Encouraging predatory insects in your garden

Our normal instinct upon finding any pest species, such as aphids, in or anywhere near our gardens is to eradicate all of them. However, is this always the best course of action? An important part of integrated pest management is encouraging predatory species of insects in your garden. Predatory insects need a certain level of pest insects to feed on, otherwise their populations will decline. The lack of predatory insects can then lead to even higher levels of pests in the next life cycle.

It is a challenging task to tolerate enough pest insects in our gardens to feed the beneficial insects without causing too much harm to our crops. One risky option is to keep watching insect populations on your crops and only intervening when they are causing significant damage to your crops. Another option is to observe your local native plants that host large numbers of plant feeding species of insects, but species that do not feed on your crops. One example of this are Milkweed Aphids (Aphis nerii) which only feed on Oleander and Milkweed (Asclepias sp).

Planting milkweed in or around your garden will usually attract Milkweed aphids but this species of aphid will not attack your crops. These aphids in turn attract all kinds of predatory insects. The patch of milkweed in this photo, after being infested with aphids, attracted a large number of predatory insects. Five different species including Ladybird Beetles, Assassin bugs, Long legged Flies, Parasitic wasps, and Hoverfly larvae were all found feeding on the aphids in this Milkweed patch. These Milkweeds serve as a predatory insect “bank” so that when other species of aphids try to establish on any nearby crops, the predatory insects are already there to keep them under control.

If you have any examples of plants that serve as predatory species banks like this, we would love to hear about them in the ECHO Community.