Moved from Ripiphorus.

Hi Joyce. I've been studying Ripiphorus some more, and worked a bit on identifying the beetle in your images here and in the companion post below:



Using the key in Rivnay(1)(1929) for your images leads to R. nevadicus. But that doesn't fit because it has 8 flagellomeres (see this MCZ image) whereas your 2nd image in this post clearly shows 9 flagellomeres.

On the other hand, your specimen goes to either R. diadasiae or R. sexdens in the key in Linsley & MacSwain(2)(1951)...two species described by them in 1950, 21 years after Rivney's treatment. Females of those two species are separated by the following terminal couplet of the 1951 key:

    5a) Pygidium but little longer than broad with disk transversely rugose or striate;
          posterior tarsal claw with ten inner teeth. 8-9 mm. California...........................R. diadasiae
    5b) Pygidium one and one-half times as long as broad with disk smooth; posterior
          tarsal claw with six inner teeth. 6.5 mm. Southern California to Washington.......R. sexdens

Unfortunately, neither the teeth of the tarsal claws nor the pygidium (= dorsal plate of last visible abdominal segment) are visible in your images here. However, since you deposited the specimen in the Essig Museum, maybe you or I can take a look at it some time and try to determine which of the two species this is. Apparently the Essig has specimens of both species available for comparison (database listing here). The teeth of the tarsal claws are tiny and will require high magnification to inspect (see the full size image here to get an idea of what they look like). Some line drawings of pygidia of various aspect ratios appear at upper right of this plate from Rivnay (1929). Body length is the third factor to check...R. diadasiae should be noticeably longer than R. sexdens.

It may also be of interest to note that Ripiphorus diadasiae is recorded to use the bee Diadasia bituberculata as a host. That species belongs to the same subgenus, Diadasia (Coquillettapis), as the bees shown visiting flowers of Malacothamnus fremontii below:



If their larval bee hosts visit Malacothamnus flowers, that would explain why a female Ripiphorus might be found on the flower's buds (ovipositing, as in your companion post).