Dr. Neil Holliday

Research on root maggots of canola

The cabbage root maggot, Delia radicum, was first observed feeding on canola roots in Manitoba by Dr Baldur Stefanson in 1958. Adult cabbage root maggots are similar to house flies, but greyish and smaller. Female flies lay eggs near the base of stems of canola and other members of the cabbage family. The eggs hatch into legless, headless maggots, which burrow through the soil until they reach a suitable root. Then they feed on the root, producing surface grooves and deep tunnels. Maggot feeding on canola roots often is associated with root rots. Large numbers of maggots reduce yield, and can cause plant death.

In the last four decades there has been a steady increase in root maggots in canola. Since the 1980s, there have been significant economic losses in Alberta, with estimated losses in some years of $100 million. In Saskatchewan and Manitoba, economic damage is not normal in commercial canola fields, but the trend of increase has reached a point where the prospect of economic loss in Manitoba is no longer distant.

No insecticides are available to control root maggots in canola because the vulnerable maggot stage occurs in mid-July. Insecticides that could be applied at seeding and would still be active in July are too persistent to be used. So, faced with the trend for increasing maggot severity and the absence of insecticides, we have been doing research to find non-insecticidal methods of maggot management.

Dr Neil Holliday and Dr Ulli Kuhlmann
in a canola plot in Switzerland that
was established to study response
of parasites to plant spacing.

Damage to a canola root
by cabbage root maggot.

These methods include manipulations to production practices that can be implemented now, and explorations of biological control that may provide a permanent solution in the future. In a three year study funded by ARDI and the Canola Council of Canada, we examined the effect of tillage regime and seeding rate. We found that maggot numbers and root damage were lower in zero-tilled plots, compared with plots that received conventional fall and spring tillage. This may be because two species of predatory beetles were more numerous in the zero-tilled plots. Our findings showed that when seeding rates of 4 kg/ha and 8 kg/ha are compared, the root damage ratings of canola plants were invariably lower at the higher seeding rate. Relative to the lower rate, the higher seeding rate gave a higher density of smaller plants. The lower rate of root damage when plant density was high was confirmed in a survey of 525 commercial fields in 1999 and 2000. These field surveys, carried out by Manitoba Agriculture and Food and Agriculture and AgriFood Canada, also revealed an effect of the duration of the crop rotation cycle. In each year of the survey, the fields with the highest levels of damage were those with the shortest rotation cycle: fields of canola that had been in canola the previous year had the highest damage of all. On the basis of these studies, we conclude that farmers can minimize root damage from maggots by using longer cycles of crop rotation, by using a zero tillage regime before seeding canola, and by seeding at a higher rates.

Cabbage root maggots are good candidates for biological control because they originate in Europe. There may be specialist natural enemies in Europe that are not present in Canada. Introducing those absent natural enemies to Canada could permanently suppress the root maggot population here with no subsequent cost for sustaining the biological control. Three years ago, with funding from ARDI, and in collaboration with Agriculture and AgriFood-Canada and the Commonwealth Agricultural Bureau Institute (CABI) in Switzerland,we began to examine possible candidate agents for biological control. The first step was to find out what natural enemies are already present in the prairies. In 2000, we collected over 13,000 immature root maggots from the three prairie provinces and reared them; we found a range of parasite species of which the most important were two species of parasitic beetle that attack the resting stage of the maggot, and one parasitic wasp that attacks the feeding maggot. In 2001 and 2002, similar collections were made from a wide range of brassica crops in Europe. Although the parasite communities are similar in Europe and Canada, one species of beetle (Aleochara bipustulata) was found in Europe but not in Canada. This species is particularly abundant in southern Sweden — an area with a growing season of similar length to that in the prairies. Relative to our most important Canadian parasitic beetle, the European species seems likely to be better synchronized with prairie root maggot development, and to perform better in the smaller maggots characteristic of canola. Recently, we received funding from the Western Grains Research Foundation to undertake detailed studies of Aleochara bipustulata to determine its suitability for introduction for biological control. If all goes well, these studies may produce a self-sustaining and environmentally-friendly solution to the cabbage maggot problem.

Dr. Rob W. Currie

Research into methods to control the honey bee parasite, Varroa jacobsoni Oud.

The mite, Varroa destructor, commonly called "varroa" is an external parasite of honey bees that was recently introduced into North America.Varroa lay their eggs and develop on immature honey bees (brood), moving to adult bees to complete their development.

Varroa poses a serious threat to the beekeeping industry because mites damage both brood and adult worker bees, ultimately affecting colony productivity.The prairie region of Canada is one of the most productive regions in the world for honey production. Our commercial beekeepers typically average production levels of well over 70-90 kg of honey per hive. As beekeepers in Manitoba derive most of their income from honey sales the potential for lost honey production is their most serious concern. Our research on varroa has shown that relatively low levels of this parasite cause significant reductions in honey production. Spring infestation levels of varroa on adult bees at average rates as low as 2% (2 mites per 100 bees) reduce honey production by 40 to 50%.

