Chemical messages of Soft-winged Flower Beetles are still not understood

Collops quadrimaculatus

 Our Mesquite trees are blooming for the second time this year. Among the insects drawn to nectar and pollen are colorful little Melyrids (Soft-winged Flower Beetles) probably of the species Collops quadrimaculatus. The whole genus is in need of revision, so who knows.
The larvae of Melyrids are predatory. Several species live under bark and prey on wood boring insects. Adults feed on pollen, nectar, but also other insects or their eggs.

Collops bipunctatus feeding on moth that a crab spider dropped

 I've even seen Collops grab prey from crab spiders, and I often find them lurking around the webs of cribellate spiders.
 These observation raise the question how these soft little guys can dare to be so bold?
Vivid aposematic (warning) colors seem to indicate that they are distasteful or even toxic.

Collops bipuntatus specimen with protruding vesicles photo Sam Droege

In addition, when disturbed the beetles can protrude red vesicles from the sides of prothorax and basal abdominal segments. But so far, attempts have failed to show that  predator deterrents are either on those pouches or are released from them. 

Now to some friendlier aspects of chemical signals: In males of the genus Collops several basal antenomeres are greatly enlarged. I have watched a male approach a female and present his vibrating antennae for her inspection, touching them to her antennae and sweeping the knobs across her head and pronotum. It looked as if he was maybe releasing pheromones towards the chemoreceptors on her antennae. Some literature suggests that he might release a substance that she would lick - which would make her receptive to his advances. In the case that I watched, she was not interested. He kept waving his antennae at her very persistently, but she eventually walked off. So my observation does not allow to decide whether he presents just pheromone communication or offers gifts and treats.