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In 1980 and 1982, the temporal pattern of Colorado potato beetle, Leptinotarsa decemlineata (Say), damage to individual field-grown potato plants was manipulated by five schedules of insecticide application. The insecticide applications resulted in plants that sustained either minimum damage, damage during the vegetative phase, damage during the tuber-bulking phase, or damage during the entire season (maximum damage). Plants were harvested weekly, and polynomial growth curves were fit to the data. The only treatments that significantly affected the plant growth curves were maximum damage and damage during the tuber-bulking phase. Damage during the vegetative phase delayed the occurrence of maximum haulm and tuber growth rates, whereas damage during the tuber-bulking phase permanently reduced these growth rates. This indicates that plants damaged before the initiation of tubers were able to recover from beetle damage, but plants damaged after tuber initiation were not. Plants receiving maximum damage or damage during the tuber-bulking phase appeared to have reduced tuber and total relative growth rates, indicating a decrease in the efficiency of dry matter assimilation. An important factor behind the changing temporal sensitivity of potato growth to beetle damage appears to be the dramatic difference in leaf area ratio between plants in the vegetative phase and plants in the tuber-bulking phase. Plants in the vegetative phase have approximately 200 cm 2 of leaf area to support each gram of dry plant tissue; plants in the tuber-bulking phase have only 50 cm 2 of leaf area per gram of dry weight. Loss of leaf area caused by Colorado potato beetle during the tuber-bulking phase should have a greater relative effect on assimilation than proportionately equal reductions in leaf area during the vegetative phase.
Dripps et al. (Sun,) studied this question.