On aphids

Awmack & Leather, Host Plant Quality and Fecundity in Herbivorous Insects, 2002.
* sap-suckers prefer high amino acid levels in phloem
* herbivores in general don't like high carbohydrate and lipid levels, because it dilutes their target nutrients. Although aphids were *more* successful under high CO2 conditions, so it might not be that simple.
* Plants produce defense compounds which can put off some insects (including aphids). This is more true of generalist feeders, whereas species-specific feeders don't seem to mind so much.

So at a guess, your plants might have *too much* nitrogen, which is why they look great but are suffering from aphids. And/or they are lacking some micronutrients which means they can't produce sufficient defense compounds. If your greenhouse is well-sealed, then elevated CO2 might favour aphids as well.

(I have seen this in brassicas. Once I started soil testing and balanced my soil, my aphid problems disappeared. Then I ran out of organic fertiliser pellets so substituted in blood and bone, and got an aphid infestation. I figure the highly soluble nitrogen from the B&B over-dosed by plants on N, making them more attractive to aphids.)
 
Powell et al, HOST PLANT SELECTION BY APHIDS: Behavioral, Evolutionary, and Applied Perspectives, 2006
* aphids use a whole range of methods to choose which plants to feed on
* during flight they are attracted to yellow wavelengths, rather than green, so are more likely to be drawn to leaves which are young, sick or senescing
* they are also attracted/repelled based on odours, but that seems to have more to do with finding the right species, rather than the health of the plant (though there are so many compounds they can sense it might be much more complex than that).
* once they get on the plant they "taste it" to get a feel for what the nutrient levels are like and the presence of defense compounds.

These reviews are getting old, though, so perhaps there is more up-to-date knowledge out there.

Summer garden

Here is a photo of our garden down here in Tasmania. It's going great! (Click for a bigger version.)


The chickens are up in the back left. We have seven of them. Three are young chicks that hatched a couple of months ago. We still don't know if they are hens or roosters yet. If they are boys, then we'll be having a roast dinner! Our original chickens were all bantams, but the chicks came from non-bantam stock (I think) so they are rapidly out-growing the old guard. So many chickens makes for a fun feeding time.

The corn is in old chicken soil, so it is growing like crazy - pushing seven feet tall! Hopefully we'll get a good crop in another few weeks. We've a few pumpkins, one of which has its roots in under the chicken coop, and so is gradually taking over the yard. I've trained a couple of others up on the fence, and have some nice young pumpkins hanging there, rapidly expanding in size. Will be great to get a bunch of pumpkins and store them away for the winter.

We've about 30 tomato plants, most of them along the right hand fence. They haven't ripened yet, and some of them haven't even set fruit. So not sure what sort of a harvest we'll get. We're banking on a big one so we can do lots of preserving.

Down the front left are some Scarlet Runner beans, climbing up the fence. These are lush, but I suspect a possum has been getting at the beans, because there haven't been too many for us! Our bush butter beans have been more successful, and are wonderfully juicy. Also down the front is our small strawberry patch, which produces the occasional gem of a strawberry. Nothing like home-grown berries!

A bunch of things have gone to seed, so it's about time we pulled them out and thought about getting our autumn/winter crop in.