Technical profile: Insecticides for pest control

by Teresa Acklin
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   Contributed by suppliers, technical profiles feature new technology, products, specific applications or proprietary concepts. This article was contributed by P.J. Rankin, insecticides product manager, Zeneca Agrochemicals, Fernhurst, Haslemere, Surrey, U.K.

   It is predicted that wheat production may fall by as much as 2% in the 1992- 93 season. Shortages in Africa and in other regions of the world affected by adverse weather or political unrest will again make extra demands on the global reserves of stored cereals. How will this demand be met?

   If grain harvests are not protected and, if necessary, disinfested when put into storage, quality loss and commercial rejection may soon occur. The presence of as little as four or five grain weevils per kilo of grain will lead to economic loss. Insects are great travelers, and with ever increasing trade, insect species that were once confined to specific regions of the globe now are cosmopolitan in their distribution, limited only by climatic extremes.

   Residual insecticides can give long-term protection against insect attack, and several have been cleared through the joint FAO/WHO Food Standards Program, the CODEX Alimentarius Commission, for use on stored grain. To achieve CODEX clearance, it must be shown that the addition of minute amounts of insecticide to grain does not present a risk to man or animals. The criteria used to assess and quantify the risk associated with these chemicals, the Acceptable Daily Intake (A.D.I.), and the Maximum Residue Limit (M.R.L.), are the result of detailed toxicological studies. As long as the products are correctly applied, these standards ensure that grain entering the food chain is safe to the consumer.

   The most commonly used grain protectants fall into two classes: the organophosphates (O.P.), including malathion, pirimiphosmethyl and fenitrothion, and the pyrethroids, including permethrin and deltamethrin. All these products have initial contact action against the different pests and varying degrees of residual activity enabling the grain once treated to be protected for several months. Long-term protection is a major advantage of these grain protectants over the fumigant option, especially because the insects are so mobile. Long-term protection allows the grain handler to be confident that the grain will remain in top condition.

   The major grain pests belong to three specific groups: beetles, including the sawtooth beetle, Oryzaephilus surinamensis; the rice weevil, Sitophilus oryzae; moths, including the Indian meal moth, Plodia interpunotella, and the angoumois grain moth, Sitotroga cerealella; and mites, a main example being the common grain mite, Acarus siro.

   A key characteristic of a successful protectant is the need for a wide spectrum of activity. Pirimiphos-methyl, Actellic from Zeneca, has just such a spectrum which, coupled with strong fumigant action to penetrate the whole stack of grain, helps explain its success as a leading grain protectant.

   Actellic is used in most major trading countries and is registered and sold in more than 70 countries. The chemical has low mammalian toxicity, is safe to operators and consumers, when used as recommended, and has a full CODEX clearance.

   Actellic acts by contact, ingestion and fumigant action on a wide range of pests, can eradicate an established infestation and protect grain for up to one year with a single application. When applied to cereals, Actellic does not taint the grain or grain products, nor does it have any effect on germination. Versatile formulations and application techniques make the product suitable for use in both developed and developing countries.

   In general, the new pyrethroid-based grain protectants do not offer the same wide spectrum of activity as the O.P.s, nor do they offer fumigant activity. But, the pyrethroids are very effective against the Bostrychid beetles, Rhizopertha dominica, the lesser grain borer and Prostephanus truncatus, the larger grain borer. Both beetles have always exhibited a degree of tolerance to organophosphate products but are very susceptible to pyrethroids. It is for this reason that Zeneca has combined the breadth of activity of pirimiphos-methyl with the specific activity of Zeneca permethrin to produce Actellic Super. This new product is initially targeted at situations where the larger grain borer has emerged as a major new threat to the safe storage of maize. Like pirimiphos-methyl, permethrin has a CODEX clearance for grain and offers the same safety to both operator and consumer but with the enhanced activity against two of the major grain-storage pests.

   Zeneca's Actellic and Actellic Super provide the means to protect stored grain and reduce annual losses from insect attacks.