BIOLOGICAL CONTROL 



OF INSECTS IN ORNAMENTALS 



Dr. Patricia]. Vittum 



IN RECENT YEARS greenhouse and nursery manag- 

 ers have been encouraged to use fewer pesticides 

 and to use them less frequently. As a result many 

 managers have begun to look into the possibility of 

 using non-traditional pest control approaches. One 

 such approach involves using biological control 

 agents to control insects. Biological control agents 

 are living organisms or products of living organisms 

 which kill or interfere with the metabolism of tar- 

 get insects. These agents may be parasites or preda- 

 tors, bacteria, viruses, fungi, nematodes, or insect 

 hormones. 



Predators and parasites are handled very differ- 

 ently than traditional insecticides, and will be dis- 

 cussed in a separate article. However, bacteria, 

 nematodes, and insect growth regulators are all ap- 

 plied to crops through standard hydraulic sprayers. 



There are several bacteria which cause diseases 

 in insects. Perhaps the most familiar such bacte- 

 rium is Bacillus thuiingiensis, or BT, which has 

 been available commercially for several years. The 

 bacterium produces a toxin inside the insect which 

 interferes with the digestive system and ultimately 

 paralyzes that system. A target insect may not die 

 immediately but normally it stops feeding shortly 

 after becoming infected. 



There are several "strains" of BT, and each strain 

 is particularly effective against certain kinds of in- 

 sects. The "kurstaki" strain is effective against 

 most caterpillars, including cutworms in the green- 

 house and gypsy moths outdoors. There are several 

 formulations of BT kurstaki, including Dipel™, 

 Thuricide™, Steward™, and Javelin™. The labels 

 vary with regard to crops listed, but all of these 

 materials are sprayable formulations and can be ap- 

 phed with standard equipment. 



The secret to success when using the kurstaki 

 strain is to apply the material when the caterpillars 

 are in the smallest stages. With gypsy moths, this 

 will be a week or two after peak egg hatch, while 

 with greenhouse caterpillars, only regular monitor- 

 ing of the crops will tell you when caterpillars are 

 becoming active. Larger caterpillars (from their 

 middle stages up) are generally much less suscep- 

 tible to the bacterium. 



Another strain of BT which should be of interest 

 to greenhouse managers is the "israeliensis" strain, 

 which is effective against fungus gnat larvae and 

 some other dipterous (fly-like) insects. This strain is 

 currently marketed commercially as Gnatrol™. Field 

 experience has indicated that the material should be 

 applied to the soil every five to seven days for at 

 least three applications. This is because again the 



smallest larvae are most susceptible, but fungus 

 gnats tend to occur in a range of sizes at any given 

 time. So the first application should control the 

 small larvae that are present, but it will not affect 

 the larger stages. When these individuals complete 

 their development and lay eggs to start a new gen- 

 eration, the follow-up applications will control the 

 new young larvae. 



Ornamentals and nursery managers should be 

 aware that there are a couple other strains of BT 

 which might be of interest. In particular the "san 

 diego" strain appears to be quite effective against 

 leaf feeding beetles, such as the Colorado potato 

 beetle. While there are not a lot of potato beetles 

 on our omamental plantings, there are beetles like 

 elm leaf beetles which are also quite susceptible. 

 There are a couple relatively new formulations of 

 the san diego strain which are available commer- 

 cially, including One™ and M-Trak™. 



A second approach to biological control is the 

 use of entomopathogenic nematodes. 

 "Entomopathogenic" simply means causing disease 

 in insects. Entomopathogenic nematodes penetrate 

 target insects, usually through the mouth or 

 through holes in the side of the body through 

 which the insect breathes. Once the nematode gets 

 inside the insect, it releases some bacteria which it 

 carries naturally. These bacteria begin to break 

 down the internal tissues of the target insect. The 

 nematodes then feed on all the decaying material, 

 reproduce, collect some of the bacteria, and move 

 out of the insect cadaver to find new hosts. 



These nematodes are not capable of attacking 

 plants. Although they are very small (nearly micro- 

 scopic), they are mobile so they can make their way 

 through the soil in search of another victim. They 

 are very susceptible to desiccation, however, so the 

 soil must be reasonably moist at the time of appli- 

 cation, and in most cases the nematodes should ei- 

 ther be applied as a drench or be watered in very 

 thoroughly immediately after application. 



Not surprisingly, entomopathogenic nematodes 

 come in different shapes and sizes. The one which 

 is currently available commercially is Steineinema 

 caipocapsae, sold as Exhibit™, BioSafe™, 

 Orthoganic™, and other names. The nematodes are 

 packaged in a gel-like material in a plastic con- 

 tainer. When a plant manager wants to use the 

 nematodes, he adds water and an "activating agent" 

 (really a material which breaks up the gel) and 

 shakes the container thoroughly. He then dilutes 

 the mixture in his regular sprayer and applies the 

 nematodes directly through the sprayer. These 



December 1992 & jAhnjARY 1993 

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