WINTER SAMPLING TO DETERMINE OVERWINTERING SITES AND ESTIMATE DENSITY OF ADULT FLEA BEETLE PESTS OF RAPE (COLEOPTERA: CHRYSOMELIDAE)

The three most important flea beetle pests of western Canadian rape crops appear to be selective in choosing their overwintering sites, as the greatest densities of overwintering adults of Phyllotreta cruciferae (Goeze) and Psylliodes punctulata Melsh. were found in leaf litter and turf beneath hedges and(or) shelterbelts, while that of Phyllotreta striolata (F.) was found in these materials beneath groves of native trees. Most beetles overwintered near the surface in leaf litter and turf rather than in the underlying soil. Within a habitat, sample to sample variation for each species was usually large and the overwintering populations appear to have an aggregated distribution pattern. Winter samples over a 6-year period from all five habitat types combined or from parkland groves reflected the continuously low level of the field population of Psylliodes punctulata, and a marked increase in the field population of P. striolata that occurred in one year. Winter samples taken from hedges and(or) shelterbelts provided little information on population sizes or trends except for indicating the general low level of the Psylliodes punctulata population. Winter mortality was low for all three species. The foregoing information will be useful for developing future sampling plans so that overwintering flea beetle populations can be estimated more reliably.