PHOTO BY MARTIN SCHWALBE

An unwelcome new pest - the pea leafminer - is tunnelling its way through Ontario's vegetables, and U of G researchers are trying to find effective and environmentally responsible ways to stop it.

  Pea leafminer larvae "mine" their way through vegetable leaves, devouring tissue from both the upper and lower surfaces. Prof. Rebecca Hallett, Environmental Biology, and master's student Andrea Martin are studying the insect's ability to survive in the province's climate, how it interacts with various host plants and the timing of emergence of the adult stage in the spring. Their goal is to develop methods to protect crops against this devastating pest.

  "There are insecticides that growers might be able to use," says Hallett, "but the only registered one is undesirable, and there are restrictions on its use. We're looking for a safer pesticide, as well as alternative methods."

  The pea leafminer, which is also found in California and South America, was first discovered in celery fields in Ontario's Holland Marsh area in August 1999. Already, it has devastated crops of celery and Asian vegetables. It feeds on a wide range of host plants and has also affected lettuce, spinach, onions and greenhouse ornamentals and cucumbers. The Holland Marsh is dense with crops, so there's great potential for the insect to make a home on other plants as well.

  For control purposes, Hallett and Martin must first determine if the pea leafminer is capable of surviving over the winter. They collected insects in the fall in the pupal stage (the stage before they become an adult) and put them into growth chambers, which are adjusted for a variety of different temperatures. The temperature in the chambers will be brought back up to warmer conditions in the spring, and the researchers will collect data on the timing of emergence at various temperatures. With this knowledge, they can determine when it might be necessary to monitor for the insects' presence and provide some type of control.

  Hallett also hopes to devise new control methods by examining how the pea leafminer interacts with its host plants. She plans, for example, to investigate how the insect fights off or avoids the natural protective compounds in celery that guard against such pests.

  In addition, she intends to look at the chemicals in plants that govern which insects are attracted to them. This information could be used to develop genetically engineered plants that resist the pea leafminer. Knowledge of such chemicals could also be used to attract the insect away from the crops and into a trap or to repel the insects from the plants.

  Although new insects are introduced all the time, it's rare for one to do so much damage in its first year, Hallett says.

  "The stage in the development of the pea leafminer between when the egg is laid and the larva emerges could be less than a week." she says. "This means it's possible for several generations to develop over the summer."

  This research is sponsored by Food Systems 2002 and the Canada-Ontario Safety Net Research and Development Fund.