This ripiphorid was ovipositing on a
Monardella exilis flower-head in bud. In
another post, Ron Hemberger also photographed a female
Ripiphorus ovipositing on a flower-head of
Monardella in bud. Motivated by a comment from Hartmut Wisch, Ron hypothesized that laying eggs
on buds might serve to synchronize the emergence of hatchlings with the opening of fresh flowers. The freshly opened flowers would, in turn, attract host bees that the triungulin larvae could hop aboard and ride to the bee's nest...where they could parasitize the brood. After thinking about Ron's observation, I read in
Wheeler (1997) that
Ripiphorus are indeed known to "often oviposit on flower buds".
More specifically, I noticed that almost all BG posts of ovipositing
Ripiphorus were on buds of flower-
heads... i.e. dense agglomerations of many small, individual, flowers packed within surrounding bracts. Except for Ron and my sightings on
Monardella, and a lone sighting by Joyce Gross on a member of the mallow family, all the posts appeared to be on plants in the family Asteraceae, as seen below:
Joyce's posts was an exception among the others...it showed oviposition on the
single-flowered bud of
Malacothamnus fremontii in the mallow family (Malvaceae):
It would be interesting to know the extent to which
Ripiphorus exhibit preferences for certain plant groups or morphologies, and whether those corresponds to flower preferences of their hosts. For instance,
Diadasia are mentioned in Linsley & MacSwain
(1) as hosts for
Ripiphorus in CA, and according to
this web page, a majority of the 38 new world species of
Diadasia specialize on flowers in the Malvaceae (and others specialize on flowers in the Asteraceae). Below is a thumbnail for a post of Hartmut's, showing a male
Diadasia inside a flower
Malacothamnus fremontii...the same species appearing in Joyce's
Ripiphorus post referred to above:
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For more info on the species ID for this post, see 1st image in the series.