For the Encyclopedia of Food Science and Technology, 2Nd Edition

For the Encyclopedia of Food Science and Technology, 2nd Edition

POST-HARVEST INTEGRATED PEST MANAGEMENT

Thomas W. Phillips, Richard C. Berberet and Gerrit W. Cuperus

Department of Entomology and Plant Pathology

127 Noble Research Center

Oklahoma State University

Stillwater, OK 74078 2

Effective management of pests within systems where food is produced, processed, and distributed is critical for maintaining an abundant, affordable, and safe food supply. Over

100,000 pest species are known to cause losses in crop and livestock production, and in the systems designed for processing and distributing food commodities (1). It has been estimated that at least one-third of the food supply potentially available to the population of the United States is lost on an annual basis due to pest infestations during production and post harvest. In addition, nearly $8.5 billion is spent annually on chemical pesticides applied in agriculture and industry as farmers and processors attempt to reduce losses (2).

In food production and processing systems, the primary approach to pest control has been one of eradication, with the objective of total elimination of pest populations (3). This approach has resulted from concerns, arising foremost in production of fresh fruit and vegetables, that any pest injury would cause these commodities to become aesthetically unacceptable to consumers (4). Also, these commodities have such high value that it is considered unreasonable to risk the possibility of reduced yields or grades of produce (5).

Demands for eradication of pests have resulted in excessive reliance on chemical pesticides to the extent that applications often been made according to schedules without assessment of pest infestation levels.

Gradual changes in approaches to pest control are now occurring in food production, processing, and distribution systems. Whereas there once was little consideration given alternatives to chemical pesticides, greater interest now exists for implementation of controls that are less threatening to the environment and non-target species (6, 7). Integrated Pest Management (IPM) concepts are gradually being incorporated into the systems that supply food for the world’s population. With acceptance of principles of IPM has come willingness on the part of farmers and

2 3 processors to implement control programs that are aimed, not at eradication of pests, but are designed to reduce infestations while monitoring closely the benefits vs. costs of control measures.

The goal of this chapter is to review general concepts that are basic to IPM as developed in the production agriculture venue and to provide an overview of the current issues, methodologies and practical concerns relevant to pest management in the post- harvest food industry. The topics included pertain to management of insects or other arthropod pests that infest durable commodities such as grains, nuts and dried foods, and all the processed food products derived from these commodities. Pest issues related to post-harvest handling of fresh commodities will be discussed briefly. Canned or otherwise processed fruits and vegetables are discussed in other chapters of the encyclopedia as is prevention of microbial contamination.

WHAT IS IPM?

Integrated pest management is a systematic approach to pest regulation that emphasizes increased sampling to assess pest infestation levels and promote improved decision- making so that control costs can be reduced and social, economic, and environmental benefits can be maximized (8). From the standpoint of benefit/cost in IPM, the basic goal of control programs is defined by the concept of economic injury levels. The economic injury level (EIL) is defined as the pest infestation level at which the loss due to pest is equal to the cost of available control measures. The EIL concept is used as the basis for determining economic thresholds (often called ‘action thresholds’), defined as the level of infestation at which the potential loss due to a pest infestation exceeds the cost of an available control measure. In decision-making regarding chemical pesticide applications, the economic return from use of a pesticide is maximized when the application is made at

3 4 the time the pest population reaches the economic threshold level. Implementation of

IPM has typically resulted in reduction of purchased inputs because of more effective assessment of pest infestation levels and well-defined criteria for determining when controls are warranted. In crop production systems, programs involving entomologists, plant pathologists, weed scientists, and economists working together have yielded cost- efficient tactics for suppressing pests while limiting contamination of the environment and the harvested food commodities. Integrated pest management concepts are now being emphasized for post-harvest systems with employment of benefit/cost principles to guide pest control decisions in storage and distribution systems just as has occurred in field settings. Considering ecological, as well as economic concerns, IPM is regarded as an essential approach to preserve a safe food supply and healthy environment, while keeping U. S. agriculture competitive and profitable.

Explaining the context in which the terms pest and management are used can be quite helpful to understanding concepts of IPM. The term pest has historically referred to insects, weeds, plant pathogens, and rodents that compete for resources valued by humans in production, processing, and distribution systems for agricultural commodities.

Thus, species attain pest status in the context of their association with plant and animal species used by humans as sources of food and fiber. The abundance of these species, and hence their importance as pests, is often enhanced in modern production and distribution systems for agricultural commodities because these systems result in abundant habitats and vast supplies of resources unlike anything that occurs in natural ecosystems.

Integrated pest management employs decision-making processes needed to produce commodities in carefully planned systems intended to keep pest populations

4 5 from reaching economically damaging levels, while maintaining profitability of the enterprise with limited adverse environmental and social effects. The process of managing pests has significantly broadened in definition and scope over the past 30 years from unilateral controls applied against single species; to integrated controls employing multiple tactics against single species; to IPM programs designed to regulate insect pests, pathogens, and weeds in production systems; and finally, to quite broad concepts of bio- intensive IPM (1) and integrated resource management (9). There is a substantial need for increased research and implementation efforts to keep pace with the theoretical development of management concepts. Practical aspects of implementation have tended to lag far behind IPM theory (1).

DEVELOPMENT OF IPM PROGRAMS

Basic changes in decision-making processes are important to development of effective

IPM programs. In the past, eradication of pests was often the primary objective, now programs must address ecological, economic, and health-related concerns in conjunction with acceptable levels of pest regulation as defined by the EIL concept. Integrated pest management programs require time and expertise devoted to assessment of problems and decision-making to gain maximum returns on inputs such as chemical pesticides.

