Predatory Bugs

May 8, 2025

Status: draft

This post documents my experience using biological control methods against thrips. I focus on growing cacti, which creates a challenge: most predatory insects need high humidity, while cacti require drier conditions. Though I’ve only dealt with thrips, these observations might help with other pests.

I’ve tried Neoseiulus (formerly Amblyseius) californicus and cucumeris, but it’s hard to say how well they performed. I suspect the relative humidity in my apartment and in my tents is too low; at least 60%, ideally 70% is recommended. I got some californicus because they should tolerate lower humidity, but thrips are not their preferred prey (they are better for spider mites, for example).

Then I tried Chrysopa (lacewing) larvae. They did seem to eat some thrips nymphs (I actually have video proof of that), but I have the feeling they like eating each other even more. They were really fun to watch, but eventually I felt that it was expensively fun.

In February, I got 100 Orius. They are small, very fast, and can fly, so I was not able to watch their behavior as I could with the Chrysopa. I moved a few weeks later and didn’t find any Orius in the new apartment. I believe I had too few thrips for them to settle, and I did not provide any additional food. As a result, they probably died of cannibalism and then hunger.

In late March, the thrips infestation got quite bad. On a whim, I decided to buy 2,000 Orius nymphs as well as Ephestia (flour moth) eggs to feed them. I got some supplies to try to replicate the breeding setups I found in some research papers, with the goal of keeping them alive and breeding separately from the plants. I think I put around a third to half of them in petri dishes and a larger plastic box, and released the others around the plants. A week later, I had adults in the enclosures, but they soon died because I did not maintain humidity.

However, the ones I released in my tent of Trichocereus seedlings matured and actually bred. In mid-April, I found newly hatched nymphs. I’m writing this in early May. I’m still seeing young nymphs, and I don’t know whether they hatched later or if they are the third generation.

I haven’t seen any thrips on my Trich seedlings or nearby plants for a week, ever since I watched an Orius nymph eat an adult thrips (I actually managed to make two videos of that, totaling more than one hour until the nymph threw the carcass away).

In my experience, Orius were definitely worth it, but only combined with Ephestia eggs. My plants are in open grow tents. It would be even better in an enclosed cabinet. I’m not sure how well it would work if the plants were fully in the open.

My plan now is to grow pepper plants and keep a few of them in a tent. This is known as keeping “banker plants”: plants that you maintain to support a population of predators to protect other plants. Orius can thrive on sweet pepper plants, feeding on nectar and pollen.

If I had known from the start what I know now, the total cost would have been around 60 euros: 30€ for 100 Orius and shipping from Rootsum, plus 30€ for Ephestia eggs and shipping from Bioplanet. See below for links to suppliers.

I don’t think I would recommend predatory mites for cacti and succulents because of the high humidity requirement (except for Amblyseius degenerans which are expensive – in France at least – and which I haven’t tested). However, I’ve been keeping cucumeris in my humid propagator where I have seedlings, and Stratiolaelaps scimitus could be good for soil pests when you can keep the substrate moist, like for seedlings. I don’t have anything to share regarding their effectiveness.

Chrysopa larvae might be worth it, especially if you have other issues besides thrips: they are more generalist, being particularly effective against aphids and mealybugs. Thrips and spider mites are secondary prey for them.

Some things I should mention:

  • Orius can bite humans; it happened to me twice: sharp, non-lasting pain. Nothing special when you regularly get pricked by cacti. From the research I did, there don’t seem to be any risks involved, but maybe some people can have allergic reactions.
  • I believe predatory mites can cause allergic reactions similar to common house dust mites.

Resources

Genna’s videos

Breeding mites

Thrips (focused on biological methods but not exclusively)

Where to buy

Western Europe

Rootsum (Belgium, ships to France, Luxembourg, Netherlands)

They are the cheapest option I know of for small orders of Orius, mites, and Chrysopa. They usually send orders the same day and I receive them the next day.

I only had an issue once: they sent the package to me by mail, just before Easter public holidays. Only 4 or 5 Orius out of 100 were still alive. I called them and they immediately shipped them again, this time via express UPS shipment.

Bioplanet (France only)

This is where I got the Orius nymphs. Cheaper than Rootsum for larger amounts of bugs, but expensive delivery. I believe their customers are mostly professionals. They sell Ephestia eggs.

Orders must be placed before Monday morning for delivery on Wednesday or Thursday.

Crisop (France, ships to Europe)

They sell Koppert products. I only bought Ephestia eggs from them, which came with cold packs, but the delivery was quite expensive.

They ship to Europe, but there are probably cheaper alternatives outside France.

Banker plants

Small overview of the principles of growing banker plants: https://www.canr.msu.edu/news/common_banker_plants_in_insect_biological_control_systems

Papers