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Photo#1393577
Stem-boring moth, yucca - Prodoxus

Stem-boring moth, yucca - Prodoxus
Decorah, Winneshiek County, Iowa, USA
June 13, 2017
02/07/17 Dried flower stalk of yucca collected from garden in Decorah; multiple larvae noted inside the stalk



At the time I thought they were maybe beetle larvae. Wrong, wrong, wrong!!

Batch rearing, dead stem

06/12/17-6/13/17 Holy cow, 8 bogus yucca moths emerge from the flower stalk, which I had cut into several pieces and overwintered. All 8 moths emerged in one 24-hr period. The first image in the series (shown above, on this page) depicts a piece of the flower stalk on the 13th, after four moths had emerged from it; note the protruding exuviae. Ruler units are sixteenths of an inch.

06/13/17-06/19/17 Thirteen more moths emerge, bringing the grand total to 21! Yep, twenty-one moths out of one flower stalk...and not a single parasitoid. That's some impressive population density! To give you an idea of just how impressive, I crunched some numbers.

Total length of all pieces of flower stalk collected for batch rearing = 22.5"
Average diameter of flower stalk (from 12 measurements made along its length) = 0.3875"
Approximate volume of flower stalk = 22.5 x pi x (0.3875/2)^2 = 2.65 cubic inches
Stalk volume available to one larva = 2.65 / 21 = 0.126 cubic inch

which is the same as the volume of roughly 3.25 M&M candies.* That's the maximum amount of space each larva had in which to mature! Since not all of the stalk was consumed by the larvae (not even close, really), we could estimate that each larva developed to maturity within an area the size of three M&M's. And that's almost surely an overestimate...

Back in 2006 Jim McClarin contributed a nice series showing life stages of Prodoxus decipiens, which he reared from yucca stalks in New Hampshire:



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* See www.npr.org/templates/story/story.php?storyId=1703595

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