Patterns of diapause frequency and emergence in swede midges of southern Ontario

Abstract

1 The swede midge is an invasive pest of crucifers in North America and exhibits temporal plasticity in diapause; diapause frequencies change throughout the growing season and spring emergence is typically bimodal. Factors controlling the timing of swede midge diapause events are not well understood. 2 Pre-diapause larval swede midge populations were isolated within cages in the field and tracked for emergence over 3 years. 3 Diapause frequency was inversely correlated with photoperiod and absolute maximum air temperature, however photoperiod did not influence emergence timing. Emergence from diapause occurred in two large peaks, in mid-June and early July, with a third, smaller peak in late August. Emergence phenotypes may correspond to different diapause durations from 236 to 296 days, or post-diapause development requiring between 516 and 1449 degree days. Approximately 2% of swede midges overwintered for 2 years. 4 Early control efforts would be most effective if they targeted the diapausing cohort (i.e. adults emerging June to July) to prevent damage by subsequent generations. Although few individuals overwintered for 2 years, prolonged diapause should be considered when crop rotation is employed for swede midge management.

A Single Swede Midge (Diptera: Cecidomyiidae) Larva Can Render Cauliflower Unmarketable

“…Our trials tested larval densities that are much lower than would be experienced in an infested field where females oviposit clusters of 5–20 eggs on host plants ( Readshaw 1966 ). Traditional scout and spray IPM approaches remain inappropriate for managing swede midge in cauliflower because market-relevant damage can result from any larval feeding and adults can emerge throughout the growing season ( Hallett et al 2009a , Chen et al 2011 ; Samietz et al 2012 ; Hallett and Sears 2013 ; Des Marteaux et al 2015 ).…”

Swede midge (Diptera: Cecidomyiidae) diapause initiation under stable conditions: not a family affair

“…Since its introduction from Europe in the late 1990 s (Hallett and Heal 2001), the swede midge has spread rapidly across the northeastern United States of America and Canada and (in the latter) now ranges from Saskatchewan to Nova Scotia (Hallett 2017). Swede midge population control has proved challenging, partly owing to the considerable variation in the timing of diapause entry and emergence (Hallett et al 2009;Des Marteaux et al 2015;Hallett 2017). This variation in overwintering phenology likely contributed to the successful invasion of the swede midge, not only by allowing for multivoltinism but also by providing a means of population bet hedging (Hopper 1999;Ghalambor et al 2007;Mahdjoub and Menu 2008).…”

“…For the swede midge, facultative diapause in the third instar is initiated in response to photoperiod (with some temperature modulation), and population diapause incidence increases sigmoidally as day lengths and temperatures diminish over the growing season (Rogerson 1963;Des Marteaux et al 2015). For example, in West Wheldon, United Kingdom (the native range), swede midge diapause incidence increases from 2% in early July to nearly 100% by early November (Readshaw 1961(Readshaw , 1966.…”

“…For example, in West Wheldon, United Kingdom (the native range), swede midge diapause incidence increases from 2% in early July to nearly 100% by early November (Readshaw 1961(Readshaw , 1966. Similarly in Elora (Ontario, Canada), diapause incidence increases from 4% in late June to 100% by October (Des Marteaux et al 2015). An abrupt population shift from direct development to diapause entry (i.e., a population diapause incidence of 50%) occurs under diapause-critical conditions (typically the critical day length).…”

A Bucket-Type Emergence Trap for Detecting Overwintered Dasineura oxycoccana (Diptera: Cecidomyiidae) and Its Parasitoids in Cranberry

“…It is not known if eggs laid later in the season are progeny of overwintered or subsequent generations. If cranberry tipworm adults have a prolonged period of emergence from overwintering, as do adults of the swede midge, Contarinia nasturtii (Kieffer) (Diptera: Cecidomyiidae) (Des Marteaux et al 2015), then a proportion of eggs laid throughout the growing season would originate from overwintered females.…”