Caterpillar droppings do affect plant growth

[John Beaulieu]

The question posted in the Conservation file reminded me of a little experiment that I did this summer. Since a lot of Monarch caterpillars munching on milkweed in a pen or old aquarium produce a lot of frass (droppings), I wondered if this Monarch manure was of any value as a plant fertilizer. After all, look at worm castings and how useful they are.

I grow plants of the Gesneriad family, which includes the African-violet. I had a number of Sinningia seedlings of equal size and thought that they woud be good for this test. All seedlings were potted in a regular soil-less mix (Pro-mix BX) but half the seedlings has Monarch manure added to the mix. All other conditions and care were the same.

After a coupe weeks it became clear that instead of helping the plants by providing extra nutrient, the exact opposite was happening. The plants with Monarch manure became stunted and pale. I guess the chemicals that make the caterpillars distasteful also hinder the growth of other plants. When I repotted the suffering plants into the mix without manure, they recovered and began to grow normally.

I thought I would mention this in case anyone else gets the idea to sprinkle the frass on their houseplants.

John

[Keith Petrosky]

If im correct, one of the pots used with monarch manure has an albino leaf! Thats cool looking! I would definetly save that plant, mabye try to clone it. Tons of people would buy an albino african violet.

[psi_chemie]

How much did you use? If the mix was really strong, it may have been too much.

[John Beaulieu]

It was a light sprinkle of the frass, mostly on the surface, so that top watering would wash down nutrients further into the mix with each watering. The results were not the same as if it were fertilizer burn from too much.

The white plant was not albino or showing variegation. Normal colour returned (with normal growth) after being repotted in plain potting mix with no frass.

These gesneriads are sinningias, not African-violets. The gesneriad family does include AVs as well as other popular plants such as Goldfish Plant (Columnea), Lipstick Vine (Aeschynanthus) and the Florist Gloxinia (with is a sinningia too). Sinningias are a tuberous plant which resprout after a dormant period.

I will try some further tests next summer, with varying amounts and other plants.

John

[Teresa]

Very interesting!! I'd never have thought to try that.

[harpo787]

Is it safe to assume that the droppings that fall where they may are not harmful for the health of the plant?

I guess I'm asking do I need to keep the leaves fairly clean of frass? It sounds like from the experiment conducted above that I should certainly try and keep the base of the plant clear of frass, because since they are on the soil surface, they will drop their "nutrients" into the soil upon watering.

[John Beaulieu]

It's only a guess, but I think the droppings would have no effect on the milkweed plant, since the toxic chemicals came from the milkweed. In nature this might dicourage other plants from crowding out the milkweed patch. Of course in nature we do not see the frass in the concentration that we get in our rearing containers.

John

[freda]

Thanks, John for the tip. After changing caterpillar bedding for a week now I had the same thought: "this stuff must be good for something!" I began adding it to my compost box. After reading about your experiment I'll leave it alone. Thanks!

[margaran]

One thing to consider is that infection is spread via frass. I used to keep the frass on the MW with good effect to the MW. The problem is that when the cats crawl around (to switch stalks or go walking), they can become contaminated and get sick.

Maggie

[Lindabird]

Thanks for sharing the findings of your experiment John. Last year I threw all of the frass in a flower bed outside my backdoor because I thought it would be a great fertilizer too. I can't say that it has had any effect on my plants. However, it was a larger area and not as concentrated as your potted plants.

It's nice to know what you found though. Thanks!

Linda

[mommalepapillon]

John,
Your postings are so interesting and useful to this site. Thanks!!

Christine
Sutton NH

[laurel]

This experiment is really interesting. While I haven't done any formal experimentation, I've noticed that Monarch frass seems to have a fabulous growth effect on the my milkweed plants. It makes sense that as the plants and the butterflies evolved together, the plants would benefit from the caterpillar droppings, otherwise the milkweed would not have flourished. Most animal-plant relationships in nature are symbiotic.

So why did your African violets do worse with frass? I'm not sure exactly, but knowing that different plants have different nutrient requirements, I will guess that the nutrient content of Monarch frass does not meet the needs of the African Violet, which is native to Tanzania, Africa - a region that does not have Monarch butterflies.

I would be curious to know the mineral/nutrient content of Monarch frass, as compared to the nutrient requirements of the Violets. Once the nutrient content of the frass is determined, the experiment could be repeated on plants with similar requirements. Or the experiment could be repeated with plants that grow in the same environment as Milkweed.