Grape Leafminer moth -- a new species of Phyllocnistis

[rjlittlefield]

The current best reference for this beast is https://www.washingtonwine.org/wp-conte ... 236191.pdf , whose summary says:

SURVEY AND MONITORING OF THE INCIDENCE AND ABUNDANCE OF A NEW LEAFMINING PEST OF WINE GRAPES IN EASTERN WASHINGTON
DAVID G. JAMES
Final Report 2021- 2022 Washington State Grape and Wine Research Program

Leafminer damage on wine grapes was first reported from vineyards in the Tri-Cities area in September 2020. We determined that the damage was caused by a new, undescribed species of leafmining moth in the genus Phyllocnistis. This species is the first leafminer pest to be recorded damaging commercial wine grapes in North America.
...
Our research has shown that the Grape Leafminer, a new, undescribed species, can occur in large populations in eastern Washington vineyards with much visible evidence of leaf damage. However, as of 2021, it was only abundant in a few vineyards in the Tri-Cities area in the Columbia Valley AVA. It is possible or even likely that this pest will spread in the future and for populations to increase region-wide. However, it seems likely that Grape leafminer will principally be a cosmetic leaf pest issue. Affected leaves look unsightly, but economic damage to mature grapevines is unlikely. The impact of Grape Leafminer on nursery and newly-established young grapevines could be more significant, however, and needs further study.

My own grapes started showing leaf mines about the same time, but they were not a problem and I did not investigate further. This year I got curious about them, for no particular reason. A few quick searches suggested that the mines were likely small moths, and the fact that they were on grape led quickly to https://www.washingtonwine.org/research ... ning-pest/ and then to David's full report. I harvested a few leaves with intact cocoons, brought them indoors in small plastic boxes, and waited a few days for adults to emerge. David confirms that this is the beast he was writing about, and I'm happy to take his word for that because this is the first time I have paid attention to such small moths.

Total length of the moth from tip of head to tip of wings is only about 2.8 mm.

To put that in perspective, here is the same moth photographed next to a penny:



Here is a different specimen, dead, photographed at 10X and rendered in crossed-eye stereo.



In this stereo view, the moth's right front leg (left side of photo) appears cut off because of limited stack depth. Everything else matches what I noticed through a dissecting scope.

The above specimen died with its proboscis extended, and since the proboscis was so short, I wondered if perhaps it was not coiled in life.

But in fact it is coiled as usual. Here is the same live individual seen in the first view:




It's not immediately apparent at the size and scale of these images, but these moths have a fantastic set of misdirection markings. In life, looking through a 10X magnifier, the first thing I see is the expanded wing tips with big black eyespot and black stripes, and that end looks exactly like the head and legs of some critter I don't recognize. I can easily imagine being a spider, and thinking that's an obvious target for lunch. But then imagine the surprise when there's nothing there but scales! Here is my attempt at reproducing the effect:



These moths were photographed using a variety of equipment. The full body side view was Canon T1i with Canon MP-E 65 at about 3X, single flash with softbox, a short stack by turning the lens ring. The subject was inside the small cage shown in the second image. The stereo pair was shot with Canon R7 using Mitutoyo M Plan Apo 10X NA 0.28 on Raynox DCR-150 tube lens, three flashes through LED tube light diffuser, 139 frames at 5 micron step. The stereo rendering initially had extensive transparent foreground, which I retouched from targeted stack-selected pairs. The live ventral view was cell phone through the eyepiece of a zoom dissecting scope at nominal 45X.

None of the views here really does justice to how shiny these moths are. I think I'll need a video for that.

--Rik

[wwheeler48]

Rik
Nice job of documenting. Those things are tiny. I will redouble my efforts to find really small stuff for surprises!

[Lou Jost]

Great to be able to document this new species! I bet these are the best photos of it in existence.

[JayMcClellan]

Really cool photos! Assuming that the scales are more-or-less similar in size to those of larger moths, the tiny size of the moth means there isn't room for very many scales and it makes them look more like bird feathers, especially in the stereo view.

[MarkSturtevant]

Beautiful work! I was immediately thinking a similar thing -- that the wing markings are a deception, first off, and that it may be going for spider mimicry.
Many insects are suspected to do this. I've probably shared this paper before, but its so interesting it should be shared again:
https://peckhamia.com/peckhamia/PECKHAMIA_179.1.pdf

[rjlittlefield]

Thanks, guys!

Those things are tiny.

This becomes painfully clear whenever I try to manipulate one to photograph some part in particular. I know that some people pin and spread these things. I have actually watched that process being done, but I still have no hope of doing it myself. Their thorax is barely large enough to tolerate a standard minuten pin (0.17 mm diameter). Simply removing "large" body parts like an entire leg is challenging.

