Waging War Against Pest Insects

Compiled by Lee Spindler

Fight fire with fire, not chemical warfare. Controlling pest insects these days using chemical sprays have caused a great amount of concern to both gardeners and consumers in general. Concerns that involve our environment, the health of our children, pets and for the gardeners themselves who are dispensing such chemicals or are working with the plants after they have been sprayed. Unfortunately, many of these chemicals are "non-selective" in other words, they don't just kill the target pest, they tend to kill an entire range of insects, both good and bad.

Today's biggest concern is where toxic products are applied to products that are grown for human consumption. As a result, many indoor gardeners have turned to using beneficial insects to control their pest problems.

Just what are "beneficial" insects? Beneficials are insects that help gardeners by killing pest insects and eliminate the need for using toxic chemicals. Mother Nature has developed her own system to balance out or regulate pest infestations, by using the "good bugs" to control the "bad bugs".

Beneficial insects eliminate pest insects generally in one of two ways. They either parasitize them or they are a predator of them.

Parasitic beneficial insects actually depend on pest insects for their survival because they must lay their eggs in or on them. The immature stages of the beneficial insect actually develop in or on the "host" pest insect, feeding on its body and thereby killing the "host".

Predator beneficial insects are beneficial insects that actually eat the pest insect. Therefore, they actually depend on the pest insects for their survival.

Some of the most effective beneficial insects are a group known as parasitic wasps. These wasps usually lay their eggs inside a specific pest, while the pest is very young - in the egg, larval or pupal stage of their life. These wasps are incredibly tiny, generally not even one-tenth the size of the wasps that will sting you and are almost impossible to see with the naked eye - the largest parasitic wasps are generally no bigger than a 1/4 of an inch and the smallest being the size of the period at the end of this sentence. The "host insect" generally are not as lucky as we are, for the wasps' larvae develops inside the pest, the pests die and then the wasps thrive and emerge looking for a new host in which to lay their eggs and continue on the cycle.

Most wasps seek out only one species of pest, for instance Encarsia Formosa, seeks out only the whitefly eggs. Encarsia lays eggs inside the whitefly eggs (this is when the whitefly is at an immobile stage). When the Encarsia eggs hatch, the larva feeds on the whitefly embryo, then forming a pupae inside the whitefly egg, killing it if they hadn't already. The adult Encarsia wasp emerges from the whitefly egg casing by chewing an exit hole and flies off in search of a new host to lay its eggs. A female Encarsia can lay between 50 to 100 eggs in a lifetime - which is excellent when you consider that their "lifetime" is only two to three weeks.

In order to keep these beneficial insects in your greenhouse you need to supply them with the essentials for life; food and water. Generally most parasitic wasps like nectar, the sugary fluid secreted by flowers. If the wasps have the essentials for their survival, they will live longer and thus seek out more host insects to lay their eggs, thus eliminating more pest insects, as well creating successive generations of biological control.

Remember that the smaller the wasp, the greater the need for plants with small flowers, where the nectar is easier for the wasp to get at. A great plant to grow for beneficial wasps is dill. Even though the plant grows tall, it has hundreds of tiny flowers clustered together which make the nectar in these tiny flowers easy for tiny wasps to flock to. Other good plants to grow to help keep beneficial wasps around are fennel, caraway, parsley and coriander. I took a close look at my parsley plant just the other day. The flowers were emerging on some of the stems and it had three ladybugs crawling on it, feeding on the nectar - and hopefully other pests that had also took up residence. In a period of five minutes while I was sipping on a cup of tea, the parsley also had three bumble bees visit it. Keep in mind my parsley plant is out of doors, however I will be planting one in my newly constructed greenhouse!

Parasitic wasps visit the tiny flowers for nectar, but the predator insects also stop by to eat the pollen, especially juvenile and adult ladybugs and lacewing.

Another beneficial insect that works by parasitizing its host is the Beneficial Nematode.

Nematodes migrate through growing medium finding insect larvae by detecting either a slight increase in temperature or release of methane gas. Once they have found a "Host", the nematode enters the host body through natural openings such as the mouth. Once inside the host, they release a symbiotic bacteria that paralyzes the host and kills it within 24 - 48 hours. The nematodes feed on the bacteria and the decomposed host tissue where they reproduce until their numbers drive them out to find a new host. Larvae nematodes can survive without a host for up to a year provided moisture levels and temperatures remain favorable for them.

