YIELD LOSSES IN CANOLA CAUSED BY ADULT AND LARVAL FLEA BEETLES, PHYLOTRETA CRUCIFERAE (COLEOPTERA: CHRYSOMELIDAE)

The temporal aspects of the effect of feeding damage to canola seedlings by adult flea beetles on yield were determined by protecting plants in 0.836-m2 field plots from beetle attack with screen cages for varying periods. Yield was reduced most when plants were damaged during stages 1.0–2.2, 5–10 days after germination, but was not reduced when they were damaged after reaching stages 2.3–2.4, 20 days after germination. Plots exposed to attack for periods greater than 5 days before protection had smaller yields and fewer plants than plots protected from the time of germination for 5 or more days before exposure to flea beetle attack. Yield losses caused by larvae were measured by growing plants inside field cages to stage 2.3–2.4 before exposing them to feral adults to establish larval populations; yields of plots treated subsequently with drenches of carbofuran to kill larvae were then compared with yields of untreated plots. A yield loss of 5% was observed at larval densities of 0.16/cm2, estimated from soil core samples and captures of adults in emergence cages. The results confirm that continuous protection of canola during and after germination is superior to post-germination protection and suggest that activities of flea beetle larvae reduce yield.