According to field observations by allotment holders across the UK, brassica crops under attack from large and small white butterfly caterpillars trigger an airborne distress signal known as a kairomone, which summons the parasitic wasp Cotesia glomerata to inject eggs inside the living host. This complex multispecies interaction highlights how natural biological networks operate in domestic vegetable plots, turning common garden pests into hosts for developing wasp broods.
How Cotesia Wasps Target Brassica Pests
When herbivores like cabbage caterpillars munch on prize brassicas, the plants react immediately. The damaged leaves release an odour cloud that instantly catches the attention of female Cotesia wasps.
The tiny insect hones in on the scent and uses a rapier-like ovipositor to pierce the caterpillar’s body. She deposits between 15 and 50 eggs directly inside the living host. This symbiotic relationship relies on precise chemical cues shared between the plant and the predatory wasp.
Did you know?
Each wasp egg is coated with a specialized Bracovirus that integrates into the wasp’s cells. This virus actively disables the caterpillar’s immune defenses, altering its growth and behavior to protect the developing parasites.
Inside the Host: The Internal Consumption Phase
Over a two-week period, the wasp larvae slowly consume the caterpillar from the inside out. According to biological observations, the parasites deliberately leave essential organs untouched to keep the surrogate womb alive while they grow.
Once fully grown, the larvae paralyze the host. They rasp at the inner lining of the caterpillar’s skin using specialized tooth-like projections around their mouths before bursting out in a dense, fuzzy mass. Even after this grizzly extrusion, the caterpillar’s role isn’t finished.
The Zombie Security Guard Effect
Manipulated by the lingering virus, the dying caterpillar does not crawl away to perish quietly. Instead, it spins a protective silken pad directly over the cluster of wasp cocoons.
According to researchers, the host remains rooted in place as a zombie security guard, actively protecting the Cotesia cocoons for another 10 days until the next generation of wasps emerges.
Hyperparasitism: When Wasp Attacks Wasp
Nature rarely operates in simple two-party loops. In many summer seasons, over half of all Cotesia broods fall victim to a stealthy cousin: the hyperparasitic wasp Lysibia nana, according to ecological surveys.
Pro Tip for Allotmenteers:
Understanding multi-layered food chains helps gardeners appreciate that natural predators often regulate pest populations without heavy chemical intervention. Observing unusual caterpillar behavior can often reveal active parasitism in your beds.
When the Cotesia infection alters the caterpillar’s salivary concoctions, the host cabbage responds by shifting the gas mixture it releases into the air. This altered scent profile is picked up by Lysibia.
Drawn to the vulnerable setup, the hyperparasitic wasp lays its own eggs directly inside the developing Cotesia larvae resting within the caterpillar. Additional predatory species may even target Lysibia in turn, creating a deeply layered food chain right above the soil.
Frequently Asked Questions
Do all cabbage caterpillars get targeted by parasitic wasps?
No, but small and large white butterfly caterpillars frequently fall prey to species like Cotesia glomerata when brassicas emit kairomones in response to feeding damage.
Does the caterpillar die immediately when the wasp larvae emerge?
No, the host remains alive long enough to spin a protective silken cover over the wasp cocoons, acting as a guard before finally perishing.
What is a hyperparasite?
A hyperparasite is an organism that parasitizes another parasite, such as the Lysibia nana wasp targeting developing Cotesia larvae inside a caterpillar host.
Join the Conversation: Have you spotted unusual wasp activity or parasitized caterpillars in your vegetable garden this season? Share your observations in the comments below, explore our gardening pest archives for more expert guides, or subscribe to our weekly allotment newsletter for timely updates.
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