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Ozone and Carbon Dioxide Effects on Spider Mites in White Clover and Peanut

USDA-ARS, Plant Pathology Dep., North Carolina State Univ., Raleigh, NC 27695.

R. L. Brandenburg

Entomology Dep., North Carolina State Univ., Raleigh, NC 27695.

J. C. Burns and J. E. Miller

USDA-ARS, Crop Science Dep., North Carolina State Univ., Raleigh, NC 27695.

^* Corresponding author.

ABSTRACT

Effects of O₃ and/or elevated CO₂ on two-spotted spider mites (Tetranychus urticae Koch) grown on an O₃-sensitive and an O₃-resistant clone of white clover (Trifolium repens L.) were measured in greenhouse and field experiments. Peanut (Arachis hypogeae L.) ‘NC-9’ was used in one greenhouse study with O₃. In field studies, O₃ treatments were charcoal filtered air (CF), nonfiltered air (NF), and two NF treatments with O₃ added for 12 h d^–1 at proportions of 1.25 and 1.50 times the ambient O₃ concentration. In greenhouse studies, constant amounts of O₃ were added to CF for 6 h d^–1 to achieve mean concentrations ranging from 5 to 100 nL L^–1. For the greenhouse O₃ x CO₂ experiment, CO₂ concentrations were ambient and approximately twice-ambient for 24 h d^–1. Plants were exposed to O₃ and/or CO₂ for 7 d before infestation with mites; daily exposures continued for 14 to 28 d to allow reproduction for at least two generations. Leaves were sampled to count eggs, larvae, nymphs, and adults. Ozone caused more chlorosis and necrosis on the O₃-sensitive clover clone (NC-S) than on the O₃-resistant clone (NC-R). Carbon dioxide enrichment increased shoot growth of both clones by 33%. Statistical analyses indicated significant O₃ effects in some experiments and nonsignificant O₃ effects in others. A trend toward increased mite populations with increased O₃ occurred, however, on NC-S in all trials. No consistent trends occurred with NC-R. With peanut, a significant linear increase in mite population occurred with increased O₃. Carbon dioxide enrichment increased the rate of population increase on both clover clones, but more so on NC-R. At 22 to 28 d after infestation, the total population in the twice-ambient CO₂ treatment was 65% greater than in the ambient treatment for NC-R and 22% greater than in the ambient treatment for NC-S. There were no statistically significant interactive effects between CO₂ and O₃ on mite population growth. The apparent clone effects on mite population response to O₃ and CO₂ strongly suggest that responses were mediated through the host plants.

Cooperative investigations of the USDA-ARS and the North Carolina State University. Funded in part by the North Carolina Agricultural Research Service.

Received for publication November 22, 1993.