Progress 08/01/01 to 07/31/04
Outputs
Objectives for this project were to run greenhouse trials to determine if releases of the phytoseiid mite Neoseiulus cucumeris could effectively suppress population growth of western flower thrips (Frankliniella occidentalis), either alone or in combination with the insecticide spinosad. We ran three trials. Trial one was done in six commercial greenhouses filled with spring bedding plants. There were two replicates of each of three treatments (mites at the commercial rate, spinosad at label rate, or both). As the measure of outcome, we trapped adult thrips with yellow sticky cards. Under commercial greenhouse conditions there was too much variability in plant species in the greenhouse and too much between-greenhouse movement of plants by growers to see clear treatment effects. In one block, spinosad alone was highly effective, but in the other it was not. Mites were not highly effective in either block. Trial two was run in University greenhouses in pure impatiens
monocultures, with two replications (over time) of the same three treatments as in Trial 1. Using thrips per flower as the measure of outcome, mite releases caused ca 50% reduction in both larvae and adults of western flower thrips. To see if a higher mite release rate might increase the level of control, Trial 3 was run in the same university greenhouses, with three replications (over time) of two rates of mite release (the commercially recommended rate and 3.8X that rate) plus an untreated control. In two replicates, the higher mite release rate was better than the commercially recommended rate, providing ca 80% control of larvae in flowers, but having no obvious effect on adults per flower. A manuscript has been prepared covering these trials and has been submitted to the journal Biological Control and is in review. The other objective of this grant was to assess the compatibility of spinosad with N. cucumeris. This was done by measuring mortality and oviposition of mites exposed
to spinosad residues. This compound was found to have only minimal effects on this mite. The results of this study are being prepared for publication.
Impacts
This study provides evidence that releases of N. cucumeris are only partially effective in suppressing WFT within a ten week impatiens crop, even at 3.8X the commercially recommended rate. Spinosad was found to be highly effective and to have no impact on N. cucumeris, so the two approaches can be used together without conflict, and the combination should be useful in slowing the development of resistance by thrips to spinosad. One impact of this work is to advise growers that this particular biological control method is not highly effective.
Publications
- No publications reported this period
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Progress 10/01/02 to 09/30/03
Outputs
Obj. 1. Because the trial run in 2002 under commercial condition was too variable in crop composition and starting pest levels among greenhouses available to assign to treatments, in 2003, we repeated the trial with N. cucumeris (mite alone, mite+spinosad, or spinosad alone) in UMASS greenhouses with impatiens as the only crop, replicated twice over time. Treatments were imposed and results scored as either WFT adults caught on yellow sticky cards (weekly) or as numbers of WFT (adults and larvae) counted in randomly chosen flowers. Based on sticky card counts, both spinosad alone and spinosad plus N. cucumeris suppressed thrips to 1 or fewer thips per card per week, in both of the trials. In contrast numbers in the untreated control exceeded 20 per card in the April-March trial and 80 in the May-June trial. For plants treated only with N. cucumeris, thrips catches peaked at 7-10 per trap per week. In counts on flowers, we saw the same order of treatment effectiveness.
From both the catch per trap and thrips per flower data sets (still being analyzed), we conclude that spinosad was highly effective and that N. cucumeris alone, at the rate applied, was partially effective. We found no difference between spinosad alone compared to the combination of spinosad and N. cucumeris. Obj 2. In laboratory trials we found freshly dried (2h) residues of spinosad at the full labeled rate were not repellant to either N. cucumeris or I. degenerans and did not increase mortality for either mite species, compared to that of untreated controls. In contrast, the same batch of spinosad was highly toxic to WFT adults. From this we conclude that spinosad is highly effective against WFT and highly compatible with the two species of phytoseiid mites tested. Remaining work is to assess the impact of spinosad on mite oviposition and to complete data analysis and publication.
Impacts
This study provides evidence that releases of A. cucumeris are at least partially effective in suppressing WFT within a ten week impatiens crop. Spinosad was found to be highly effective and to have no impact on A. cucumeris, so the two approaches can be used together without conflict. These findings imply that growers can combine the use of spinosad and A. cucumeris release.
Publications
- No publications reported this period
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Progress 10/01/01 to 09/30/02
Outputs
In 2002, we performed the first of the greenhouse tests, with A. cucumeris alone, spinosad alone, and the combination, as the three treatments. We enrolled nine greenhouses filled with spring bedding plants in the trial (three replicates each of the three treatments). We experienced considerable difficulty maintaining cleanly defined treatments due to variation in the plant composition of "bedding plants" grown in each greenhouse. At the best site (Mahoney), where all three greenhouses were filled with impatiens, order of suppression of treatments was as expected from best to worst: mites plus spinosad, spinosad alone, and mites alone. For the last three weeks of the crop, mites alone were significantly different (more thrips) than the other two treatments, but those two (spinosad alone, spinosad with mites) did not differ. For the second group of greenhouses (Valley), the order from best to worst was spinosad alone, spinosad plus mites, and mites alone. Each
treatment was significantly different from the others. However, in these greenhouses the spinosad treated greenhouse had distinctly lower thrips at the start of the trial, a condition that did not change. Thus, the low thrips counts for this treatment reflect starting conditions, not treatment effects. The third set of greenhouses could not be analyzed because growers did not apply the treatments correctly. Work on the laboratory tests will begin in January of 2003. Also, in spring of 2003, the greenhouse tests will be repeated in UMASS research greenhouses, all filled with impatiens and inoculated evenly with thrips to create better conditions for a comparative trial.
Impacts
The expected impact of this work will be to make biological control of western flower thrips in bedding plant crops more highly and reliably suppressive. Trials we have run for this and other related projects have led us to believe that the currently recommended rate of five applications of 106 mites per sq meter does not strongly and consistently suppress western flower thrips. This trial is an attempt to determine if this rate might be adequately effective if combined with a mid crop application of spinosad. (Other efforts involve looking at higher mite release rates, use of pollen to stimulate mite population increase in the crop, and use of another species of mite). Tests of each of these factors will eventually lead to a recipe that is reliable. Lack of reliability impedes the adoption of biological control by growers. Results of this trial should make adoption more likely. Use of biological control by growers will slow down development of resistance to
pesticides by western flower thrips and give growers better protection from INSV virus outbreaks in their crops.
Publications
- No publications reported this period
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Progress 10/01/00 to 09/30/01
Outputs
As the start date for this project (August 1, 2001) indicates, there was only one active month for the project in this reporting year. No work has been accomplished yet. The USDA APHIS has not yet issued an importation permit for one of the two mite species to be examined (A. montdorensis). We will begin with A. cucumeris and reevaluate in one year to see if APHIS has issued a permit for importation of the second species.
Impacts
The project has not yet had any impact, as the work has not yet been done. We expect that the project will help define how to successfully use one or more predators with spinosad for western flower thrips control in greenhouse bedding plant crops.
Publications
- No publications reported this period
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