I had a similar problem late summer last year. I wondered if it was the cooler nights, had spray had drifted from gardens nearby or something in the plant's chemistry had changed. I sprayed my plants with fresh water using a small plastic spray bottle – better than using a fine spray on the hose when the pillars are weak. They came right very quickly so I presumed I had washed something from the surface of the leaves. This dry summer I've often freshened up my plants that way.
Of course that's okay, Jacqui!
Number/species of milkweed plants:6 giant
Community/suburb:Birkdale, Auckland
Have you had typical summer weather or describe: No, very windy and changeable. Very wet October/Nov but not much rain since.
Adult Monarchs (e.g. butterflies) seen around milkweed: 1 every day for the past 10 days
Larvae/pupae observed: 4 monarchs hatched early October. Currently approx 20 caterpillars in various stages on 5 covered plants.
Eggs observed: At present approx 15 on one exposed plant.
Praying mantises: 3 killed today!
Aphids: single figures on various plants
Ladybirds: none
Bees: yes, honey but more bumble
Wasps: surprisingly few
Ants: constantly