Introduction

Insects are the most diversified living organisms in forests, but they are nevertheless likely to go unnoticed. More than 35,000 insect species have been recorded to date in Canada, and it is predicted that an equal number of species remain to be identified. Once an insect causes serious damage in an extensive forest ecosystem though, its presence becomes only too noticeable. However, less than 1% of the insect species in Canada are considered harmful.

Insect morphology

The main morphological characteristics of insects are as follows:

Adults:

• Segmented body divided into three sections: head, thorax, abdomen.
• Mouth including mandibles.
• Three pairs of legs attached to the thorax.
• One pair of antennae.
• External skeleton (exoskeleton)
• Usually, one or two pairs of wings attached to the thorax

 

Larvae of some holometabolous insects (with complete metamorphosis), such as the Lepidoptera:

• Body with a highly sclerotized (hardened) head and 13 segments, the last two of which are fused together.
• Thoracic segments with three pairs of articulated legs.
• Some abdominal segments with pairs of prolegs bearing hooks that allow the larvae to cling to objects.
• The larva has a cuticle, a special membrane, as part of its external skeletal structure.
• Mouth parts with glands for the secretion of silk.

 

Types of metamorphosis

Insects without metamorphosis (ametabolous)

At eclosion, the insect resembles the adult, except that it is smaller. Development therefore simply involves increasing the insect's size by going through successive moults.

 

Insects with incomplete metamorphosis (hemimetabolous)

 

• The nymph (or larva) resembles an adult without wings; the wings grow larger at each moult.
• The larva reaches the adult stage at the final moult.

 

Insects with complete metamorphosis (holometabolous)

 

• At eclosion, the larva looks very different from the adult and it generally has a very different lifestyle.
• When its growth is completed, the larva forms a pupa. Inside this protective envelope, the larva undergoes major structural changes, eventually emerging as the adult stage.
• Slideshow on the transformation of a larva into a pupa

Control methods

Forest ecosystems, which cover more than 45% of Canada's land surface, are of paramount importance in terms of preserving biodiversity as well as providing raw materials for the industry. Various measures have been developed over the years to protect this resource against pests such as insects and diseases. The different control methods can be classified as follows:

Physical

• Trapping of insects
• Mechanical control by collecting the affected parts(pollarding).

Biological

• Release of live organisms (predators or parasitoids) or pathogenic microorganisms (viruses, fungi or bacteria).

Chemical

• Use of insecticides to suppress organisms considered harmful (chemical control is not employed very much in forestry nowadays).

Cultural (silvicultural)

• Wise selection of species for reforestation purposes, suitable vegetation composition, reduction in forest cover density, increased tree vigour promoted through pruning or fertilization, etc.

The purpose of this site is to describe the diseases and insects found in Western Canada's forest ecosystems. If you would like more information on the use of control methods or chemical products, we recommend that you contact the individuals or organizations listed in the Yellow Pages under "Tree Consultants", "Tree Service", "Horticultural Consultants", "Forestry Consultants" and "Agronomists".

For more information on the registered products used to control a specific insect or disease, please contact the Pest Management Information Service of the Pest Management Regulatory Agency (PMRA), at the following toll-free number: 1 800 267-6315.