Significant resources must be committed to training of personnel or hiring consultants who have the necessary expertise to accurately monitor production fields and post- harvest facilities for the presence of pest infestations and decide on appropriate management options. Before IPM programs were developed, many applications of pesticides were made according to schedules as insurance or prophylactic treatments.

However, current trends in response to economic, environmental, and social concerns addressed in conjunction with IPM programs require greater time commitments for

5 6 assessment of pest infestation levels to assure that controls are employed in the most judicious manner.

As has been learned in field settings over the past 30 years, food processors and distributors must now realize that most pest management decisions have consequences far beyond the time and location that pests must be controlled. Comprehensive plans for pest management greatly improve effectiveness, profitability, and safety of pest control efforts over what can be achieved with piecemeal approaches. Important keys to effective, profitable, and environmentally-safe pest management are careful monitoring of pest populations, complete records of infestation levels and controls applied, and comprehensive benefit/cost analyses. To provide necessary training and technology, IPM programs must be supported by multidisciplinary research and extension efforts through the USDA and Land-Grant universities working in cooperation with the food industry.

The broad range of control options now available for incorporation into IPM programs include:

1. Biological Controls = using natural enemies such as parasites, predators, pathogens, and competitors of pest species in applied control programs.

2. Cultural Controls = methods such as tillage, host plant resistance, and crop rotation to reduce pest infestations in production systems.

3. Chemical Controls = a variety of chemical toxicants, repellents, protectants, growth regulators, germination inhibitors are used to regulate populations of insect pests, plant pathogens, and weeds.

4. Mechanical and Physical Controls = approaches that have their greatest application in post-harvest pest management include heat and cold treatments, sanitation, and protective packaging.

5. Legislative Controls = imposition of inspection and quarantine regulations to prevent importation and spread of introduced pests in living plants and animals or in harvested commodities.

Integrated pest management programs feature combinations of the above control options to achieve the safest and most cost-effective regulation of all types of pests in food production, processing, and distribution systems.

SETTING THE STAGE FOR IPM: THE PESTICIDE ERA

Throughout most of the history of agriculture, a lack of highly effective, unilateral control measures such as modern-day chemical pesticides resulted in use of various combinations of controls (e.g., integrated control) to reduce losses caused by pest species.

Controls included a variety of cultural measures such as cultivation and crop rotation; removal of insects and weeds from crops by hand; and application of inorganic pesticides containing active ingredients such as sulfur, lime, and arsenic. It was not until the advent of the “modern insecticide era” after World War II that use of highly effective compounds like DDT and BHC (benzene hexachloride) introduced a new philosophy of pest control. Within a few years of their first applications, these organochlorine insecticides were being used extensively with the objective of eradicating pest populations. Little concern was given the potential for deleterious consequences to non- target species, hazards to farm workers, or harmful residues in human food. The ready availability and high degree of effectiveness of these pesticides resulted in reliance on them as a unilateral controls. By 1966, nearly 150 million pounds of insecticides were being applied per year in the United States, most of which was used in crop production

(10). Although insecticides were the first of the chemical pesticides to be used in such vast quantities, research efforts led to discoveries of phytotoxic chemicals that resulted in

7 8 usage of herbicides which peaked at over 450 million pounds per year in 1982 (10). The increase in the quantity of fungicides applied has been much more modest, from 21 million pounds in 1966 to 37 million pounds in 1992 (2).

Certainly, the availability of highly effective chemical insecticides has been an important factor contributing to significant reductions in incidence of arthropod-borne diseases in humans and domesticated animals. Also, availability of effective chemical pesticides of all types has been an important contributor to a 230% increase in productivity of agriculture in the United States from 1947 to 1986 (11). Ease of application and relatively low cost of these broad-spectrum pesticides have been important assets resulting in their tremendously high levels of use in food production and processing systems. By 1970, insecticide use in cotton in the United States had exceeded

70 million pounds per year. By 1985, herbicide use in corn alone had reached 250 million pounds per year (10).

This extensive reliance on the chemical pesticides has led to some serious problems and resulted in many questions relating to continued use of these compounds.

These questions have resulted in the cancellations of registrations for many uses of these products. In extreme instances, as many as 40-60 applications of pesticides have been made per year in cotton (12), with the result being serious issues of environmental pollution and mortality of non-target species. Among the problems resulting from excessive use of chemical pesticides are the following:

 Environmental contamination where pesticides in soils have entered

surface and groundwater threatening the safety of water supplies for

human and animal consumption (2, 10).

 Increasing human health risks resulting from exposure to residues in food

and water supplies, particularly relating to the potential of some pesticides

to cause cancer, disrupt the endocrine system, and interrupt normal

development of the central nervous system in children (2). Despite

cancellation of registrations for nearly all organochlorine insecticides,

residues of these compounds are still commonly detected in food products.

 Threats to non-target organisms such as wildlife species in both terrestrial

and aquatic environments (2).

 Mortality of beneficial parasitic, predatory, and pathogenic species that

often serve important roles in regulating pest populations (2, 13).

Destruction of beneficial organisms contributes to problems of pest

resurgence and outbreaks of secondary pest species.

 Development of resistance in pest species to chemical pesticides is a

growing problem for all types of pests worldwide, with over 400 arthropod

species, over 100 species of plant pathogens, and over 50 species of weeds

exhibiting resistance to insecticides, fungicides, and herbicides,

respectively, by 1986 (14).

 Increasing costs associated with intensive usage of chemical pesticides in

crop production (10).

