Forest insects in the spotlight

Insects make up the most diversified group of living organisms on the planet. Recent estimates have placed the number of insects on Earth at between 5 and 30 million, of which only 1 million have been discovered. Insects are an important part of Canada’s fauna and they reflect the complexity of existing habitats and of biodiversity as a whole. They participate in most of the ecological processes that sustain ecosystems. The entomology researchers at the Laurentian Forestry Centre (LFC) of the Canadian Forest Service (CFS), are have a keen interest in the ecology and physiology of forest pests, because of the considerable damage they cause to Canadian forests. They are also studying insect taxonomy and the ecology of insect communities with a view to assessing the effects of forestry practices on biodiversity.

TRAPPING INSECTS

Entomology research calls for the development and use of versatile and effective tools. Dr. Christian Hébert and his team have tested the use of a miniature light trap for studying insect biodiversity. This device, called the Luminoc^© trap, was developed at the CFS - LFC. It can be suspended from a tree to sample the canopy insects or be placed on the ground to study soil-dwelling insects.

Luminoc insect trap.

The Luminoc^© trap was also tested in research on soil-dwelling insects. To do this, the researchers dug a hole in the ground and placed the trap in it; it thus served as a pitfall trap with a light to attract insects. In all the environments studied, the Luminoc^© used as a pitfall trap proved to be much more effective than a conventional pitfall trap without a light. The researchers observed that three times as many Coleoptera as usual (representing twice as many species) were caught with the help of this trap. It can also be used to capture many other groups of terrestrial insects and arthropods which play an important role in the equilibrium of forest ecosystems. Owing to its versatility and its effectiveness, the Luminoc^© trap could become a leading tool for monitoring species that serve as indicators of environmental changes in the forest.

TRACKING MOTHS

Insect marking or labelling is one of the techniques that have been developed for use in tracking the movements of insect populations. Dr. Johanne Delisle undertook a study, in collaboration with the ministère des Ressources naturelles du Québec, on the feasibility of using rubidium to mark spruce budworm (SBW) moths and shed light on their dispersal. This insect species remains an ongoing concern for the entomologists who have been studying its behaviour, physiology, population dynamics and other aspects for many years now.

Rubidium is an alkaline metal that is rapidly absorbed by plant tissues when applied as an aqueous solution. Insects that feed on such rubidium-enriched plants become labelled. As rubidium is not abundant in insects, scientists can distinguish individuals that have ingested this element by feeding on plants sprayed with it from those that have not by measuring their rubidium concentrations.

Laboratory tests were performed to determine the doses need to mark adult spruce budworm without affecting their physiology or their behaviour. In the field, about 20 trees in a white spruce plantation heavily infested with SBW were treated with rubidium chloride at a time when the insect was beginning its the sixth instar. To track the movements of the marked moths, traps were installed around the treated area and the moths thus captured were analysed in order to tally the marked individuals.

Foliage spraying with rubidium.

Rubidium proved to be an effective marker for SBW moths. However, the current method for identifying marked subjects is very time-consuming for such a large number of captures. As a result, Dr Delisle’s team is exploring alternative approaches that may facilitate field research on the moths’ movements. One such approach involves using a virus that carries the green fluorescent protein gene as a marker for adult SBW. This technique would permit rapid detection of marked individuals through visual examination under a UV lamp.

A WASP AS THE SOURCE OF NEW INSECTICIDES ?

Tranosema rostrale

Conventional chemical insecticides have been removed from the arsenal of pest control weapons because of their serious environmental impacts. Unfortunately, few alternative methods have been devised. Therefore, experts only have some biological insecticides at their disposal that are based on Bacillus thuringiensis (B.t.), a bacterium that produces a toxin that kills the caterpillar stage of the spruce budworm and other insects. Although the efficacy of these insecticides is acceptable and they do not pose a threat to the environment, some experts are concerned that repeated use of these substances over a lengthy period will lead to the development of resistance in insects. This phenomenon has already been observed in some species subjected to similar insecticide treatments.

	An outstanding collection Over the years, the forest entomologists at the CFS - LFC have collected and studied tens of thousands of specimens of insects. This collection grouped at the Laurentian Forestry Centre gave birth to the René-Martineau Insectarium, which contains 200,000 specimens, most of which are forest insects. Each specimen has a corresponding file card, which indicates the date on which it was collected, specific conditions and so on. The Insectarium also has a unique collection of 40,000 slides covering more than 900 insect species. The Insectarium, which is constantly evolving, is used mainly for the identification, comparison and validation of specimens collected under research projects on insect biodiversity in the forest environment. It can be used by scientists, researchers, teachers, students and individuals interested in entomology. The René-Martineau Insectarium is located at the Canadian Forest Service’s Laurentian Forestry Centre in Sainte-Foy.

