic threshold is zero. A single pest attack may cause the death of a valuable tree, a domestic animal or human. A good example is Aedes aegypti which transmits yellow fever.

In grain storage, ETL is influenced by consumer attitudes, Export regulations often specify nil-tolerance of any live insects, be it injurious or benefucial.

COMPONENTS OF IPM

Five general types of single component control methods may be used in IPM programs in stored ecosystems. These are: chemical control, physical and mechanical methods, biological control, host plant resistance and regulatory control.

Chemical Control:

A variety of insecticides and acaricides have been and are continuously being developed for control of insect pests. However, these chemicals are but one tool and should be used in combination with other tactics in an IPM program. The total reliance on chemicals has led to a crisis situation (including pest resurgence, insect resistance, secondary pest outbreaks, environmental contamination, and hazards to human health). However, IPM does not advocate the complete withdrawal of pesticides. That would be impractical. IPM simply demands use of pesticide only when necessary and at rates compatible with other strategies.

Physical and Mechanical Methods:

Physical and mechanical methods are direct or indirect (non-chemical) measures that completely eliminate pests, or make the environment unsuitable for their entry, dispersal, survival and reproduction. Physical-mechanical control measures may include environmental manipulation (temperature, relative humidity, control atmosphere), mechanical barriers, light taps, irradiation, thermal disinfestation, sanitation, etc. Many times, mechanical and physical methods require considerable extra equipment, materials and labor, hence, they may only be economical in certain situations. For field pests, these methods are rather inefficient but in a storage ecosystem, many of the physical techniques are effective and have great potential for use in an IPM system.

Biological Control:

Biological control may be defined in a narrow sense as "the manipulation of predators or patho. yens to manage the density of an insect population". This definition does not include the naturally occurring control agents, but only parasitoids, predators and pathogens that are purposely manipulated by man. In a broader sense, it includes "the manipulation of other biological facets of the pest life system, such as its reproductive processes (i.e. sterile male technique), its behavior (pheromanes), the quality of its food and so forth."

There are some constraints to the potential use and success of natural enemies. Predators, parasites and pathogens found amongst the grain will be regarded as contaminants by consumers and grain exporters. Thus, it makes it very difficult to maintain a pest population level that will enable the biological control agents to establish themselves. The use of pheromones is one of the potentially useful biological agents that could be utilized in IPM for monitoring and partially suppressing pest population not only in agricultural fields but in storage ecosystems.

Host-Plant Resistance:

The manipulation of the genetic make up of the host so that it is resistant to pest attack is called host plant resistance. Over the years there have been numerous successes in breeding for resistance to a variety of pests and currently many crops are being selected for this purpose.

This approach has not been attempted to any great extent in stored products protection systems Investigations in this field have been few. However, research (mainly of rice, maize, wheat) has provided evidence of the utility of varietal resistance in grain storage. Unless research on varietal resistance to storage pests is integrated with breeding of plants that are resistant to field insect pests and deceases the potential of this tactic in storage IPM is limited.

Regulatory Control:

Fundamental regulatory control principles involve preventing the entry and establishment of foreign plants and animal pests in a country or-area, and eradicating, containing or suppressing pests already established in limited areas. Under the auspices of various quarantine acts, numerous control measures are implemented in an attempt to exclude potential pests, to prevent spread and to supplement eradication programs. Ports of entry are the first line of defense against the introduction of new pests. Pests which break through the port of entry are eradicated or contained within limited areas. Quarantine action is used only against insects of economic importance, although it is sometimes necessary to contain insects which are of no economic importance in another country until their behavior in a new environment can be studied

Trogoderma granarium is a most serious pest of stored commodities and every effort is extended to prevent its spread in international trade. In many countries, imported consignments found to contain J. granarium are segregated and immediately fumigated with methyl bromide (at a dosage of 80 9/cu³ m for 48 hours). Lately, Prostephanus truncates originating from Central America has become a pest of international quarantine importance.

Component Integration:

Each of the many methods in insect control has its place in IPM. There are many situations where two or more can be used in an integrated program. Not all methods, however, are suitable for use in every situation.

