Why “when” and “where” matters: characterizing mating behavior of swede midge (Contarinia nasturtii; Diptera: Cecidomyiidae)

Pheromone mating disruption (PMD) is a pest management practice that involves the large-scale release of synthetic female sex pheromones of a pest, which effectively prevents male insects from locating female mates. To date, the most widely adopted PMD systems are used for pests of perennial high-value crops and are not cost effective for annual crops. We investigated the ecological constraints for developing a PMD system in an annual cropping system for the swede midge, an invasive pest of North America that infests Brassica crops. Phytophagous insects within the family Cecidomyiidae exhibit host-associated mating, and are highly attracted to volatile compounds from their hosts and copulate preferentially in their presence. These reproductive mating attributes could promote the success of PMD within an annual cropping system. On the other hand, lack of host-associated mating can lessen the efficacy of PMD, since midges can mate outside of the treated area and re-enter the field where offspring can infest the crop. Specifically, we asked: (1) is midge mating more successful in the presence of Brassica host plants, and (2) in what time frame does mating occur? To determine whether host-associated mating occurs, midge mating behavior was observed in cages both with and without Brassica host plants and in the presence of non-host plants. Midges were observed over 24h to determine diel mating patterns. We present our results on swede midge temporal and host-associated mating behavior and recommendations for development of a PMD system.