Saturday, May 9, 2009

Lady Bird Beetles

We have over 400 kinds of lady bird beetles in the United States. You may have grown up calling them ladybugs, which is just fine but also a bit confusing. They’re really not bugs at all – not true bugs, at least. True bugs have mouthparts somewhat like a hollow needle that they use like a straw. Lady bird beetles, like other beetles, have mandibles instead. Bugs also have characteristic wing covers that partially overlap unevenly when at rest on their back. Beetles have wing covers that come together in a straight line down their back.

At a more fundamental level, bugs grow up looking somewhat like their parents, only without wings. Beetles, on the other hand, grow up as grubs or worm-like creatures that sometimes look like a caterpillar. They look a lot different than their parents.

This difference in development is the reason for a lot of confusion among many lady beetle enthusiasts. Take for instance the excitement of a child discovering the twenty-spotted lady beetle (or one of its relatives). This beetle is colored a pale tan with several (often 10) black spots on each of its wing covers. It isn’t red, black or yellow like some of the lady beetles we’re used to, but it’s still obviously a lady beetle. It’s also less than half the size of other lady beetles.

“Look Mommy,” says the child, “a baby ladybug.”

“Yes Johnny, how nice,” is our reply, since we don’t know what else to say.

The only problem with this dialogue is that Johnny hasn’t really discovered a baby ladybug at all. He has discovered an adult, albeit a small one, of an interesting kind that feeds on fungus and not aphids. Of course this is an understandable mistake. We do have, after all, hundreds of kinds of lady beetles in our country. Some are even smaller that the twenty-spotted lady beetle (which is roughly the size of a pepper seed).

Beetles in the genus Scymnus, for example, are only half this big, and are usually all black. Some of them can actually eat aphids but often they prefer smaller animals like mites. Some even specialize in eating insect eggs.

Then there are the really big lady beetles in the genus Anatis. (Sorry to say they don’t even have a common name yet). These insects can get as big as a chocolate chip. They aren’t common in suburban gardens but can be found in more rural areas. These beetles are sometimes called “giant” ladybugs – and this is probably as good of a name as any, so long as Johnny doesn’t understand this to mean just an overgrown individual of a more common species.

The sad truth about lady beetle development is that most people have no idea what a “baby” looks like – hence our mistake with Johnny. They really are not all that uncommon. Most observant gardeners will have undoubtedly seen them and yet perhaps not known what they were. They look like little alligators and are normally black with orange or yellow markings. They have thin legs up front that stick out noticeably and their long abdomens often have jagged edges or spines projecting out in different directions. You usually find them in the same kinds of places that you find the adults – around aphids.

Lady beetle larvae can be voracious, and the bigger they get, the more they eat and the faster they crawl. Part of the reason, no doubt, is to get around better and find more aphids. But sometimes when aphids are available, they fail to be all that discriminating in what they eat. In fact lady beetles larvae are known to eat each other. This isn’t all that unusual among predatory insects where the mother lays many eggs. The first larvae to emerge are able to get a jump on life by eating their weaker siblings.

Lady beetle larvae often have no reservations about this kind of cannibalism. In fact they even go one step further and enjoy eating the larvae of other kinds of lady beetles too. Why go to the trouble of marking a territory when you can just eat your rival?

But you have to admit, eating your relatives is not what we normally expect from nature. Lions don’t hunt for leopards. You may think your neighbor’s Doberman Pinscher wants to eat you, but when it comes to other dogs, you expect him to just chase them away – even though he might be salivating as he goes.

Lady beetles, on the other hand, are notorious for their fratricidal feasts. And, in reality, this unusual habit has served them just fine for a very long time. Unfortunately, it’s getting them into a lot of trouble now though. Many of our native species are getting replaced (likely eaten-up) by natives from overseas. Sometimes these exotic lady beetles find their way to the Americas by hitchhiking. Sometimes, however, we bring them here on purpose; not as pets, mind you, but as ammunition.

We discovered many years ago that lady beetles and other beneficial insects could help us keep plants free of aphids and other soft-bodied insects. When pests started showing up from other places, and our own predators didn’t like to eat them, we brought in species from elsewhere that did.