Nematodes require a moist, dark environment. Provided soil temperatures are kept consistent for indoor growing, you will not have to worry about the nematodes hibernating. It is only when there is a drop in temperature during the the winter that nematodes will burrow deeper in the soil and begin hibernation; as temperatures rise in the spring they move closer to the soil surface. Unfortunately, their return usually lags behind that of soil pests. So for the most effective control re-introduce beneficial nematodes early each spring or each time the growing medium is changed.

Beneficial Nematodes will control over 250 different species of soil pests including some of the most damaging, like weevils, wire worms (particularly damaging to new plants), fungas gnats, grubs, earwigs, sow bugs and pill bugs. The majority of soil pests can be controlled with regular applications of beneficial nematodes, in the spring and fall or each time the growing medium is changed.

Predators also include Mites. Two-spotted Spider Mite is generally a huge problem for indoor growers. They have a lifecycle of 15 days, but can reap an incredible amount of damage in that time - as well the female can lay a further 50 - 100 eggs. All stages of spider mite development cause plant damage, by the spider mite feeding on plant cells. The cells will turn yellow which cause a speckling of the leaf. When the damage is increased the leaf will turn completely yellow and die off. If you believe you have spider mites, you can generally find them by looking on the underside of your plants leaves. When you start to see webbing on the plant, it means that your spider mites have reached infestation levels.

But incredibly, one of the best controls for spider mites is a predatory mite - Phytoseiulus Persimilis. Persimilis is a red pear-shaped mite with long legs. Be careful not to confuse summer spider mites that turn orange or deep when they hibernate with Persimilis.

An adult Persimilis will eat 5-20 prey (eggs or mites) per day. What makes them so effective against spider mites is that they reproduce more quickly at temperatures above 28°C (82°F) than the spider mite and they feed on all stages of the pest spider mite. However, Persimilis must have high humidity temperatures - above 60% , which also affect the pest spider mite to reduce their egg laying.

Persimilis are very voracious and have one of the highest consumption rates. Almost 75% of European greenhouse vegetable production relies on Persimilis for spider mite control, and the California strawberry industry also use this species for control. Persimilis is also used in interior plantscapes and conservatories and greenhouse ornamentals growers have long relied on their ability to control pest spider mites.

Because these mites are such efficient hunters and dispersers, they can cause extinction of their spider mite prey, which is extremely desirable where little or no spider mite damage can be tolerated, such as in ornamental plants. Typically, Persimilis will eventually exhaust their food supply and starve and so it must be reintroduced when new spider mite infestations occur.

Another excellent predator for spider mite is the predatory midge, Feltiella Acarisuga. This midge is about 1/12 of an inch long and is a pinkish brown colour. The female Feltiella will lay its eggs inside the spider mite colony and as soon as the young larvae hatch, they begin their feast on spider mite eggs. The young larvae feed mainly on the eggs while the older larvae feed on all stages of spider mite. A larval Feltiella can feed on about 50 spider mites before pupating. The lifespan of the Feltiella from egg to adult is 10-15 days and the female will lay about 12-14 eggs. Like Persimilis, when the food supply is exhausted they will also starve and thus must be reintroduced when new infestations occur.

Some of the best beneficial predators to purchase are the ones that will stay around after you release them - especially the ones that haven't developed their wings yet.

Voracious aphid eaters are lacewing larvae and ladybug larvae, these are such good eaters because in essence they are teenagers with huge appetites and are not yet sexually active and distracted from the task of eating! These larvae generally stay and "clean-up" much better as they are only able to crawl in search of their meal, and they haven't developed their wings to fly away in search of a mate. The adult ladybug will eat the aphids, however as lacewing become adults they become strictly pollen feeders.

For gardeners the best control recommendation is to use a combination of controls i.e. parasite and predator for control of a problem. An excellent example is aphid control: use adult ladybugs to eat the adult aphids, as well to lay eggs in the colony of aphid eggs, but also use Aphidius Colemani (a parasitic wasp) to control the eggs and larvae.

And most important of all when using beneficial insects, avoid using pesticides as they will adversely affect both the beneficial insects and the pests.