Monthly Mystery #12: Sea Lavender Miners

I’ve just arrived on Nantucket, where this weekend I’ll be presenting at the 5th Biennial Nantucket Biodiversity Research Conference about my multi-year survey of gall-making and leaf-mining insects on the island.  So for this month’s mystery, I thought I’d feature a leaf mine I’ve found here about which I’m completely clueless.  I first noticed it last June in Maine’s Penobscot Bay, but when I encountered the host plant here a year later, it didn’t take me long to find the mines here too.

The plant is sea lavender (Plumbaginaceae: Limonium carolinianum), and it can be found all along the Atlantic and Gulf coasts.  In June in New England, it looks like this:

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(That photo was obviously taken in Maine; rocks are virtually nonexistent on Nantucket.) By August, it is clear how it got its name:

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When I first saw discolored patches on the leaves, I wasn’t sure I was looking at leaf mines…

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…but as I continued to investigate, I found many that were distinctly linear, with a hole at one or both ends.

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One thing that is clear is that the organism responsible for these does not complete its development within a single mine as many leafminers do.  Many of these mines clearly have two small holes–an entrance and an exit–whereas a larva that makes just one mine would start feeding where it hatched from its egg, only leaving a hole when it departs the leaf.  The four groups that include all known leafminers–true flies, moths, beetles, and sawflies–all include some species that have the ability to exit and reenter leaves multiple times, so this feature doesn’t help much in narrowing down the possibilities.  Plus, the fact that these plants grow in the intertidal zone leaves open the possibility that the mines are not even made by insects, but by tiny crustaceans, marine worms, or…?

Since I am largely ignorant of marine life, it’s entirely possible that these sea lavender leafminers are well known to someone out there.  Then again, since I also found on sea lavender (both in Maine and on Nantucket) an insect belonging to a genus not previously known to occur in North America, it’s clear that not enough people have been paying attention to what feeds on this plant around here.

About Charley Eiseman

I am a freelance naturalist, endlessly fascinated by the interconnections of all the living and nonliving things around me. I am the lead author of Tracks & Sign of Insects and Other Invertebrates (Stackpole Books, 2010), and continue to collect photographs and information on this subject. These days I am especially drawn to galls, leaf mines, and other plant-insect interactions.
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3 Responses to Monthly Mystery #12: Sea Lavender Miners

  1. David McIntyre says:

    Very cool! One thing that strikes me as interesting about these mines is that they appear to be outlined with necrotic tissue. This is a defense by the plant, usually in response to an infection, and other leaf mines (based on a quick Google images survey) don’t seem to trigger necrosis. Part of the response involves shutting down plasmodesmata between cells; these are openings that permit relatively large molecules to pass through the cell walls, and by shutting them down, the plants can prevent an infection from spreading. I suppose the response might be triggered in sea lavender, regardless of how an injury occurs, just to keep salt water from entering the leaf during high tides (Do leaf mines in spartina, if there are any, show the same thing? Do sea lavender leaves respond the same way to other kinds of damage?), but perhaps there’s something about whatever is mining this leaf that triggers the necrosis.

    The double-holed mines leave me wondering if this is a marine critter that can’t tolerate the mid-day sun, even within the relative safety of a leaf. Perhaps it hides in the mud during low tides and feeds only while the leaves are submerged. Conversely, perhaps it’s an insect that can’t survive while the plant is submerged, so it only feeds during low tides (but if it’s larval, how would it escape the highest tides?).

    This is of course all just wild speculation. I have no idea what might be creating these mines, but personally, I’m rooting for a crustacean or annelid.

    • Excellent point about the necrosis. Although, as you suggest, it could be something about the way sea lavender responds to any kind of injury, it does seem to indicate that the miner doesn’t belong to a long line of creatures with sophisticated adaptations for leaf-mining. Members of the major leaf-mining groups cause minimal damage to the plant, and in some cases even manage to keep the surrounding leaf surface green when it should be senescing.

      There are no known miners in sea lavender, so we’re unable to compare this damage to that of a more specialized miner on the same plant. I have reared ephydrid flies from Spartina, and they did not cause necrosis around their leaf mines.

  2. Pingback: A Complete Guide to Things That Eat Sea Lavender | BugTracks

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