In North America, jewel beetles (family Buprestidae) routinely associated with flowers usually belong to the genus Acmaeodera. Often black with yellow and/or red elytral markings (e.g., A. immaculata, A. macra, A. ornata, A. neglecta, A. tubulus, etc.), these beetles are especially diverse in western North America and bear a striking resemblance to stinging bees and wasps (maintaining the charade even during flight by holding their fused elytra together above the abdomen). A few other less speciose genera (e.g., Anthaxia and Agrilaxia) also regularly visit flowers, but for the most part outside of these genera encounters on flowers are at best incidental.
Of course, exceptions are the rule in biology, and in the genus Agrilus there are few species that are found almost exclusively on flowers. One of these, Agrilus muticus occurs in Texas, Oklahoma, and Kansas and has been found only in the flowers of winecup, Callirhoe involucrata (Fisher 1928). The species is fairly routinely encountered wherever these plants are found in bloom, and I have observed adults in these flowers on numerous occasions feeding on the petals and mating (and see this BugGuide photo of group sex!). While winecup can be presumed to be the larval host, it has never been reared from this (or any other) plant, and in fact I am not aware of anything beyond descriptions and catalogue listings that have been published for the species. I suspect the larvae tunnel within the stem base or main roots of living winecup plants (and, thus, making them more difficult to rear than species associated more typically with dead wood).
Only one other North American Agrilus has been documented routinely visiting flowers. Agrilus blandus is frequently encountered on flowers of Eriogonum, and these plants have also been confirmed as larval hosts (Nelson & Westcott 1976). None of the remaining species of Agrilus in North American are known to routinely visit flowers, and in fact the vast majority of them are associated with woody rather than herbaceous plants. The latter include A. concinnus, which breeds in the base of living Hibiscus (MacRae 2006), and A. malvastri, which is usually found on Sphaeralcea (Fisher 1928), although whether that plant also serves as the larval host remains unconfirmed. It is interesting that most of these non-woody plant hosts (Callirhoe, Hibiscus and Sphaeralcea, but not Eriogonum) all belong to the same plant family—Malvaceae. Plants in this family also serve as known or suspected larval hosts for several species of jewel beetles in the genus Paragrilus—a close relative of the genus Agrilus. Again, these beetles are normally found on the foliage and not on the flowers.
MacRae, T. C. 2006. Distributional and biological notes on North American Buprestidae (Coleoptera), with comments on variation in Anthaxia (Haplanthaxia) viridicornis (Say) and A. (H.) viridfrons Gory. The Pan-Pacific Entomologist 82(2):166–199 [pdf].
Nelson, G. H. & R. L. Westcott. 1976. Notes on the distribution, synonymy, and biology of Buprestidae (Coleoptera) of North America. The Coleopterists Bulletin 30(3):273–284 [pdf].
Fisher, W. S. 1928. A revision of the North American species of buprestid beetles belonging to the genus Agrilus. U. S. National Museum 145, 347 pp. [Smithsonian Libraries].
© Ted C. MacRae 2015