The increasing urgency to find solutions to the problems listed above has resulted in passage of several major pieces of legislation by the federal government in the United

States. The Federal Environmental Pesticide Control Act of 1972, comprised of extensive amendments to the Federal Insecticide, Fungicide, and Rodenticide Act of

1947, and the Food Quality Protection Act of 1996 will continue to have great impacts on availability and use patterns for chemical pesticides for the foreseeable future. These problems have also generated great emphases for research and extension efforts to develop and employ alternative controls.

SETTING THE STAGE FOR IPM: ENTERING THE IPM ERA

Although environmental contamination and food safety concerns have resulted in some increased interest in development of integrated control programs to reduce reliance on chemical pesticides, the major impetus for reduction in usage of these compounds has resulted from political activism. Publication of the book Silent Spring by Rachel Carson

(15) served as a catalyst resulting in a strong negative reaction by the general public to the extensive use of chemical pesticides, especially the organochlorine insecticides such as DDT. Public reaction to threats of environmental pollution and contamination of the food supply by pesticide residues (16) has resulted in cancellation of all registrations for most organochlorine insecticides. Although insecticides belonging to the organophosphate and carbamate classes replaced the organochlorine compounds for most uses, growing support among farmers and consumers for integrated control programs has resulted in reduced reliance on these chemical insecticides and movement from an industrial to an ecological model of pest management (17).

Public support for the IPM concept has led to gradual development of a philosophy that integrates pest control tactics and crop management from both agronomic and economic standpoints (18). From an original, relatively narrow focus on field-crop production (19), application of principles of IPM has now attained a much broader focus to include processing and distribution systems for food commodities. In relation to crop production, application of IPM provides a basis for continued profitable production of

10 11 food and fiber commodities with much less threat of environmental degradation or harmful residues in food. Employing principles of IPM in processing and distribution of commodities is an additional, important step in maintaining a safe and wholesome food supply.

FOOD SAFETY AND IPM

Many countries maintain strict guidelines for the wholesomeness and safety of food products sold to end-user consumers. Food products must be free of contamination by harmful chemical residues and biological organisms, such as insects or microorganisms.

They must also comply with standards of purity, composition, and preparation that are specified by regulatory agencies (20). The food safety challenge for industry requires delivery of products that are free of pest contamination while also containing pesticide residues that are below legal minimum levels.

Pests, Pesticides and Regulations

Hundreds of species of insects, mites, and microorgansims are known to infest grain and other raw commodities in storage, and many of these same organisms infest grain-based food products after processing and packaging. There is often an additive effect in terms of damage caused with infestations by multiple species. For example, infestation of bulk- stored grains by insects can result in weight loss of the grain, as well as, increased heating and moisture levels that facilitate growth of molds and spread of mycotoxins. The end result of these combined infestations by insects and molds is that grain may be rendered unusable (21).

Most insects infesting grain being prepared for milling can be removed with sieves before grinding into flour, however, eggs of some species may survive cleaning and contribute to subsequent infestations in processed foods. Additionally, insect larvae

11 12 and pupae inside grain kernels can not be removed, but are milled with the flour and remain as fragmentary contaminants. Insect fragments, rodent hair, feces, and other foreign material, are classified as filth that must be kept below acceptable levels. Though not toxic, insect fragments can have direct human health effects as allergens for some persons (22). Contamination by insect-related filth signals an overall low level of quality and wholesomeness of food products.

Chemical insecticides are used in two principle ways to limit infestation of stored grains by insects. Insecticides in the form of residual protectants are used quite commonly as grain enters storage facilities to prevent infestation during storage (23).

Fumigant insecticides are used to eliminate insect infestations that have developed after commodities are placed in storage. Fumigants such as phosphine and methyl bromide leave little or no residue that may contaminate food. For this reason, they are not considered significant threats to food safety, however, the lack of residual effects with these chemicals means that they do not protect grain from re-infestation following treatment. By contrast, residual protectant insecticides used to treat raw grain and applied throughout the food system in the treatment of structures and equipment where foods are processed and packaged foods stored may pose problems through contamination by residues. Insecticide residues can remain in stored grain for months or years because the storage environment having low light or darkness, stable or gradually changing temperatures, and relatively low moisture levels slows chemical degradation.

Milling, and to a greater extent, baking or cooking do cause substantial degradation of residues. However, some residues may still remain as the original chemical used in treatment or in the form of degradation products (24).

Pesticide residues in food pose both proven and suspected health risks to humans

12 13 and generate much public concern and governmental regulatory action throughout the world (25). The commonly used residual insecticides applied in grain storage facilities belong to the organophosphate and pyrethroid chemical classes. In the United States, relatively few organophosphate insecticides are registered for application directly to grain, however, additional organophosphates and certain pyrethroids can be used in structural surface treatments (23). The Codex Alimentarius Commission has established international guidelines for permissible residues of organophosphates and pyrethroids in both raw grain and processed food products. Individual governmental regulatory agencies in most countries have generally concurred with these guidelines by passing appropriate regulations for enforcement.

In the United States, surveys of stored grain for detection of for pesticide residues have not revealed levels above established tolerances, however, the majority of samples have contained detectable residues of organophosphates (Table 1). In spite of evidence for compliance by the food industry with established tolerance levels for pesticide residues, consumer advocacy organizations have called for stricter tolerance guidelines.

The Food Quality Protection Act (FQPA) passed by the U.S. Congress in 1996 mandates a reassessment of all existing pesticide registrations with strict attention to human safety.

The FQPA emphasizes accumulated risk resulting from exposure to classes of chemical pesticides, not just to individual active ingredients. For example, all organophosphates used in a variety of applications to food commodities, inside homes, on lawns, and in public areas will be considered together in estimating accumulated exposure. Risks will be assessed based on the most sensitive members of the population, that being infants and children. Residues in food appear to constitute the highest exposure risks because they result in direct ingestion of pesticides.

