Saturday, 10 August 2013
Balcony beasties – cabbage whites and their enemies
It is true you do not have to go far to see wildlife, even in the midst of a big city. Invertebrate scholars are particularly fortunate in this regard as insects, arachnids etc. really are everywhere, in your home and even on you. Here in my student room in Earls Court, London I have a little balcony which I have used to grow salad and tomatoes. Being an entomologist I soon became more interested in the creatures eating my vegetables (and eating them!) than the produce.
I watched a large white (Pieris brassicae) lay clusters of eggs on my kale a couple of weeks ago. Now if i was a ‘proper’ gardener I would remove these but as an entomologist I take pleasure in watching them develop so don’t begrudge them my salad. The caterpillars hatched and grew rapidly, first feeding together then spreading out on the container of plants. I later found a single small white (Pieris rapae) caterpillar which I had missed, as these are laid singly and must have been overlooked.
Large White caterpillars feeding on my kale on the balcony
Small White caterpillar (note the leaf mines on the kale, I will discuss these in another post)
By early August they were ready to pupate but I have only found on successful pupae, the rest being devoured inside out by the braconid wasp Cotesia glomerata.
The only successful large white pupa
All but one of the infected caterpillars mostly moved away from the food plant, climbing up the balcony to find a place to pupate, instead the braconid larvae emerged from the caterpillars and spun silk cocoons, the moribund caterpillar remaining attached and hunched over the cocoons. The caterpillars were still alive for sometime after the parasitoid larvae had emerged and pupated.
Cotesia glomerata larvae emerging from large white caterpillar, this one remained on the food plant.
Caterpillar on the side of the balcony with Cotesia glomerata in their silk cocoons underneath.
The small white caterpillar had a different fate, though no less gruesome. I woke up one morning to find it being macerated and carried of piecemeal by a wasp. Amongst the remains it could be seen it was also infested by Cotesia glomerata larvae.
The next balcony bugs post will focus on the flies in my vegetable garden.