Russian Wheat Aphid and Varroa Mite
Two recent events highlight the importance of biosecurity for Australia in general and Australian agriculture in particular:
1. The spread of the Russian wheat aphid;
2. The appearance of the Varroa mite in Queensland.
1. Russian wheat aphid is a major pest of cereal crops in other grain producing countries, identified at multiple sites in Victoria and in South Australia.
Grain growers are advised to monitor their crops for infestations of the newly introduced Russian wheat aphid and to report suspected infestations but to hold off spraying wherever possible until spring. That’s the advice from the Russian Wheat Aphid National Technical Group that has been set up by Plant Health Australia (PHA) to help manage the pest.
The group, which comprises experts from across the country, advises growers to monitor their crops for unusual aphid activity, being careful not to spread the pest in the process. Growers and agronomists are asked to take an image of the pest and its damage and to report any suspected infestations using the Exotic Plant Pest Hotline 1800 084 881 so that the range and rate of spread of the pest can be monitored. Chlorpyrifos and pirimicarb are chemicals that are now listed for control of Russian wheat aphid under Emergency Use Permit APVMA 82792 but there are good reasons to hold off spraying until high thresholds are seen:
• Sprays are not preventative;
• Insecticides will reduce numbers of predators and other beneficials which is likely to result in a spike in numbers of Russian wheat aphid (and other aphids) in spring when temperatures increase;
• Foraging honey bees will succumb to sprays and must be protected (speak to local beekeepers);
• Spraying can also foster resistance in pests so must be used only when required.
A blanket spraying approach is not recommended: on the contrary, overseas experience suggests that an integrated pest management strategy that protects
beneficials is the best approach in the longer term.
If growers face a heavy infestation sprays are permitted.
International advice for determining whether sprays should be used supports an economic threshold of 20% of plants infested up to the start of tillering and 10 per cent of plants infested thereafter.
Research is underway to provide local advice on thresholds for spraying. Trial work is underway to provide more specific advice on management of Russian wheat aphid in Australia, including the effectiveness of a broader range of insecticide options.
2. Another pest which has been detected at Townsville QLD is the varroa mite.
There are 2 species of varroa mite, the Varroa destructor and the Varroa jacobsoni.
Native to Asia, varroa mites are a pinhead-sized parasite of honey bees. Varroa destructor affects both Asian honeybee and European honeybee.
Now found in much of Asia, Europe, the USA, South America and New Zealand, Varroa destructor has caused the collapse and death of European honey bee colonies wherever it is present.
Adult bees are weakened by mites sucking on them, and new bees are born with deformities. Varroa jacobsoni has a wide distribution on Asian honey bee (Apis cerana) throughout Asia but does not affect European honey bee.
The Varroa jacobsoni has been detected in Townsville, North Queensland, and Biosecurity Queensland is implementing a surveillance program to prevent any spread of the mite. An incursion of Varroa destructor will be catastrophic for bee keepers and agriculture generally in Australia.