In a storage ecosystem, hygiene and good warehouse management are essential. It provides the framework for other supplementary infestation control methods. An IPM system would therefore supplement sanitation and good warehouse keeping with one or more combination of the following practices:

1. improved harvesting and threshing techniques
2. judicious use of residual insecticides
3. use of fumigants (MeBr; PH3)
4. use of ambient aeration, and refrigerated aeration
5. atmospheric gas modification (hermetic; CO2; N2)
6. thermal disinfestation
7. irradiation techniques
8. insect resistant packaging
9. insect growth regulators: (IGRs: methoprene, hydroprene)
10. biological control (parasites, predators and entomopathogens, pheromones)
11. Use of resistant varieties if possible
12. Storage management (FIFO)
13. Adequate grain cleaning prior to storage storage.
14. Storage design (for pest exclusion, principally for rodont and bird pests)
15. Adequate grain cleaning prior to storoge
16. Monitoring, evaluation and inspection of stored commodities, storage structures and their immediate surroundings.

Summary chart insect pest management (After Osmun, 1985)

Insect Pest Management for Stored-Products

There is a number of differences for IPM for stored-products compared to field agriculture. There is far greater variety of tactics that could be employed for storage pest management. In both situations, a systems approach is usd in order to facilitate monitoring and implementation.

Comparison of IPM Between Field Agriculture and Stored-Product Pests

Field Production

1. Ecological condition - more complex and dynamic.
2. Sanitation process - difficult to implement.
3. Economic threshold - appropriately applicable.
4. Physical control - often impractical and expensive.
5. Mechanical control - often impractical and expensive.
6. Regulatory control - more complex and require intensive logistical support.
7. Chemical control - considerable impact on the ecosystem.
8. Biological control - field
9. Host - plant resistance - whole plant modification relatively easier.

Stored · Product Setting

1. Relatively simple and manageable.
2. Easier and alone could provide complete control.
3. Not generally applicable, food industry often require zero infestation.
4. Most physical factors could be manipulated under storage condition.
5. More feasible by as built - in feature of storage.
6. Detection and implementation generally selfcontained.
7. More contained and limited in spatial proliferation.
8. Problem of contamination.
9. Genetic manipulation to render resistance to seed only more complicated.

In both situations three additional elements must be incorporated to the development of IPM: 1) appropriate people, 2) a systems approach, and 3) adequate evaluation. Aside from the individual expertise of the team members it is important that the people involved must develop a good personal and working relationship in the pursuance of the common objectives.

REFERENCES

FLINT, M.L. and VAN DEN BOSCH R. 1981. Introduction to Integrated Pest Management. Plenum Press, N.Y. and London. 240 pp.

GLASS, E.H. (ed.) 1975. Integrated Pest Management, Rationale, Potential Needs and Implementation. Entom. Soc. Amer. Spec. PubI. 75-12,141 pp.

METCALF, R.L. and W. LUCHKMAN (eds.). 1975. Introduction to Insect Pest Management. John Wiley & Sons, N.Y. 587 pp.

STERN, V. 1973. Economic Threstholds. Annul Rev. Entomol. 18: 259-280.

WATSON, T.P., L MOORE, G.W. WARE. 1975. Practical Insect Pest Management. W.H. Freeman & Co. San Francisco. 196 pp.

OSMUN, J.V. 1985. Insect Pest Management and Control. In Bauer, F.J. ed. Insect Management for Food Storage and Processing. American Association of Cereal Chemists, St. Paul, Minnesota. pp. 15-24.

Some basic economic principles in pest management

Belen Morallo-Rejesus
and
Romeo S. Rejesus

INTRODUCTION

Entomologists and biologists defing pests as those organisms reaching a certain biomass or population level enough to cause physiological damage to crop and eventually impair either the quantity and quality of the produce. The concern used to be concentrated solely on devising control strategies with the aim of increasing the pest-kill efficiency and/or minimizing the control's unwanted side effects on the environment. In doing so ,a damage function (one that relates yield loss or crop damage to pest density levels) and a kill-function (one that measures the efficiency of a particular control strategy in terms of percent pest killed) are determined simultaneously. Perhaps, the ultimate goal of these efforts is to realize the yield potential of crops by eliminating pest hazards which is possible only where there is maximum protection. In years past, maximum protection was closely associated with prophylactic dosages of pesticides.