Organophosphate insecticides have been targeted as a class for initial review and potential elimination by the U.S. Environmental Protection Agency because of their activity as neurotoxins and their potential as endocrine disruptors (26). Cancellation of registrations for organophosphates currently applied to grain and used throughout the food industry would creat a great need for effective controls as replacements.

The fumigant methyl bromide is a fast-acting, residue-free chemical that is used routinely in grain storage bins, flour mills, food processing facilities, and warehouses to control insect infestations. It has perhaps been the most effective insecticide used in the food industry, but registrations for this product are slated for cancellation. Because methyl bromide is an ozone-depleting substance and may pose a threat to the protective atmospheric, ozone layer around the earth, its production and application is scheduled to cease in the United States by the year 2005 as mandated by the Clean Air Act. Other industrialized and developing countries worldwide are eliminating or severely reducing use of methyl bromide over the next several decades in compliance with an international agreement known as the Montreal Protocol (27). In this case, an environmental rather than a food safety concern is fueling the campaign for cancellation of an effective and residue-free insecticide for the food industry. This cancellation could possibly lead to increased use of residual insecticides. Ideal substitutes for methyl bromide have not been found, but much research and discussion are aimed at developing safe alternatives for the food industry. One alternative that may become quite important is IPM, an approach that could keep chemical insecticide usage at a minimum while utilizing a variety of alternative controls to limit pest populations.

The Case for IPM in the Food Industry

It seems apparent that the impacts of more stringent regulations on pesticide use in the food industry in combination with growing consumer demands for more wholesome and pesticide-free foods must result in more extensive adoption of IPM practices. Although purchase contract specifications for grain now commonly stipulate that there can be no detectable pesticide residues, also stipulated is the requirement that the grain be of relatively high quality with little insect damage (28). In addition, the tolerance levels for insect contaminants in value-added, finished food products are even lower than those for raw commodities, essentially a zero tolerance. For the future, it is clear that raw commodities destined for use in food products must be kept in good condition by combined action of several preventative measures employed through an IPM program.

Similarly, pest-free, finished products in warehouses and retail outlets that are at risk for reinfestation must be protected until purchased by the consumer.

Managers at all levels of the food processing and marketing continuum, from bulk storage of commodities to retail outlets of high-value, finished products, must adopt IPM strategies that include sanitation, prevention, effective monitoring, and informed decision-making regarding pest suppression tactics. Informed decision-making based on cost/benefit analyses is the cornerstone of IPM, and should guide pest control decisions at all levels of the food industry. The economic injury level concept explained earlier in this chapter must become the basis for these decisions. Because the relative value of products varies greatly through the different levels of the food industry, so also will the economic thresholds used to guide control decisions.

IPM FOR FOR FRESH COMMODITIES WITH ZERO PEST TOLERANCE

Fresh fruits and vegetables are sold as soon after harvest as possible and there is typically little time or need for post-harvest IPM. However, IPM is practiced during production of these commodities to prevent damage, and those involved with post-harvest handling must be concerned with quality preservation. Only undamaged, blemish-free fruits and vegetables are selected for the fresh table market. Not only must producers work to avoid damage that is evident in an exterior examination, but also to eliminate insects confined within tissues of harvested produce. These pests are not only serious problems for the domestic market, but in the export market are often the targets of legal quarantines enforced to prevent the spread of pest species.

Fumigants such as methyl bromide and ethylene dibromide were once commonly used to insure that fresh fruits and vegetables for export were pest-free (29), but these chemicals are now being replaced by non-chemical methods. Safe and effective physical controls are being used commercially, such as cold treatment to eliminate codling moths from apples and vapor heat treatment to kill fruit flies infesting papayas (30). Ionizing radiation is an effective treatment for killing immature insect life stages inside fruits and vegetables while maintaining product quality (31). However, radiation has only limited commercial adoption for use with fresh produce because of serious opposition in some locations by consumers who reject irradiated food. Research on controlled atmospheres using high carbon dioxide concentrations or low oxygen levels shows promise for controlling post-harvest pests of fresh commodities, but practical limitations in maintaining proper treatment conditions has hindered commercial adoption of these methods (32).

POST-HARVEST IPM FOR RAW, DURABLE COMMODITIES

Although IPM methods discussed here address stored grain almost exclusively, the same concepts and methods apply to other durable commodities such as legumes, nuts, dried fruits, and other dried commodities that can be stored in bulk. Cereal and feed grains comprise the most important basic inputs to the world food supply, and because of their seasonal growth patterns they must be safely stored and maintained for year-round consumption.

Grain Storage: Pest Prevention and Sanitation

Insect pest problems in stored grain can be prevented or delayed by limiting access to the storage facility. With exception of a few species that may infest ripening grain to a limited extent before harvest, stored grain insects do not infest crops in the field and normally do not enter storage facilities with the new harvest (33). Insects that become pests in storage facilities must have dried grains or other appropriate food on which to feed and reproduce. Typically, the source of insects infesting a newly stored commodity is from populations already infesting some previously stored material. A common source of infestation is from residues of grain in ‘empty’ storage structures (bins or silos), harvesting and conveying equipment, and transportation vehicles. Grain storage structures and grain handling machines must be thoroughly cleaned of residual grain before a subsequent crop is stored. If grain is stored in an insect-free structure then the only source of insects to infest grain is by immigration into the structure. Every effort must be made to repair leaks and close openings in grain bins and silos to prevent insect entry. Complete exclusion of insects from grain storages is extremely difficult, but minimizing entry points does reduce potential routes of infestation. Once storage structures are cleaned and sealed, surfaces should be treated with a residual spray of a

17 18 registered insecticide to provide protection against insects that may remain hidden within the structure or that may immigrate into the bin soon after grain is stored.