One of the first examples of this occurred when the citrus industry was just getting started in California. A small snowy-white creature (somewhat like an aphid) had managed to hitch a ride from Australia to Southern California. It’s known as the cottony cushion scale and it likes to eat citrus leaves and branches. As it grows, the female develops a fluted waxy covering over its back to protect her eggs – whence the name.

By the mid 1880’s, the insect had become so bad that California was about to stop growing citrus altogether. In a last ditch effort, money was raised and a scientist named Albert Koebele was sent to Australia to see if he could find any natural enemies of the scale. Once there, he found a small parasitic fly and a small lady bird beetle predator (known as the vedalia beetle). Koebele’s boss got quite excited about the fly and only suggested, somewhat in passing, that the beetle would also be interesting.

Koebele seems to have understood the priority and proceeded to collect around 12,000 flies that were then sent to California. His first shipment of lady beetles amounted to 28 individuals. Notwithstanding the few insects, Koebele’s colleagues in California quickly released the beetles onto a scale-infested orange tree that had been surrounded by a tent. The beetles made short work of the pests. Soon other shipments arrived and the vedalia beetle was released into surrounding orchards.

It was so successful that growers started showing up with scale-infested orange branches. These were placed under trees with the lady beetles which quickly flew to the source of – shall we call it cotton candy? The beetles were then taken to their own struggling orchards.

It wasn’t long before the California citrus industry was saved and Koebele was recognized as a hero. In fact for many years, biological control of insect pests was called the Koebele Method in Germany (where Koebele was born).

A not-so-amusing situation developed a few years later in Florida. A grower who had heard about the success in California, wondered if the little Australian beetle might develop an appetite for Southern insects. He, accordingly, asked for some to be sent his way.

His California colleague, wanting to make sure the lady beetles arrived fat and happy, packaged them up with a branch full of cottony-cushion-scales. To his credit, the scales helped the beetles arrive safely. To his discredit, some of the scales arrived safely too, and soon began enjoying the Florida citrus trees as much as they had enjoyed the California ones.

To this day, the vedalia beetle serves as a useful way to keep cottony-cushion scales under control. Theirs is clearly a success story, and success likes to be imitated. Through the years there have been hundreds of attempts to bring exotic lady beetles into the US. Nobody thought much about it at first. How dangerous could the cute little insects be - at least to something other than a soft-bodied insect?

But things did go wrong. The first thing was that not all of the exotic lady beetles that were brought to the US had the desired effect. Some of them refused to eat the pests that they were supposed to eat. Some of them just flew away and settled somewhere else - far away from the scientists’ fields. Most of them survived by eating whatever they could find in their new country. Sadly, many of them have been able to out-compete native US lady beetles. (This is typical of exotic animals and plants that land on a distant shore away from the normal diseases and predators that keep their numbers down in their native land.) Some of them, as we have seen, actually eat them for dinner.

Take for instance the multi-colored Asian lady beetle. Some of you know it as the Halloween beetle or the harlequin ladybird. You may have recognized it in your garden as a new visitor in the mid-1990’s - when it started taking up residence in North America. It’s a bit bigger than most lady beetles and has a number of black spots on its otherwise orange back. There are other color patterns (with fewer spots or reddish wing covers - rarely black) but they are less common.

These are the beetles that like to congregate near human habitations in the fall. They are particularly fond of tall isolated structures (like your house) that happen to be white (when available). And they prefer the south side where it is warmer.

All of this might be fine except they’re quite willing to come indoors if given the chance. Even worse, they’re likely to leave little red or brown stains behind, if you disturb them (their way of getting even, I guess).

This happens because of a process called reflex bleeding - a habit that many lady beetles have. If you’ve ever picked one up and turned it over, you may have seen little orange or red droplets forming in a number of places. These droplets contain alkaloids and are very bitter. They are meant to convince predators to not eat them. It’s a nice strategy outside. Inside, however, it can be an ornery way to treat your host.

A lot of people would really like to get rid of the critters. In fairness, though, they are pretty good at eating aphids - especially the ones that like to eat soybeans and other crops. The fact that they like to get together into groups can’t be held against them. A lot of lady beetles do the same thing.