Economists view pest problems and solutions quite differently. For one, pests are those organisms that destroy what man has produced, compete for resources needed by man in the production of food and fiber, or contaminate the environment in such a way that man finds it unhealthy or unattractive (Headley and Lewis, 1967). An economist would not be very particular about the exact levels of pests, damages, and mortalities; but would pay more attention to the value of pest damage and the costs of alternative control strategies with or without special consideration to time. Usually, he would not desire for the yield potential of crops because he knows that it does not always pay to spend for maximum protection. In fact, the urge to control pests does occur to him until he finds that the cost of doing so is more than offset by the benefits. Biologists, to a great extent, do not worry about costs in as much as they find delight in quantifying apparent yield increases due to control action.

Almost for two decades now, attempts have been made to reconcile the disciplinary concerns of both the natural and social scientists to benefit the farmers and the public at large. To put their interests together, the US National Academy of Sciences (1969) states that: entomologists develop and perfect various methods of insect control and determine their physiological impacts on crops; economists depend on entomologists for information regarding various inputs combined to produce a particular outcome. To some extent, pest management was conceived to pool together the concerns of people coming from various fields in a most coordinated fashion. Pest management is defined as an ever-changing process of attacking pest problems by applying (in the field of storage) whatever economically feasible control of combination of controls that produces the best combination of immediate and long-term results in terms of both reduced pest damage and the absenec of unwanted side effects (Beirme, 1967). This implies that pest management may utilize a single-component-tactic or it may be accomplished through a complicated integrated pest management system as discussed earlier. Some Terms and Assumptions in Economic Analysis:

We start by making an assumption about the behavior of individuals: a rational farmer would maximize profit or minimize costs and would seek more than increase in yield or decrease in the use of input in his production decisions. He is knowledgeable about the exact outcome of the decisions and the prevailing prices in the market.

In the analysis of crop protection, it is necessary to define what are we putting in and what are we getting from this activity in order to evaluate if such is really worth it.

Input/Cost. The factors of production such as buildings, machines, materials, labor and management skills are called inputs and if valued at their respective prices are called farm costs or expenses. Let x = quantity of input and Px = Price of input. Then Cost = (Px)(X)

Output/Beturn. Through some physical or biological processes, the above inputs are transformed into usable products or output. Similarly, it can be valued by its price to get the return, revenue or benefit. The benefits from pest control is indicated by the increase in yield or added returns.

Let X = yield (increase) and Py = price of corp. Then Return or Revenue = (Py)(Y)

Pest management. Pest management is becoming more essential in our modernizing agriculture as problems about pests and damages increase with time. As an input it has 5 components: pest control materials, labor and management or knowledge about pests, expected damage, and alternative control methods.

Pesticides. Pesticides used to be the single most important protectors of crops from insects, weeds and pathogens but because of the ever-increasing price and unwanted side effects, nonchemical methods are being tapped. Nevertheless, continued dependence on pesticides in the near future is a reality that pest managers have to reconcile with. Generally, pesticides form a regular feature of the farm cash expenses.

Non-chemical control. This method is likewise called labor control because it relies heavily on a farmer's manual efforts. Non-chemical methods do not necessarily mean that the materials needed for its utilization are cost-free.

Efficiency. We define the most efficient pest control strategy as one that requires the least combination of labor cash input for a given level of yield increase, their factors held constant. The definition combines the "efficiency" and effectiveness concepts presented by Semple (1985). According to him the efficiency of an insecticide is the minimum dosage required to reduce the population of target pests by a fixed proportion (80%) regardless of pest pressure. Effectiveness, on the other hand, is indicated by the number of surviving insects of the extent of yield damage after the treatment. It is determined not by the "efficiency" of insecticides but by the strength of pest perssure as insecticides by the over-all farm operations. One needs to know the compatibility of his control measure to his pest problems and an effective manager does.

Optimum thresholds. At least, there are two sets of pest population thresholds found in pest management literature, one being a shadow of the other. Studies regarding plant physiology in relation to phytophagous organisms that reveal there is a tolerable level of plant destruction due to pests wherein the crop is still able to recover and remain vigorous. Apparently, economic injury level (EIL), sometimes termed as the biological threshold level (BTL) is the critical pest density level going beyond what is tolerable to crops. With the EIL, biologists justify control actions. For the economists, such could never be unless the cost of control is zero. Economic threshold level (ETL) is the level of pest density at which suppression action is initiated, the control cost at least equals the value of expected damage. Some IPM specialists prefer to use the term control action threshold (CAT) for EIL since it connotes immediately that it is that level control action is necessary. The mathematical expression for ETL below tells the basic relationship between the critical pest density level and economic variables. If we assume d and K as pre-determined (constant) variables then only the cost and crop prices affect the ETL. Note the prohibitive character of cost control action. If prices of pesticides would be very, very high, ETL would also be and control action may not be economically warranted. However, if the crop is of high value or if the market requires high quality products, ETL will be small and the propensity for control action will be high.

