stages during which they are most effective — and 

 often they will attack certain stages of the pest 

 more readily ot more efficiently than other stages 

 For example, the Encarsia wasp which attacks 

 greenhouse whiteflies attacks the third and fourth 

 nymphal stages more readily than other stages. It 

 also survives much more successfully when it at- 

 tacks these larger stages. Most beneficial insects 

 also have certain temperatures at which they are 

 more effective. Some of these insects prefer 

 warmer temperatures while others prefer cooler 

 temperatures. It is critical to be aware of the pref- 

 erences of the parasite or predator, so that you 

 can time releases so they have the greatest 

 chance of success. 



One of the keys to success in a biological con- 

 trol program is to understand the life cycles of the 

 pest and the beneficial insect. If a grower releases 

 Encarsia wasps when most of the whitefly popula- 

 tion is in the adult stage, the wasps probably will 

 not have much success, because there will not be 

 enough large nymphs to feed on. (Note that the 

 wasps are usually released in their pupal stage, so 

 it takes a little while for them to mature to adults 

 and search for whiteflies. All of this must be taken 

 into account when timing releases.) 



Perhaps the most important key to successful 

 use of parasites and predators is careful monitor- 

 ing of the crop throughout the process. Pest in- 

 sects must be identified early enough to enable a 

 grower to order and receive the appropriate ben- 

 eficial insect. Monitoring includes obtaining some 

 sort of "count" of the number of insects present, 

 but it is at least as important to know what per- 

 centage of the population is in each stage of de- 

 velopment. This enables a grower to time the re- 

 lease of the beneficials when the target insects 

 are in the most susceptible stage. 



There are several examples of parasites and 

 predators which are being used in commercial set- 

 tings in the United States, Canada, and Europe. In 

 some cases, parasites or predators are used dur- 

 ing stock plant production and early plant devel- 

 opment and then traditional insecticides are used 

 for the latter stages of crop development. In such 

 a setting, the number of insecticide applications 

 can be reduced substantially. Some establish- 

 ments have made a commitment to using benefi- 

 cial insects and some of the "softer" insecticides, 

 such as insect growth regulators, soaps, and oils 

 exclusively. 



Growers may already be familiar with some of 

 the parasites and predators which are currently 

 available commercially. Encarsia formosa is a para- 

 sitic wasp which attacks greenhouse whiteflies, 

 preferably in the third and fourth nymphal stages. 

 It can be quite effective, particularly at warmer 

 temperatures (70-75 F) when used regularly, but 

 the wasp is quite sensitive to many of the insecti- 



cides used in greenhouses This species of wasp 

 does not appear to be nearly as effective against 

 the sweet potato whitefly (or whatever it is being 

 called this month!), in part because that whitefly 

 is smaller and does not provide an adequate 

 food supply. 



Phytoseiulis persimilis is a predatory mite which 

 attacks spider mites. The predator is very efficient 

 and hunts down all stages of spider mites, from 

 eggs to adults. In fact, these predators are often 

 so efficient that they will eliminate a spider mite 

 population and then starve to death. They are 

 very mobile and can be seen moving on the sur- 

 face of the plant, but they do not attack plants or 

 animals. 



Amblysius cucumeris is another predatory mite 

 which is being used against various species of 

 thrips. It is another very mobile species and is 

 quite efficient. The "mealybug destroyer" 

 (Cryplolaemus sp.) is a predatory beetle which 

 seeks and destroys mealybugs. This predator has 

 become a popular option in interior plantscape 

 settings, but some customers have complained 

 because they have seen the predatory beetle lar- 

 vae on the foliage and thought they were mealy- 

 bugs 



Currently research is being conducted at sev- 

 eral universities and in commercial settings. New 

 predators and parasites are being tested in con- 

 trolled conditions. Several predators and parasites 

 have shown promise against leafminers, whiteflies, 

 spider mites, and thrips. Even more research is 

 being conducted in the nursery and ornamentals 

 setting. For example, a couple parasites have 

 been released in Massachusetts to control euony- 

 mus scale. These parasites have survived the New 

 England winters and there appears to be a strong 

 possibility that these parasites will establish suc- 

 cessfully in the Northeast. 



Growers who wish to incorporate the use of 

 parasites and predators into their operations 

 should: 



1 . START SMALL. 



Experiment with one range before trying to con- 

 vert the entire operation. Learn how to release 

 the insects. In some cases they are attached to a 

 card which is then clipped onto the foliage, while 

 in some cases they are in a small vial and the 

 grower shakes the insects onto the plants. 



2. FIND A REPUTABLE SUPPLIER. 



Many firms are providing beneficial insects now. 

 In most cases they serve as a "middleman" and 

 obtain the insects from commercial insectaries 

 Find a firm which has a commitment to quality 

 control and which can fill orders on short notice. 



3. LEARN ABOUT THE LIFE CYCLES OF THE 

 PEST AND THE BENEFICIAL. 



The Plantsnian 

 22 



