Sightings of bronze aphid mummies in canola signal a rise in parasitic wasp activity.
Signs of aphid mummification have been observed in canola signaling the presence of beneficial parasitoids in crops.
University of Melbourne PhD candidate Samantha Ward is currently investigating aphid parasitoids in grain crops in rural Victoria.
In her most recent field visit during late September, Samantha visited 6 paddocks in Central Victoria, where she observed her first aphid mummies for the season.
What is an aphid mummy?
An aphid mummy occurs when a parasitic wasp deposits an egg inside the body of an aphid with a piercing, tube-like appendage known as an ‘ovipositor’.
A grub-like wasp larva hatches from the egg and eats the aphid from the inside.
Eventually the outside of the aphid host takes on a bloated, swollen golden or bronzed appearance.
The wasp completes its development inside the aphid host, emerging as a winged adult through a hole cut away from the aphid shell.
Keep in mind that when an aphid host takes on the typical aphid mummy appearance, wasp development is almost complete.
So, the level of parasitism in a crop is higher than what can be seen by eye.
For instance, despite seeing very few instances of mummies in canola, Samantha collected some green peach aphid samples from these paddocks, which were found to be in the very early stages of mummification when later viewed in the laboratory.
Beneficial allies in crops
Aphid parasitoids can be effective at controlling low to medium density populations of aphids within post-establishment crops.
However, this assumes that parasitoid populations have been allowed to persist undisturbed by broadspectrum insecticides during earlier stages of crop development when aphid populations are beginning to build up.
‘Softer chemicals’ (e.g. pirimicarb) can be used against aphids with minimal impact on beneficials.
Samantha Ward, PhD candidate (University of Melbourne)