www.ukbutterflies.co.uk

Hi

Being a newbie to butterfly spotting and conservation, I've been reading up and have a question about the larval foodplant information on this website, specifically the page http://www.ukbutterflies.co.uk/foodplants.php.

I see that for each foodplant, the butterfly species that it is the primary and secondary foodplant for are listed. So far so good. But then I noticed that for many butterfly species, several foodplants are listed as being the / a primary foodplant. For example Green Veined White has eight:

Charlock Green-veined White
Cuckooflower Green-veined White
Garlic Mustard Green-veined White
Hedge Mustard Green-veined White
Large Bitter-cress Green-veined White
Water-cress Green-veined White
Wild Cabbage Green-veined White
Wild Radish Green-veined White

So now the question. To help me understand the information in the foodplant page, what are the definitions of the terms Primary food plant and Secondary food plant please? I'm hoping to understand how the GVW can have 8 primary foodplants.

The context of the question is that I volunteer at a couple of woodland parks and the volunteer groups are involved with butterfly conservation. It is intended to survey current foodplants and then manage food plants to provide suitable habitats for butterfly species.

Thanks

Graham

Graham,

A primary foodplant is basically a larvae's favourite food. Certain species (i.e Our native Swallowtail "brittanicus" which feeds solely on Milk Parsley) will only ever have one primary foodplant and no secondary. Others are slightly less fussy and have secondary foodplants that they will happily munch on, in the absence of / in addition to the primary.
The Green Veined White is typical of a larvae that is happy to try several plants without having a particular set preference (hence several primary plants as listed). Nasturtiums are another that is not on your list.
This is why they are feared by those with vegetable patches or allotments, where Brassicas (genus of the mustard family) are grown. This family includes those on your list in addition to cruciferous vegetables like cabbages.
So you see, the GVW is a little like my teeange son. Not that choosey about what it eats.

If you have any of the these plants in your garden, now is a good time time to check the leaves for eggs. They are easily found.

Happy Butterflying
Kev

To put the question in an evolutionary context, there are two independent aspects of a butterfly's relation to a particular foodplant. Firstly, the plant is a food source. Secondly, it is the physical environment of the caterpillar.

Plants are constantly coming up with physical and chemical devices to stop things eating them - basically, all plants are toxic. Herbivores are constantly coming up with physical and metabolic ways of getting round these defences. So plants have to come up with new ones and then animals respond, and so on and so on. The evolutionary upshot is specialist feeders, adapted to deal with one plant or group of plants but liable to be poisoned by, or just not be able to extract nutrition from, other ones. Because related plants often have similar toxins, particular species of butterfly can often in principle (captivity) survive on a range of food sources.

However, in adaptive response to their own predators and parasites, caterpillars evolve behaviourally and morphologically to blend into their environment. Related plants, with similar toxins and other defences, might be physically quite different. So, for example, brown hairstreaks can in principle eat birch as well as sloe. But the caterpillars have evolved to be almost invisible on a sloe leaf and there is a very strong preference for this plant. There are doubtless other features of particular species of plant that make the environment they provide for the caterpillar better or worse in terms of its specific behaviour and morphology.

A female butterfly will only lay on or near a foodplant her caterpillars are physically capable of eating. Within that range, she will lay on a second choice plant if a first choice plant is not available. I don't know if that corresponds exactly to what Pete means by primary and secondary foodplants but I think it is at least a partial explanation of what is going on. I presume the 8 primary foodplants of the green-veined white are all pretty much equally suited to the caterpillar from the point of view of being its environment.

Guy

Thanks for the evolutionary explanation because for a number of years I have been watching our two "cabbage" Whites laying on Horseradish Armoracia rusticana a brassica. Last year with the large increase in Whites I was searching for caterpillars because I could see no damage to the leaves, only to find that the larvae perished as soon as they hatched. There were marks on the leaves where the ova had been, presumably made by the mandibles of the hatching larvae, but after that, nothing. I was forced to the conclusion that horseradish is poisonous to butterfly larvae.
Following your explanation then horseradish, or just my horseradish, has developed a toxin because it was fed up with being eaten. I trust that this is limited to its leaves!
This year I planted some cabbage nearby with the intention of seeing which plant was preferable to the butterfly but unfortunately the pigeons interfered with my domestic experiment. I must try something more scientific next year.

kevling wrote:Graham,

Certain species (i.e Our native Swallowtail "brittanicus" which feeds solely on Milk Parsley) will only ever have one primary foodplant and no secondary.

Happy Butterflying
Kev

Hi Kev, not strictly so. Over forty years ago, in Norfolk, found Swallowtail ova on a distant beautiful Umbellifer relative of Milk Parsley: Angelica. ( Angelica sylvestris ).

I was so surprised by this observation that I wrote a note which was published in The Entomologists' Record about 1970.

Mind you, back then, it was not difficult to find the early stages of this butterfly along unkempt ditches and hedgerows, untidy damp corners of agricultural fields and other such places. Far less chance of that now with sanitised ditches and efficiently farmed fields.

I know from personal observation that many species of butterfly will lay their ova on a wider variety of foodplants than the literature leads us to believe.

All those years ago, I raised our Swallowtail on both Angelica and Milk Parsley growing in damp pots of soil. With good care, the plants will grow to near two meters or, six feet in old money...

On Milk Parsley, the larvae try to avoid the latex like glutinous sap from the plant which immediately exudes a blob when the larvae take a bite of the leaves. This is often followed by some frantic jaw wiping on the plant stem to remove the stuff. I then observed that the larvae 'prepare' the foodplant in such a way as to reduce the chances of gummed up jaws. They crawl down to the lower stems of the plant and take bites there. I deduced that this reduces the sap pressure higher up in the plant ~ bit annoyed seeing them do this to my fine specimen plants so carefully grown ... some signs of wilting ... so the larvae can then eat without that gummed up jaws annoyance ...

I have also seen GVWs lay on a minute species of 'cress' in my garden. So small that I'd be surprised if there was sufficient plant material to support one larva let alone two or three eggs laid. Mind you I have found their pupae on the garden fences as well as those of the Orange Tip. No idea what that fed on in the garden.

Funny old game Nature ...

Thanks for the comprehensive replies and discussion. Very informative.
Graham

I have seen Papilio Machaon Britanicus larvae in Norfolk feeding on Fennel, so i think they will also use that if they find it.

I wonder if something similar (toxicity) occurs in humans?

For example, although enjoyed by most people, I simply cannot stand tomatoes. I know that they aren't actually toxic to me - tomato products are unavoidable in many prepared foods, but I find the taste unacceptable. Even worse is the smell of tomatoes being cooked. On one occasion when flying, fried tomatoes served to the passengers as part of the breakfast smelled worse than usual. I was so disgusted by the smell that I had to go on to oxygen

I only needed oxygen for a few minutes, but just imagine that I had needed it for long enough to use a significant amount.
A Technical Log entry would have raised some eyebrows: "Oxygen used in flight to mitigate smell of tomatoes. Quantity check required."

Jack

It's also worth remembering that adult butterflies do not always lay on the larval food plant. For example, the Heath Fritillary usually lays on the underside of bramble leaves, from where the newly emerged larvae make their way to the food plant! Thus, if eggs are found, they may not necessarily be on the food plant!

Mike