In wild parsnip, that reward is nectar (Bell, 1971).
Although the treatments in this pilot study were replicated primarily at the level of the flower (floret) or inflorescence (umbel), and not at the organism level, the results of our experiments suggest several ways in which the wild parsnip's reproductive effort is negatively affected by the feeding behaviors of the parsnip webworm.
Plant plasticity, phenology, and herbivore dispersion: wild parsnip and the parsnip webworm.
Oviposition patterns and hostplant suitability: parsnip webworms and wild parsnip. Am.
Although burns from wild parsnip and giant hogweed are often mistaken for a reaction from the better known poison ivy, there are several differences.
My encounter with wild parsnip made me aware of how common this plant has become and of the lack of public knowledge about it.
While there are many plants that look similar to giant hogweed, it is hard to confuse wild parsnip if it is in bloom.
Wild parsnip can be controlled by digging or cutting the root below ground level.
Wild parsnips do not differ appreciably from cultivated ones, except in that they tend to have a less symmetrical form--and this is due entirely to their growing conditions.
There are hundreds of parsnip recipes to be found in traditional cookbooks, and any of them will work with wild parsnips as well.