Cucumber beetle

Images of undisturbed subjects in their natural environment. All subject types.

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zzffnn
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Cucumber beetle

Post by zzffnn »

ImageCucumber beetle 2 by Fan Zhang, on Flickr

ImageCucumber 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.

rjlittlefield
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Post by rjlittlefield »

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

Saul
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Post by Saul »

Nice macro, Fan. Interesting things on the beetle's back ;)

zzffnn
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Post by zzffnn »

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.

rjlittlefield
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Post by rjlittlefield »

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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Post by Chris S. »

Very fine images, Fan. :D

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.

zzffnn
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Post by zzffnn »

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.

luxuspeter
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Post by luxuspeter »

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

Susan Smitha
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Post by Susan Smitha »

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

zzffnn
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Post by zzffnn »

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

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