Beneficials to look for while scouting

Lygus, bertha armyworm and diamondback moth have a number of natural enemies that will keep populations in check. These beneficial insects may not control an immediate pest threat that has already exceeded thresholds — growers will still have to spray in that case — but beneficials can keep a lid on populations. The key to preserving beneficial insects is to follow thresholds and spray only when necessary. Here are some beneficials to watch for while scouting:

Cotesia wasps lay eggs in diamondback larvae. When the cotesia eggs hatch, the larvae eat diamondback larvae from the inside out. You may notice parasitized diamondback larvae while scouting. Source: Lloyd Dosdall.

Lacewing larvae are beneficial insects that eat lygus nymphs and aphids in canola crops. Insecticide sprays will take them out.

Adult lacewing

Banchus is a parasitoid of bertha armyworm. Source: Lloyd Dosdall

The hover fly is a beneficial pollinator and its larvae are predators.

Lady beetle (ladybug) larvae eat lygus nymphs. Source: Lloyd Dosdall

Lygus enemies. Laboratory studies show that lacewing larva consumed seven Lygus nymphs every 24 hours. Damselbugs and crab spiders also consumed large numbers of lygus nymphs. Lady bugs (a.k.a. ladybird beetles) consumed low numbers of third, fourth and fifth instar Lygus nymphs. This suggests to us that these general predators all play a role in suppressing Lygus in canola within the canopy, and may have “feeding niches,” with each predator preferring specific nymphal instar stages as prey.

Diamondback larvae pressure seems to have eased off the past few weeks, and it may be because of two natural enemies — Diadegma and Cotesia. These wasps lay eggs inside diamondback larvae. When the larvae hatch, they feed on the diamondback moth larvae from the inside out, killing them.

Bertha armyworm has a few natural enemies. They are an orange wasp called Banchus, which lays eggs in the bertha armyworm, and Tachinid flies, which lay eggs on the backs of bertha armyworms. Tachinid eggs hatch within minutes, and the tiny larvae bore into the bertha’s body. When these two natural parasitoids reach levels where they’re attacking 60% of the bertha population, we can expect to see bertha populations drop the following year and enter the downward side of their cycle.

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