YIELD RESPONSES OF POTATOES TO DEFOLIATION BY THE POTATO FLEA BEETLE (COLEOPTERA, CHRYSOMELIDAE) IN MANITOBA

Individually caged potato plants, of the cultivars 'Norland' and 'Russ et Burbank', were grown in field plots in Manitoba. For 'Norland' tria ls, adult potato flea beetles, Epitrix cucumeris (Harris), were mainta ined in cages at constant multiples of naturally occurring field densi ties for the duration ofthe growing season. 'Russet Burbank' trials we re performed in the same way except that, in half of the treatments, l arval and adult Colorado potato beetles, Leptinotarsa decemlineata (Sa y), were maintained during the early part of the growing season. In th e absence of Colorado potato beetle injury, both cultivars exhibited c ompensatory to slightly overcompensatory yield responses at low levels of potato flea beetle feeding. No yield loss was observed at up to 65 and 190 flea beetles per plant for 'Norland' and 'Russet Burbank', re spectively; above this density, yield was inversely proportional to fl ea beetle density. When 'Russet Burbank' plants had sustained early se ason Colorado potato beetle injury, there was no compensation by plant s, and yield was inversely proportional to density throughout the rang e of flea beetle treatments.