Effects of field applications of paraquat on densities of Panonychus ulmi (Koch) and Neoseiulus fallacis (Garman)
Pfeiffer, Douglas G.
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Neoseiulus fallacis (Garman) is the most important acarine predator of the European red mite, Panonychus ulmi (Koch), in sprayed apple orchards in the eastern United States [Poe, S. L., and W. R. Enns. 1969. Predaceous mites (Acarina: Phytoseiidae) associated with Missouri orchards. Trans. Missouri Acad. Sci. 3: 69-82; Berkett, L. P., and H. Y. Forsythe. 1980. Predaceous mites (Acari) associated with apple foliage in Maine. Can. Entomol. 112: 497-502]. Populations of this predator are often present only at very low densities in Virginia orchards, however. The herbicide paraquat has been shown to be toxic to N. fallacis using slide-dip bioassays [Rock, G. C., and D. R. Yeargan. 1973. Toxicity of apple orchard herbicides and growth-regulating chcmicnls to Neoseiulus fallacis and twospotted spider mite. J. Econ. Entomol. 66: 1342-1343; Hislop, R. G., and R. J. Prokopy. 1981 . Integrated management of phytophagous mites in Massachusetts (U.S.A.) apple orchards. 2. Influence of pesticides on the predator Amblyseius fallacis (Acarina: Phytoseiidae) under laboratory field conditions. Protect. Ecol. 3: 157-1721. Paraquat is commonly applied in Virginia apple orchards in early spring while N. fallacis is still in its overwintering site in the orchard ground cover. The purpose of this study was to determine if field applications of paraquat affect densities of P. ulmi and its predator, N. fallacis, in the tree canopy. Slide-dip bioassay data, while very useful for comparing toxicity from topical applications of pesticides, are highly artificial and do not reflect other factors in mortality (contact with dried residues, behavioral responses, habitat modification). Other methods should be employed to complement slide-dip data (Dennehey, T. J., J. Granett, and T. F. Leigh. 1983. Relevance of slide-dip and residual bioassay comparisons to detection of resistance in spider mites. J. Econ. Entomol. 76: 1225-1230).