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Sunday, June 19, 2016

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.


  1. Do you keep your worm bin in the house or outside? If outside how big is it and do you have to do anything to keep it cool? Could you do a post about how you care for your worms?

  2. Chitinase is an extracellular enzyme complex that degrades chitin and has a molecular mass of approximately 30 kDa. Chitin is degraded to N-acetyl-D-glucosamine in 2 enzymatic reactions. Firstly, chitobiose units are removed from chitin by chitodextrinase-chitinase. The second reaction involves N-acetyl-glucosaminidase-chitobiase, chitinase

    1. Give us some citations of its success in peer reviewed literature. So far I have seen the possibilities but no reports that it works to suppress the bad guys. Thanks.

    2. I just found this citation but it relates to cold storage of peach and increased storage life. American-Eurasian J. Agric. & Environ. Sci., 18 (1): 27-33, 2018
      ISSN 1818-6769
      DOI: 10.5829/idosi.aejaes.2018.27.33
      Corresponding Author: M.M. Gad, Department of Horticulture, Faculty of Agriculture, Zagazig University, Egypt.
      Coating Florida Prince Peach Fruits with
      Nano-Chitosan for Increasing Storage and Shelf Life