We care about our plants. We care about the food we eat. We care about out environment. But that also means we need to grow healthy plants. Sometimes pests get the better of us and our hands are tied to using pesticides. For the most part, though, we do our best to refrain from using harsh pesticides and instead strike a balance of natural and synthetic controls. Sometimes, however, the feedback to our environmentally responsible methods is far from ideal. There's a perception that plants need to be "perfect" in every sense of the word and any imperfection is negative. The reality is, good bugs aren't much prettier than bad bugs. Insect monitors are ugly in the greenhouse. Does that mean our plants are lower quality or infested or diseased? No. Not at all. So let's delve just a little into the world of insect warfare and to see what I'm talking about.
Who Are You?
The first step in being a responsible grower is identifying the insects that are a problem. Inspecting the plant is one way and we do that all the time. The next most common way is to use indicator cards. Those are those ugly sticky cards than hang throughout the greenhouse with various insects stuck to them. Yes, insects do get stuck to them and we watch what insects are on there and how many. One or two insects in a field is not something that's a problem. It's when the insects get over a certain threshold that they need to be dealt with. It's unfortunate, but some people are totally appalled by the sticky cards and believe that, because they are there, we are a poor grower infested with insects, which couldn't be further from the truth. Incidentally, there are both yellow and blue cards and the colour of the cards attract different insects for different crop, depending on what insects we monitor for.
There are some insects that are more annoying and more visible in the greenhouse. Whiteflies are a common issue in greenhouses, though we have rarely have to spray for them any more because of biological controls. They resemble, well, small white flies for lack of a better description. They love poinsettias and fuchsias and some other plants and hide under the leaves until they get scared away where they can turn in little white clouds surrounding your plant - not good. They suck the sap from the plant and make them look all mottled and not nice. Yuc.
Aphids are another common insect we've been able to get better control over, though we're still working on those buggers. Aphids are incredibly resilient insects purely because of their ability to reproduce so quickly. Not only do aphids lay eggs, they can also give birth to live young. And if that wasn't bad enough, it's also possible for an aphid to give birth to a live young that is already pregnant! How's that for resiliency. Aphids can be black or green, or even a reddish colour. If there are too many aphids in an area or a lack of food, some will sprout wings to fly to another source of food. These insects like to suck the sap on plants and are often found around flower buds and tender new shoots on plants. In the garden, ants will even "farm" aphids since the ants feed on their "honeydew" as a by-product. They will protect the plant and aphids from anything that may want to hurt the aphid. It's the honeydew that can make your plant seem sticky, especially houseplants. It's rather nasty, but can also be quite fascinating.
Looking For A Snack?
We have lots of spiders in our greenhouse, and some real monster spiders at that. The less pesticides we use, the more spiders we have and the more good they do. But the do get big and can be mean looking. Spiders do like to snack on insects, that's for sure.
Ladybugs can sometimes be seen in the greenhouse and they eat other bugs like aphids. Unfortunately, they're also rather dumb and tend to get sucked out of the greenhouse by our cooling fans (stay away from the light!).
Praying mantis also like to eat other insects, but they also eat good bugs. And they tend to wait for the bugs to come to them, so they make a great school project, but not so much of a greenhouse control.
Lacewings are another relatively new insect you see in the greenhouse. It's a flying insect with large delicate wings. The larvae is rather scarly looking and they really move quickly over the plant with a verocious apetite.
Nematodes are used to control fungus gnats in the soil. Those are the annoying insects that look like fruit flies around your plants and they live in the soil. Nematodes are a broad family of small and mostly microscopic worms. They work great for dealing with fungus gnats or even grubs in your lawn, but each nematode is specific to each prey.
The Unsung Heroes
Probably the most common group of beneficial insects are ones that are hard to see. Parasitic wasps probably make us the bulk of these. The wasps are really small and, no, they do not bite us humans. Instead, the female wasp flies around looking for a host - aphid, whitefly, or others depending on the wasp. There are quite a few different parasitic wasps out there. Once they find the host, they quickly stab it and inject one or more eggs into the host. How's that for nasty? The egg typically hatches soon after and the larvae starts feeding on the host - from the inside at that. They will typically hollow out the host, pupate into the adult wasp, then leave the hollowed out mummified remains on the plant.
There are also some very small beetles that can be used in the greenhouse. These guys are the hunters of the insect world searching out things like thrips or whitefiles. Again, each insect has a specific prey or host so there's no single solution for all our insect problems.
The Good, The Bad, The Ugly
Now to make things even more confusing, some beneficial insects look a lot like the insects they're out to destroy. The two-spotted spider mite can be a problem for some plants like Angel's Trumpet or even Strawberries. These little buggers are small - really small, considerably less than a millimetre in size. If you are lucky enough to be able to look close and see them, you can also notice two even smaller dots on their backs, hence the name two-spotted spider mite. Luckily for us, there are quite a few predatory mites that attack and destroy this spider mites. The problem - they look almost the same to the naked eye. Amblyseius are still only 1/2 mm in size and are slightly orange without the two dots. Phytoseiulus persimilis are also nearly the same size, but are more red. We had a good population of these predatory mites on our Easter hydrangeas one year, but they weren't very well received by our customers, unfortunately. There predatory mites hunt out and feed on other mites, and that what's hard since it is a mite eating another mite.
Now for the most annoying insect and it's predator. The mealy bug is a small white cottony looking insect, usually common on houseplants. The insect has a waxy coating making it impervious to many insecticides. It's found on many indoor plants like Palms, Coffee Plants, Citrus, and many others. It's small, fuzzy, and just plain not nice looking and it gives many people the heebie-jeebies. It has a predator as well, though it's less effective than we'd like. This predator simply eats them, but it likes to disguise itself so the mealy bug doesn't know it's coming. How? Well, it just plain looks like a big mealy bug. You would not believe the complaints we have had with these little buggers in the greenhouse. The adults look a little like dark ladybug which, visually are not bad, but they also receive many complaints because they fly around and crawl all over plants looking for mealy bugs to eat. Imagine what Sue thought when I brought home a vial of 500 Cryptolaemus and set them free in our house!
It's All Good
So the next time you wander the greenhouse and see sticky cards or what looks like could be a bug, don't panic. Look closely and ask questions. Sometimes, there are bugs that we haven't gotten which can happen when you are reducing pesticides. Or sometimes those bugs are good bugs just doing their jobs. We all need to realize that not all insects are bad and sometimes it's not so bad living with a few good bugs in your house.
For more reading on the subject, visit the Wikipedia article on Biological Pest Control