One of the most common questions I hear from beginning gardeners is “How do I keep insects out of my garden?” The idea of a garden without insects makes me imagine a dome-shaped force field programmed to exclude six-legged creatures or something equally outer-spacey, but instead I suggest getting to know one’s garden insects, and taking steps to increase their diversity.
The best way to do this is to grow plenty of flowers, which attract beneficial insects with protein-rich pollen and sugary nectar, while providing reasonably safe places for them to hide from danger.
Numerous studies have found that well-fed beneficial insects that inhabit flower-filled gardens work harder, live longer and have more offspring compared to those under stress. Once a beneficial insect such as a braconid wasp (which lays its eggs in leaf-eating caterpillars) finds a pleasing habitat with plenty of available food (nectar), it gets busy finding its next victims. This is where the concept of balancing comes into play. You accept that there will be some pests present in your garden, and tweak the environment to make it more attractive to species that play important roles protecting plants – the ones we call beneficial insects.
Which is not to say that we are exactly clear on the who’s who of beneficial insects. This may be changing with the help of entomologists armed with video cameras, which can observe insect activity passively for review later. In a recent study that videotaped beneficial insect activity in an Ohio pumpkin field, researchers thought they would see ground beetles consuming the eggs of pesky cucumber beetles and squash bugs. Instead, they discovered that the main predators were ants, daddy long-legs, and crickets.
One of the largest groups of beneficial insects are those that pollinate crops by spreading pollen from flower to flower. But bees and other pollinators may be doing even more good by spreading beneficial microbes about with their dancing feet, creating a more diverse microbial community in the plants’ blossoms and surrounding tissues.
This subtle shift can reduce fruit rots, as was found in a four-year study of New York strawberries. Scientists put beneficial Trichoderma fungi in honeybee and bumblebee colonies, and let the bees deliver it to the nooks and crannies in strawberry flowers. With the bees’ help, strawberries were bigger and better than those from plants sprayed with fungicides.
Butterflies perform pollination and inoculation services, too, and the same plants used to attract butterflies will lure in other beneficial insects, especially if they are chosen for a long season of bloom. Insects quickly figure out how to approach new flowers that come into bloom, and honeybees are especially adept at finding their way in quickly. It can take bigger bumblebees up to an hour to learn how to retrieve nectar from complicated flowers they have never encountered before, but once the approach is mastered the bees become efficient feeders.
Recent studies have suggested stunning numbers on how many insects are consumed by the world’s spiders, which by weight may be twice as much meat and fish protein as is consumed by humans.
This time of year I see spiders running frantically when I disturb the mulch around the garlic, but most of this year’s baby garden spiders are hiding in grass and shrubs, safe from being eaten by birds. On the down side, spiders are indiscriminate killers that eat what they catch. I wasn’t happy to see that the crab spider hunting in the sunflower blossom (above) had snatched up a beneficial hoverfly, but it’s a bug-eat-bug world out there. All we can do is help keep things in balance.
Don’t forget to report any bugs you see – whether pests or beneficials – to The Big Bug Hunt to help develop a pest prediction service that will enable you to take preventative action when pests are likely to be heading your way.