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Observed from a distance, it had been seen that a butterfly landed briefly on a leaf, to determine if it was a suitable place to lay an egg. This had lead some to a "feet tasting" theory or assumption.
A male Pieris brassica or Gonepteryx rhamni had also been observed "leaf tasting" in search of females that had not been mated.
When landing (and looking to lay), a female touched briefly an unsuitable leaf before flying off.
I thought that I might of had some evidence, on at least one occasion, that a female Pieris brassica, when I looked at her in slow motion, used her proboscis to help taste a leaf briefly, before flying away, to find a better place to lay her eggs.

As one knows, some butterflies, when disturbed from nectaring, fly off before, retracting their proboscis.

Here was a video link:

https://youtu.be/1bi_S9Suvzg

Kind Regards

female heliconid butterflies make a noise [buzzing] with their feet, when tasting the passiflora, to see if the correct chemicals are in the leaf, and will protect the larvae and adults later in their life cycle.

it seems that the foodplant in the last instar is the key, if you need to change the laying prefs for the next generation of butterflies, feed the last instar on it, and females will prefer to lay on the same species when they hatch.

have done this with Heliconius Erato, changed their food to xerogona species of passiflora from their usual decaloba species, as had lots of the former, and very little of the latter. Their offspring then used this indoors over winter.