The first time I saw this behavior was on the back side of Mount Whitney in eastern California. I was traveling with a couple of aquatic entomologists looking for winter stoneflies. We were high enough in the Sierra that the snow was several inches deep on the pines but was melting on the ground near fallen logs and exposed boulders.

I had worked my way around a large conifer to a small stream when I saw something red in the matted grass. When I looked closer, I was surprised to see hundreds of ladybird beetles sound asleep on the vegetation and on top of each other. I picked up a handful and poured them like so many small marbles from hand to hand. I had never seen so many live beetles together in one place before in my life. When they started to wake up and crawl all over my coat, it felt like a great entomological moment.

A few years later I came upon a small bag of lady beetles in a hardware store. The bag was really just a secured netting to keep the live beetles from running or flying away. They were being advertised as a natural way to control aphids.

I knew immediately that somebody had discovered an over-wintering mass like I had. I wondered how many beetles they had found and how big their margin was. It isn’t often that the entomological mind turns entrepreneurial but it almost happened then. I almost bought a bag. Fortunately I was broke at the time.

I say fortunate because it very likely would have been a waste of money. Unless you release the beetles into a confined area - like a greenhouse - they won’t stick around to eat your aphids. In the mountains, where they are gathered by the thousands, they are prepared to fly off as soon as they wake up.

In the autumn when the weather turns, the beetles fly from the valley up into the hills for the winter. In the spring, when they wake up, they fly up into the air and back to the valley to eat and reproduce. Since the bagged bugs in the store have almost always been gathered, en masse, in the mountains, their first inclination, once they are released into your garden, is to fly up and away. No doubt, they do a fine job of finding and eating somebody’s aphids. Unfortunately, they probably won’t be yours.

This brings me to another interesting part of lady beetle biology – their feeding that is. Considering how well known lady beetles are, it seems odd that we’re still not sure how, exactly, they find their food. But such is indeed the case.

Most of the time, lady beetles are stationary. It does happen that we find them walking around occasionally. But try as you might, it’s next to impossible to figure out what they’re thinking. Even if you start with the assumption that they’re looking for food (probably correct) figuring out how they go about such a basic effort is not simple.

Sometimes they walk in a fairly straight line - as if they knew just where they wanted to go. But then they surprise you by walking right past a group of perfectly fat and happy aphids. Certainly, you reason, they must not be hungry. The aphids, after all, were in plain sight.

So then you decide to watch more closely to see what it is they are really up to, only to find them stumbling into an aphid somewhere else apparently by accident. No sooner does it find the insect then its mandibles close around the soft and savory body and then the whole insect is promptly devoured. By Golly you admit to yourself, it was hungry all along. Probably just a little near-sighted.

Now, if you manage to stay interested in the lunching behavior of lady beetles, you’ll soon discover something totally different. Our little cocinelle no longer walks so confidently. Instead it begins to wander around looking a bit tipsy, in random half circles. If there is one aphid around here, there must be more, or so it seems to be reasoning.

Not long ago a group of researchers in Canada discovered a way to ask the beetles how they actually do find aphids. No inverted megaphones were used to listen to the small animals. It was soon discovered that nobody knew their language anyway. Instead, the researchers fitted a beetle into a tube with an intersection - a culinary crossroads, you might say.

One branch of the tube led to a plant without aphids. The other tube led to a plant infested with aphids. They discovered that the lady beetles preferred walking down the tube containing aphids, even though they couldn’t see them. Somehow their little clubbed antennae could sense where they were.

But that wasn’t the end of the story. When the scientists replaced the aphid-infested plants with clean plants that had aphids added manually, things changed. the lady beetles got confused and just walked around randomly in the tubes. It was as if they couldn’t smell the aphids anymore.

What could have been the difference? Did the aphids smell different? It turns out that it wasn’t the smell of the aphids that interested the beetles. They were cued in to a smell from the plant - a smell that emanated from the aphid-pierced plant tissues. That’s a pretty sophisticated sense of smell. Not bad for a bug.

All this just goes to show just how little we really know about what makes these interesting creatures tick. They obviously live in a world quite different from the one we’re used to - even though we might share the same address. There is still a great deal to be learned about even our common species. What we actually know about the less common species is very little indeed. And this is a problem. It’s hard to understand why we’re losing so many species when we know so little about them.

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