Monitoring Storage Conditions

Insect population growth in grain is dependent primarily on temperature of the air and/or grain, moisture content of the grain, and the quality of the grain as a food source (33).

Because most grains and grain products are nutritionally adequate, unless they have been severely degraded by microbial agents, food quality is rarely limiting for insects infesting stored grain. Temperature and grain moisture may vary greatly among storage situations are very important for insect survival and population growth. Biological factors such as development time from egg to adult, survival rates, and the number of eggs produced by females all attain maximum levels within optimal ranges of temperatures and grain moisture. Typically, these life history variables decrease at temperatures and moisture contents either above or below the optimal zone (Fig. 1). Insects that feed as larvae inside grain kernels are more sensitive to grain moisture content than are the external feeders. Optimal grain moisture levels for growth and survival of internal grain feeders ranges from 12 to 15%. Optimal temperatures for growth and development of stored grain insects are between 25 and 32 C. Most species experience mortality or reduced population growth at prolonged periods above 40 C and cease development below 15 C

(34). It is clear, therefore, that insect population growth can be slowed by maintaining grain in a cool, dry condition.

It is essential for effective stored grain IPM to have the best information possible about the current status of the commodity being managed and the potential pest populations at any time. As grain enters the storage facility, it should be characterized for quality factors such as bulk density, percent composition comprised by broken kernels and foreign material, and moisture content. Information on initial moisture content is critical because high moisture grain may need to be stored separately, mechanically died, or later blended with drier grain to attain a composite grain mass that is safe for storage.

The storage structure should be equipped with thermocouple cables or similar devices to monitor grain temperature at various locations throughout the grain mass during the storage period. Temperature cables are typically hung from the roof of a storage structure and extend vertically through the grain mass. Thermocouples are positioned on cables at a spacing of 2-3 m from bottom to top of the mass and a series of cables should be deployed at 5-10 m intervals so that the grain mass is evenly monitored.

Temperatures from each monitoring point should be recorded on a regular basis, ideally weekly or bi-weekly, and any abrupt increases in temperature over a short period of time should be investigated by sampling the grain mass. Temperature cables are useful in detecting “hot spots” where moisture, mold growth and insect infestation may have begun. Temperature monitoring is also important to check the progress of grain cooling during aeration.

The species and numbers of insects in stored grain can best be monitored by direct and systematic sampling of the grain, and by use of traps. Direct grain sampling is the best monitoring approach, but it is labor-intensive and requires a certain level of skill.

Managers of grain storage facilities can easily learn the required methods and implement grain sampling for insects as part of their regular commodity management routine.

Samples can be obtained to a depth of 1-2 meters by using a spear-shaped sampler to withdraw grain from the mass, or sampling may be done as grain is moved from bin to bin within a facility using a cup-type (pelican) sampler (Fig. 2). Increasing the numbers of samples enhances the level of accuracy achieved in estimating insect population density (35). For example, five-1 kg samples must be taken from each 27 metric tons

(1000 bushels) of grain to determine with 90% accuracy if a grain mass contains as many as 2 insects per kg; a common economic threshold for control decisions. Grain samples must be processed with an appropriate sieve or sifting device to remove insects for identification and counting. Grain probe traps are also available that capture insects as they move through a grain mass (Fig. 2). These traps are effective for detection of insects at low population densities (36), but the data obtained are not easily converted to numbers of insects per unit of grain volume.

Decision-making for Insect Control

Correct interpretation of insect sampling data is important for making control decisions in stored grain IPM. As indicated earlier, decisions should be based on cost-benefit analyses that incorporate assessments of the quality parameters. Raw grain is marketed based on quality, which is quantified by a numerical grade in the United States. The highest quality grain, in addition to having a high bulk density (test weight) and little or no foreign material, contains no live insects, and has no measurable damage from insects.

Damaged kernels result from feeding within by species such as weevils in the genus

Sitophilus and the lesser grain borer, Rhyzopertha dominica, that chew holes through kernels. If one or more members of these species are found in a grain sample or probe trap sample then more extensive sampling should be conducted. Discovery of damage by internal feeders may warrant a fumigation treatment to eliminate the infestation and

20 21 prevent additional damage.

The presence of large numbers of external feeding insects, which cause no direct grain damage, may be revealed in grain or trap samples, but they can be tolerated until the time of sale as long as grain quality, temperature and moisture remain acceptable.

Live external feeding insects can be eliminated with an effective fumigation before grain is transported. It should be noted that many international markets will not tolerate even dead insects in grain, so treatment decisions must be adjusted accordingly.

Non-chemical Controls for Stored Grain Pests

Effective IPM programs for stored grain involve a variety of approaches intended to prevent the occurrence of damaging pest infestations. Sanitation was discussed earlier as a preventative measure employed before grain enters the storage facility. Among the most effective non-chemical means for pest prevention or suppression after grain is in storage is use of ambient air cooling with aeration. This is achieved with air flow from fans mounted at the base of the storage structure that either blow air into the bottom of the mass and force it upward, or draw air through roof vents downward through the grain mass. Effective aeration cooling occurs only when the outside air temperature is below the temperature of the grain. Thermostatically controlled fans can be used to insure that they operate at the proper ambient temperatures (37). Because insect developmental rates are directly influenced by temperature, lowering the temperature of the grain mass below the optimum level for insect growth (below 15 C for most species) can significantly reduce population increase and the potential for damage. Low grain temperatures are achieved most efficiently in temperate regions after seasonal changes from summer to fall result in lower ambient air temperatures. However, even if grain cannot be cooled below

15 C immediately, marginal cooling can be effective in reducing rates of insect

21 22 population increase (33).

