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Fruit Notes |
Can Apple Maggot Fly Control Benefit
from Sprays of Provado Aimed at Killing Leafminers and
Leafhoppers? |
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Fruit Notes |
Xing Ping Hu, Andrew Kaknes, and
Ronald Prokopy
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Fruit Notes |
The insecticide Provado (containing imidacloprid as the active ingredient) was synthesized by Japanese Chemists in 1985. In 1995, it was labeled for use on apple in the United States. One of its greatest perceived advantages is its high toxicity to several major apple pests but comparative lack of toxicity to beneficial predators and parasitoids. Indeed, Provado has proven very effective against leafminers, leafhoppers, and aphids in apple orchards of Massachusetts and other states [Fruit Notes 60(4)]. Provado may be used effectively when applied against either first-generation leafminers and leafhoppers at petal fall in May, or against second-generation leafminers and leafhoppers in late June. Application in late June conceivably also could provide control of early-invading populations of apple maggot flies. One reason for believing this might be so stems from recent tests of Provado applied, together with latex paint, on red spheres aimed at killing alighting apple maggot flies. Results of these tests showed high toxicity of Provado against the flies even at very low doses [Fruit Notes 62 (4)]. Here, we evaluated effects of Provado against apple maggot flies when applied to the foliage and fruit of apple trees. Materials & Methods Provado was provided by Bayer Corporation (Kansas City, MO). Flies used in bioassays were obtained from pupae collected from unsprayed apple drops. Five apple trees were selected from an abandoned orchard near Amherst, Massachusetts. Branches of four trees were sprayed to runoff at a dose of 0.03% a.i. of Provado, the rate labeled for controlling sucking insects in apple orchards. The fifth tree was not sprayed and used as a control. For each tree, four branches were selected for caging flies, using 30x50-cm cloth screen net. Two fruit were allowed to remain on each branch. Four leaves on each branch received an aqueous slurry of a mixture of 8% sugar and 10% bird droppings to serve as a food supply for flies. Two cages per tree received 20 flies (10 males and 10 females) immediately following spray application. The other two cages received like numbers of flies 24 hours later. Mortality counts were made daily for 7 days. To determine possible effects on fly reproduction, apples and surviving flies from each cage were brought back to the laboratory on the 7th day. Apples were examined to determine the effects of Provado on fly oviposition behavior by counting the number of oviposition punctures and number of eggs laid. Female flies were dissected to determine effects of Provado on egg load by counting the number of mature eggs in fly ovaries. Results Our results indicate that application of Provado to apple tree foliage and fruit neither effectively reduced fly survival (Figure 1) or fly reproductive ability (Figure 2). Less than 20% of flies caged immediately after spray application were killed over the 7-day test period, too low to provide effective control. Mortality was even lower (8%) for flies released into cages 24 hours after spraying. This was essentially no greater than the 5% mortality of flies in the control cages. The results suggest a rapid decline of Provado activity on leaf and fruit surfaces after application. Figure 2 shows that fly oviposition behavior was only slightly reduced for flies exposed to sprayed compared with unsprayed leaves and fruit. Groups of flies exposed to foliage and fruit immediately after spraying with Provado made an average of 16 ovipositional punctures and laid an average of 14 eggs over 7 days, compared with 19 ovipositional punctures and 17 eggs laid by flies exposed to foliage and fruit 24 hours after spraying, and 21 ovipositional punctures and 19 eggs laid by control flies. The egg load per female remained at essentially the same level for all the treatments. These results suggest that Provado applied to apple foliage and fruit had minimal effects of fly oviposition. Conclusions Even though Provado has proven excellent in providing season-long control of sucking insect pests on apple trees, and even though our laboratory tests showed high toxicity of Provado to apple maggot flies, the results generated here indicate that Provado applied to apple tree foliage and fruit has little or no effect on apple maggot fly mortality and oviposition. There may be two reasons for the ineffectiveness of Provado spray on tree foliage and fruit against apple maggot flies. First, Provado is a systemic insecticide, and is quickly absorbed by foliage (and perhaps also fruit) once sprayed. Thus, it kills pests that suck sap from the interior of foliage but does not remain on plant surfaces long enough to kill pests, such as apple maggot flies, that do not suck plant sap. Second, Provado on exterior surfaces of plants is subject to rapid degradation by sunlight. Nevertheless, when applied together with latex paint to red spheres, Provado, even at very low doses, has provided excellent control of apple maggot flies alighting on treated spheres for up to three months after initial application. Thus far, it has proven more effective than any other insecticide that we have evaluated for this purpose. Acknowledgements We thank Richard H. Ackerman from Bayer Corporation for providing us with samples of imidacloprid and John Clark and David Ferro from our department for helpful suggestions. This work was supported by funds from USDA Cooperative Agreement 58-3620-104, the Northeast Regional IPM Competitive Grants programs and the Washington State Tree Fruit Research Commission. |
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