Tips for Organic Gardeners to Control Bugs in the Greenhouse

BC Greenhouse Cottage in White set in a garden

Success in the greenhouse is simple

The doorbell rings and the Purolator truck pulls away as I open the door. A shoebox-sized package is waiting on my step: my greenhouse bugs have arrived!

Package of greenhouse bugs
A showbox sized package of greenhouse bugs on the front steps

It is officially spring and I am busy seeding vegetables and flowers and transplanting strawberries in my greenhouse. It is spring break so the grandkids have joined me, helping me plant strawberries, so we make a video in my Greenhouse Garden. But in really big news 1100 bugs have just arrived!

Populations of flying, crawling, breeding bugs are going through the roof in my greenhouse and I am a happy camper. Sort of. Some of the bugs in my greenhouse are my friends and some are a nuisance. To balance the populations I occasionally order more of the good bugs and that’s what has just arrived. The Encarsia formosa and Delphasius catalinae are here to parasitize and eat whiteflies and I am heading up to the greenhouse to release them. (Source

If you an organic gardener, curious about bugs in your greenhouse, here are some of the ways you can control them. If you are a greenhouse grower who prefers spraying chemicals you are on your own. Adding beneficial bugs is a waste if you spray because sprays of all kinds will damage both the good guys and the bad guys.

Climbing Cutworms:

Big fat greasy-looking larvae climb out of the soil and up into my plants at night where they gnaw at my bok choi and cauliflower leaves. Similar to cabbage worms, but twice as fat, they are easy to spot and handpick. At night in the greenhouse, I pick them off and squish them with my shoe. I removed 20 last year and 9 so far this year. I think they are all gone now because I haven’t seen any for a few weeks. Problem solved. PS if you are squeamish about picking and squishing bugs use nematodes to do your dirty work:  (

climbing cutworm
climbing cutworm


Spider Mites:

These are the very tiny – almost invisible guys that eventually speckle and web leaves. Mites travel on the wind and on animal fur and clothes so they come in with new plants and with people.  Accidentally carrying in mites on your sweater from your living room palm tree to your greenhouse is the most common way they spread.

spider mites

Bean leaves full of spider mite webbing


If you think you eliminated spider mites last fall, think again. They go dormant over winter, hiding on the frames and ledges in your greenhouse and reappear with longer, sunnier days.  See photos here:

Luckily spider mites are super easy to spot and deal with. I bought spider mite predators (Persimilis) a couple of years ago and now I use a hand lens to check on new plants before I bring them into my greenhouse.



Last year I bought a single pepper plant and it was covered with aphids in a week. Luckily the hungry orange larvae of Aphidoletes ate the aphids like lions on a gazelle in the Serengeti. These immature bugs eat their heart out and when I see them on my plants I celebrate.

Like flipping a switch, warmer spring soil means a big hatch of aphid predators. I start seeing the long skinny legs of Aphidoletes as they emerge in my greenhouse every spring. These good bugs look a lot like tiny mosquitos and they thrive in my greenhouse, always on the look-out for aphids. It’s been a while since I have seen aphids, but you never know.

Last year I bought a single pepper plant and it was covered with aphids in a week. Luckily the hungry orange larvae of Aphidoletes ate the aphids like lions on a gazelle in the Serengeti. These immature bugs eat their heart out and when I see them on my plants I celebrate.

Aphidoletes are strong flyers, and nothing escapes their x-ray vision. I rarely see aphids anymore because these predators are so efficient and so universal. They are found naturally outdoors around the world, but of course we need a supply of predators in our greenhouse early so I am glad they love my greenhouse and live here year-round.


For some reason I have whiteflies in my greenhouse this year and they are super noticeable because #1 they are white and #2 they don’t move until you touch or move the plant.

I think whiteflies survived over winter on snapdragons I left in the greenhouse. I left the snapdragons in place because they are so hardy and they bloom early in spring. Apparently they have also been providing an overwintering site for whiteflies and now with spring here, whiteflies are everywhere.


Aphidoletes - nothing escapes their x-ray vision


So this week I ordered insect to control whiteflies. The super cheap Whitefly Preventor (Encarsia formosa) come in packs of 1,000 pupae. The more expensive Whitefly Predator (Delphastus catalinae) are sold in bottles of 100 hungry beetles.  The predator physically eats all stages of whitefly it finds. The beetles are scavengers and ravagers. No whitefly is safe in their presence. The cheaper parasites emerge and look for mature whitefly pupae to attack. Parasites and predators are the one-two punch needed to eliminate whitefly.

The Big Picture:

Except for the new problem with whitefly I have been mostly pest free in my greenhouse for four years and this is because the predators and parasites I ordered years ago keep thriving in my greenhouse.

Buying bugs for your greenhouse is a fantastic way to control insect populations before they become outbreaks.



Small black beetles (Delphastus) eat all stages of whitefly on plants.

Encarsia (white fly parasites) are raised on tabacco leaves. The black dots are the pupa.
Lacewing Larva are a great bug for your greenhouse - it eats all the bad guys!

I am happy to spend a few dollars to control a crowd of bugs before it becomes a mob. I also know, from experience, that certain plants – like green beans – are better left to outdoor gardens. The conditions in your greenhouse are perfect for spider mites and their favourite food is green beans. This is why the international commercial suppliers of bugs – like Applied Bio-nomics in Saanich, BC raise their predator mites on green beans and ship them to you that way. Avoid the plant and you’ll avoid the bug. At least for now.