Insect and Mite Control on Woody Ornamentals and Herbaceous Perennials

Bulletin 504

Insect and Mite Management Alternatives

The Control Options

Biological Controls

Biological control is using parasites, predators and pathogens (diseases) to control pests. We have to realize that in the urban landscape and nursery, there is a multitude of beneficial insects and mites which can prey on pests. In many cases, these naturally occurring beneficials will do a good job of controlling the pests if we do not disturb the system too much. As stated above, we usually disrupt this system by over using pesticides which kill the beneficials better than the pests. On the other hand there are occasions where we can actually increase these biological controls. The classical way to implement biological controls is through introductions, conservation and augmentation.

1. Introductions of exotic parasites, predators or diseases are made when foreign pests become established. This is an attempt to create some of the checks and balances found where these pests are naturally controlled. Occasionally, foreign biological controls are found which may better control native pests.
2. Conservation is using other control tactics, usually pesticides, so that they have the least adverse affect on predators and parasites. It can also be the providing of habitat or food needed by biological controls to improve their survival. In the urban landscape or nursery we can use targeted sprays to those specific plants where pests are getting the upper hand. We can also plant flowers which provide nectar and pollen to feed the adults of many of the parasitic insects.
3. Augmentation is usually the rearing and release of biological control agents. Unfortunately, this technique is usually expensive and we must use those biological controls which fit into the definition of a "good" biological control.

What is meant by a "good" biological control? Not all predators, parasites and pathogens are useful in their ability to be used in pest management. Useful ones have the following characteristics:

1. High Reproductive Potential - they must be able to keep up with the high reproduction of the pests.
2. Good Mobility - they must be able to search out the pests or come into contact with the pests.
3. Host Specific - they should not be generalists which may adversely affect other, sometimes beneficial, organisms.
4. Persistent - they should remain when pest populations become low and carry over from season to season.
5. Easily Reared or Encouraged - this will allow them to be inexpensive and competitive with other controls.
6. Tolerant of Other Controls - in order to fit into a true IPM system, they need to be tolerant of cultural and chemical controls if used.

In order to illustrate these concepts, let's look at a preying mantis versus a lady beetle. The preying mantis has one generation per year, eats anything in sight (including each other and other beneficials), usually ignores the small insects such a aphids, mites and scales, often doesn't survive the summer to lay another egg case and is very sensitive to any pesticide. Therefore, preying mantids do not qualify as a useful biological control. On the other hand, lady beetles have many generations per year, they only eat a narrow range of pests (usually they are aphid, mite or scale specialists), usually overwinter well and can often withstand some of the softer pesticides, especially soaps and oils. Therefore, lady beetles easily qualify as a useful biological control.

Unfortunately, we often think that we have to actively introduce predators and parasites in our urban landscapes. Since most of these animals already exist, we merely have to be able to recognize them and avoid using cover sprays of pesticides.

Predators which you should learn about are:

1. Lady Beetles are commonly sold as adults and are useful control agents if properly handled. The adults need to be fed some honey (to resemble aphid honeydew) in a cage (to suppress a strong migration urge) before release in the garden. Larvae are often mistaken for pests because they look like leaf beetle larvae or some other pests (e.g., the "mealybug destroyer" lady beetle larva looks like a mealybug).

2. Green Lacewings are not to be confused with the pest, lace bug. The larvae feed on aphids, scales and mites. Eggs are purchased and sprinkled where small pests are noted to be active. The larvae must search for the pests because they do not have wings.

3. Ground and Rove Beetles are active predators present in most soil/turf habitats. Both the adults and larvae feed on a wide variety of pests but are highly intolerant of pesticides.

4. Syrphid Flies (=Hover Flies) are very common yellow and black flies which have voracious larvae (maggots) which eat aphids.
5. Predatory Bugs are commonly found attacking a variety of ornamental pests. The spiny soldier stink but, assassin bugs, minute pirate bugs, predatory plant bugs, and bigeyed bugs are the most commonly seen beneficials in this group.

1. Trichogramma Wasps (=Egg Parasite Wasps) are microscopic (usually less than 0.5mm long) and lay their eggs in the eggs of other insects. They are usually very host specific and generally limited to butterfly or moth (caterpillar) pests.
2. Ichneumonid and Brachonid Wasps are small wasps which commonly attack caterpillars and aphids. The larvae usually emerge from the dying host and spin small white or yellow cocoons.
3. Tachiniid Flies are generally medium to large flies which lay eggs on caterpillars or various leaf feeding beetles. The eggs hatch into maggots which feed on and eventually kill the host insect.

Pathogens are simply a variety of diseases which kill insects. They are usually bacteria, virus, fungi and protozoa. Insect pathogens are fairly ideal in that they are very host specific. They are also very non-infective to vertebrates. Examples are:

1. Bacteria have been the easiest of the pathogens to utilize because they can often be reared "in vitro" (in artificial culture) and form spores fairly resistant to adverse environments. Examples are:
   1. Bacillus thuringiensis (Bt) - has several strains which produce toxins lethal to various insect groups (and are thus technically a chemical control). The most common types are:
      1. Bt ‘Kurstaki’ - which affects only young caterpillars.
      2. Bt ‘Israelensis’ - which affects aquatic fly larvae such as mosquitos and black flies.
      3. Bt ‘Tenebrionis’ - which affects some leaf feeding beetles.
   2. Bacillus popilliae (= white grub milky disease) - has one strain available which kills Japanese beetle grubs. Other strains have been identified which kill other species of grubs but these strains are not commercially available.

2. Fungi have been identified but are difficult to utilize because the spores are easily dried out or need high moisture and/or water to germinate. Examples are:
   1. Beauveria bassiana strains, the "white fungus" of insects, have been identified infecting a wide variety of insects including bugs, caterpillars and beetles. Commercial preparations are available for control of a variety of insects on ornamentals and in turf. High humidity is necessary for maximum activity.
   2. Metarrhizium anisopliae strains have been identified infecting numerous soil insects including white grubs. No commercial strains are available in the United States.

3. Viruses are common pathogens of insects but are one of the most difficult to use because they require living insects to grow. Recent development of insect tissue culture has allowed for rearing of some of the virus strains but the only product registered is Nucleopolyhedrosis Virus (NPV) - for gypsy moth control under the trade name of Gypcheck™.
4. Entomopathogenic Nematodes are a group of tiny parasitic roundworms which carry a bacterium lethal to insects. Once the nematode gains entry into an insect it regurgitates the bacterium which paralyzes, kills and preserves the insect cadaver. The nematode then feeds on the bacteria, develops and reproduces. (See: Alternative Products) The most commonly mentioned species are:
   1. Steinernema carpocapsae, S. riobravis, & S. feltia are species that each have different attributes which make the good at attacking insects which live in the soil or on the soil surface. Several commercial preparations are available.
   2. Heterorhabditis spp. are better at attacking insects which live deeper in the soil. This group can also bore through the insect cuticle.

In summary, there are multiple alternative control methods which can be used in the urban landscape. The concept of integrated pest management provides a framework in which to use all of the alternatives in a systematic fashion. Of most importance is the idea that we must monitor for pest problems and then select the best targeted control available.

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