Small green caterpillars, black flies with red heads, tunnel damage - Answered

Aim:

I've returned from Joplin. Lots to tell about the tornado and the destruction it left behind. I will save that for another day. While I was there, Mom asked me to take a look at her hollyhock in the back yard, which has some problems. For one thing, its lower leaves are all eaten out.

I found the culprit fairly quickly - caterpillars. They are very small and well camouflaged, so Mom had missed seeing them without her glasses. Here are some pictures. It's sort of like Where's Waldo. We counted at least 7 in this photo:

Here is another picture of one caterpillar actually chomping on a leaf:

We picked all of them off and squished them by hand. Well, I squished them and Mom said "eeeew." I find it oddly satisfying to squish them, but I'm pretty sure Mom would prefer a remedy that does not involve green goo on her fingers. Perhaps beneficial predators? I was wondering if lacewings would do the trick.

Black Flies
The caterpillars are not alone. In addition, there were at least 6 or 7 of these black winged bugs hanging out on the plant as well:

The hollyhock may serve merely as a singles bar for these bugs, though, as they appeared to be doing some dirty deeds with each other:

We don't know whether they are eating foliage, or eating the bad guys, or merely mating (or farting on each other, because frankly that's what it looks like). Thoughts?

Tunneling
Aside from the caterpillar damage, there are also several discolored tunnels on the foliage with no visible culprit. It looks like trails left behind from a wiggling creature, but the discoloration almost seems to be embedded in the leaf rather than on top of it. The trails are not stains on top that you can wipe off. If you lift the leaf up to the sun, more light comes through the discolored tunnels than through the undamaged leaf part. I've never seen this before. What do you think?

White insect husks
This hollyhock is home to an entire ecosystem. I kept examining the leaves and finding more insects. Another potential concern were several white insect exoskeletons perched around the plant. They are no longer alive, but since there were so many of them (about 5) it caused me to wonder whether they had turned into something else.

I am not as concerned about these given that they are dead and therefore incapable of doing additional damage to the plant. However, I've never seen them before and would like to know what they are. Did they give birth to the caterpillars?? Are they related to any of the other creatures who call this hollyhock home?

Love,
Rachel

Answer

Rachel and Mom,

I was all set to write a post on the wonders of Bt, because it is the best organic control for caterpillars. BUT. Looking at the pictures, it seems the first two culprits are the same thing: Sawflies. I think it's the Black-Headed Ash Sawfly, if we want to get specific. So Bt wouldn't work, because these guys only look like caterpillars. Rachel, you won't encounter this species in Seattle. They range from the east coast to the great plains. You might encounter another type of sawfly, though. Sawflies are in the Order Hymenoptera, which is generally a helpful order including bees and parasitic wasps. But these guys are pests. The grubs skeletonize leaves, like you see here, eating everything but the leaf stems. Some people call this windowing, but that technically applies to a different type of damage. Other species of sawflies can mine or window instead. The Black Headed Ash Sawfly really likes ornamental plants and shrubs. They're gregarious, meaning they often line up 5-6 in a row while feeding.

Here's a picture:
They have black heads in the larval stage, which are visible in your pictures. Most of them I've seen have whitish, clearish bodies - like those to the left. I think yours are green because of how much hollyhock they've ingested. But the black heads are clearly visible, and the damage fits. You also caught the adults both mating and ovipositing on the leaves.

Here's an adult:








Established plants can handle a surprisingly large amount of sawfly damage. These are attacking the lower leaves and leaving the upper foliage intact, but the damage is a little worrying. They have a lot of natural enemies, which usually provide sufficient control. For whatever reason, there don't seem to be many natural enemies preying on these guys. You should probably order some lacewings to release, and they'd be good for your entire yard/garden anyway.
http://www.gardensalive.com/product.asp?pn=5030

Yellow flowers in the area might attract some parasitic wasps and syrphid flies. The adults feed on the nectar and oviposit nearby if they detect prey. It's not a guarantee, but it doesn't hurt either. Meanwhile, picking the sawflies off and squishing them is a good idea. If that's too icky, you could simply remove the damaged leaves with larvae on them. Don't use any broad spectrum pesticides, because that also kills the natural enemies. The sawfly population will likely bounce back well before the natural enemy population. So pesticides can actually make the problem worse. If you know you're going to lose a given leaf, you could apply an oil. Don't do this on the whole plant though, because that will clog the plant's stomata (or breathing tubes) and kill it. But if a given leaf is already pretty much gone, oil is an alternative to picking them off. It could also trap some of the adults who land on the plant. You might even try knocking them off with water from the hose. Don't know if it'll work without damaging the flowers, but it's worth a shot.

Tunneling
That's some kind of leafminer, but I can't identify it without seeing an adult. It's probably some type of fly, but there are lepidopteran (moth) and hymenopteran (other species of sawfly, etc) miners too. It doesn't matter, though. Leafminers rarely cause damage. Well, they cause cosmetic damage, so commercial outfits hate them, but they rarely hurt a plant. I wouldn't worry about it unless they start killing leaves. I highly doubt that will happen. I kind of think the mines are pretty, but I'm weird that way. Just FYI, spray pesticides rarely work on leafminers. As you noticed, they're inside the leaves. There are systemic pesticides (that were supposed to be safe) but we're finding out they destroy bee populations. (Well, the data has become so convincing that even the pesticide companies are starting to acknowledge it). So it isn't good to use them on anything that blooms. If you really want to get rid of leafminers, best to dig them out. Treat the mine like a maze and follow it to both ends. One is the beginning and the other is the end of the path. They only go forwards. If you find a largish hole in one end, then you're too late. The sucker has already escaped. If not, scoop out both ends and you'll likely get the larva.