ETL = c/pdk

Where
c = cost of control action
r = price of crop
d = damage coefficient
k = kill efficiency

Partial Budgets: A Guide to Pest control Decision

A private farmer, faced with a limited cash budget and credit would think twice before he puts in money into an otherwise biologically attractive innovation. He might not be doing detailed accounting of the proposed change but deep in his mind, he calculates and balances the relative benefits and costs of every new undertaking. If the perceived economic net gain is positive and acceptable, then he evaluates the resource requirements and explores ways finance it.

Partial budgetting is perhaps the most popular decision tool employed in the conduct of applied research by the entomologists in an attempt to add economic substance to experimental results. Partial budgets are designed to show, net profit or loss for the farm as a whole (this is called costs and returns analysis), but the net increase (decrease) in farm income resulting from a (proposed) minor change in the on-going operations. It contains 4 major items bearing exact information about the changes in monetary terms, namely: added returns, reduced costs, added costs, and reduced returns.

Added returns is the value of the increase in yield and/or the value of quality improvements.

Reduced costs is the value of inputs no longer used under the proposed change. If previously the farm is using 6 man-days of labor but the new technology requies only 4 man-days, then the wage that should have been paid to 2 man-days represent a reduction in cost.

Added costs is the value of additional inputs as a result of the proposed change. This is the exact opposite of reduced costs. The classical example is the cost of additional fertilization, labor and machine service associated with modern farming.

Reduced returns is the value of forgone output. It the proposed change diminishes yield, then it reduces returns. In some instances, the increase in production is shared with the landlord and harvester/thresher so that the value of harvest that went to them is accounted as reduced returns.

The procedure for partial budgetting is straightforward. Analysts have just to be keen the details in the change of process. Given data on market prices, he can put values to each change item and determine if such diminishes or adds to returns or costs. After which, he can compute for the net change in income by subtraction the sum of Added costs and Reduced returns from the sum of added returns and reduced costs:

Net gain/loss in income = (Added returns + Reduced Costs) - (Added costs + Reduced returns)

Biological studies on pest control strongly assume that farmers do not control pests; this is the implication of comparing- treated as against the untreated plots. Such standard experimental procedures directly ease out computations involved in the economic analysis but, at the expense of intuitive value of practical content. It does not provide the analyst a grasp of the general and actual problem situation because at this time very few farmers are indifferent to pests. Pesticide consumption growths observed for rice, vegetables and bananas indicate that pest control is very active in our agricultural/farming system. Quite recently, field studies on the control of rice pests use farmers' practice as a separate benchmark for comparison.

It is quite necessary that analysts look for flexibilities in the data set and mold the framework according to the dictates of the local problem situation. In that case, he could come up with a matrix of problem situations and alternatives. For each situation, the dominant alternative may be decided based on at least 2 criteria: (1) magnitude of net change in income (2) resource requirements and accessibility.

Other Decision-Making Models

In reality, farms are multi-enterprise in nature. There is also substantial interdependency in decision across crops and over time. Uncertainties or lack of information about pests, damage, controls and prices also exist. In other words, the type of control a farmer applies to his main crop influences his control decision for the second crop. Similarly, his control practices in the previous season greatly affect his decision in both present and future cropping. Imperfect knowledge and limited skills concerning pest control decisions and the presence of natural disturbances may render actual decisions "inferior" to that predicted by the partial budget model. And as one tries to develop realistic models, the analytical tools tend to be conceptually complicated and computationally irksome. This leads us to a brief discussion of the various models developed recently.

Whole farm budgets. This is merely an extension of the partial budgets. It recognizes interdependent decisions which means that an adoption of technology in one enterprise affects the rest. Thus, the entire farming system is changed. Oftentimes, it will be hard to distinguish the cause from the effect. Taking the entire system as the unit for analysis makes it simpler.

