Virgin births took place on our dining table at Christmas. After a frost-free December, I had cut the last rosebuds from the garden and by Christmas Eve they had opened enough to make a table decoration. It was left forgotten on the windowsill until Twelfth Night, when the withered flowers, infested with rose aphids (Macrosiphum rosae) and sticky with honeydew, were about to be consigned to the compost heap.

Unnoticed, overwintering aphid eggs had experienced a premature spring. What followed was spectacular, thanks to these insects’ capacity for parthenogenesis, asexual reproduction from an unfertilised egg, without male involvement. When they emerge from an egg they are all females, multiplying via virgin birth, cloning themselves with production-line efficiency: a rosarian’s nightmare. It only takes one greenfly hatchling to start a population explosion.

Rose aphid feeding while giving birth

A rose aphid feeding while giving birth via parthenogenesis. Photograph: Phil Gates

I watched over the course of an afternoon. First a small, elongated blob appeared at the tip of a mother’s abdomen, swelling into an infant whose legs finally extended as she lowered it on to the rose stem. Throughout, the mother’s stylet, acting like a hypodermic syringe, tapped the rose’s sugary sap: seamless feeding and breeding, each newborn gravid with developing embryos for the next generation, even before inserting its own stylets for the first time.

Scores of aphids were aligned head-to-tail along the flower stems but their food source was dying, so some had transitioned into the dispersal phase of their life cycle, when winged adults take flight in search of a fresh host plant. This would be the moment when gardeners hope salvation will arrive, in the form of natural predators like hoverfly, ladybird and lacewing larvae that wreak havoc on greenfly populations, or wasps that can’t resist eating these sweet treats.

Winged rose aphid

A winged rose aphid, ready to fly to a new host plant. Photograph: Phil Gates

Our precocious Christmas population would never reach the final step in the breeding cycle, when males appear in autumn and fertilise the new generation of overwintering eggs that females will lay, before dying.

I dropped the dead roses in the garden compost bin. A wren was searching for food among withered stems of last summer’s flowers: for every aphid egg it finds, there will be thousands fewer greenfly on the roses next summer.


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