Beneficial insects necessary in the garden

May 20, 2004
Victoria County Master Gardener

This column's monthly Ground Rules and Tools article, published on May 6, provided information on maintaining the balance of good and bad insects in the environment. Integrated Pest Management, or "IPM" for short, was also discussed, stating the various management control options that can be used to control pests. In particular, non-chemical cultural control addressed planting or positioning "trap" plants, and also eliminating mosquito breeding by constructing controlled water features. The article strongly encouraged avoiding chemical control, or pesticides, if possible. Or, if necessary, at least first selecting those that are the least toxic.

Now let's go further to look at the ways insects are beneficial to the garden and which pesticides can be used, if absolutely necessary.

As any gardener can attest, insects can be a real pain when we're trying to grow beautiful, tasty vegetables, or when we're sprucing up our landscapes. However, some of these insects that we so flippantly label "pests" are actually ones that could be helping us with our problems. People have gone to great lengths and expense to destroy insects, only to later learn that the destroyed insects were not only harmless, but were actually engaged in saving their crops by eating destructive insects.

Insects are beneficial to the garden in the following ways: Insects aid in the production of fruits, seeds, vegetables and flowers by pollinating the blossoms; in fact, insects pollinate most common fruits. Many vegetables also require insects to carry their pollen before their fruit will set, and many ornamental plants (such as chrysanthemums, iris, yucca and orchids), both in the greenhouse and outdoors, are pollinated by insects.

Beneficial parasitic insects (small wasps) destroy other injurious insects by either laying their eggs in insect bodies or actually living on the injurious insects. This is the method now being promoted and researched as a possible solution to the fire ant problem. Some insects are beneficial in that they destroy various weeds. Insects also improve the physical condition of the soil, as well as act as scavengers by burying carcasses and dung.

There is no better control of injurious insects than insects fighting among themselves. Some common "natural" enemies for insect pests are often referred to as "biological control" and are as follows:

·  Trichogramma wasp - these tiny wasps attack the eggs of more than 200 pest species, including cutworms, armyworms, fruit worms, and many moth eggs deposited in orchards and field crops. Results depend on several factors, such as timing, species of the wasp, environmental conditions, and placement of wasps near host egg masses.

·  Green lacewings - their larvae prey on many garden pests, including aphids, spider mites, leafhoppers, thrips, moth eggs and small larvae. Lacewings when introduced to the garden must have an ample food supply or they will leave.

·  Praying mantis - the drawback, if any, with praying mantis is that they are cannibalistic immediately after hatching - so few nymphs survive the first week of life. The praying mantis is a voracious predator, but is somewhat lazy and will not search for food but will wait for the prey to come to it. Food preferences include grasshoppers, crickets, bees, wasps and flies.

·  Lady beetles - aphids are the preferred host here but they also enjoy mealy bugs and spider mites. Lady beetles, like lacewings, will leave the area if there is not an ample food supply of live munchies.

Because of the importance of beneficial insects, it is vital to limit the use of pesticides and look for more earth-friendly, safer insecticides along with using other integrated pest management principles such as cultural, biological and mechanical control. Irrational use of insecticides to kill off the "bad insects" may unfortunately eliminate many of the "good insects" also. Several garden centers sell beneficials or can order them. The timing of their release with their food supply, your pest problem, is very critical. While purchasing beneficials is an option, research has shown that the best advice is to manage your environment to increase the numbers of beneficial insects that are native or naturally present and use the least toxic measures to control pests, thereby increasing the population of native beneficials to do the work for you.

Next time you think you need a pesticide, research if you really do need one, or if beneficials are already taking care of your problem. Then if you actually do need some man-applied intervention, research further the use of the least toxic means of control, ones that will preserve your beneficials. Examples of this would include products such as: Bt, Confirm, and different formulations of spinosad such as Bulls-EyeTM Bioinsecticide, Conserve® SC, Entrust®, Justice, Monterey Garden Insect Spray®, Ferti-lome® Borer, Bagworm, and Leafminer & Tent Caterpillar Spray.

Spinosad (pronounced spin-OH-sid) is a relatively new insecticide that quickly and safely controls a variety of caterpillar, beetle, ants, thrips and other pests. Spinosad is derived from the fermentation juices of a lowly soil bacterium called Saccharopolyspora spinosa. To chemists, spinosad is a complex molecule known as a "glycosylated macrolactone;" but to gardeners with a hankering for safer products, it may be a godsend. Spinosad is not particularly new, having been granted organic status by the USDA National Organic Program (NOP) in 2003. However, few home gardeners are aware of its potential uses.

Spinosad is especially effective on caterpillars and thrips. If you are a flower gardener, your ears should perk up on this one. Thrips and caterpillars are the two most important pest groups on annual and perennial flowers. Perhaps the best thing about spinosad-containing products is their safety for people and beneficial insects. Although applications should be judiciously used where butterfly larvae feed, spinosad is safe for adult butterflies and many insect predators and parasites. It falls into the safest human health category as well.

Taking care in the control of insects will help insure benefits for your garden. Help make sure that fruits, vegetables and flowers are pollinated, various weeds are controlled, and soil condition is improved by the existence of beneficial insects. Remember to add the least toxic pesticides only when absolutely necessary.