They exist to eat plants. The best control is to live where it's too hot and dry for them to live. Those types of climates are also where it's too hot and dry for most diseases, so your pressure to spray anything for any reason is greatly reduced. But, those are also the climates which DEMAND air conditioning and more water for gardening. Kim

The harm that the adult sawflies do is to lay eggs which become rose slugs.

Well, their only upside to date is to give me a 'green thumb' (and forefinger too).....:-))))

Me again with more questions about these voracious little beasts. Can you remind me: do the larvae that we see on the roses (that eat the leaves to lace) lay more eggs? or is that only done by the adult sawfly? And when does that happen in the cycle? If I am squashing the larvae, which I am !!!!, is there another part of the puzzle? Is there a time when eggs can be eliminated? These guys really are getting the better of my 250+ roses, and I think my squishing and squashing is not keeping up.

Basic entomology lesson #1: Larvae are immatures. Adults are matures. Only mature organisms can reproduce. (glossary definition: mature = capable of reproduction.)

basic life cycle of insects: egg, larva, pupa*, adult. Eggs hatch to larvae. Larvae eventually pupate to adults, in insects with complete metamorphosis*. Adults lay eggs or otherwise produce the next generation of larvae.

*Those with incomplete metamorphosis do not need a pupal stage as the larva is much like an adult without the reproductive organs. Aphids and grasshoppers have incomplete metamorphosis. Larvae look much like adults and there is no pupal stage. Sawflies and butterflies have complete metamorphosis - the larva is very different from the adult and there's a complete change in body in the pupal phase.

My own experience with rose slugs is that squishing will not keep up and spraying with a systemic insecticide will be necessary, the sooner done the better. As soon as squishing is no longer keeping up.