The Herbal Insectary (Part Three)

In Part Two of The Herbal Insectary, we talked about ways to handle destructive beneficials like dill and parsley worms in your garden by creating a haven in a perennial insectary created just for them. Plus, we covered a few additional ways to make the insectary an even more appealing place to call home by adding places for them to hide, hibernate, multiply and overwinter. Today, I’ll show you how to deal with destructive beneficials in your garden and how to identify insect allies so you can plan to provide the best insectary possible.

The Three P’s

Beneficial insects are generally recognized as being predators, parasites or pollinators, but the truth is that many beneficials fill more than one role in the garden. Predators prey on bad bugs for food, while parasites lay their eggs in or on bad bugs, which the young larvae consume al la carte. Of course, pollinators can be any insect that moves pollen from flower to flower as they feed or hunt, helping gardeners produce more fruits and vegetables.

Tachinid flies are perfect examples or parasitoid beneficials. These small, quick, and often noisy flies have two very deadly ways of utilizing other insects to feed their young. The first is when the female lays her eggs on leaves that are then eaten by chewing insects or caterpillars. The eggs develop inside their hosts, consuming them from the inside out. The second method the female tachinid uses is to lay eggs on the skin or inject living larvae directly into the host insect. As the young grow, they burrow down into their host, slowly sucking the life right out of them.

A tomato hornworm parasitized by tachinid fly larvae. Image copyright Jill Henderson All rights reserved. showmeoz.wordpress.com

And while each beneficial specializes in one of the three P’s, many fulfill multiple roles as they morph from larvae to adult. And since adults and larvae often look nothing like one another until their metamorphosis is complete, it is important to learn how to identify beneficials in all their forms. Remember that larvae are powerful predators, often consuming many more pests than the adults, and you don’t want to accidentally kill them because you didn’t recognize them.

In fact, some beneficial insects actually look a lot like their pesky counterparts. For example, the spined soldier bug (Podisus maculiventris) looks an awful lot like a destructive stink bug because the two are closely related. Yet, where stink bugs (and there are many kinds) are a hard to control pest, the spined soldier bug is a beneficial eater of Colorado potato beetle and Mexican bean beetle larvae.

Use this short list of some of the more important beneficial insects to search for images of adult insects and their larvae that you may find in your garden and herbal insectary:

Braconid and Ichneumonid Wasps (Hymenoptera)
Damsel Bugs (Heteroptera)
Earwigs (Dermaptera)
Ground Beetles (Coleoptera)
Lacewings (Neuroptera)
Ladybugs (Coleoptera)
Mantids (Mantidae)
Mealybug Destroyers (Coleoptera)
Minute Pirate Bugs (Heteroptera)
Soldier Beetles (Coleoptera)
Spiders (Araneae)
Syrphid and Hover Flies (Diptera)
Tachinid Flies (Diptera)
Trichogramma Wasps (Hymenoptera)

Protect Your Assets

An insectary is a place for beneficials to find food, shelter and water, but they also need your protection – both inside the insectary and throughout your vegetable garden and orchard. Almost all pesticides used in-season will kill good bugs and bad bugs without discretion. And don’t think that just because you only use organic insecticides that your beneficials are safe from harm. After all, beneficials are insects, too.

If you feel that you absolutely must use some type of insecticide to control a pest in the garden, focus on those that do not have an immediate “knock down” effect. Pyrethrum, pyrethrins (along with the synthetic pyrethroids), nicotine and rotenone are all examples of extremely powerful organic insecticides that kill or permanently paralyze insects on contact, including beneficials.

The same is true for seemingly innocuous products like insecticidal soaps or lightweight horticultural oils meant to suffocate eggs, larvae and scale-type insects. Use these products with caution and apply them only to the target pests early in the morning or late in the evening to avoid injuring beneficials, which are more active during the warmer daytime hours.

Growing cabbage under netting protects beneficial insects by eliminating the need to use pesticides in the garden. Image copyright Jill Henderson showmeoz.wordpress.com

A few relatively safe insecticidal options are available to the organic gardener wanting to protect as many beneficials as possible. Pure neem oil used as directed (see product label) and applied with precision to foliage only (avoiding flowers) is an excellent option because it only affects insects that eat the treated vegetation.

Microbial insecticides are another organic option for treating insect pests while protecting beneficials. According to the Clemson University Cooperative Extension paper HGIC 2770, entitled Less Toxic Insecticides, “Microbial insecticides contain microorganisms (viruses, bacteria, fungi, protozoa, or nematodes) or their by-products. …Insecticidal products comprised of a single species of microorganism may be active against a wide variety of insects or group of related insects (such as caterpillars) or they may be effective against only one or a few species. Most are very specific. Since there is such a narrow range of insects killed, they spare the beneficial insects almost entirely.”

As a gardener, I know how difficult it is to resist the temptation to address pest issues in the garden with a “magic bullet”. Yet, in the 25 years I’ve been an organic gardener I have had few issues handling pests without the use of insecticides of any type. Handpicking pesky hornworms, using spun-bonded polyester fabrics and screens to keep pests off target crops and the use of pheromone traps, scent deterrents and interplanting vegetable and fruit crops with fragrant deterrent plants and herbs have always done the job well enough.

And once my garden was free of indiscriminate insecticides, the beneficials arrived in droves and are now a permanent part of the landscape. Even the tomato hornworms are kept to minimum by parasitic flies that I never had before.

Beneficial insects are a boon to gardeners and food producers everywhere. And with the rising incidence of insecticide resistant species and the decline of pollinators and other beneficial insects due to overuse of potent chemical insecticides, the herbal insectary may be one of the best investments you will ever make in the garden and, perhaps, the world.