There has been a sharp decline worldwide in honeybee colonies since 2006. A recent study from the Harvard School of Public Health has found the cause is imidacloprid, one of the most widely used pesticides. This is the second study that links this pesticide to a phenomenon called colony collapse disorder, where droves of adult bees abandon their hives. They found it does not take much of the pesticide to affect the bees. Bees are prime pollinators for crops such as fruits, vegetables and nuts, and livestock food like alfalfa and clover. This could result in the loss of billions of dollars due to lack of bees. Imidacloprid was introduced in the early 1990s, but now, scientists are alarmed by the losses of between 30% and 90% of honeybee colonies since 2006. Until now, they posed many theories as to the cause, like pests, disease, pesticides or migratory beekeeping.

HARMLESS SPOTS ON MAPLES

A few years ago, a faithful reader called me to ask about white spots on maple trees that he had planted years earlier and was concerned these white spots might have been killing his trees. At the same time, I was doing surveys on the Niagara Escarpment in Simcoe County for American Hart's-tongue fern for an Ontario Municipal Board hearing case I was working on at that time. I found one stand of maple trees with the bark on the tree trunks covered with these white spots. I took a sample and put it under the microscope, as well as several photos of the spots. I then observed an increase in the occurrences of white spots about the size of a Canadian dollar or two-dollar coin. I was unable to find out if these were fungi or lichens at first, even after consulting my many reference books. I took photos and sent them to experts who were also unable to help me with the species. I was also told by some experts this was verticillium wilt, which will attack and kill maple trees and also produce marks in the wood, but this information was incorrect. Verticillium wilt is a very different fungus, usually discolouring the heartwood of the tree and attacking the tree from inside out. It can lie dormant in the soil for many years, then enter the tree through the roots, causing abnormal colour changes in the leaves, leaf scorch and dieback of the branches and partial defoliation. The presence of verticillium wilt can be confirmed by cutting the branch and observing the vascular tissue. If wilt is present, the vascular tissues will be streaked or discoloured olive-green in maples and from tan, brown, green and even black in other species of trees. The trees with the white spots did not have any discolouration.

It was only recently that I found they were the first part of the association of a lichen with the white stain fungus growing on the maple and looking for an alga associate. In most cases, these are just the un-lichenized fungus Julella fallaciosa, or white stain fungus, which is lacking algae partnership to make it a true lichen. Lichens are composite organisms consisting of a symbiotic association of a fungus and a green alga living together. They usually grow on rocks, trees, dead wood or leaves using these objects as a substrate, but obtaining nutrients from the air and not the object they are growing on. Sometimes lichens can completely cover gravestones, making it difficult to read the inscriptions. Therefore, lichens do not harm the tree or other living matter that they are growing on and obtain their mineral nutrients from the air. A fungus living as a symbiont in a lichen is more successful in deriving the essential nutrients and can withstand periods of low moisture for prolonged periods, so about 20% of all fungal species have acquired this mode of life.

In our case, those white blotches on the tree are just the white stain fungus looking to become a lichen and, although unsightly, will not harm or kill the maple trees.

Lichens are classified by their major growth forms. They can cover the substrate like a crust (crustose), appear leafy (foliose), branching like small trees (fruticose), hair-like (filamentous), powdery (leprose), scale-like (squamulose) or soft from absorbing and retaining water (gelatinous). They reproduce sexually by producing spores like mushrooms. There have been more than 18,000 species of lichens described worldwide and they are common and occur everywhere from the Arctic, where they can survive extreme cold temperatures, to the desert, where they can survive in very hot, dry conditions. Some colonies of lichens are 9,000 years old, and they have been used to pack ancient Egyptian mummies.

You encounter many species of lichens every day in nature, but may fail to recognize them. Lichens have been used by man as food, medicine, toxins and colour dyes. Lichens can also be used to measure air pollution. I have now noticed this un-lichenized fungus is growing on the invasive common buckthorn shrubs that have been growing along the trails for many years. The white spots on these shrubs are new since I do not remember them growing on the buckthorns when I first started to walk the trails more than 10 years ago. I had figured out the spots were Julella fallaciosa last year, but forgot to write about it or to tell my reader I had answered his question. He will now know these spots will not harm his maples trees.

SIGNS OF SPRING

April 18: Merlin kills mourning dove on my front lawn, but could not lift it off the ground after several attempts since the dove was bigger than the falcon.

April 19: Wild ginger in bloom in Scout Valley, eastern pine elfin butterfly and more than 100 red admirals flying around the forests and in gardens in Orillia.

April 20: Serviceberry (shadbush) in bloom, plants of Dutchman's breeches, squirrel corn and bracken fern pushing up from the ground. Chokecherries starting to bloom.

April 21: Invasive species update: Tartarian honeysuckles well leafed out and buckthorns leafing out. Basel rosettes of garlic mustard everywhere and growing taller every day, 12 to 15 centimetres. Giant hogweed leaves are growing fast and are now 20 centimetres high. Japanese knotweed new shoots are now about 15 centimetres long. No sign of new growth of phragmites or dog strangling vine. Hermit thrushes are back from the south.

April 22: Early saxifrage, pale corydalis and jack-in-the-pulpit in bloom and blueberries in bud.