A HIDDEN pest is causing trouble in the Mallee. Up to 5 millimetres long, brown in colour and usually covered in dirt, the Mandalotus weevil is hard to spot in the field but its damage is not.
These tiny insects burst onto the scene as a serious pest in 2003 after they destroyed 500 hectares of emerging canola in Bow Hill in the Murraylands.
Feeding on the fleshy, herbaceous seedlings, the small weevil ringbarked and lopped the young canola during emergence, leaving paddocks completely bare.
Lentils, cereals, lupins, medic pasture, peas and beans are also on its menu, and its neighbourhood is expanding.
The native insects were initially found mainly in Mallee country on lighter soils but are appearing in the Mid North, the Yorke and Eyre peninsulas, with the Wimmera and Mallee regions of Victoria and New South Wales' Riverina also affected.
Mandalotus were first recorded feeding on grain crops in the 1920s and did not resurface until 1997 when they were found damaging canola crops at Cooke Plains. Now, their spread is sending the alarm bells ringing.
About a year ago, the GRDC funded a program to improve understanding of its biology and develop management strategies.
Mandalotus are a group of weevils categorised under more than 150 different Australian species. Until now, little was known about their biology and most species were undescribed.
SARDI entomologist Kym Perry, who is co-leading the research, says the two-year program has contributed to knowledge about the Mandalotus.
"I feel like we've had a pretty productive year," Mr Perry said.
"We weren't even sure we could find paddocks with weevils in them to do work - insects are so unpredictable.
"Last year we managed to identify some problem paddocks in the Murraylands and were able to conduct regular field monitoring on three properties throughout the growing season to follow their life history.
"Understanding the lifecycle is always the first step in developing effective managing strategies."
SARDI researchers found that weevils complete their entire life cycle within the paddock each season and that most of this takes place underground.
"Adult weevils appear in paddocks during summer, up to 30cm below the soil surface," Mr Perry said.
"They emerge onto the soil surface during April and May, sheltering under weeds, and begin feeding, mating and laying eggs right through until August.
"Unfortunately for farmers, adult weevils seem to be at their peak feeding activity right when crops are emerging, when the crops are very vulnerable to damage."
Mr Perry said larvae feed on plant roots under the soil surface and move deeper into the soil profile through winter and early spring before pupating in late spring.
"Mandalotus are found mainly on lighter soil types," Mr Perry said.
"They do by far the most serious damage in canola and in high densities, can destroy large ares in a short time. We're not yet sure if these weevils have a host plant preference for canola, or whether that's just a particularly susceptible crop.
"Mandalotus can also lop lentil seedlings off, but lentils have the capacity to produce a secondary shoot so they are not as susceptible."
*Full report in Stock Journal, February 16 issue, 2012.