D3430: Overwintering sites and spring emergence patterns of flea beetle (Coleoptera: Chrysomelidae) in organic vegetable farms in Quebec

The crucifer flea beetle Phyllotreta crucifera (Goeze) and the striped flea beetle Phyllotreta striolata (Fabricus) are important pests of cruciferous crops in Québec. For organic growers, control methods are limited to exclusion insect netting and spinosad applications. Even with an adequate use of exclusion nets, flea beetle populations increase in protected crops, raising questions about the capacity of those pests to overwinter directly in the field. The project aimed to validate the overwintering sites of P. crucifera and P. striolata on diversified organic farms in Québec. The experiment was realized on six farms, where emergence in the field and in forest edges were compared. Number of adults of each species were recorded weekly between March 24^th and May 31^st within four 0.25 m² emergence cages in each environment in every site. Phyllotreta striolata emergence patterns indicated the highest emergence between April 20^th and May 3^rd. Phyllotreta crucifera emergence peak happen later on May 18^th. For both species, cumulative emergence was significantly higher in the forest edges compared to the field emergence (P. striolata: 34.8 ± 30.6 ind./m² (± SE) vs 0.3 ± 0.3 ind./m² , P = 0.0093; P. crucifera: 14.7 ± 7.2 ind./m² vs 0.3 ± 0.2 ind./m² , P = 0.0089). Those results support the established knowledge about overwintering sites of P. crucifera and P. striolata and provide valuable insight of flea beetle crop colonization in organic farms.