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

Abstract

Abstract Effects of O 3 and/or elevated CO 2 on two‐spotted spider mites ( Tetranychus urticae Koch) grown on an O 3 ‐sensitive and an O 3 ‐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 O 3 . In field studies, O 3 treatments were charcoal filtered air (CF), nonfiltered air (NF), and two NF treatments with O 3 added for 12 h d −1 at proportions of ≈ 1.25 and 1.50 times the ambient O 3 concentration. In greenhouse studies, constant amounts of O 3 were added to CF for 6 h d −1 to achieve mean concentrations ranging from 5 to 100 nL L −1 . For the greenhouse O 3 × CO 2 experiment, CO 2 concentrations were ambient and approximately twice‐ambient for 24 h d −1 . Plants were exposed to O 3 and/or CO 2 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 O 3 ‐sensitive clover clone (NC‐S) than on the O 3 ‐resistant clone (NC‐R). Carbon dioxide enrichment increased shoot growth of both clones by ≈33%. Statistical analyses indicated significant O 3 effects in some experiments and nonsignificant O 3 effects in others. A trend toward increased mite populations with increased O 3 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 O 3 . 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 CO 2 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 CO 2 and O 3 on mite population growth. The apparent clone effects on mite population response to O 3 and CO 2 strongly suggest that responses were mediated through the host plants.