Production Function Analysis. It is basically statistics in form and is widely used in production economic research. A production function tells the average relationship between the farm product and its factors of production. It bears powerful estimates of the precise contribution of each input to the total product. Headley (1968) formalized the economic study of pest control and applied this framework in the analysis of pesticide expenditure in US agriculture. He concluded that pesticides are indeed productive inputs placing a $4 contribution to the value of agricultural production per dollar spent on it. He thus predicted an expanding market for agricultural pesticides in the 70's and challenged the technical faculty to develop a less hazardous but comparatively productive substitute.

Reichelderfer (1980) criticized the common practice of using pesticides as a proxy for pest levels to explain variability in production. Note that it is the pest and not the control action that directly affects yield. She pointed out that production functions for pest control are unrealistic if they do not express yield as a funtion of pest levels. Since this practice is necessitated by lack of (pest infestation) data, economists are reminded to be careful in the interpretation of results. For one thing, the so-called productivity of pesticides is dependent completely on pest pressure. It is important, therefore, that the economists understand the biological system with which they are working

Benefit-cost analysis. BCA is probably the most comprehensive analytical tool unfortunately, it requires voluminous data and it is usually not workable. BCA treats pest control as an investment or a folw of costs and returns. Though time is the core of B-C analysis wherein discounting methdods are used to calibrate the flow of money in order to come up with timeless measures of efficiency the internal rate return (IRR) and the benefit-cost ratio (BCR). The ideal situation is for the IRR to be greater than the market interest rate and for the BCR to be greater than 1. BCA's can be done both at the farm and the community levels. For the latter, we call it extended BCA. This is of great use in analyzing pollution problems related to pest control which is quite beyond the concern of farmers and yet it bears tremendous impact to the is shown below (Table 1,)

Space fumigation using PhostoxinR for a warehouse of approximately 980,000 cubic feet volume (or 27,750 m³). The quantity of corn stored was 147,000 sacks x 75 kilograms or approximately 11,000 tonnes. The total value of corn at current prices of P2.40 per kilo is P26,460,000.00. The reported loss due to Sitophilus granarius (L.) infestation over a period of three (3) to four (4) months was 10% to 15% of the total weight. In real terms, this is equivalent to 1,102,500 kilograms or P2,646,000.00. The cost of fumigation at the current prices of P150.00 per 1,000 cubic feet, is P148,200.00. Equating this figure to the possible loss if no fumigation is done, there is a saving of P2,497,000.00.

Risk analysis. Finally, the latest add-on to our list views the resurgence of pests as an involuntary risk (unlike gambling which is voluntary) taken by farmers, pest control actions as means to minimize the risks or variability of yields and profits, and control costs as the premium farmers pay to avoid it. This analysis exerts less pressure on biological data requirements, specifically, pest infestation levels. This type of analysis has the potential of influencing pest control policies particularly crop insurance and pest information services.

We conclude this paper by saying that the economic research on pest control is catching up with our needs. In the same way that economists try to understand the biological system, the biological science community must likewise understand the economic system.

Table 1. Costs of fumigation with methylbromide (MBr) and phosphine generating forumulations (PH3 tablets) for various applications.

where 1 ft³ - 28.3168 liters or 1000 ft³ 28,3168 m³
P14 = 1 USD

The prices quoted include labor, contractors tax, and all other expenses incidental to the fumigation. Applicable only to Metro Manila Area, cost of transportation, board and lodging for at least three (3) personnel must be added.

Source: Fumigation Specialists Inc., Aurora Blvd., Q.C.

REFERENCES

Beirme, B.P. 1967. Pest Management. London: Leonard Hill Publ.

Headley, J.C. 1968. Estimating the productivity of agricultural pesticides. Amer. Jour. Agric. Econ. 50: 13-23.

Headley, J.C. and J.N. Lewis. 1967. The pesticide problem: an economic approach to public policy. The John Hopkins Press. 141 pp.

National Academy of Sciences. 1969. Economic principles of pest management. In "Principles of Plant and Animal Pest Control." NAS, Washington, D.C.

Reichelderfer, K.H.1980. Economics of integrated pest management: Discussion: AJAE 62: 1012-13.

Ruisink, W.G.1980. Economics of Integrated Pest Management - An Entomologist's View of IPM Research Needs. Amer. J. Agric. Econ.162(5): 1014-1015

Semple, R.L. 1986. Entonomics: economics of integrated pest management. In "Insect Pests of Stored Grains and Their Control". Vol. 9. IPM Part I.

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