Battle of the Bugs: A Guide to Beneficial Insects

Nothing disturbs the production of a flourishing garden or the disposition of a horticulturalist like pest insects. These nasty buggers can wreak havoc on a plant’s ability to perform while frustrating the gardener into a frenzy of despair. Most gardeners’ first reaction is to buy an insecticide. Don’t get me wrong, there are some great insecticides on the market; however, before you reach for that can of poison, consider some recruiting beneficial insects to do the job for you.

Beneficial Insects in Nature

Horticulturalists who have grown plants both indoors and outdoors notice a difference in terms of pest insects. Indoor infestations are generally much more destructive and overwhelming than outdoor pest problems. The reason for this is nature’s natural predators. Indoor gardens are safe havens for pest insects, whereas pest insects in outdoor gardens are subjected to predatory bugs, birds and other critters that keep their populations in check.

Some insect predators are actually drawn to plants by pheromones produced by the pest insect and/or the plant itself. Nature is a diverse and powerful force that provides balance in all ecosystems. This balance can be used to a horticulturist’s advantage: For every pest insect there is at least one predatory counterpart that can be introduced into a garden in order to naturally battle the bothersome bugs. Here are a couple examples:

Pest Insect: Spider mites

Beneficial Insect: Predator mites (Phytoseiulus persimilis, Mesoseiulus longipes, and Neoseiulus californicus)

Most gardeners would agree that the worst of the worst pest insect is the spider mite. This is especially true in indoor gardens or greenhouse environments, where entire crops can be wiped out in a matter of days. There are some effective predatory insects that can be used to combat these relentless bugs and the three species of predatory mites (listed above) are the most effective at treating a spider mite problem.

Most beneficial-insect suppliers will offer a combination of these three predator mites in one package. This is helpful because they all reproduce in slightly different environmental conditions. In introducing all three predator mites simultaneously, the hope is that at least one of the species will find the garden’s environment suitable for reproduction. Of the three, Mesoseiulus longipes is probably the most suitable for an indoor garden. They have the widest range of preferable humidity and temperature. Most importantly, they find lower humidities - which are generally found within indoor gardens - suitable for reproduction.

Pest Insect: Spider mites

Beneficial Insect: Spider mite destroyers (Stethorus punctipes)

The spider mite destroyer is another excellent defense against the infamous spider mite. These tiny beetles are related to the ladybug and feed specifically and exclusively on spider mites. Spider mite destroyers are best used in conjunction with the predator mites due to a long establishment time.

These tiny workhorses will eat around 50 spider mites a day and adult females will lay up to 15 eggs a day. The total life cycle (from egg to adult) of a spider mite destroyer is around 18 days, with a total life span of about eight weeks. When established, spider mite destroyers will reproduce at a rate that is fast enough to destroy a spider mite infestation, hence their appropriate name.

Pest Insect: Thrips or Fungus gnats

Beneficial Insect: Predator nematodes (Steinernema nematode and Heterorhabditis nematode)

Besides being a huge nuisance, thrips and fungus gnats have something else in common: they both rely on soil or medium for a portion of their life cycle. A great way to treat any pest insect that lives a portion of their life cycle in the medium is to use predatory nematodes. Predatory nematodes are tiny, worm-like creatures that feed on the eggs and larvae of soil-born insects.

As soon as any signs of thrips or fungus gnats appear, predatory nematodes should be watered in to the medium. Most beneficial insect suppliers sell a combination of both Steinernema and Heterorhabditis nematodes because they work at different depths in the soil. Combined with sticky traps to catch adults, predatory nematodes are an effective and non-toxic option for completely eradicating a thrip or fungus gnat problem.

Pest Insect: Whiteflies

Beneficial Insect: Whitefly parasites (Encarsia formosa) or Whitefly predators (Delphastus pusillus)

Whiteflies are one of the easiest pest insects to identify. If you have an abundance of tiny white bugs, you guessed it, they’re whiteflies. Whiteflies themselves do little damage to the plants and are more of an annoyance than anything. When left untreated, however, the honeydew that the whiteflies deposit on the plants will eventually grow a pathogenic black mold that is detrimental to the plants.

Whitefly parasites are a grower’s best defense against these annoying buggers. A whitefly parasite deposits its eggs in developing whitefly pupae. When the egg hatches, a whitefly parasite comes out instead of a new generation of whiteflies. This cycle continues until the whiteflies have been eradicated. Whitefly parasites work best on greenhouse whiteflies (the most common variety), but also work well on sweet potato whiteflies and other whitefly varieties.

If you have a sweet potato whitefly problem, it may be beneficial to use whitefly predators. These beneficial warriors consume 200-800 whitefly eggs per day and prefer the eggs of sweet potato whiteflies (but are generally less effective on greenhouse whiteflies).