Methods to control this pest that are compatible with our management systems are crucial to ensure the success of the beekeeping industry. The objective of our research is to develop a method of fumigating colonies of honey bees during winter storage to control parasitic mites. The method of wintering honey bee colonies indoors is unique to the prairie provinces of Canada. This method of wintering presents Manitoba producers with a tremendous opportunity to increase their competitiveness by developing highly reliable and cost-effective methods of controlling honey bee parasites through the winter fumigation of colonies in wintering buildings. The results of this study will produce several benefits for the industry. First, it will greatly reduce labour input costs associated with treatments using formic acid. Second, it will reduce the amount of chemical used, as the quantity of formic acid required to obtain effective control of these parasites should be lower than in traditional treatments. Third, it will improve worker safety by reducing the exposure hazard to formic acid relative to field applications where employees working colonies are repeatedly exposed to low doses. Finally, because these applications will occur under highly controlled conditions the reliability of treatments should increase dramatically. The information gained from this study should have broader applicability to help us to improve our understanding of the variability in efficacy that is observed when formic acid is applied to individual colonies in early spring and fall applications.

This project will produce significant economic benefit to honey producers throughout the prairie provinces. The economic savings in one year alone would total approximately $770,000 from direct reductions in the chemical costs. Beekeepers will receive even greater benefit from the reduced labour costs compared to the current method using numerous treatment applications in individual colonies.

Dr. Terry Galloway

Applying Molecular Techniques to the Study of Insects

There has been a tremendous increase in the application of molecular techniques in agriculture including entomology. Molecular systematics involves the analyses of the structure of genes and/or molecules to make inferences about population processes and species identification. Researchers have developed techniques to make use of only a small piece of an insect specimen to obtain molecular markers for identification, pathogen transmission, biological control and population structure.

Since the DNA of a species is identical in all life stages, immature and adult stages can be associated (e.g. between the adult stage identified by conventional methods and an unknown egg or larval stage). This has proven to be a tremendous asset in a project on the natural enemies of horse fly and deer fly eggs. No one has attempted to describe the egg masses of these important pests of humans, livestock and wildlife.

Egg mass of the horse fly,
Hybomitra nitidifrons nuda, a
common pest of livestock in Manitoba.

The Manitoba horse fly trap was
developed in the Department
of Entomology in the 1960's,
and is now used the world
over to collect adult horse flies.

However, to be able to assess the host specificity of tiny wasps that parasitize horse fly eggs, it is essential to be able to identify which species of fly has laid a particular egg mass that is discovered in the field. Many species of adult horse flies can be collected in large numbers using the Manitoba Horse Fly Trap. Then, using a recognized molecular technique, RFLP-PCR (restriction fragment length polymorphism - polymerase chain reaction), it is possible to extract and characterize the DNA from the easily identified adult female flies. By searching wetland areas, prime breeding sites for horse flies and deer flies, egg masses previously laid by unknown species of flies can be collected and held in the laboratory until the eggs hatch. By the same technique, DNA is extracted from the larvae, and the corresponding bands can be matched with that of known females to reveal the identity of the species in question. When the parasitic wasps emerge from that egg mass, we now know what host species has been attacked, and the extent to which the parasites affect that particular species of fly. By describing the physical characteristics of the egg masses of each of the various species, we can eventually gain an understanding of the nature and variation of horse fly and deer fly eggs masses. All this information is eventually summarized and formulated into a museum database that will become available to researchers around the world. The use of molecular techniques offers an exciting new arena for investigation of entomological questions, of applied and basic nature. The horizon for our research has broadened as a result of their implementation. File: nuda.jpg Egg mass of the horse fly, Hybomitra nitidifrons nuda, a common pest of livestock in Manitoba.

Entomology Museum Open to the World

This year has been a landmark for the J.B. Wallis Museum of Entomology, in which the museum now has a completely new face. With $280,000 support in the form of a Canada Foundation for Innovation grant, the museum space has been expanded, the holding capacity increased, and electronic cataloguing is well under way. Dave Holder, technician in the Department of Entomology, and Ariel Patio are bar-coding and entering collection data for each individual of our one million or more specimens. Under the new system, requests for loans are easier to manage and specific information can be transmitted simply and easily anywhere in the world. This will greatly facilitate current collaboration with entomologists and acarologists elsewhere in Canada, the United States, Costa Rica, New Zealand, Australia, Russia, and Belgium, and open up new avenues and opportunities around the world.

Graduate student, Jashim Uddin,
at work in the J.B. Wallis Museum

Other Research Highlights

Dr. Robert Lamb, Adjunct Professor in the Department of Entomology, and scientist at the Cereal Research Centre of Agriculture and AgriFood Canada, received the most prestigious Canadian award for Entomology. He was awarded the 2002 Entomological Society of Canada Gold Medal for outstanding achievements in research, teaching and extension entomology.

Mr David Holder, technician in the Department of Entomology, has been immortalized by having an insect named after him. In support of Dr Terry Galloway's research, David spends part of each week washing lice, mites and other parasites from the feathers of birds ranging from humming birds to eagles. These are birds that died while in the care of the Manitoba Wildlife Rehabilitation Organization. In recognition of David's dedication, Terry and a co-author dubbed a newly discovered feather mite of the Sora rail Metanalges holderi.