Larval Development and Parasitism in the Large White Butterfly

 Back in early spring, just as we were entering lockdown, the weather was gloriously warm and sunny. Like many other amateur entomologists, I spent a lot of time in the garden watching the comings and goings of butterflies and other insects. 

Garlic Mustard is a wild plant that is regularly used as a foodplant by several species of Pieridae butterflies and in late April, I watched a female Large White (Pieris brassicae) ovipositing on the underside of a garlic mustard leaf. This would provide a good opportunity to monitor larval development, hopefully through to pupation and the emergence of a summer brood of Large Whites. 

The parasitic wasp Cotesia glomeratus specialises in laying its eggs in the larvae of the Large White (P. brassicae) and can sometimes kill large numbers of caterpillars but the predator-prey cycle always ensures that, over time, numbers of predator and prey species are kept in balance.

Large White (Pieris brassicae) 

(female ovipositing on garlic mustard)

(egg batch on garlic mustard)

(egg batch showing developing larvae, one day before hatching)

(1st. instar larvae, one day after hatching )

(2nd. instar larvae, with 3rd. or 4th. instar larva wandering along leaf edge)

The following sequence of images show a 5th. instar larva being pestered by attendant Cotesia wasps. The larva is clearly aware of its peril and constantly made attempts to keep them away.

The following image is of a 5th. instar larva with a Cotesia wasp on its back, injecting its eggs.

This final image shows a 4th. or 5th. instar larva surrounded by the pupal cocoons of the Cotesia larvae that have emerged from its body. You can also see a Cotesia larva in the process of emerging from the 5th. segment of the caterpillars body.

This small colony of Large White larvae was overwhelmed by the onslaught wrought by the parasitoids and I am pretty certain that none survived to pupation.