Abamectin

SPINOSAD

Use of spinosad in a rotation of pest management products can help eliminate Western flower thrips.

WESTERN flower thrips (WFT), Frankliniella occidentalis, has been and is still a major insect pest in greenhouse production systems due to direct feeding injury. It also is a vector of the tospoviruses, impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV). The primary means of dealing with WFT is through the use of insecticides. However, continual reliance on insecticides may lead to control failures due to resistance, which is why rotation programs - switching modes of action on a designated basis will help to preserve the longevity of currently available insecticides. The principal insecticide sold in the greenhouse industry and used for WFT is Conserve, which contains the active ingredient spinosad. This product has provided excellent control of WFT since it was introduced and commercially available for use in greenhouses in 1998.1 spent three years working with Dow AgroSciences in testing this active ingredient against WFT on a variety of floral crops, prior to introduction, and was impressed with the level of control (based on percent mortality). In all our trials, we consistently obtained mortality values near 100 percent for both the adult and nymphal stages of WFT. Since, at that time, there was really no single insecticide providing the level of control that greenhouse producers needed, I knew the availability of this product would be beneficial to greenhouse producers. However, 1 also knew that once greenhouse producers realized the potential control exhibited by spinosad that the likelihood of over-use was high. For instance, in California, leafminer resistance to Conserve was documented after one chrysanthemum producer used Conserve weekly in violation of the label for the first two years the product was on the market. In this article, I discuss spinosad (Conserve) from a perspective standpoint including background, characteristics and the future of this insecticide in the greenhouse industry.

A Bit Of History

The initial development of spinosad started in 1982 when a vacationing scientist (yes, scientists do take vacations), working for the then Natural Products division of Eli Lilly, collected soil samples from an abandoned sugar rum distillery in the Caribbean. These soil samples were returned to the laboratory for initial processing to assess the potential for biological activity. It was eventually determined that the fermentation products from these samples demonstrated insecticidal activity. From these initial tests came spinosad.

Spinosad is derived from a species of Actinomycete bacteria, Saccharopolyspora spinosa, that when fermented creates metabolites called spinosyns. Two are biologically active compounds that are responsible for the insecticidal properties, spinosyns A and D. Spinosad is highly active on insects in the orders lepidoptera (caterpillars), diptera (flies), hymenoptera (bees and wasps) and thysanoptera (thrips). In addition, spinosad has been shown to be effective against the larvae and adults of certain beetle species.

Spinosad is effective in controlling greenhouse insects including thrips, leafminers and caterpillars. Spinosad works quickly, killing insects within one to two days after ingesting. Although the material kills insects by contact and ingestion, it works best when ingested, which is why it has minimal effect on phloem-feeding insects such as aphids, whiteflies, mealybugs and soft scales. Spinosad is generally not effective in controlling mites, although control is ratedependent. Because there are already a number of effective miticides available, spinosad should not be used when both spider mites and WFT are present, as this increases selection pressure on both pests. Soil-dwelling insects such as fungus gnat larvae are typically not affected by applications of spinosad because it is tightly bound to growing medium particles and rapidly broken down. Spinosad has minimal fumigant activity due to the low vapor pressure (2.4 x 10-10). Materials with a vapor pressure less than 10-6 are essentially nonvolatile. Spinosad is relatively stable at a water pH of 5 to 7, and has a half-life of approximately 200 days at a pH of 9. In addition, it has low-to-moderate water solubility and short persistence in the environment. The major route for breakdown of spinosad in the environment appears to be ultra-violet degradation.

Spinosad has rapid contact and ingestion activity. Control takes one to three days with residual activity up to two weeks. The mode of action involves excitation of the insect nervous system, leading to paralysis and death. Spinosad disrupts the binding of acetylcholine at nicotinic acetylcholine receptors located at the postsynaptic cell junctures, and negatively affects the gamma-amino butyric acid (GABA) gated ion channels. Spinosad has a mode of action that is similar to the neonicotinoid-based insecticides and macrocyclic lactone insecticides/miticides. However, the neonicotinoid-based insecticides including imidacloprid (Marathon), thiamethoxam (Flagship), acetamiprid (Tristar), dinotefuran (Safari) and clothianidin (Celero) act at a different target site than spinosad. In addition, the macrocyclic lactone insecticide/miticide abamectin (Avid) attaches to a different site in the insect/mite nervous system than spinosad. Spinosad does not have any systemic properties (it is not translocated through the xylem or phloem) when applied as a foliar spray; however, it does exhibit translaminar movement through leaf tissue. The addition of a surfactant enhances penetration through leaves and translaminar movement increasing activity against insects such as leafminers and thrips. Spinosad has been shown to be safe to most horticultural crops-exhibiting no phytotoxicity. The label for Conserve states that this insecticide should not be applied more than 10 times in a year inside a greenhouse. The restricted entry interval (REI) is four hours.

