Gardening

Look-alike garden insects

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. Right then, 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.

Rose sawfly larva damage first shows up as holes in the leaves. Then the entire leaf is eaten.

Cross-striped cabbage worms also eat holes in leaves and can be very destructive to cabbage and related plants.

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 order Hymenoptera (wasps) while the cross-striped caterpillar is in the butterfly/moth order (Lepodoptera). About the only thing you can say about their relationship 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 Dluzen
As a result of being a gardener for more than 40 years, 30 of those as a professional, Bob's gardening has become an integral part of his life. "It's the ever-changing seasons and the wide variety of plants and gardens that keeps me intrigued," he says. Bob lives and gardens in rural Monroe County.