Acute ozone stress on eastern cottonwood (Populus deltoides Bartr.) and the pest potential of the aphid, Chaitophorus populicola Thomas (Homoptera: Aphididae)

The effect of acute ozone exposure of eastern cottonwood (Populus deltoides Bartr.) on the survivorship, reproduction, and development of the aphid Chaitophorus populicola Thomas (Homoptera: Aphididae) was investigated. Cottonwoods were exposed to 397 microgram/m3 (0.20 ppm) ozone or charcoal-filtered air and infested with aphids on leaf plastochron index 5, 40 h after fumigation. Aphid performance was not significantly different on plants exposed to ozone compared with charcoal-filtered air-treated control plants. These data do not support the notion that aphid performance will directly increase on air pollution-stressed plants. We also examined settling and feeding preference of aphids for cottonwood leaves of different developmental ages. Aphids significantly preferred leaf plastochron index 5 to all other leaf ages. These data support hypotheses relating aphid leaf preference to stages of leaf development. Reproduction of the cottonwood leaf rust fungus (Melampsora medusae Thum.) and the imported willow leaf beetle (Plagiodera versicolora Laicharting) are reduced on ozone-fumigated plants (reported elsewhere). If aphid populations are affected by competition with these cottonwood pests for leaf resources, then aphid pest potential may actually increase in areas characterized by episodic ozone concentrations because of ozone-induced decreases in populations of M. medusae and P. versicolora