Borer beetle… what to do?

Henk Geertsema: former forest and timber entomologist: Plant Protection Research Institute

I have been contacted by some local residents concerned about the African bark beetle – the gist of their queries has been to get advice to carry out at least some control measures instead of the present drastic control method as practised by the City Council.

Many species of bark beetles show preference for certain species of trees and there may be more than one species present.

The general mode of attack by these beetles is the start of an entrance hole by boring through the tree’s bark to reach the cambium, the live outer tissue of the tree, and to establish under the bark a so-called brood channel.

In this process the beetle will inoculate the channel with a fungus and start laying eggs all along the tunnel.

The fungus will grow and provide food for the emerging larvae who, while feeding, at the same time will create radially outward tunnels, creating the typical bark beetle pattern.

When fully-grown, the larvae pupate in the tunnels and eventually leave the tree via the brood channel’s original opening or create their own escape holes.

No insecticide for the control of bark beetles has been registered in South Africa.

However, the concerned home owner can, by the simple application of a dab of creosote (use a paintbrush) on the beetle’s entrance/exit site, help to control small infestations as many tree species are able to overcome less severe beetle attack.

By marking the holes with creosote and carrying out regular inspections, and treatment, for new signs of infestation, trees, if not seriously affected, can be saved.

Creosote, besides being a deterrent, can kill all stages and/or prevent escape of emerging beetles, providing at the same time an indication of the severity of attack.

It should be emphasised that bark beetles are considered secondary pests, the condition of the host tree determining the potential for attack.

The chop-and-chip policy of the council is expensive in terms of manpower, machinery and energy required.

It would make much more sense to deposit the felled and sectioned the centre of local townships, providing a social service to their inhabitants by donating a free supply of fire wood.

Any bark beetle escaping from such timber will be too far away from the nearest source of trees.