During a tour yesterday with our new small fruit plant pathologist Akif Eskalen and Tom Gordon we happened into some blackberry canes hollowed out by sphecid wasps, most likely of the genus Pemphredon.
As one can see from the photo below, as is typical with these wasps the pith of the cane is hollowed out and the pupae lined up within. While this particular cane didn't seem to be dying back too much from this activity (since the vascular elements of the plant are in the surrounding stem and not the pith), it's still interesting to see this. As I've written before, these wasps are aphid feeders and their incidence in the field is sort of rare here (and hence cause for excitement with our group on their discovery!), I wouldn't consider doing control measures and indeed the grower echoed this.
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