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What tests are necessary before release?
Before planning release, information should be available on the distribution of P.t., size of populations and stored-food loss situation so that the results of the control method can be evaluated with reference to those baseline data. The incidence and relative frequency of P.t. can be determined through surveys using pheromone traps, or by taking samples from farmers' stores in the major maize farming zones. The pheromone traps contain the same attractant used by the beetles to attract other members of the same species.
For these baseline surveys, a number of traps need to be set-up, located at least 100 m from maize fields or stores. As a rule, delta traps are used. The survey should cover different types of biotope such as fields and bush land, since P.t. is a wood borer, often found far away from maize stores, and which propagates in wood.
Collect and analyse data on a two-weekly or monthly basis, and over a several month period at least (ideally for one year), in order to capture seasonal fluctuations within the insect population.
An NRI brochure gives further details on the use of pheromone traps and where to obtain them (see end of the brochure for address).
A quick estimate of stored-food losses can be obtained by visual inspection. If there is a high density of P.t. in the region, it should be possible to detect the Larger Grain Borer three to four months after storage of the products, by means of random sampling in the store. Infestation by P.t. in stores is always non-uniform and at least 10 cobs should be taken at random from each store, and approximately 30 stores examined per selected region. Assess monetary losses by asking market women or merchants to inspect undamaged cobs and cobs displaying various degrees of infestation, and estimate their market value. Affected farmers can also be surveyed for their personal estimate of losses.
To keep costs (e.g. travel expenses) as low as possible, extension officers or other personnel from the relevant local institutions can carry out routine monitoring activities before and after release.
Once a picture has been obtained of the countrywide incidence of P.t. and associated financial losses. the sites of release can be identified. The key prerequisites are regular occurrence of the pest, and high P.t. populations. Where resources are limited, preference should be given to a small number of releases from widely distributed but promising sites, to increase the likelihood of the predator becoming established in the field.