Friday, February 18, 2011
As a child, I remember being fascinated by ladybirds. They were everywhere with their armour-like wings that formed a shield when folded. I used to be like every other child - I would hold a ladybird delicately on my finger and sing the old rhyme. "Ladybird, ladybird, fly away home. Your house is on fire, your children alone." Then I would blow ever so gently on the little luck bug to speed her on her way home. Now, I rarely see one; but, they still enthrall me.
One of the great mysteries of the insect world right now ranking up there with the loss of winged pollinators in general is what has happened to North America's native ladybug species? About 20 years ago, they started to "fly away" just like the nursery rhyme. There are still ladybugs to be found; but, the chances are they are not native ladybugs. One formerly widespread species, the nine-spotted ladybug, is now virtually extinct in northeast North America.
While ladybirds can still be seen, they are likely to be an invasive species such as the Asian lady beetle. Invasive ladybird beetles now account for two-thirds of all ladybugs in the United States and Canada.
Other countries are faring no better. The UK is suffering a serious invasion of Harlequin ladybugs. These aliens are taking over and pushing out the native species there as well. Many more countries are fighting their own battle with invasive alien ladybird beetles.
A luck bug. Photo courtesy: bumblebee.org
Until the 1980s, the US Department of Agriculture repeatedly tried without success to introduce imported (alien) species of ladybugs to help in control of insect crop pests like aphids, moths, mealybugs and caterpillars. These invasive species did little more than hang on until lately. Now they are flourishing and the native ladybirds are gone. What changed?
It would appear that more of man's meddling is coming to fruition and we are reaping the rewards. John Losey, one of the world's leading experts on ladybugs, believes climate change could be a driving force behind native ladybug declines. He has enlisted the aid of thousands of "citizen scientists" - especially children - in both the USA and Canada to record sightings. Through his website, Lost Ladybug Project, he has collected over 10,000 reports and is still analyzing all the data.
Warmer temperatures may be a godsend for sun worshippers; but, they are a disaster for ladybirds. Warmer weather means less winter snow to cover the ladybugs' overwintering sites. They hibernate in grass, leaves and bark at the base of trees. The snow cover keeps the ground temperatures at a constant 0oC which is cold enough for them to remain dormant all winter without freezing to death.
Constant temperatures are the key to the little beetles successful hibernation. If the temperature drops too low, they freeze to death; and, if there is a warm spell, they could wake up, fly off leading to an early demise if the temperatures drop again.
John Losey says: "Overwintering mortality could be an important factor" in the declines.
Ladybugs are the workhorses of the pest suppression species. They eat many times their weight in aphids and other plant-eating pests. Photo courtesy: gardenerstips.co.uk
The new introduced species have a unique overwintering habit that allows them to flourish regardless of the climate. In the wild, they use the cracks and fissures in cliffs for overwintering; but, in developed areas they find gaps and holes in the walls of houses and buildings. When the weather turns colder, they all mass there together in the chinks they have found or behind a bit of loose siding or anywhere that affords them a little protection for the weather.
However, one of the unforeseen consequences of importing the Asian ladybug is this habit of invading homes in swarms making it a nuisance. They have been nicknamed the "Halloween ladybug" because of the time of year they seek shelter inside. Invasive ladybugs are capable of biting though it is not dreadfully painful. However, when frightened they give off a yellowish ooze that can stain wall and smells bad. What an endearing quality!
To get an idea how beneficial these little guys can be in the plant-eating pest eradication department, read on. Ladybugs and other predator insects are so effective and so voracious, they add $4.5 billion to the US economy each year through natural pest suppression.
Additionally, there are hidden financial and environmental benefits that are not reflected in the $4.5 billion. For every acre that is treated by use of natural pest suppression, no chemicals are bought and used. Not only does the farmer save the price of the chemicals, there is no damage to the environment in that area.
There is another theory put forward by Scott Black, executive director of the Portland, Oregon-based Xerces Society for Invertebrate Conservation. He feels the problem may be that native ladybirds are specialists while the invasive species are generalists. The native species have been here so long they have specific food, temperature, foliage; and, other requirements. If they are unable to find these conditions, they die rather than adapt.
The alien species; however, are generalists able to adapt to many changing conditions. If the conditions change, they change too. One theory is that introduced species like the Asian ladybug have pushed the native species out of their favoured habitat; and, the native species being unable to adapt are dying.
Another idea is that the number of parasitic wasps that prey upon ladybugs increased with the introduction of alien ladybugs. Changes in cropping patterns and loss of agricultural land also may have played a prominent role.
Volunteers: Jaya Walsh and her son Gaelen look for ladybugs as part of the Lost Ladybug Project near Ithica, N.Y. Photo courtesy: Christian Science Monitor
The truly worrisome aspect is the impact of the invasive species on the native species; not to mention, the wider ecosystem. It turns out that the imported ladybugs are highly aggressive predators that may be able to eradicate our own species. One of the most critical dangers of reduced ladybird diversity is that if there is a disease outbreak, there are fewer species to fall back on. We could lose ladybugs altogether; and, we cannot afford to lose even one species of winged pollinator.
John Losey says it very succinctly: "If you get a disease that wipes them out, you don't have a backup."