Hi, welcome to Taiga Bonsai, in this article we discuss some of the insects that are devastating both agriculture and horticulture.

Introduction – borers are perhaps the most harmful to trees, they originate from many countries causing great damage to native species that have no defence. How they were introduced to the western hemisphere is predominantly via wooden packaging.

The Asian Longhorned beetle – Anoplophora glabripennis native to eastern China, and Korea has been introduced into the United States, where it was first discovered in 1996, and in Canada and several countries in Europe including, Austria, France, Germany, Italy and UK.

A. glabripennis primarily infest maple, poplar, willow, and elm trees. In the United States it has attacked birch, katsura, ash, planes and Sorbus. In Canada on maple, birch, poplar, willow and in Europe on maple, alder, birch, hornbeam, beech, ash, planes, poplar, Prunus, willow and Sorbus.

The Bronze Birch borer – Agrilus anxius a wood-boring buprestid beetle native to North America, numerous in warmer parts of the continent where it thrives. It is a serious pest on birch trees Betula frequently killing them. If this insect came to Europe there would be no hope for Birch forests, as the trees have no resistance against this species of insect. Hence the effect on Scandinavia’s Birch industry would be devastating.

The Emerald Ash Borer Agrilus planipennis, a devastating alien pest of ash trees was first detected in Europe and in Moscow in 2003. Its outbreak in the cities of Europe and Russia seriously damaged plantations of Ash trees Fraxinus pennsylvanica. It was introduced from North America.

This alien pest posing a major threat to ash trees all over Europe has spread to Ukraine and the south of Europe severely damaging the green ash F. pennsylvanica. Research indicates that will appear in other European countries soon with the potential to destroy F. pennsylvanica plantations.

The Chinese emerald ash borer found its way to America via international shipping, when it gained its freedom. It was greeted with a fresh new smorgasbord of North American ash trees Fraxinus americana, thus making itself a new home in which to reside. To date the amount of devastation to millions of ash trees is now in the tens of millions across 25 states.

Airborne invasion – we know that many pests and disease have migrated throughout the world by conventional methods. In packaging containing merchandise and sometimes in the merchandise itself. Mainly via land sea and air.

However, these modes of transportation is not the only way for pests and disease to migrate to other realms. There are those whom are able to take to the wing and reach altitudes of 2,000m some actually fly, whilst other drift on the air currents.

For example, the Desert Locust Schistocerca gregaria a periodically swarming, short-horned grasshopper from Africa, destroys thousands of hectares of crops on its migration eastwards. These pests can easily reach and altitude of 2,000ms and cover a distance of up to 200 km in a single day.

Those that tend to drift on the air currents and travel vast distances include pathogens that are microscopic, the average size of most bacteria is between 0.2 and 2.0 micrometre, (diameter). Fungal spores typically range in size from 2 to 50 μm in diameter, with most allergenic spores in the respirable size range of 3 to 10 μm.

Such pathogens when earthbound are able to create their own colonies if conditions allow. They can attack vulnerable vegetation including food crops, flowering/fruiting plants and trees. At this juncture methods of control are inadequate. The old adage that ‘Prevention is better than cure’ is meaningful, but the devastation of these ‘unseen enemies’ only becomes visible when it is too late to react.

Sirex wood wasp Sirex noctilio a species of horntail native to Europe, Asia, and North Africa. Is an invasive species in other realms including Australia, New Zealand, North and South America and South Africa, where it has become a significant economic pest of pine trees especially Pinus radiata.

The wasp can attack a wide variety of pine species, although some species seem to be more susceptible than others and stressed trees often are attacked. It is believed that this insect was introduced on unprocessed pine logs imported from Europe.

P. radiata were first planted in the late nineteenth century in Australia, Chile, New Zealand and in South Africa during the early 1900’s. Their excellent growth provided the basis for thriving lumber and paper industries.

During 1920’s and 30’s the lumber industry stagnated because the demand for small logs from thinning operations decreased. This made plantations susceptible to S. noctilio and its associated fungus, Amylostereum areolatum. By 1947, high levels of tree mortality were occurring, primarily in the un-thinned plantations causing devastation to the lumber and paper industries.

Adult sirex wood wasps vary in size from 9 to 36 mm (0.35 to 1.42 in), during oviposition the female will lays 2 eggs often with a mucoid substance and a symbiotic fungus to feed on once hatched. This mucoid substance is toxic to trees as are the ascospores from symbiotic fungus Amylostereum areolatum. A species of crust fungus originally called Thelephora areolata, it was given its current name by French mycologist Jacques Boidin in 1958.

The hidden menace – Dutch elm disease (DED) first appeared in the north-west of Europe about 1910. Between 1914 and 1919, several Dutch scientists carried out influential research on the cause of the disease. According to https://www.forestresearch.gov.uk this disease “Is one of the most serious tree diseases in the world.”

The fungus that causes the disease is spread by bark beetles triggering foliage and tip dieback in all of Britain’s native elms. Including the English elm Ulmus procera, smooth-leaved elm U. carpinifolia and wych elm U. glabra. The disease first spread to Britain in the 1920s, where it killed 10-40% of elm trees. Although the initial epidemic died down, a more aggressive species of Dutch elm disease fungus was accidentally introduced into Britain in the 1960s.

A second epidemic took hold of lowland central and southern Britain where there were English elms in the early to mid-1970s and by 1980. Most mature English elms had died. Although scattered pockets of mature elm occasionally survived, where the geographic situation has facilitated an effective and continuing sanitation control program.

By the late 1980s the bark beetles used up most of the mature elms that they relied on for breeding material. Hence beetle populations declined and the disease virtually disappeared from many southern and south-western areas.

In 1982, Forestry Commission research on the biology of Ophiostoma novo-ulmi, an extremely virulent species from Japan has devastated elms in Europe, North America, Asia and now is spreading across across Eastern Europe. (Romania to Poland)

This suggested that the disease would not decline in intensity or contrast to the first epidemic, caused by O. ulmi. The new pathogen, O. novo-ulmi, would return in a continuing cycle to attack the following generation of small elms once they were large enough to support beetle breeding.

Cryphonectria parasitica a pathogenic fungus a member of the Ascomycota (sac fungi) native to East Asia and south-east Asia. It was introduced into Europe and North America in the early 1900s spreading rapidly causing significant tree loss in both regions.

This disease came to be known as ‘chestnut blight’ due its infestation of Chestnut trees Castanea dentata and has had a devastating economic and social impact on communities in the eastern United States.

Once a tree begins to decline it is often dead within a few years and eradication efforts by cutting and burning the infected plants/trees have mostly failed; at this present juncture there are no chemical management options for control.

Thus far the consequences of mankind’s actions over the millennia do not paint a good picture. In fact the problems we have tried to solve many of which we cannot are only increasing at an alarming rate.

As stated there are no chemical management options for control, should we concentrate our efforts to find more potent solutions to eradicate pests and disease; we have already tried this approach with negative consequences. Until next time, BW, Nik.