Insect Parasites of the Darksided Cutworm in Ontario
Imagine walking through a quiet Ontario tobacco field at dusk. The seedlings stand in orderly rows, their leaves glistening with evening dew. All appears peaceful, but beneath the soil surface, a silent war rages. A hungry darksided cutworm larva emerges from its earthen tunnel, ready to sever a young plant at its base. But as it begins its destructive work, it carries within it a hidden enemy—a parasitic wasp larva that will soon consume it from the inside out.
This isn't science fiction; it's the complex reality of natural pest control that scientists have been unraveling for decades. The darksided cutworm (Euxoa messoria) has long been a formidable agricultural pest in Ontario, particularly threatening to tobacco and other crops 1 . What makes this story fascinating isn't just the cutworm's destructive habits, but the secret army of parasitic insects that have been enlisted by nature to keep its populations in check.
Scientists collected 3,970 cutworm larvae in their study, with 701 parasites emerging from them 1 .
Before we meet the cutworm's enemies, we should understand the enemy of our crops. The darksided cutworm is a nocturnal moth larvae that operates under cover of darkness. Like something from a horror film, these pests hide in the soil during daylight hours and emerge at night to feed, often severing young plants at ground level and dragging the remains into their subterranean lairs 2 .
Their life cycle is perfectly synchronized with the agricultural calendar. They overwinter as eggs in the soil, hatch in early April, and begin feeding on whatever green material is available—often cover crops initially, then moving to newly transplanted cash crops 3 . By late May and early June, when the larvae have reached their more destructive later stages, they can devastate a field of young plants virtually overnight.
In 1973 and 1974, scientists embarked on a systematic investigation to uncover the natural enemies of the darksided cutworm in Ontario 1 . Their approach was both straightforward and painstaking:
Researchers gathered 3,970 fourth- to seventh-instar cutworm larvae from fields near Delhi, Ontario.
The collected larvae were carefully transported to laboratory conditions and reared individually.
Scientists waited and watched as parasites emerged from their hosts rather than the expected adult moths.
Each emerging parasite was identified, catalogued, and studied.
The results of the study revealed a surprisingly diverse community of parasitic insects targeting the darksided cutworm. From the 3,970 collected cutworms, an impressive 701 parasites emerged, representing six species of Hymenoptera (wasps) and four species of Diptera (flies) 1 .
| Parasite Type | Number of Species | Examples | Key Characteristics |
|---|---|---|---|
| Hymenoptera (Wasps) | 6 species | Various ichneumon, braconid, and chalcid wasps | Internal parasites, often host-specific |
| Diptera (Flies) | 4 species | Tachinid fly species | Broad host range, lay eggs on or near hosts |
| Total | 10 species | All primary, internal parasites |
Discovery Significance: Only two of these ten species had previously been documented as parasites of the darksided cutworm 1 . The other eight represented newly discovered relationships, highlighting how much remains to be learned about even relatively well-studied agricultural systems.
The parasitic insects discovered in the Ontario study employ remarkably varied strategies to exploit their cutworm hosts:
Some parasitic wasps practice what's known as egg loading—the female wasp carries a lifetime supply of eggs when she emerges, having developed from a single fertilized egg through a process called polyembryony 1 . This strategy allows a single wasp to rapidly establish a significant population even with limited mating opportunities.
Other parasites are active searchers. The female flies or wasps must locate cutworm hosts—no simple task given the cutworm's nocturnal habits and soil-dwelling lifestyle. These parasites use various cues including plant damage signals, soil vibrations, or chemical traces to find their hidden prey 7 .
Once a host is located, the real invasion begins. The parasite may lay eggs directly inside the host or attach them to the cutworm's exterior where the newly hatched larvae will burrow in. Inside, these uninvited guests consume the host's non-essential tissues first, skillfully keeping their victim alive until they're ready to pupate 1 . The parasite eventually emerges from either the dying cutworm or its pupa, depending on the species.
| Research Tool | Primary Function | Application in the Study |
|---|---|---|
| Field Collection Equipment | Gathering cutworm larvae from agricultural fields | Used to collect 3,970 larvae from tobacco fields in Delhi, Ontario |
| Laboratory Rearing Containers | Maintaining individual larvae under controlled conditions | Prevented cross-contamination and allowed tracking of parasite emergence |
| Taxonomic Identification Guides | Classifying and identifying parasite species | Essential for determining the six hymenoptera and four diptera species |
| Data Recording Systems | Documenting emergence rates and parasite success | Tracked the 701 parasites that emerged from collected cutworms |
The discovery of this diverse parasite community has significant implications for sustainable agriculture:
The 701 parasites that emerged from just 3,970 cutworms demonstrate that natural biological control is already actively working in Ontario fields 1 . When we understand these existing relationships, we can work to preserve and enhance them.
Understanding the cutworm's natural enemies offers potential for developing biological control strategies that could reduce dependence on chemical pesticides 7 . This is particularly valuable for cutworms since their soil-dwelling habits make chemical treatments often ineffective and environmentally problematic.
The study found that after two or three years of cutworm infestation, populations of beneficial organisms usually build up enough to naturally suppress cutworm numbers 2 . This highlights the importance of conserving biodiversity in agricultural landscapes.
| Control Method | Effectiveness | Environmental Impact | Long-Term Sustainability |
|---|---|---|---|
| Chemical Pesticides | Variable; often limited by cutworm's hiding behavior | Can harm non-target organisms; resistance development | Decreasing effectiveness over time |
| Natural Parasites | Modest but consistent; part of integrated approach | Minimal negative impact; enhances local biodiversity | Self-sustaining and potentially increasing |
| Combined Approach | Highest effectiveness | Balanced and reduced chemical load | Most sustainable long-term solution |
The Ontario parasite study, now several decades old, continues to inform modern integrated pest management approaches. Recent research has expanded to include other biological control agents such as entomopathogenic nematodes 7 and gut bacteria that affect cutworm development and pesticide resistance 4 .
What makes the original parasite research so enduringly valuable is its demonstration that even problematic pests exist within a web of natural checks and balances. By understanding and working with these natural systems rather than constantly fighting against them, we can develop more sustainable approaches to agriculture that protect both our crops and the ecosystems they depend on.
The next time you see a moth fluttering through an evening field, remember—it might be a cutworm mother seeking a place to lay her eggs, or it might be one of nature's tiny assassins, looking to continue the secret war that keeps our agricultural systems in balance. In this hidden drama, basic scientific research provides our window into a world we're only beginning to understand.