Lookalike insect pests

This week while scouting for garden for pests, I came across an interesting coincidence. Two look-alike, but completely unrelated, insect pests showed up at the same time. They were in the same general area but on different plants in nearby gardens.

The first insect I spotted was rose sawfly larvae feeding on the roses. There were quite a few of them and were pretty big by the time I saw them.  They had eaten quite a bit of the foliage. If I hadn’t spotted them, they would have completely defoliated the bushes.

The other insect I came across, just minutes after seeing the sawflies, was cross-striped cabbage worms feeding on some cauliflower plants. It struck me how similar the sawflies and cross-striped caterpillars look. At that stage in their particular lifecycles, they were nearly the same size.

Even though they were each feeding on their preferred food, if you didn’t know better, you could easily confuse the two. However, cross-striped cabbage worms would never be found on roses and like-wise, rose sawflies would turn up their noses at cauliflower.

The sawfly larva at this stage looks like a caterpillar but is not.
The cross-striped caterpillar is a true caterpillar.

Both of these insects eat leaves and the damage they do is quite similar looking too as they both chew holes. That’s where the similarities end. They are unrelated species. The rose sawfly belongs to the wasp family while the cross-striped caterpillar is in the butterfly/moth family (Lepodoptera). About the only thing you can say about them is they are both insects.

That doesn’t make too much difference when it comes to killing them with chemical insecticides, but if you are an organic gardener, it can make a huge difference. For example the biological insecticide Bt (Bacillus thuringensis) infects butterflies and moths so will kill cross-striped caterpillars. But rose sawflies, because they are wasps and not Lepodoptera, are un-phased by Bt spores. They can eat Bt all day long and not be affected in the least.

I see cases of mistaken identity all the time. This is a good example of how easy it is to misidentify something if you’re not careful.

Bob