When I went out to water my raspberries this afternoon, I saw the back end of a little bug disappearing into a hole at the top of one of the canes. Here are the holes: holes in my raspberry canes

And here's the bug:

the bug

It's about 3/4 cm long, with a narrow waist like a wasp (but not as long as a blue mud dauber), and iridescent blue. I'm pretty sure they burrowed in, because there's a little pile of what looks like sawdust underneath, and the fourth cane didn't have a hole (not did any when I bought them).

I'm in the mid-Atlantic USA.

What are these little beasts? How bad are they? What can I do about them?

  • 1
    What part of the world are you in? – Bamboo Apr 30 '17 at 18:02
  • @Bamboo 3 mid-Atlantic USA – MissMonicaE Apr 30 '17 at 21:53
  • Okay thanks, doesn't change my answer either way, it was based on an assumption you were probably in USA, regardless of what it says in your profile! – Bamboo Apr 30 '17 at 21:54
  • Are those holes natural? Some stems are naturally hollow. – JStorage Jun 8 '17 at 21:45
  • @JStorage I trimmed them back, per stormy's advice, and they weren't hollow lower down. – MissMonicaE Jun 9 '17 at 12:44

I had similar holes in my raspberry plants, but I did not locate the actual insect. However, according to this article, it may be small carpenter bees:

image from linked article

Happily, in the case of these bees, the answer is no[, they do not cause damage]. They make their nests in dead tissue, excavating the soft center pith of twigs. They then lay eggs in these nests and provision them with pollen and nectar. The bees do not injure the twigs or canes themselves and are likely taking advantage of tip die-back following pruning. In fact, we may be unwittingly creating pollinator habitat when pruning which may be beneficial during bloom!

While twig-nesting bees do not generally cause problems in perennial crops, the tip die-back they take advantage may be a symptom of a problem in some crops. [Some typos from original corrected.]

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  • Looks like it is the one! – J. Chomel Jun 8 '17 at 9:20
  • Yes, this is what I saw! Thanks! (I edited some detail into your answer in case NCSU takes their page down; hope that's ok with you.) – MissMonicaE Jun 8 '17 at 12:37

Wherever you are, although I'm not sure what that insect is (it's not a raspberry cane borer), it's likely it's bored into the stems to lay eggs - cut the stems down, initially to the next set of buds - if the hole is still visible, take it down to the next set of buds. You're attempting to remove the eggs in case whatever hatches then wants to eat its way through the interior of your raspberry plant. To stop anything else doing the same, I suggest you use some fine mesh/netting, fine enough to keep out anything of a similar size, and cover the raspberry with that for the next month or so.

Someone else may recognise the insect and therefore what it's up to and give more knowledgeable advice, but if they don't, that's what I'd suggest.

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You've got some very dead canes that will attract all kinds of bugs for homes and decomposing. I would cut off the dead cane, scrape the top of the soil around your raspberry for eggs or what not. Looks like you've used potting soil, yes? Are you planning to transplant in your garden? I hope so. Raspberries are TOUGH and need an area with which to make home to produce more raspberry canes.

Cut off the dead cane back to an OUTSIDE bud angling the cut so water will not collect nor get dumped on the live bud. Transplant into your garden. This dude is not a problem at all.

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  • Are my canes dead because of these bugs? – MissMonicaE May 1 '17 at 16:33
  • 1
    No no no. I am sorry. After these canes are cut to sell, if they are cut below a bud or if they cut and damage a bud the cane below dies back to a viable bud. Very normal, you'll see this with roses as well. – stormy May 1 '17 at 18:44

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