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Cucumber beetle

 
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zzffnn



Joined: 22 May 2014
Posts: 1796
Location: Texas USA

PostPosted: Sat Apr 27, 2019 12:29 pm    Post subject: Cucumber beetle Reply with quote

Cucumber beetle 2 by Fan Zhang, on Flickr

Cucumber beetle 1 by Fan Zhang, on Flickr

Image magnification on micro 4/3 sensor is about 1.55x. Raynox 250 was used over Oly 40-150 used at around 150 mm. Single frame lit by flash at f/22.
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 19840
Location: Richland, Washington State, USA

PostPosted: Sat Apr 27, 2019 12:52 pm    Post subject: Reply with quote

Very interesting! I'm guessing those triangular white things on the beetle's back are large pollen grains. But they don't look like pictures I find of cucumber pollen. I'll be interested to hear ideas of what they might be.

--Rik
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Saul



Joined: 31 Jan 2011
Posts: 1407
Location: Naperville, IL USA

PostPosted: Sat Apr 27, 2019 12:53 pm    Post subject: Reply with quote

Nice macro, Fan. Interesting things on the beetle's back Wink
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zzffnn



Joined: 22 May 2014
Posts: 1796
Location: Texas USA

PostPosted: Sat Apr 27, 2019 2:39 pm    Post subject: Reply with quote

Thank you for your interest, gents.

Rik: I am guessing those are pollen grains from that pink flower. I will try to identify it in a few days. This "cucumber beetle" was sleeping deep inside that pink flower, before I woke him up this morning.

Edit: the pink flower was Oenothera speciosa and pollen shape looks correct for this ID.
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 19840
Location: Richland, Washington State, USA

PostPosted: Sat Apr 27, 2019 8:44 pm    Post subject: Reply with quote

zzffnn wrote:
the pink flower was Oenothera speciosa and pollen shape looks correct for this ID.

Excellent, thanks for the ID. Looks like you have it nailed. I don't recall having run into Oenothera pollen before.

--Rik
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Chris S.
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Joined: 05 Apr 2009
Posts: 3243
Location: Ohio, USA

PostPosted: Sun Apr 28, 2019 12:19 am    Post subject: Reply with quote

Very fine images, Fan. Very Happy

I appreciate photographs that make me think. Yours did. May I share some musings and invite responses?

    1) Ironic that such an attractive insect is also a significant agricultural pest, both in its larval and adult forms. (The larval form of the spotted cucumber beetle is known as the "southern corn cutworm"; the adult beetle attacks cucumbers and their allies, as its name implies, as well as other crops.)

    2) I wonder if the striking coloration of cucumber beetles is a warning to predators that the insect is toxic? I don't know that the adult beetle is toxic, but have some hints. Adult cucumber beetles are relatively unharassed by predators. (The preceding clickable source may not seem strong, but echoes my personal experience with predator avoidance of cucumber bugs.) If these bugs are indeed toxic, I wonder if they become so by consuming leaves of their preferred food—cucurbits and their relatives (cucumbers, pumpkins, gourds, etc.)—whose leaves contain a family of cytotoxins dubbed "cucurbitacins" by scientists. These protect the leaves of cucurbits from most grazers, but cucumber beetles find them an attractant. For information on cucurbitacins, see here and and here. Could cucumber beetles have evolved immunity to cucurbitacins, and built pathways to concentrate cucurbitacin cytotoxins in their own tissue for protection from predators? Certainly seems possible.

    3) Perhaps your spotted cucumber beetle has entered the primrose flower specifically for the purpose of eating those dramatically large, triangular pollen grains you’ve documented? A relative of your spotted cucumber beetle, the striped cucumber beetle, is more familiar to me, as I had to deal with it repeatedly when I raised pumpkins for market. For the striped cucumber beetle, "adults emerge in the spring when soil temperatures reach 13°C (55°F), and feed on pollen and foliage of alternative host plants, such as willow, apple, hawthorn, goldenrod and aster, when cucurbits are unavailable. (Dill and Kirby 2016)."

    4) A bit of reading about your primrose (Oenothera speciosa) shows interesting variation between the northern and southern portions of this plant's range. Northern variants tend to have white blossoms that bloom at night; southern variants tend to have pink blossoms that bloom by day. White blossoms opening at night suggest that the primary pollinators are moths. I don't know what pollinators are suggested by pink blossoms opening by day, but suspect it's not nocturnal moths. But I wonder: Are these large, triangular pollen grains particularly adapted to moth transport?

--Chris S.

--AdminCS edited slightly to make sure quote about striped cucumber beetle emergence displays clearly as quote from attributed source, rather than appearing--wrongly--as words of my own.


Last edited by Chris S. on Sun Apr 28, 2019 10:44 pm; edited 1 time in total
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zzffnn



Joined: 22 May 2014
Posts: 1796
Location: Texas USA

PostPosted: Sun Apr 28, 2019 5:54 am    Post subject: Reply with quote

Thank you, Chris S, for sharing your knowledge. I found them fascinating, especially about cucurbitacins (which had occasionally poisoned humans too).

Most of your questions and comments would need response from a plant biologist.

I did also see a few striped cucumber beetles in an afternoon a few days ago at the same location. Edit: I cannot remember which flower/plant they were on though, probably not on evening primos. I think I also saw some soldier beetles (Chauliognathus spp.) eating nectar inside evening primos fowers.
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luxuspeter



Joined: 24 Jan 2019
Posts: 9
Location: Germany

PostPosted: Tue May 07, 2019 4:29 am    Post subject: Reply with quote

What a beauty! So colorful! I love the entire composition.
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Susan Smitha



Joined: 21 Feb 2019
Posts: 11
Location: Dhaka, Bangladesh

PostPosted: Tue May 07, 2019 6:29 am    Post subject: Reply with quote

Magnificent photo! like the color of the photo. Great capture!
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zzffnn



Joined: 22 May 2014
Posts: 1796
Location: Texas USA

PostPosted: Tue May 07, 2019 3:24 pm    Post subject: Reply with quote

Thank you for your kind comment, luxuspeter and Susan Smitha.
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