Simulation models of temperature-dependent insect population growth rates have been developed for the most damaging stored grain pests. These models verify the benefits of aeration for suppression of pest populations (Fig. 3). Although costs of aeration depend on local electricity costs, in most cases expenditures are justified based on reductions in insect infestations that can be achieved (38).

Biological controls and biologically-based pesticides may provide additional non- chemical methods for pest control in stored grain. The community of insect species that infests stored grain includes those that consume the grain itself, those that feed on molds which infect the grain, and entomophagous parasitoids and predators. Studies have been published in which experimental populations of grain pests have been reduced by addition of natural enemies to storage containers (39). A recent study conducted in grain bins has validated the efficacy of introducing parasitic wasps to suppress populations of the lesser grain borer (40). The objective of these studies has been to identify benficial species that can maintain pest populations at below the economic injury level (Fig. 4).

Although some companies mass produce and sell parasitoids and predators of stored grain pests, the use of beneficial insects in grain storage facilities has not yet been widely adopted.

(Add some additional material about basics of Bt crops here)

Genetic engineering to incorporate genes into crop plants for production of microbial agents toxic to insects is being adopted for several major agronomic crops.

The potential is being investigated that these toxins may be present in sufficient quantities within grain produced by these crops to control insects which feed on that grain in storage. These toxins are not harmful to humans, and may be a valuable asset in IPM

22 23 for stored grains if they prove to be effective for post-harvest pest control.

Chemical Insecticides for Stored Grain Pests

When alternative non-chemical controls fail to maintain insect pest populations below economic injury levels, chemical insecticides remain the most effective tools for pest suppression in stored grain. Fumigant insecticides are ideal for bulk-stored commodities because they are released as gases that penetrate the commodity in place.

Phosphine gas, or hydrogen phosphide, is the most commonly used fumigant for stored grain worldwide (41). Phosphine formulated as pellets or tablets remains a relatively inexpensive control costing a few cents per bushel (38). Phosphine is liberated from pellets or tablets of aluminum or magnesium phosphide upon reaction with water in the air. Because phosphine has a density close to that of air, it penetrates bulk commodities well. It must be stated, however, that this same low density property can be a detriment as it allows phosphine to dissipate easily if structures are not sealed well. Aluminum phosphide pellets are typically added to grain that is being transferred from one storage structure to another or to a transport vehicle, allowing even distribution throughout the grain mass.

Re-circulation methods have been developed that allow adequate penetration by the gas even when pellets are applied just to the top of a large grain mass and/or to a bottom access via the aeration plenum. Phosphine accumulated in the headspace above the grain is drawn through a pipe in the roof of the structure and reintroduced at the bottom of the mass where it travels upward through the mass and attains even distribution

(42). Phosphine is relatively slow-acting and several days exposure at optimum temperatures may be required to produce insect mortality. Long exposure time for bulk grain is usually not a problem as considerable time is available during storage or

23 24 transport. Treatment times may be reduced by use of phosphine gas dissolved in carbon dioxide and contained in gas cylinders now becoming available in some countries. This formulation also provides a means for rapid, even distribution of gas througout a storage structure.

Grain protectants are among the most commonly used controls for insects in stored grain. These residual insecticides are applied to grain at the time it initially goes into storage to provide protection against infestations for several months. Although more expensive than phosphine on a per bushel basis, protectants are the preferred control if a high risk of infestation exists. Among the disadvantages of grain protectants, as mentioned earlier, is the potential for residues to remain in the grain at the time of sale.

Also, as the time grain is kept in storage increases, the possibility exists that the insecticide may lose effectiveness. There is also evidence that some species are not effectively controlled due to development of resistance to the insecticides (43).

Malathion, for example, remains a commonly used grain protectant in the United States, though it is well established that many populations of the common stored grain insects have evolved resistance to this compound (43). Because of these problems and the growing expense of protectant applications, the future of this approach to control of stored grain insects is in doubt. In addition, the use of protectants is not consistent with principles of IPM because they are often applied with little assessment of potential pest infestation levels. It is possible that use of insecticides as preventative measures will be restricted to applications as residual sprays in empty structures as part of a comprehensive sanitation program.

Diatomaceous earth is a naturally occurring absorbent dust that poses no chemical residue or food safety problems. This material kills insects by eroding waxes from the

24 25 exoskeleton that function to seal the insect against loss of water. Death occurs due to desiccation (44). However, diatomaceous earth is as expensive to use as synthetic chemical insecticides, and it reduces the bulk density and the value of grain with which it is thoroughly admixed. And, because its effectiveness is yet to be well-established, the future contribution of diatomaceous earth to IPM in stored products is not clear.

IPM FOR FOOD PROCESSING

The information below relates to any facility in which a raw commodity such as grain is processed in any way to make a more valuable product; such a product may be ready for the consumer market or it may be an intermediate product that is processed further at another facility. Thus food processing here refers to activities of flour mills, bakeries, pet food plants, breakfast cereal manufacturers, snack food plants, chocolate factories and confectioners.

Stored-product insects that infest food processing facilities are essentially the same species that infest raw grain, but the species composition and their relative importance is different. Internal grain feeding insects such as weevils and borers are not as important in processing environments because the concern for grain damage is no longer an issue. Species considered secondary in importance in raw grain because they feed only on broken kernels, such as flour beetles, sawtoothed grain beetles and storage moths such as??, are considered of primary importance in food processing because they can easily infest milled products and contribute to problems with contaminants. For example, the Association of Operative Millers has listed the red flour beetle as the most important insect pest of flour mills because of its ability to survive and reproduce in flour.

