Comparison of pesticide efficacy against insects and mites for

Summary

Sector:
Cereals & Oilseeds
Project code:
PR233
Date:
01 October 1998 - 30 April 2000
Funders:
AHDB Cereals & Oilseeds.
AHDB sector cost:
£51,946 From HGCA (Project Number: 1890)
Project leader:
P D COX, P G CLARKE, H L FORD, C P MORGAN AND L E COLLINS Central Science Laboratory, Sand Hutton, York YO41 1LZ

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About this project

Abstract

At present the control of invertebrate grain storage pests relies heavily on the use of organophosphate pesticides which are the only ones cleared in the UK for use in contact with stored cereals. However, there are no data available with which to compare the relative efficacy and residuality of pesticides against UK pests on a range of construction materials commonly used in storage facilities. The purpose of the laboratory study reported here was to investigate the relative efficacy of ten pesticides for the control of beetle and mite grain storage pests when used as treatments for grain store structures, and to assess their residual effectiveness over periods from one day up to six months after spraying.

The pesticides selected were five organophosphates, three pyrethroids, one carbamate and one organophosphate/ pyrethroid mixture, and represented those that are either already approved for use in UK grain stores or that could become so should approval be sought to widen their current use in food premises. The pesticides were sprayed onto squares of three types of substrate that are commonly used in grain store construction, namely wood, concrete and steel, and were applied at a rate equivalent to the label recommended field dose for each substrate type and pesticide. Batches of 25 beetles or mites were placed on each treated and untreated control substrate. The beetle species used were the saw-toothed grain beetle, Oryzaephilus surinamensis, the rust-red grain beetle, Cryptolestes ferrugineus, the grain weevil, Sitophilus granarius, the rice weevil, Sitophilus oryzae, the rust-red flour beetle, Tribolium castaneum, the foreign grain beetle, Ahasverus advena and the hairy fungus beetle, Typhaea stercorea. The mite species tested were the flour mite, Acarus siro and the cosmopolitan food mite, Lepidoglyphus destructor. Strains with high and low tolerance to pirimiphos-methyl were included for all species except T. stercorea and A. advena.

Recommendations for the structural treatment of grain stores to control beetle and mite pests, based on the results of these laboratory tests together with pesticide usage regulations in the UK, are:

1. For immediate treatment of infestations, use an organophosphate pesticide; pirimiphos-methyl, chlorpyrifos-methyl and etrimfos gave the best performances generally overall. Chlorpyrifos was also particularly effective against beetles on concrete but can only be used on surfaces that do not come into contact with food.

2. For longer-term treatment of areas that come into contact with food, use an organophosphate pesticide; fenitrothion performed best overall.

3. For longer-term treatment of areas that do not come into direct contact with food, use the pyrethroid permethrin. However, chlorpyrifos was more effective than permethrin against beetles on concrete.

Summary

At present the control of invertebrate grain storage pests relies heavily on the use of organophosphate pesticides which are the only ones cleared in the UK for use in contact with stored cereals. However, their continued use is under threat because of concerns about safety to humans and the environment, and increasing pest resistance. Some pesticide users are worried about operator exposure to pesticides and there is public concern about residues in food. Currently the Pesticides Safety Directorate is reviewing the use of all organophosphate pesticides, and the advice from MAFF is for farmers to avoid their use altogether unless there is no alternative. At the same time the demand for invertebrate-free grain continues, and it is often a legal requirement in the grain trade. Recently the control of post-harvest grain pests has become even more important following the designation in 1995 of those grain stores containing cereals intended for human consumption as food premises under the Food Safety Act; now all these grain stores are subject to inspection to ensure that adequate pest control measures are in force and are maintaining an appropriate level of control.

The UK cereal industry has responded to these concerns by setting up the Scottish Quality Farm Assured Cereals and the Assured Combinable Crops Schemes. These schemes are based on the principle that the industry will only use methods and products that are recognised as "Best Practice". With the change of status of most grain stores to food premises there is an opportunity for a wider range of lower toxicity pesticides, currently only available to the food industry, to be considered for use in grain stores.

However, at present there are no data available with which to compare the relative efficacy and residuality of pesticides against UK pests on a range of construction materials commonly used in storage facilities. The purpose of this study was to investigate the relative efficacy of ten pesticides for beetle and mite control when used as treatments for grain storage structures, and to assess their residual effectiveness over periods from one day up to six months after spraying.

The pesticides selected were five organophosphates, three pyrethroids, one carbamate and one organophosphate/ pyrethroid mixture, and represented those that are either already approved for use in UK grain stores or that could become so should approval be sought to widen their current use in food premises. The pesticides were sprayed onto squares of three types of substrate that are commonly used in grain store construction, namely wood, concrete and steel, and were applied at a rate equivalent to the label recommended field dose for each substrate type and pesticide. Batches of 25 beetles or mites were placed on each treated and untreated control substrate. The beetle species used were the saw-toothed grain beetle, Oryzaephilus surinamensis, the rust-red grain beetle, Cryptolestes ferrugineus, the grain weevil, Sitophilus granarius, the rice weevil, Sitophilus oryzae, the rust-red flour beetle, Tribolium castaneum, the foreign grain beetle, Ahasverus advena and the hairy fungus beetle, Typhaea stercorea. The mite species tested were the flour mite, Acarus siro and the cosmopolitan food mite, Lepidoglyphus destructor. Strains with high and low tolerance to pirimiphos-methyl were included for all species except T. stercorea and A. advena.

Recommendations for the structural treatment of grain stores to control beetle and mite pests, based on the results of these laboratory tests, are:

1. For immediate treatment of infestations, use an organophosphate pesticide; pirimiphos-methyl, chlorpyrifos-methyl and etrimfos gave the best performances generally overall. Chlorpyrifos was also particularly effective against beetles on concrete but can only be used on surfaces that do not come into contact with food.

2. For longer-term treatment of areas that come into contact with food, use an organophosphate pesticide; fenitrothion performed best overall.

3. For longer-term treatment of areas that do not come into direct contact with food, use the pyrethroid permethrin. However, chlorpyrifos was more effective than permethrin against beetles on concrete.

Possible reasons for the relative performance and residuality of each pesticide on the various substrates are discussed, and topics for further study are suggested to help explain the differences. Attention is also drawn to the difficulties the grain industry will face if further restrictions on the use of organophosphate pesticides are introduced.

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