Releasing predator pests into the greenhouse environment isn’t as easy as it sounds. Each predator must have a sufficient food source in order to survive, otherwise the predator population crashes. One way we help the predators we release, is by offering them a series of ‘banker’ plants. The banker plants provide food and shelter for the food source and the predator. For example, we grow wheat grass as a host for a specific type of aphid that only feeds on cereal grasses. Since we don’t grow cereal grasses in the greenhouse, these aphids will not multiply on our healthy plants.
The parasitic wasp that we release to keep the aphid population in check will still be able to find food on the banker plants once they have eliminated any aphids on our other plants. The parasitic wasp does this by laying eggs in numerous aphids. As the larvae grows inside the aphid it effectively kills it, resulting in an aphid mummy.
Predators can be voracious eaters, so we have to protect some of the banker plants, with their aphid populations, in a safe environment where the aphid population can multiply. We create this environment using an aquarium covered with netting. The banker plants stay here until they are needed as food.