A new fumigation strategy for chemical-resistant insects should help cement Australia’s reputation as a supplier of clean insect-free grain to world markets: a $6 billion annual export earner.
Stored grain researchers with the Queensland Department of Primary Industries (QDPI) developed the new fumigant practices after finding that Australian psocids, or booklice, could modify their egg development to overcome the effect of fumigation. The research was supported by growers and the Federal Government through the GRDC.
QDPI researchers found that the currently registered phosphine rate of 720 parts per million for seven days failed to control resistant psocids, and increasing the rate had little effect.
They found an effective strategy is to extend the duration of exposure from seven to 11 days at a lower concentration of just 72 parts per million.
Under current regimes “when exposed to phosphine, the psocid egg development is suspended, with insects hatching a few days after the end of the fumigation,” according to Manoj Nayak, an entomologist with the QDPI’s Agency for Food and Fibre Sciences.
The new protocols will also help reduce the problem internationally where similar resistance is being observed. Dr Nayak said regular monitoring shows the problem is on the rise in the eastern and southern states. A common species, Liposcelis bostrychophila, presents the greatest threat.
“The ability of one surviving egg of this species to completely reinfest the grain storage represented a serious threat to grain exports from Australia where a ‘nil tolerance’ principle applies to the delivery of insect-free grain to the international market.
“Bulk grains fumigated at grain terminals may carry over psocid infestations through egg survival and end up at the importing country.”
Outsmarting the psocids
Dr Nayak said that psocids resistance is a major threat to the industry because of the pest’s terrific survival strategies including broad distribution, short developmental period of just three weeks from egg to adult, long adult life (70-140 days) and the ability to survive up to 40 days without food.
“Perhaps, most important in relation to the need for complete control is that eggs do not need to be fertilised and all progeny are females. That means a single individual surviving a control operation can lead to a new population build up.”
He said physical control measures can also help. These include cooling grain with aeration (below 20°C), use of carbon dioxide and drying the grains before storage, coupled with proper hygiene and housekeeping.
Contact Dr Manoj Nayak 07 3896 9431
North, South, West