White Insect Husks
Close guess, they are what the larvae turn into. I think these might even be the sawfly pupae (or cocoons). But I've never seen a pupa of this species. If so, you captured the entire generation of sawflies in pictorial form! The adults do their "dirty deeds" (as you put it), and the female deposits the eggs on the leaf. The egg hatches and the sawfly larva eats and eats and eats. Then it pupates - or builds a cocoon and stops doing outside activities to focus on changing it's entire body style. When it's done with that, the adults emerge to use the hollyhock as a singles bar again. These are the casings left behind after the pupa emerge to adults. Mom, if you see any of these that aren't empty, kill them too. They're kind of cool to pick up and see if they'll wiggle for you. But they don't have mouths or the ability to poop on you either. That way you'll have fewer adult pests in the area. Incidentally, did you notice all the little black dots on the leaves? That's frass, or bug poop.

Love,
Aim

Addendum: Syrphid Larvae are natural enemies
In answering Laurence's question about sawflies in Alaska, I talk about syrphid fly larvae - an important natural enemy. I haven't seen these predators covered as much for home gardeners, and they could be confused with sawfly larvae if you aren't looking for them. They are voracious hunters, and will help control aphid populations as well. The adults will pollinate your flowers and the immatures will help control all manner of pests. So I've added some pictures.

Here's a picture of the generations of syrphid flies


Here's a picture of a larvae, chomping on an aphid


And here's another picture of a syrphid fly larva.

If you see these on any plant, leave them. They're pretty awesome.

Lacewings & Lupines

Amy:

Remember my first post on this blog about a leaf curl problem in my lupine?  Couldn't figure out exactly what it was, but you sent me some lacewing larvae to sprinkle around it.  I'm happy to say that solved the problem.  After applying the larvae, my lupine recovered within about 3-4 weeks.  This spring, it has emerged free of problems.  I still am not sure exactly which pest was curling the leaves, but whatever it was, there's no more leaf curl.

For anyone else out there with this problem, try lacewings!  http://www.gardensalive.com/product.asp?pn=5030

Here's my lupine this spring:

Lacewings

Amy:

Thanks for the gift of the lacewings.  I released them recently by sprinkling the larvae in several different areas of my garden.  I'll report back on how they are doing periodically.  In the mean time, here are a couple of pictures, including the instructions that accompanied the lacewings. 

Purple Coneflower

Rachel's Question

Something is wrong with my purple coneflower. All the sepals around the bud are curling and looking mangy. Upon a closer examination, I noticed that there was a very small centipede-looking creature - see the far left-hand side of the second photo. Additionally, there are a lot of very, very tiny white dots. You can barely see them in this photo. Are these two separate pests or are they related somehow?

Amy's Answer

The "centipede" thing is good. It's an immature lacewing, and it's eating the bad things. Lacewings are seriously bad-ass. They're also very pretty. So don't disrupt anything that looks similar to these pics.

The dots are pest eggs. Wipe them off with a damp cloth. I see some immature leaf hoppers on the plant. I've circled them in the picture. This is kinda bad, actually.

Leaf Hoppers are piercing/sucking feeders that feed on the phloem of the plant (much like aphids, but not as easily removed as slow, clunky aphids). They're hard to treat with a surface deterrent, because they eat the sugary syrup inside the plant. Unlike aphids, they also produce more winged adults, so they can just come back after you clean them off. Do it anyway, though. Look for the rounded little green things and GET THEM OFF. Also the dots.

So, here's the really bad news. Leaf Hoppers transmit Yellows disease to Purple Cone Flowers. Yellows disease is caused by a phytoplasma that reproduces in living plant tissue. It causes, well, yellow leaves, stunted growth, and sometimes a reddish tinge to the leaves. The flowers produced will be sterile, and organs and shoots will be deformed. I don't know if your plant has it, and the only way to tell would be to look for characteristic structures in living plant cells under an electron microscope. I'm assuming you don't have one of those sitting around the house. Also, I wouldn't even be able to tell you what to look for. This wouldn't be such a big deal except that those filthy little (even though they're cute) leaf hoppers will spread the disease to anything else they taste in your garden. Things that are affected by Yellows Disease - in addition to echinacea - include: monarda, caraway, marigold, snapdragon, aster, mum, daisy, carnation, strawflower, carrot, broccoli, tomato, radish, squash, ragweed, thistle, plantain, and dandelion. So you really don't want it in your garden.

There is no cure for Yellows Disease, other than removing the plant. Now, we don't know for sure that you have it. All of this damage could be caused by the leaf hoppers. They like to eat flowers first. If you're really worried, you could sacrifice the plant right away. First, though, I'd like to see if the plant gets better if we treat the leaf hoppers. Try removing as many as you can. Go crazy on the dandelions in your yard, just in case. Check your other plants for leaf hoppers, as well. And watch any new growth on the plant. If you can't see anymore leaf hoppers, and the new growth is still wonky, then you'll need remove the plant.

There are some systemic pesticides out there that minimize harm to other insects - you pour it into the ground and it only affects insects that feed on the phloem. But they aren't organic. Some are nicotine-based and pretty selective in damage due to the type of receptor they attack. The FDA assures us that they aren't harmful to humans. They're probably correct in that, but there is some data indicating that they might be harmful to bees. I only mention this in case it becomes clear you have Yellows Disease and you need to save the garden by killing all of the infected leaf hoppers. This is worst case scenario, and pretty unlikely. Just an FYI.

Meanwhile, I'm going to look for some IPM methods to deal with leaf hoppers. We'll see how the plant does and move on from there."