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Alternatives to organo-phosphorus compounds for the control of storage mites

RESEARCH REVIEW 42

Alternatives to organo-phosphorus compounds for the control of storage mites

by

D A COLLINS

FEBRUARY 2000

Summary

This review has demonstrated the wide range of compounds available for use as acaricides. However, the relatively limited information on the efficacy against storage mites emphasises the need for further research. Table 1 summarises the results of previous research on the use of alternative compounds against storage mites, giving details on the test species, doses, test conditions and methods of application. As seen from the table, it is difficult to directly compare results, as different researchers have used different methods of evaluation.

For compounds to be considered as potential alternatives to 0Ps, as well as being effective against storage mites, they must also meet the following criteria:

1. effective against storage insects

2. available as commercial products, preferably already cleared for use on grain

3. easy to apply

4. have low mammalian toxicity

5. provide prolonged protection over extended storage periods

6. effective under typical U.K. storage conditions, i.e. low temperatures, high r.h.

7. can be incorporated into an integrated pest management programme e.g. as a surface treatment

Table 2 provides a summary of the advantages and disadvantages in the use of alternative compounds against storage mites.

The aim of this review was to identify compounds which would seem to warrant further investigation as potential alternatives to 0Ps for the control of storage mites. Of the IGRS, methoprene, appears the most promising, as previous research with fenoxycarb has produced contradictory results, and dimilin is not particularly effective against some storage mites. Inert dusts, such as 'Dryacide', are already used as grain protectants in some countries, however their efficacy under typical U.K. storage conditions may limit their use; although some of the newer products, e.g. 'Protect-It', may prove more efficacious. Pyrethroids have shown varying degrees of efficacy against storage mites, with bifenthrin, bioresmethrin and deltamethrin seeming to warrant further investigation. Azadirachtin containing products have proved effective against storage insects, although efficacy against mites appears to be concentrated on phytophagous pests. Benzyl benzoate has FDA approval for food use and although effective against Astigmatid mites in a domestic environment, has not been assessed for storage use. Although other plant derived products have proved effective, their main limitation may lie in the tainting of grain.

Of the novel compounds, chemosterilants have proved effective against storage mites, however, they are also usually highly toxic. Propionic acid has also proved effective, although treated grain loses its germinative capacity. Tricalcium phosphate is commonly used as a food additive, but high doses are required to he effective against storage mites. Abamectin has been used commercially as an acaricide and has a wide spectrum of activity against Prostigmatid mites, although it has not been assessed against storage mites.

Of the biological control agents, the predator Cheyletus eruditus, appears the most promising and is already used in storage facilities overseas. However, the predators themselves would be considered as grain contaminants and therefore need controlling. Bacillus thuringiensis may also be promising, as commercial products have been shown to be effective against phytophagous mites and storage insects. Nematodes are unsuitable for use in a dry storage environment, viruses and protozoa are not easily available and fungi produce mycotoxins that may be toxic to mammals.

More than 20 million tonnes of grain is stored annually in the U.K., valued in excess of £2 billion/year. During storage, grain is at risk of spoilage from infestation which is estimated to cost £50 million annually. With increasing concerns over the use of 0Ps, it is vitally important to investigate the efficacy of alternative compounds as grain protectants.

HGCA Project Number: 2084
Price: £6.50

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