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Monday, July 12, 2010

Black Bug on Tomato Plant

Amy:

I have never had a problem with pests on my tomatoes until this spring. Some of the tomato leaves have bites taken out of them. Luckily, the recent hot weather and sun have given my tomatoes enough vigor to ward off the effects, but I took a couple of pictures a few weeks ago when I was concerned about them. You can see it in the first picture, below.

I noticed a little black bug on some of the leaves. I used the macro setting on the camera to take a close-up of it. Thoughts?

Like I said, the good news is that most of my tomato plants are tolerating whatever pest it is. It's not killing them completely. But I'd like to know what it is, because it's certainly taking out some of the leaves, which are very important for sugar production to fuel the tomato fruits that will arrive soon.




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Rachel:


I... really don't know what the black bug is. My first thought is that it's some sort of robberfly, which would be good. However, the wing placement is wrong. And it might be a leaf miner you caught while ovipositing. A taxonomist would be able to look at it and say, "Oh, that's a grylloblattid." (Actually, a taxonomist would never say that because grylloblattids live under glaciers, but you get my drift.) Keep an eye on the plant, and let me know if you find any more. If you do, try to get another picture. I should warn you, though, that I'm better at identifying larval stages that are more likely to be eating the plant. Most of the adult pests of tomato (ie insects that eat the leaves when they are fully grown) are beetles. If this is a pest, it's probably a female depositing her youngsters.

I'm more concerned with the tiny green things I can see below that gal. I can't tell what they are from the picture. If you could go out with a magnifying glass or loop and describe them, that would help. They could be psyllids, which are only a few millimeters long, but you said the tomatoes are doing well. Psyllids have toxic saliva, which causes the leaves to turn yellow. They probably aren't causing the holes. So, even if you have a few psyllids, the plant is overcoming them. They could also be little baby leaf miners that the mom just popped out. I really don't know.

Whatever it is, it can cause the plant to produce less fruit.

Let's talk damage: you've got a moth leaf miner, but it doesn't seem too bad from the picture. You've got something taking out large holes. Normally, I'd assume this is some kind of worm (caterpillar), probably a cabbage looper and maybe a hornworm. Cabbage loopers (see left) are small, green and cute. They hang out on the underside of leaves, and chew everything but the leaf stems. Hornworms are big, with a horn sticking out of their butts (see left below). 1 lonely hornworm can do a lot of damage to a given plant, but Home gardens don't usually have more than one or two. These caterpillar eggs are laid singly, and the insects have a relatively large generation interval. If you don't have a heavy infestation, just pick any caterpillars off when you find them. I'd hate to waste any Bt on a plant that's doing okay, because it may be something else. But check the plant. Hornworms will eat your baby tomatoes too. Make sure you check the plant when there is plenty of daylight, but the sun isn't directly shining on it. Early evening and late morning are good times to look.



There are a number of beetles that feed on tomato leaves. The small things I can't see could be flea beetles. They leave smallish holes in leaves, some of them expanding to create bigger holes. You'll see them hanging out all over if it isn't too hot out. Let me know if you find any beetles on the plant. If you find one that looks like the picture on the right, don't touch it. It might have color on it, but the body style will be similar. That's a blister beetle. They cause, wait for it... blisters! I don't think you have any of them. If you find some, let me know. We'll talk pest management then.

Finally, there are leaf miners that can cause holes to appear in a plant as well. I see some "windowing" damage, where all of the leaf is removed save for a thin layer. Sometimes these thin layers get knocked out (by watering, wind, etc) and turn it into a full-fledged hole.

Do me a favor and look closely at the holes. Does it look like they were formed by something taking small bites, and turning it into a big hole? Are the edges pretty rounded?

Look for caterpillars around your tomato plants; look for any kind of beetle as well. If you can find any of the things I circled in the first picture, try to get a better look at them. Also, if you can get another picture of the black fly-type insect. If the damage has changed at all, I'd like to see another big picture of the plant.

Also, I realize this is a little late. So if your tomatoes are doing fine, then just ignore!

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Aim,

You are a major dork. What is oviposting?? It sounds like a scientific euphemism for bug sex.

Speaking of which, the black bugs are multiplying. I examined another tomato plant this evening and found a community of the black bugs. I took some more pictures (see below). Damage-wise, the only thing I can find is some mysterious curling of the leaves. At first I though the curling had to do with lack of water, but no. So, I can't tell if the black bugs are good-guys eating something bad that I cannot see, or whether they are chomping on my tomato leaves, or whether they are just chilling and keeping it real.

But it's a little unnerving to see the congregation of them on my tomato. I'm obsessed with my tomatoes. It's hard not to be obsessed with tomatoes in the pacific northwest, where tomatoes arguably are not supposed to grow, because it is so far away from their native climate. I start them from seed in the late winter and nurture them all the way through the clouds and rain of spring.  I get very invested in seeing them eventually produce fruit.

