How to promote predatory insects
One group of
wholly-positive garden invertebrates is the bugs who consume bad insects.
Spiders, centipedes, dragonflies, mantids (aka praying mantises),
ambush bugs, assassin bugs, lacewings, ladybird beetles (aka ladybugs),
ground beetles, true wasps, digger wasps, hoverflies, and robber flies
all subsist primarily or entirely on other insects during some stage of
their life cycle.
Another category of predators is the parasitoids. Braconid wasps, ichneumonid wasps, chalcid wasps, and parasitic flies all lay their eggs on other insects, and unlike true parasites, the wasps and flies eventually kill their hosts. That's great news in the garden since many of the prey insects are bad bugs, like tomato hornworms or bean beetles, so the parasitoids keep the pests under control. As a side note, in case you're scared of the term "wasp," all of the parasitic wasps are too small to be a problem for human gardeners.
Many gardeners fall in love with the idea of
predatory and parasitic insects and decide to buy some of these critters
to seed their garden. However, I believe that you really need to
encourage all of these species at the ecosystem level. I've heard
of people opening a container of expensive insects, only to have them
all fly away because the garden isn't a hospitable environment for the predators
to live in.
Instead of spending your money on insects, why not
spend a bit of time encouraging the good bugs you already have to stick
around and reproduce? Many depend on flowers during some stage of
their life cycle, so you can encourage them just like you did native
pollinators by ensuring you have copious pollen and nectar sources available
throughout the growing season.
Weedy edges will also encourage predatory insects
since the predators need to be able to find lots of insects to
eat even when your garden pests are under control. In addition,
dragonflies need a pond into which they can lay their eggs, and many
benefit from having a very shallow body of water from which they can
drink. When attracting predatory insects, it's imperative not to
use any pesticides (even organic ones) and to allow low levels of pest
insects to fly under your radar. If there aren't any bad bugs
around, your predatory insects won't have anything to eat and will go
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