Worm Castings and Insect Control

Q. What effect do worm castings have on beneficial insects? Are there any special instructions or precautions to be considered when using worm castings around fruit and vegetable plants? 

A.  I had not heard of worm castings used as an insect repellent or an insecticide until you mentioned it and followed up with a web link to a worm farm. They mention chitinase being the "active ingredient" that has an effect on insects.The word chitinase implies that it is an enzyme which dissolves chitin, a primary component of the exoskeleton in insects.

Red wigglers from our worm bin

I had to do some digging on this subject because I knew very little about it. The claim by the worm farm is that worms produce chitinase and deposit it in the worm castings. This chitinase produced by worms has an effect on bugs. Let's keep in mind that insect exoskeletons surround good bugs as well as bad bugs. So anything that targets bugs in general kills all bugs whether they are good or bad. 

Personally, I think this is a pretty big stretch about the chitinase produced by worms. There has been quite a bit of research on the use of chitinase and developing synthetic chitinase for targeting insects for pest control. But to make the jump from the chitinase produced by earthworms reducing insect pests in the garden is a pretty big leap and one that I am not ready to take. The research is just not there to support this kind of claim.

Let's stick with something we do know. Worm castings are a great natural fertilizer and help to improve poor soils. I personally have red wigglers in a worm bin for digesting kitchen vegetable and fruit scraps.Like them a lot.