PHENOLOGY OF FLEA BEETLE (COLEOPTERA: CHRYSOMELIDAE) FLIGHT IN RELATION TO THEIR INVASION OF CANOLA FIELDS IN MANITOBA

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Abstract
A suction trap operating 1.4 m above ground and sticky traps arranged from ground level to 7 m were used to collect flea beetles during 1979–1982. The suction trap showed a peak in flight activity for Phyllotreta striolata (F.) in late April and May, but caught few beetles later in the season. The same trap showed that Phyllotreta cruciferae (Goeze) commenced flying a few days later than P. striolata, but continued to fly through the summer. The highest catch of P. cruciferae occurred in late August and early September. Prior to early June more flea beetles were caught on sticky traps at 1 and 2 m than on traps at ground level or 0.5 m. Subsequently more were caught at the two lower elevations. Beetles were captured on sticky traps up to the highest trapping height of 7 m throughout the growing season. These data suggest that the average flight elevation and level of flight activity are highest until the beginning of June for both species and then drop, and that P. cruciferae usually flies more actively and at higher elevations than P. striolata.Overwintered P. cruciferae flew only when daily maximum temperatures exceeded 14 °C. The new generation of adults was captured flying in August and September when daily maximum temperatures were as low as 4.7 °C. Throughout the season, the catch in a suction trap was negatively correlated with average wind speed.Given the extended flight period of P. cruciferae, late seeding of canola would not prevent invasion of the crop by this pest. Day to day variation in beetle catches by sticky traps or a suction trap, and trap to trap variation for sticky traps was high. Therefore, such traps would not provide sufficiently precise estimates of flea beetle densities prior to seeding to permit farmers to determine whether a field requires a seed treatment.