Laurentian Forestry Centre researchers have therefore embarked on studies to develop products that can be used on a rotation basis with B.t. A project by the team headed by Dr. Michel Cusson deals with the potential offered by a wasp, Tranosema rostrale, that lays its eggs in SBW caterpillars. After the egg hatches, the young larva develops inside the caterpillar, feeding on its tissues and eventually killing it around the end of its larval growth. Although this wasp, and others resembling it, can kill a certain proportion of budworms, their killing power is insufficient to counter surges in SBW populations. However, researchers have noticed that, during egg-laying, the wasp Tranosema rostrale transmits a virus that blocks the budworm’s immune system, allowing its own egg to keep developing. The work being done by Dr. Cusson and his collaborators is therefore also focussed on the physiological and endocrine mechanisms that underpin the observed disturbances. The researchers are hoping to isolate the genes responsible for these disturbances and to use them in developing new insecticides.

CLIMATE CHANGE UNDER INVESTIGATION

The last decade was without a doubt the hottest of the 20th century. It was marked by a variety of phenomena, including many large-scale hemlock looper infestations in regions that had not been seriously affected before. In Eastern Canada, this insect is considered the second most important pest after the spruce budworm. In Quebec, since the early 1990s, the hemlock looper has been outdoing other insect pests in terms of damage to coniferous forests. During this period, more than 1 million hectares have been destroyed. In 1999 alone, 472,000 hectares of forest representing over 23 million m³ of wood were infested, which is nearly 30 times the area of forest defoliated by the SBW during the same year. Researchers estimate that over 925,000 hectares were affected in 2000.

Although hemlock looper outbreaks are more sporadic and limited in areal extent than those of the SBW, they are more devastating. Looper epidemics develop very rapidly, since the larvae attack older foliage as well as the current year’s growth. In contrast with the budworm, the looper kills its host trees quickly, within the first or second year if the infestation is severe. Furthermore, this insect is present throughout Quebec and can also invade and develop in other types of stands because the larvae are polyphagous, that is, they will feed on many species of coniferous and deciduous trees.

A NATURAL ENEMY TO THE RESCUE

During the last hemlock looper outbreak, which occurred in the Gaspé between 1996 and 1998, scientists were able to identify a species of egg parasitoid (Telenomus sp.) that exercised biological control at a level never before reported in the literature. More than 100,000 hectares of forest were saved thanks to this natural enemy. The identity of this parasitoid is still the object of taxonomic study, and this points up the incompleteness of our present knowledge of natural control of the looper.

A team of CFS - LFC forest entomologists led by Dr. Christian Hébert is keenly interested in studies on the hemlock looper. It has already developed an effective strategy for detecting and monitoring populations of this pest and has studied certain aspects of its biology. However, in order to develop an effective forecasting strategy and gain insight into the causes of outbreaks, researchers need to be familiar with the ecology of hemlock looper and its main natural enemy, Telenomus, in a climate change context.

Telonomus sp.

The hemlock looper is a late-season defoliator, wreaking most of its damage in July. The species’ egg-laying period, occurring in autumn, limits the insect’s distribution, since at higher elevations the females are killed by the cold before they have a chance to lay their eggs. That is why the majority of past outbreaks have been reported in valleys, along rivers. With climatic warming, the forests located at higher elevations will be more vulnerable to looper infestation. Similarly, with the more rapid increase in temperatures in spring, the close relationship that exists between Telenomus, which is active during low spring temperatures, and the hemlock looper may end, giving the looper an edge and thus increasing the infestation risk. Dr. Hébert’s work also involves producing maps of the infestation risk that will exist under different climate change scenarios.

INSECTS: GOOD INDICATORS OF FOREST BIODIVERSITY

Although insects often wreak considerable damage, they can also serve as useful indicators of forest biodiversity. They are responsible for a large part of the complex interconnections that characterize forest ecosystems. The insect communities that are present in our forests help to maintain crucial ecological processes and preserve biodiversity as a whole.

Étude des insectes en laboratoire

The Staphylinidae have certain characteristics that make them an ideal target group for research on forest biodiversity: these insects are present in a large variety of habitats, they are easy to capture and they can usually be identified to the species level.

Since 1998, Dr. Klimaszewski and his collaborators have been working on developing new techniques that harness Staphylinidae for monitoring changes in the biodiversity of Canadian forests.

	A threat to our forests With the globalization of markets, there has been a sharp increase in the number of exotic species introduced into North America in recent years. Several exotic species that were accidentally introduced in the past have caused considerable damage to Canadian forests. The gypsy moth (Lymantria dispar) illustrates this situation only too well. Introduced exotic species can quickly modify the biodiversity of our forests and upset the fragile equilibrium of ecosystems. Over the past few years, several exotic insect species have been caught in the Greater Vancouver Area, and some of them, such as bark beetles, have even become quite abundant, thereby altering the equilibrium of indigenous communities. The Asian long-horned beetle has even been detected in packing wood in the Port of Vancouver. The Port of Montreal is a potential point of entry for exotic species, because of the huge tonnage of merchandise that is handled there. An inventory of the urban and peri-urban forests of Montreal, to be conducted under the direction of Dr. Christian Hébert, will provide the opportunity to determine whether there have been any recent introductions of exotic species in the Montreal area and whether they pose a threat to Canadian forests. Researchers of the Laurentian Forestry Centre of the Canadian Forest Service also provide scientific support to the Canadian Food Inspection Agency (CFIA), which is responsible for detecting exotic insects.