Anyhow, here are the mystery bugs.


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Rach,

Ovipositing is totally all about sex. Sorta. The sex has already taken place. It refers to when the female deposits a fertilized egg. And it covers all kinds of activities. A leaf miner, for instance, has a structure which slices into the leaf but not all the way through. Therefore, when the egg hatches, the larva is protected inside the leaf. Honeybees have converted their ovipositors to stingers. So a male bee can't sting you, because they don't have the sexual organs to create a stinger. Dragon and damselflies have long ovipositors because they place eggs on vegetation just below the surface of the water. You'll see the male riding piggyback on the female, until she dips her abdomen into the water. He's making sure that another male doesn't eject his sperm and replace it with his own. Some males get around this by pretending to be females. So the other guys don't know that she mated. We call these "sneaky males." Highly scientific term, there. Also, if the female has mated twice, she can manipulate which sperm she prefers while it's all mixing around in her spermatheca (doesn't that sound dirty). Insects have some pretty freaky sex. That's actually pretty tame. Don't get me started on spit balls.... Anyway. uh. So that's ovipositing.

I'm a little confused because I don't see any damage on the leaves. Is there any substantial damage? This morning I was thinking it might be leaf miners. But I don't see any mining going on in these pictures. I'm actually leaning towards psyllids again. They certainly look like psyllids from here. Also, the immatures are so small, they can be hard to see. They cause the most damage in young plants and transplants. They also cause curling of the leaves. Here's a picture of an adult psyllid.

I think I mentioned this earlier, but psyllids introduce a toxin that causes leaves to turn yellow. We don't know think the adults do this. It's possible that you had a pretty large population of immature psyllids bothering the plant, but that the adults are now hatching. They're still feeding, but they don't have toxic saliva. That might explain why the plant doesn't seem as stressed. Of course, these psyllids will reproduce. You might go through another cycle where the immatures damage the plant. It might be strong enough to overcome them at this point. I'd say just keep an eye on it. Maybe wipe off the plant and try to kill as many as you can. If the plant starts looking bad again, there are organic pesticide which seem to work okay. There are natural enemies of psyllids, like the lacewings you're releasing, but they don't seem to eat the psyllids during the time they're dangerous. So, organic pesticides work in a pinch. Specifically the Ensure version of Spinosad. This is a nicotine-based pesticide that's made from fermenting the microorganism Actinomycetes spinosa. It targets the nerve synapses by binding to the nicotine receptor site. (There are some nicotine-based pesticides that are NOT organic, just FYI). It doesn't harm natural enemies. It comes as a spray, so you don't have to worry about eating it. Just clean off the tomatoes, if you spray when you have any.

Oooo also. If you know you have psyllids in the garden, DON"T use any carbamate pesticides on any other plants. Sevin is a common name. They actually promote psyllid populations.

5 comments:

  1. Wow, you really seem to know bugs. I too, have been seeing tiny holes in tomato leaves. I used "Caterpillar Killer" last year on my petunia. I would have pretty flowers and almost as quick as the next day, all the flowers had been consumed and I would find zillions on caterpillars. Last year was my first experience with caterpillars and tomatoes. NEW GARDENER! Hooray!! Love it! I have looked closely and plucked on one caterpillar from my tomatoes. I will just keep watching for a while, but I am not against reaching for that "Caterpillar Killer" that did wonders for the petunias. I love reading about the insects. No sense killing things that don't cause much harm or can be plucked off, and you know.... Thanks!

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  2. carolynsuetoo,

    Glad you're enjoying the blog and gardening! It can work to just pick off the caterpillars if you don't have too many. A single hornworm can do a lot of damage. Caterpillar Killer is an excellent control method as well. It's made from Bt (or Bacillus thuringiensis), which is organic and only targets the caterpillars. After applying, it might take a day or two to kill the caterpillars. They'll be lethargic, though and eventually change color. This is because Bt causes crystals to grow in their stomach lining, making holes that result in an infection in the body cavity. It's completely safe for everything else, including natural enemies. I'd suggest that you apply it in the evening and when it's cloudy out (but not raining). Bt breaks down in sunlight, and it will last longer that way. While you're looking for caterpillars, make sure you take note of any other insects on there too. Some might be natural enemies and others might be causing damage that gets mistaken for caterpillar damage. Feel free to ask if you have any bug questions too! I love talking about bugs and I currently live in a place where a garden is impossible.

    Amy

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  3. Looks like an aphid to me. They come in many colors. Oh, and those tomato horn worms, if you see little white cocoons on their back. Leave them, those are tachnid wasps feeding on its prey.

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  4. Janis,

    You know, I think you're right. I was trying to find an insect that matched the damage, but the damage looks to be flea beetles with adult aphids that are highly visible.

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