Pest Insect: Aphids

Beneficial Insect: Aphid predators (Aphidoletes aphidimyza) or Aphid parasites (Aphidius matricariae)

Gardeners with greenhouses or indoor gardens find aphid predators extremely effective against aphid infestations. A single release of aphid predators is usually sufficient to establish a population, but it can be advantageous when experiencing large aphid problems to release aphid predators a few times throughout the plant’s life cycle. Another choice for an aphid problem is aphid parasites, which act as an effective control and preventative measure. Aphid parasites lay their eggs inside living aphids, essentially destroying the aphid internally until they hatch from the remaining insect carcass.

General Predatory Insects

General predatory insects are insects that feed on a variety of pest insects. These opportunist bugs are some of the most common and most effective insects released in gardens for biological control. Below are a few examples:

Pest Insects: Thrips, Aphids, Mealybugs and Whiteflies

Beneficial Insect: Green lacewing larvae (Chrysopa rufilabris)

Adult green lacewings feed on nectar and pollen, but their larvae are ferocious predators that feed on a variety of pest insects. Green lacewing larvae are true opportunists and will feed on any insect, larvae or egg that they can inject with their paralyzing venom. These tiny creatures suck the life out of helpless pest insects at an extremely fast rate. Most beneficial insect suppliers will provide green lacewing eggs, which can be distributed evenly throughout the plants. When the eggs hatch, the tiny larvae will search and destroy, traveling up to 100 feet to find their first meal.

Pest Insects: Thrips, Aphids, Whiteflies, Fungus gnat, Mealy bugs and Spider mites

Beneficial Insect: Praying mantis (Tenodera sinensis)

The praying mantis is the ultimate opportunist beneficial insect. These awesome bugs will eat anything they can catch. Praying mantis egg sacks can be hung within the garden’s environment to promote hatching. When the egg sack hatches, over one hundred miniature mantises will release their carnage on any and every pest insect they encounter.

The tiny warriors will grow into adults over a three to four month period. Mantises are very elusive creatures, so don’t be surprised if you don’t see many after they hatch. A praying mantis will wait patiently, sometimes for hours, until an appetizing insect wanders by. Then, the mantis will pounce on its prey and devour it. Adult mantises are often very territorial and a single adult mantis can claim a fairly large area as its exclusive hunting grounds. Also, mantises feed entirely on other insects making them a great choice for any enclosed garden space.

Pest Insects: Thrips, Aphids, Whiteflies, Fungus gnat, Mealy bugs, and Spider mites

Beneficial Insect: Ladybugs (Hippodamia convergens)

Of all the beneficial insects available to gardeners, none are as versatile or popular as the ladybug. Don’t let their reputation as a cute and cuddly insect overshadow their destructive power. Ladybugs are actually tiny beetles who, like the mantis, feed only on other insects. A ladybug’s favorite snack is aphids, but these opportunists will eat virtually any insect they can fit into their tiny jaws of death.

Ladybugs eat thousands of insects in their lifetime (about one year). Another great thing about an established ladybug population is that the larvae are just as carnivorous as the adults. The little larvae resemble tiny alligators and will feed on pest insects’ eggs and larvae.

In outdoor gardens, however, ladybugs tend to fly away to their preferred food source so getting them to establish on the plants can be a little tricky. A sugar water solution can be sprayed on the ladybugs to “stick” their wings together for a few days.

This is generally long enough to get them to establish on an outdoor crop. Ladybugs can also be stored at under 50ºF (10ºC) - where they’ll enter a dormant stage for multiple weeks at a time. This allows a gardener to release adult bugs intermittently in their garden while storing the remaining bugs in a refrigerator. In some cases, ladybugs that are released intermittently will establish and reproduce better than those that are released all at one time.

Pest Insects: Thrips, Aphids and Spider mites

Beneficial Insect: Pirate bugs (Orius insidiosus)

Pirate bugs are good to try when other treatments have failed. These beneficial insects feed on thrips, aphids and even spider mites. They feed on multiple stages of pest insects life cycles (eggs, larvae and adults), making them a popular choice for thrip and spider mite control. However, the adult pirate bugs will also bite humans, beware if you release a large population. Their bite is harmless, but annoying just the same.

The Benefits of Beneficial Insects in the Garden

The implementation of beneficial insects offers a naturalistic approach to solving the ongoing pest insect problems associated with horticulture. There are many advantages to such biological control methods, but the largest advantage is probably the removal of pest insects’ resistance.

Any grower who has used chemical insecticides over a period of time only to see the pest become immune will attest to the ongoing anguish of that battle. However, an insect cannot build a resistance to being eaten.

By using nature’s solutions, a grower can save their crops from devastation, relieve their frustration and feel good knowing they aren’t contributing to the creation of resistant “super” bugs.