Distribution
Larvae of this pest cause economic damage to canola in Western Australia and South Australia but are not considered to be a serious pest in Victoria.
In WA it is most abundant in the South Coast, Great Southern and Lakes areas. It is less prevalent in areas north of Perth or in the eastern wheatbelt.
In South Australia this pest is most plentiful on Lower Eyre Peninsula, Mid North and the South East.
Description
Adults are up to 11mm long and are a shiny black with a slight bronze appearance in some lights.
Larvae are dark brown and grow to 12mm long and 2-3mm wide with 12 body segments, the last one having two distinct upturned spines.
Lifecycle
Over the summer and autumn, adults shelter in crop residue, under wood, rocks or tufts of grass. They do not fly but become very active after autumn rains when a large proportion of a female’s body may be taken up with eggs.
Eggs hatch from late March depending on soil moisture. When hatching occurs early, these larvae may reach a length of five mm or more before the crop is seeded. The larger the larval stage is at seeding the more damage occurs.
In August larvae begin changing to the pupal stage and new adults appear soon after. The duration of the stages is shown below.
