Integrated Pest Management (IPM) in the Control of Storage Insects

Integrated pest management (IPM) can be defined as the acceptable use of practicable measures to minimize, cost-effectively, the losses caused by pests in a particular management system. For the measures to be cost- effective they must be appropriate to and acceptable into that system.

They may be simple or complex but they must suit the system objectives and its technical capabilities. Furthermore, in this context, cost- effectiveness requires that all costs and benefits, including sociological and environmental effects, should have been taken into account.

The term integrated pest management is used to imply that a flexible and technically informed approach is also required.

In defining this term it may be considered necessary to specify the inclusion of scientific and cost-effective pest monitoring procedures which permit judicious adjustments to the timing, choice and intensity of control actions.

It may also be advisable to point out that specific pest control measures, as distinct from general crop or commodity husbandry practices, should generally be omitted unless the circumstances warrant and permit their cost-effective inclusion.

The current emphasis upon integrated pest management is, in effect, a reassertion of the need to put traditional good husbandry in place as the fundamental basis of pest control. In grain storage, as with other durable agricultural products, it is good commodity management and good store management which are the major prerequisites.

The various options for more intensive insect pest control, which are also listed in Tables l and 2, include several which are themselves based upon traditional concepts of pest management. Thermal disinfestations, cooling and hermetic storage are examples.

These latter two methods are also examples of the opportunities, provided by the process of storage, to manage the generally enclosed storage environment in such a way that insect pests are prevented from multiplying or, as in efficient hermetic storage, effectively eliminated.

Pre-harvest problems of insect pest control are rarely, if ever, so easily managed!

Control of the storage environment is thus an essential element in grain storage pest management. It involves, primarily, the controls on in-store climate and infestation-pressure which can be achieved by technically sound store design and construction.

Equally important, however, is the climatic control attainable by scientific management of the commodity to ensure that the stored grain is itself both dry and cool when loaded or, in ventilated stores and bins with aeration equipment, that the storage procedure achieves drying and cooling sufficiently rapidly.

In a fully loaded store it is the stored grain itself which largely determines and stabilizes the temperature and humidity conditions in the store.

Commodity management can also control, to a considerable extent, the initial insect infestation level in the stored grain.

However, in tropical countries, where pre-harvest infestation by storage insects is hardly ever completely preventable, the ideal of loading insect-free grain into the store is not often attainable.

Special facilities to completely disinfest the grain before loading may not prove cost-effective. The common alternatives, if early disinfestations is required, are to treat the grain, at intake, with a suitable admixed insecticide or to disinfest the loaded grain by in-store fumigation.

Control of grain quality before storage, to minimize the intake of heavily infested and badly damaged or unclean grain, is feasible and is commonly practiced to a considerable extent.

Even at the small farm level it is possible to segregate the crop at harvest, especially with maize on the cob and unthreshed sorghum and millet, selecting relatively undamaged material with good storage potential and setting aside the more evidently infested or otherwise damaged material which, if there is no other option, can at least be used first.

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By such means, the rate of deterioration due to insect infestation can be considerably retarded in the main stock of stored grain. There is little doubt that some subsistence farmers use this form of commodity management fairly effectively.

Certainly, one can sometimes observe on farm grain stocks that have received no special insecticidal treatment, with relatively little insect damage after several months’ storage at an ambient temperature that would permit the rapid increase of any well-established initial insect population.

Scientific approaches to grain storage pest management, having regard to grain storage as a part of the food production and distribution management system, have sometimes referred to the biological ecosystem concept as a means of comprehending grain storage processes and problems.

Table 4.1: Prerequisites and Options for On-farm Storage Pest Management

Essential	Optional
Basic IPM	Additional measures
Site and store management (protection from birds, rodents and weather plus basic hygiene)	Maintenance of conditions favorable to natural control: – by cooling (where feasible) by insect parasites, pathogens, etc. and/or Thermal disinfestation by solar heat and/or Treatment with traditional additives (if sufficiently available and effective)
Commodity management (cleaning, drying, etc.)	or Treatment with synthetic insecticides (if suitable formulations sufficiently available and effective) or Hermetic storage (pits or metal drums, etc.).

Table 4.2: Prerequisites and Options for Storage Pest Management at Main Depots

Essential	Optional	
Basic IPM	Disinfestation	Prevention of re- infestation
Site and store management (protection from birds, rodents and weather plus basic hygiene)	Insecticide admixture * Fumigation! or Thermal *	Provided by the treatment Residual insecticide sprays! Physical protection! (Sheeted stacks or packaging) or
Commodity management (cleaning, drying, etc.) – with bulk storage if appropriate	Irradiation * Hermetic! Controlled atmosphere! Grain cooling!	Insecticidal space treatments! Provided by the system Provided by the system Provided by the system

Notes: * May entail double handling for in-bag storage. Efficacy is doubtful. Extra management skills and/or other inputs required.

Modern theories of pest management have also generated the concept of economic control thresholds (ECTs). An ECT is most simply defined as the level of pest damage which justifies, in cost/benefit terms, the expenditure of resources upon control actions.

It is always a variable threshold because the costs and benefits of any action will depend upon the situation and its circumstances.

An ECT is situation specific. This is especially true, and not only for post-harvest pest control, when one considers the great differences in opportunities and constraints between the small farm level in developing countries and more sophisticated levels of operation.

Nevertheless, it is possible to generalize to some extent. For insect control in grain storage the ECT is likely to be at or very close to zero:

Where consumer demands place a high value on freedom from insect damage and/or freedom from any sign of insect infestation;

Where there is a definite intention to store grain for a protracted period, in which substantial insect damage can be predicted, and where the eventual market is not insensitive to loss of quality.

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