This species is also difficult to control in flour mills (45). By comparison, the red flour beetle, though common in stored grain, is rarely considered more than a nuisance. Also

25 26 important is the consideration that once grain is milled into flour, its value increases greatly, and economic injury levels for pests decrease accordingly.

Sanitation and Prevention

Food processing facilities must devote personnel and other resources to sanitation, pest monitoring, and pest control if they are to maintain a level of cleanliness and product quality that is demanded by consumers and mandated by governmental regulations. As with stored grain, preventive measures are basic to pest management programs. For flour mills and other processing plants, the sanitation routine should include daily or twice daily cleaning of equipment and floors where flour dust can accumulate (46). Use of compressed air to blow dust from machines and floors is a popular cleaning tool, but it should used used sparingly so that dust is not simply blown into hard-to-clean areas.

Food debris that accumulates in these areas can support residual populations of pests that constantly contribute to infestation of the product. Sweeping is effective when combined with vacuum cleaning. Problem areas for dust accumulation should be identified and regularly targeted with vacuum cleaning. Spills need to be cleaned immediately and broken packages discarded. Broken windows, window screens, and other structural components should be repaired promptly to limit entry of food pests into a facility.

Rotation of raw and finished stock to utilize older products first represents a simple preventive measure to avoid the opportunity for growth of pest populations. Common sense approaches to sanitation and prevention need to be adopted, but in many facilities the simple measures are overlooked in favor of increased production.

Monitoring for Pest Infestations

Active efforts at pest detection and monitoring should be incorporated into a regular routine with sanitation and prevention efforts of food plants. Direct sampling of

26 27 products and residues from the production line can alert managers to the presence of incipient pest problems (46). As dust and siftings from different points in the milling process are cleaned up, these materials should be carefully inspected daily for the presence of insects. Similarly, floor sweepings and the residue form machinery clean- outs must be inspected. Boots of elevator legs and the bottom trays of vertical conveyor systems contain spaces where food and pests can accumulate, and should be cleaned and inspected regularly. Insect traps baited with attractants for certain species, or designed to capture any insects present, can be used throughout a facility to determine the presence, relative abundance and location of pests (47). Traps baited with pheromones are highly sensitive to the presence of the target species for the attactant. By deploying traps in a regular grid-like arrangement throughout facilities, manager can identify areas with the highest likelihood of insect infestation and concentrate monitoring efforts in these areas.

Monitoring data from traps or product and residue samples must be documented and the records maintained over time, so that trends in pest numbers can be observed and utilized in IPM decisions.

Controlling Pests (without Methyl Bromide)

Methyl bromide has been used effectively for many years to suppress pest populations in structures such as flour mills and food processing plants, so that chronic infestation problems have not persisted (48). Grain millers and other processors consider this chemical to be an essential component of their pest control and sanitation programs.

Methyl bromide will be unavailable for most uses in the United States and in most other industrialized countries beginning in the year 2005. No fumigant gas is available that can directly replace methyl bromide for rapid, effective insect control without harmful residues in food products. Phosphine is registered for use in structures containing food and leaves no harmful residues on food. However, phosphine often requires several days to achieve effective insect control, compared to several hours required with methyl bromide. Large flour mills and similar plants continue production 7 days weekly, and can not operate profitably with the long shut-downs that would be required for phosphine fumigation. Another concern of many food processors when considering fumigation with phosphine is that copper and other metal components of machinery can be corroded by phosphine at high humidities and warm temperatures (49). Electrical wiring and sensitive electronic equipment may be put at risk when phosphine is used in flour mills or food processing plants. One innovative application method for phosphine as a substitute for methyl bromide is use of relatively low doses with elevated temperatures and the addition of carbon dioxide. This method may increase activity of the insecticide and reduce potential damage to machines by shorter exposure times, especially in areas where sensitive electronic equipment is housed (50, 51). The presence of carbon dioxide and higher temperatures apparently increases respiration rates of insects and enhances mortality.

Various other physical and chemical methods have been proposed as alternatives

28 29 to use of methyl bromide for pest control in food processing, however, none can be considered an effective replacement in terms of efficiency and effectiveness (52).

Controlled atmospheres with high carbon dioxide or low oxygen concentrations have been proposed but are not practical or cost-effective for food processing facilities because of the need for enormous amounts of gases released in structures that can not be sealed tightly. Heat treatment, or “heat sterilization”, of entire facilities has been attempted with some success, however, for effective insect control it is necessary to maintain the temperature at approximately 50 C for 24-36 hrs (53). A major problem with heat treatment is the difficulty in attaining temperatures lethal to insects inside walls and machines, and close to floors in basements.

Numerous residual insecticides have been proposed as replacements for methyl bromide. Their effectiveness is limited, however, because they often cannot be applied in all areas where control is needed because of risks of contamination of food products by chemical residues. Consequently, control must be attained through residual activity on treated surfaces where insecticide residues are not likely to contaminate food products with the hope that insects may be controlled through contact with treated surfaces (43).

Also being evaluated in flour mills is a combination of elevated temperatures and thorough dusting with diatomaceous earth (54). This method also has limitations for control of insects harbored deep within structures. It seems apparent that when registrations for methyl bromide are finally cancelled, food processing facilities will be forced to develop more intensified efforts at prevention, vigilant monitoring, and specialized mitigation measures to replace the current unilateral applications of methyl bromide for pest control.