Great to be able to document this new species! I bet these are the best photos of it in existence.

Probably so, though it's only superficial appearance and the extreme shininess makes comparing photos pretty questionable. In isolation, not knowing the location or host plant, I think these could easily be taken for any of several close relatives. The report by David James, linked above, notes that

Different species of leafminers usually produce unique trails on leaves and the trails can often be used to identify species. The mines produced by Washington leafminers on grapes differ significantly from those produced by P. vitifoliella and P. vitigenella on grapes. In October 2020, I sent samples of Washington leafminer larvae, pupae and adults to Dr Eiseman. Subsequently, he sent some of this material to Dr Erik van Nieukerken in the Netherlands, who conducted genetic analyses. DNA barcoding results from these analyses confirmed that Washington Grape leafminers are a unique species of Phyllocnistis, separate from P. vitifoliella and P. vitigenella.

In Moths of Western North America, page 57, I was intrigued to find this description:

Fewer than 100 species [of family Phyllocnistidae] are described, a small fragment of the fauna; mines are found on more kinds of plants at one lowland forest locality in Costa Rica than there are described New World species. There are about a dozen named phyllocnistids in America north of Mexico, and only a few are documented in the western states and provinces.

I get the feeling that this group is a lot like the phorid flies -- pay close attention and you may find you're surrounded by new ones. Note the article by Hartop, Brown, and Disney that I discuss at viewtopic.php?p=275977#p275977 .

Really cool photos! Assuming that the scales are more-or-less similar in size to those of larger moths, the tiny size of the moth means there isn't room for very many scales and it makes them look more like bird feathers, especially in the stereo view.

Yes, it's an interesting effect. As a crosscheck, I scraped a bunch of scales off the head, juxtaposed them with a couple of wing scales from the large moth Noctua pronuba, and photographed the lot of them.

Here's what that looks like:


Sure enough, not much difference in scale size, especially given the roughly 10X larger dimensions of pronuba.

There's one aspect of these head scales that puzzles me. In real-time manipulation under the stereo scope, I had the feeling that the long skinny scales covering the eyes were not all individual scales but rather deep divisions of larger scales. In the strew, I do not see the exact structure I was expecting, but I do see several groups that appear to be tightly bound together at their bases. I don't know exactly what's going on there, and I'm not sure I can muster enough resolution to figure it out.

...probably shared this paper before, but its so interesting it should be shared again:

Yes on both counts. In the same vein, I see it's been 8 years since I posted this comment about hairstreak anal spots:

By the way, there's some recent work indicating that those "false heads" are effective against spiders as well as larger predators.

Read about the experiment run by Andrei Sourakov at the McGuire Center for Lepidoptera and Biodiversity:
https://www.flmnh.ufl.edu/science-stori ... -the-ring/

--Rik

[rjlittlefield]

When a friend looked at the earlier pictures, he immediately asked "What is that thing sticking down below the abdomen?"

I've marked the subject thing here:



Spoiler alert: it's just a tibial spur, albeit unusually large in proportion to the moth.

But I did not know that for a while, so I took time to investigate.

Here is pretty first good evidence that it's associated with the hind tibia. This is cell phone, through eyepiece of dissecting scope.



But wanting to really nail this down, I removed a leg from one specimen, glued it to an insect pin, and photographed it in isolation at 10X.

Here is the whole tibia, plus a little bit of the tarsus and femur, presented as a stereo pair.



I thought it was odd to have two pairs of big spurs on the same tibia[*], so I checked against some other moths I had handy -- the Large Yellow Underwing, Noctua pronuba.

It turns out that pronuba has two pairs of big spurs also. The "upper" pair, closer to the femur though only about halfway up the tibia, are much smaller relative to the tibia. However, pronuba's dimensions are ballpark 10 times larger than this Phyllocnistis, so in absolute terms pronuba's spurs are still much larger.

Following is pronuba's larger tibial spur, compared to the entire leg -- hip to toe -- of the Phyllocnistis. These were photographed together, same time, same place, same 5X optics.

In light of the discussion earlier in this thread, I think it's very interesting that here the size of the scales does vary roughly in proportion to the overall size of the moth so there's no impression of feathers.



Here is a wider view showing both legs in their entirety. (The smaller upper spur of the pronuba was apparently lost in handling. It should be partly visible behind the upper spur in this view.)



And finally a technical note about how I held everything in place to take these last couple of pictures.



Great fun!

--Rik

[*] In fact two pairs of spurs on the hind tibia is completely normal for lepidoptera -- see discussion at https://rcannon992.com/2020/03/29/insec ... tile-tool/ .