Spinosad And Beneficials

The impact of spinosad on natural enemies has been extensively studied since its introduction. Direct applications (wet sprays) of spinosad are extremely harmful to parasitoids including Aphidius colemani and E.formosa; however, any toxic effects generally decrease as the spray residues age although spray residues have been demonstrated to be toxic to E.formosa for up to 28 days. Spinosad applications have been shown to be toxic to the eggs of Trichogramma spp. parasitoids and the larval stage of hover or syrphid flies. Applications of spinosad have exhibited toxic effects to E.formosa and Orius laevigatus shortly after treatment, but populations of both were not seriously affected after two to three weeks. Spinosad has been shown to not harm the larval stage of the aphid predatory midge, Aphidoletes aphidimyza.

Spinosad is highly toxic to bees as a wet spray; however, once residues dry, then any toxic effects to foraging bees is negligible.

Spinosad appears to be very compatible with many predatory insects and mites. Studies have demonstrated that spinosad has no direct or indirect negative affects to green lacewing (Chrysoperla carnca), ladybird beetle (Hippodamia convergens), minute pirate bug (Onus laevigatus), big-eyed bug (Geocoris punctipes) and damsel bug (Nabis sp.). Spinosad has also been shown to not directly harm predatory mites including Amblyseius californiens, Phytoseiulus persimilis, A. cucumeris and Hypoaspis miles at the rates tested. In California greenhouse rose production systems, the ability of Conserve to control WFT without any adverse effects on P. persimilis has been critical for biological control programs using P persimilis to control two-spotted spider mite. However, certain Amblyseius spp. may be indirectly affected by direct spray applications although any effects generally decrease as the spray residues age.

As mentioned above, spinosad became available to the greenhouse industry under the trade name, Conserve in 1998. However, due to the continual reliance of spinosad, certain "battle-hardened" populations of WFT, particularly in California, have demonstrated diminished sensitivity to spinosad. Recently, research conducted at the University of Illinois has shown that greenhouse populations of WFT are resistant to spinosad. Resistant strains of tobacco budworm, beet armyworm and diamondback moth to spinosad have been assessed in the laboratory. In order to preserve the longevity of spinosad, greenhouse producers need to rotate spinosad with other insecticides having different modes of action. An example of one rotation scheme (and there are others) for WFT is provided below:

Spinosad (Conserve)->methiocarb (Mesurol)->abamectin (Avid)->acephate (Orthene)

The regular use of azadirachtin products such as Ornazin and Azatin is highly recommended for managing WFT until they fail to provide adequate control, which is when Conserve should be rotated back into the program. It is also important for green- ,; house producers to obtain spray ' \ -y records from suppliers in order to know what insecticides (and rotations) have been used, which will avoid exposing any existing WFT populations to the same mode of action that had been used previously, thus decreasing the selection pressure on the WFT population.

The future of spinosad or Conserve depends on greenhouse producers. Currently, there are no new insecticides that demonstrate the same or similar level of activity on WFT as spinosad, so it is critical that greenhouse producers avoid the routine use of spinosad in order reduce the selection pressure placed on WFT populations. The best way to avoid undue selection pressure is by scouting. The presence of one adult WFT doesn't mean that adults are present throughout the crop. Only by installing and looking at yellow or blue sticky cards regularly will you be able to determine when adult WFT are present. This will help you avoid making insecticide applications when the age structure of the WFT populations are in a stage or stages such as eggs or pupae that are not affected by spinosad, which will save time and money. Proper stewardship of spinosad will go a long way in allowing this effective insecticide to be around for an extended time period. Although this article focused on one particular product, the same information could easily apply to any commercially available insecticide, miticide or fungicide used in greenhouses.

About the author: Raymond A. Cloyd is assistant professor and Extension specialist in Ornamental Entomology/Integrated Pest Management at the Department of Natural Resources and Environmental Sciences, University of Illinois, 384 National Soybean Research Laboratory, 1101 West Peabody Drive, Urbana, IL 61801; 217-244-7218; fax 217-244-3469; e-mail rcloyd@uiuc.edu.

The author acknowledges Bruce Kidd of Dow AgroSciences (Murrieta, Calif.) for his valuable contribution to the article.

Copyright Meister Media Worldwide Sep 2005
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