Beneficial insects can be an unpaid workforce on your farm by killing pest species.
And if you don’t help out the good ones, then you’re favouring those you don’t want, says an entomologist with Manitoba’s Agriculture Department.
“Nature does not like a void,” said John Gavloski. “If you had no insects in a field or in an area, it will fill up with insects. And if you don’t have a good mix, it’s easy for us to get into a situation where pests become problems.”
‘Beneficials’ include pollinators, insects that prey on other insects, parasitoids, and ones that eat weed seeds. Others compost stubble or animal dung, or improve the soil.
Having these bugs in abundance can have a major impact on the pest insects in crops, said Gavloski, who gave a rundown of several types of beneficials during a recent Alberta Agriculture webinar.
- Read more: Website identifies your insect friends
Minute pirate bugs — just two to five millimetres long — are a “valuable seasonal predator” that feed on aphids and insect eggs. Sleek and thin damsel bugs are quick and ferocious predators.
“When they do find a diamondback moth caterpillar or an aphid, they put their beak in and inject their saliva into their potential food and then they suck the juice out,” said Gavloski. Damsel bugs can be especially beneficial because they sometimes kill more prey than they consume. They generally like small caterpillars, but also kill flea beetles and lygus bugs.
Lacewings are green insects that get their name from their large lacy wings while their larvae look like little brown alligators that quickly move through crops looking for aphids and caterpillars.
“Anything that moves, including their siblings, they will feed on,” said Gavloski. “They’re not too picky.”
There are more than 390 species of beetles in Alberta with ground beetles being especially good predators.
“They’re a very diverse group,” he said. “They will feed on any invertebrate they can overpower.”
These bugs often get overlooked because they are nocturnal, feeding at night and hiding during the day. Beetle larvae are predators too, with a taste for cutworms, root maggots and diamondback moth larvae.
“There are a few species that will climb plants and some of the ones that feed on the ground will consume wheat midge larva during their overwintering stage,” said Gavloski.
Rove beetles are a large family of bugs living in the soil — Alberta is home to about 265 species, which feed on flies, maggots, pupa, and insect eggs. The small brown beetles have two brown pads in the middle of their body that are actually their wings.
“They’re known to be good predators of root maggots — both the flies and the larva,” he said.
There are about 160 species of lady beetles, also known as ladybugs, in the province and they have a fondness for aphids.
Flies can also be beneficials and are distinguished by their one set of wings (most other insects have four wings).
Hoverflies mimic bees and wasps and, as their name suggests, move around like little helicopters. The adults lay eggs in aphid colonies and when the larvae hatch, they eat aphids and constantly consume prey.
Tachinid flies are parasitoids, laying their eggs on bertha army worms. The worms die when the flies bust through their skin. The same technique is used by many wasps — which are often tiny and never sting humans. They lay eggs right into caterpillars and the larva eat them from inside and eventually kill them.
Helping your insect friends
Collectively, beneficials can have a significant impact on reducing crop pests — and there are several things farmers can do to help them out.
“Flowering plants around the edge of the field can help parasitoids live longer, lay more eggs, and kill more things,” said Gavloski.
And since insecticides can kill good bugs and bad ones alike, producers should be judicious when it comes to spraying. Only use insecticides when pest insect populations are above economic thresholds, he said.
“You can inadvertently do more harm than good when spraying insecticides when they are not needed.”
Tank mixing insecticides isn’t always a good idea and can also do more harm than good. It’s a good idea to use selective insecticides that target certain pests such as aphids and don’t kill beneficials, he added.
“Sometimes you only need to spray patches of a field, or an edge. Sometimes that will save a reservoir of natural enemies,” said Gavloski.
He also recommends rotating crops and leaving natural habitat for the beneficials. Spraying as late in the day as possible will help avoid excess pollinator damage.