IPM FOR VALUE-ADDED FOOD PRODUCTS

At the end of the food processing continuum are the high-value, packaged products ready for retail marketing to consumers. After leaving a processing facility, these products are typically transported to regional wholesale distribution centers where they may be stored for periods ranging from a few days to many months. Although ownership of these products may reside with retail marketers, problems with pest infestations during storage and even at retail outlets, are often blamed on the food processors. Regardless of who takes the responsibility for protection of these products, substantial investments in preventive measures must be made to protect finished products from infestation.

Internal corporate regulation of finished product quality must be maintained through a system of regular inspections and business-partner accountability. As a first step, conscientious food companies should set rigorous, internal standards and conduct sanitation audits on their own facilities and those of suppliers to insure that their standards and those imposed through governmental regulations are met. Sanitation standards or specific Good Manufacturing Practices (GMPs) are sometimes specified in supplier contracts, placing suppliers at risk of losing business should their facilities fail to pass sanitation audits (55). All facilities should be inspected through the auditing system, including mills, processing plants, warehouses, and retail outlets.

Companies that produce value-added products can take several measures to prevent pest infestations through protective food packaging and even by engineering modifications to buildings. Many types of food packaging are at risk for penetration by insects, with those comprised of paper and cellophane being least resistant.

Polypropylene and similar polymer films provide some additional protection against boring and chewing insects, and their resistance to penetration improves with film

30 31 thickness (56). The greatest protection is afforded by glass and metal containers. Certain food-safe, natural insect repellents have recently been approved by EPA for use in food packages to deter insect infestation, but the effectiveness of these agents has not been proven.

Structural design features for production facilities, warehouses, and retail outlets can be improved to enhance sanitation and pest control. Cracks, crevices, and other unnecessary openings in walls and floors should be sealed. Wall to floor junctions should be protected by concave molded tile to prevent harborage of pests, and wood-to- wood joints should be avoided or appropriately sealed. Voids in double-wall construction should be eliminated in new structures as they may allow accumulation of food debris and provide excellent harborage for pests. Physical separation of raw commodity storage areas, processing areas, and warehouses will help to prevent movement of pests from raw grain storage to high-value processed foods. Building exteriors should be free from vegetation, soil, and product spills. Exterior lights should not be mounted over doors or windows, to avoid attacting insects to these openings at night. Rather, lights should be positioned away from the building and illuminate the structure from a distance.

ADOPTING IPM: CHALLENGE AND NECESSITY

The post-harvest food industry faces serious challenges in pest management due to attractiveness of food products to pests, greater public demands for safe, high-quality food products, and increasing regulatory constraints on use of chemical insecticides. It is apparent that the industry will no longer be able to rely on the ‘quick fix’ provided by chemical pesticides such as methyl bromide. The industry must develop and adopt IPM programs to meet consumer demands and comply with governmental regulations.

Fundamental components of the IPM programs for the food industry must include preventing infestations wherever possible through sanitation and pest exclusion by sealing of structures. Also, consistent monitoring programs and judicious decision- making to guide the use of chemical pesticides will be critical. Alternatives to chemical pesticides, such as biological control agents must be used when possible. Thus, IPM in the food industry will be both preventive and responsive (57).

Decision-making parameters are not as well-defined in the post-harvest food industry as in production agriculture, but economic injury levels and economic thresholds must be established for all key pests. Adoption of IPM practices is being encouraged through incentives at various levels in the industry. Some retailers are putting IPM labelling on products and report a favorable public response to these products. A positive public perception of IPM coupled with a desire to reduce pesticide inputs is giving momentum to the drive for adoption of IPM.

Need some additional explanation here.....Despite adoption of IPM, there are many unknowns regarding the safety and quality of the food supply with fewer pesticide inputs. Increased adoption of HACCP?? and ISO-9000 protocols?? will facilitate co- adoption of IPM for insect pests and should help ensure safety and quality.

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Table 1. Detection of Insecticide Residues in Wheat Samples from Grain Elevators in

Major Wheat-Producing States of U.S. 1

Percentage of Samples with Detectable Levels in a Given Year 2

1995 1996 1997

Insecticide (600) (340) (623)

Carbaryl 0.5 0.3 0.3

Chlorpyrifos 19.5 14.4 6.4

Chlorpyrifos Methyl3 54.2 73.2 55.6

Dichlorvos 0 0 0

Malathion3 71.0 70.3 68.2

Methoxyhlor 1.0 4.7 5.2

Methyl Parathion 0 0.3 0.2

1Data compiled from x y and z

2Number in parentheses refers to the number of samples analyzed in a given year

3Registered by U.S. Environmental Protection Agency for direct admixture to grain as a protectant; other insecticides residues presumably resulted from other applications.

Figure Legends

Fig. 1. Survival of lesser grain borers as a function of temperature and wheat moisture content (adapted from Hagstrum et al. 1996)

Fig. 2. Devices used to sample grain for insect population monitoring. a. A spear-shaped grain trier to extract a sample of grain from bulk storage. b. An insect probe trap that is inserted into a grain mass; insects moving through the grain pass through the holes in the trap and fall into the collection tip. c. A pelican sampler used to collect a sample of flowing grain as it falls vertically.

Fig. 3. Conceptual plot of a grain insect population size with and without aeration to cool grain and slow population growth. ET=economic threshold; EIL=economic injury level

(adapted from Hagstrum and Flinn 1996).

Fig. 4. Conceptual diagram indicating how a pest population can be suppressed by the introduction of a parasitoid, which is a biological control agent. PE=population equilibrium; EIL=economic injury level; ME=modified equilibrium (adapted from

Brower et al. 1996).