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Bug of the Month – August 2018

An example of Lygus.

Surya Acharya lost some Sainfoin seed increase plots to a mixture of adelphocoris alfalfa plant bugs and lygus. I should have taken a photo as there were hundreds of bugs of all ages in 10 sweeps in his plot. These bugs are also high in seed alfalfa and growers sprayed for them bugs.

Some may have sprayed canola when the crop reached the early pod stage, but the bugs were not as abundant in canola as in alfalfa.

At the end of July, we were still seeing the little black wasp that could be Diolcogaster parasitoid of lepidoptera larvae like diamond back moth or cutworms.

Lygus is probably my favourite insect pest to work on as I joined Ag Canada because of a lygus outbreak in 1998. I have worked at least a little every year on Peristenus wasps; a key parasitoid for lygus. There is an exotic that I may relocate here from Ontario and Quebec after it moved from the USA (without a passport!).

This year, other than grasshoppers, I have seen high numbers of plant bugs; mainly lygus bugs in a number of crops. Seed alfalfa fields in the Rosemary area reached threshold levels in the spring (5 per sweep) and growers sprayed insecticide to target them over the alfalfa weevil; which is a perennial pest in this region. Later in the summer, Sainfoin research plots near Lethbridge (LRDC) had very high numbers (5-10 per sweep) that consisted mainly of lygus, but also the alfalfa plant bugs (Adelphocoris sp). At the end of July and into August, we see very large populations of lygus bugs in canola at the pod stage; some fields have over 10 lygus per sweep and over 90% are large nymphs and adults capable of damaging seed in the less mature pods.

By far the most lygus I have seen so far is in a quinoa plot near Lethbridge (Farming Smarter site) where counting them was impossible. Attached is a shot of what Sheree’s net looked like from 10 sweeps (20-30 per sweep? Or more!).

A hemp plot a few meters away from the quinoa had also very high numbers that would be a close second to the quinoa. This reaffirms my conviction that although lygus are an intermittent pest in some crops like canola in some regions, their polyphagous nature makes them interesting and worthy research subjects. Our lab is looking at an exotic biocontrol agent (a wasp by the name of Peristenus digoneutis) that may supplement similar native wasps and we hope help us reduce lygus numbers in these crops.