Ambrosia Beetles are widespread across BC and they also attack apples, other fruit trees, ornamental and forest trees. This insect is typically attracted to trees under stress. Infestations usually cause branches or whole trees to die. Infested branches or trees often fail to leaf out in the spring, or leaf out and then appear to die on the first hot day. On close investigation you will see tiny holes about 1/8″ across, usually just below a node on branches or tree trunks from 1/2″ to several inches in diameter. There may also be sawdust at the entrance to the hole. If you bend an infested shoot they will often break at the point of the entry hole.
Ambrosia Beetles overwinter in the wood of trees infested the year before. in March or April here on the west coast the females emerge, move to a target tree and start producing a female sex scent (pheromone). The males locate them and they mate. The female then tunnels into the tree excavating tunnels (galleries). The tunneling does not kill the trees, these critters are fungus farmers. The female tunnels and inoculates the inside of the tunnel with a fungus. Then she lays eggs and after hatching the larva eat the fungus. The damage to the tree is a shock effect of the fungi growing in the tunnels or galleries, not the physical damage to the tree. If you can cut the damaged part off, the trees should recover.
Sometimes the female beetles will pick out a couple of trees in the middle of a commercial orchard that seem healthy other than the beetle damage. The assumption is that the targeted trees were stressed. Truly a puzzle.
This insect is a problem nursery and commercial orchard trees that are under stress or have been damage in some way. I have seen many infested fruit trees in retail nurseries in the Fraser Valley over the last few years, most commonly in trees overwintered in pots. Don’t buy last year’s trees with a few dead branches.
The only real control available is to cut and destroy infected branches.
Se the BC Tree Fruit Production Guide article about this pest.