21 November 1997

Pests put quality in danger

Resistant strains of grain

store pests pose big challenges

to quality assurance.

Andrew Blake reports

THE spectre of uncontrollable pests stalked last weeks National Symposium on Quality Assurance and Traceability in Grain Storage at the RASE.

Long regarded as of academic rather than practical significance, pesticide tolerance by insects, mites and rodents is coming to the fore as a key assurance issue.

To make matters worse the problem seems to be surfacing just when research cash to find solutions is drying up, says Ken Wildey of the Central Science Laboratory.

Resistant mites have become a real headache this season, he says. "In the past we have sometimes been accused of scaremongering. But time has caught up with us."

Mites surviving not just the recommended dose of Actellic (pirimiphos-methyl) but twice that have been found in commercial stores this autumn, he claims. "It is a problem now. We have had mite infestations at levels never seen before."

Similar troubles from saw-toothed grain beetles are just around the corner, he suspects. "Selection pressure has come to bear," he says. Scientists have known about beetle and mite resistance for some time. But with organochlorine products like Lindane (gamma-HCH) no longer available for use on grain, growers and store managers have had to rely more on organophosphorous (OP) products like Actellic, explains Dr Wildey.

Even the fumigant phosphine, which Suffolk-based specialist Igrox has recently begun promoting as an integrated insurance measure, is not resistance-free, he notes. "Phosphine resistance has been detected." But at current dose rates practical control problems are some way off, he believes. "There is something there, but dont lets get carried away."

Dr Wildeys main concern is the potential knock-on effects, possibly through allergenic reaction, of mite-contaminated food. 22% of cereal foodstuffs in a recent CSL survey contained mites. 15% of 61 baby-food samples were affected, he notes.

The results of clinical study to determine average daily intakes and monitor the health effects are expected in about six months.

The work ignores the more straightforward question of whether consumers want mites in their food at all, says Dr Wildey. OP mite killers have never been particularly effective, he notes. "We need a completely new chemical group."

Another worry, he maintains, is the lack of funds to monitor grain store pests and the development of resistance on a national basis.

An official CSL survey of 742 farms 10 years ago showed 14% of one mite species could already survive double-dose insecticides. Since then such studies have been confined to commercial, animal feed and oilseed stores, in 1988/89, 1992 and 1995, respectively.

Tip of the iceberg? Ken Wildey is concerned that a wide range of grain store pests are becoming resistant to current pesticides.

GRAIN QUALITY CHALLENGE

&#8226 Resistant mites and insects.

&#8226 Pest surveys too limited.

&#8226 Rat and mice research to end.

&#8226 Lip service measures inadequate.

&#8226 New toxin tests and rules.