Bio control of aphids

After too many years with agronomists finding problems for people to spray, nature is fighting back this year with aphid management.
Stories are hitting agronomy headlines such as Pestfax, with aphids are being attacked by "white fungus" disease, as well as predators. From this week's edition of Pestfax -
"James Challis (Precision Agronomics Aust.) reports that some canola growers along coastal areas in the Esperance zone have been concerned about the prolonged presence of high numbers of GPA and the impact they maybe having on advanced canola plants that are nearing the end of flowering. James has more recently seen an increase of parasitic wasps, hoverflies and aphid specific fungi which are doing a great job at halting or reducing the aphid populations. Growers are now holding off on any late aphid spray decisions and monitoring the impact of the natural bio control agents on the aphids.
Jeremy Lemon (DAFWA) reports that a national variety trial near Nyabing has canola aphids that are colonising the edge of the trial. The good news is that many of the aphids were infected by a white fungus.
Entomologist Dusty Severtson (UWA/DAFWA) reports that he has seen an increase in levels of parasitoid wasps on canola crops SW of York and is hopeful that theses beneficial insects will keep aphid levels below economically damaging levels."

A couple of weeks ago, Pestfax included this story -
"A grower near Cranbrook reported that the last time he had aphids in his barley, he sprayed with a synthetic pyrethroid before late tillering. He noticed in the barley that he had not sprayed that there were higher aphid numbers. At flowering, aphid populations in his barley paddocks crashed, whereas in his sprayed paddock, aphids were present at high numbers and the paddock was again sprayed for aphids."

These stories fit a couple of general observation over many years.
1. Aphids may build up in cereal crops to large numbers, but can suddenly disappear by themselves. This is less apparent in canola though. It should also be remembered that the research on aphid thresholds was done many years ago, and mainly with one-year response trials, which would not have captured the long term impact of predators.
2. There has been a general observation that heavy users of insecticides have more insect problems than non-users.
I wish I could offer more concrete proof, but farming is a biological system, and probably too complex to ever fully understand. In the meantime, just because insecticides are cheap, does not mean they should be used as insurance.