Diel patterns of emergence and reproductive behaviour in the invasive swede midge (Diptera: Cecidomyiidae)

Abstract

Swede midge (Contarinia nasturtii (Kieffer); Diptera: Cecidomyiidae) is a serious invasive pest of Brassica Linnaeus (Brassicaceae) oilseed and vegetable crops in Canada and the United States of America. Pheromone mating disruption is a promising new tactic for managing this difficult pest, but research is needed to determine how pheromone delivery can be optimised. With an understanding of swede midge diel mating patterns, pest managers could limit pheromone release to periods when midges are sexually active. We conducted a series of 24-hour trials to test whether swede midge exhibit diel periodicity of emergence, female calling, and male capture in pheromone traps. We found that females began releasing pheromones almost immediately following emergence within the first five hours after dawn. In the field, we found that males were most active from dawn until late morning, indicating that midges mate primarily during the first five hours of photophase. Low levels of reproductive activity during midday and nighttime hours present opportunities to turn off dispensers and reduce the cost of pheromone inputs in a swede midge mating disruption system.

Synthetic pheromone exposure increases calling and reduces subsequent mating in female Contarinia nasturtii (Diptera: Cecidomyiidae)

“…We observed female calling behavior from 0930-1330, which included the morning hours when females are most likely to call, as well as 1 h into the inactive period (1230-1330). 48 Every 15 min we recorded whether midges were calling using a binary system (yes or no) when their ovipositors were visibly extruded by at least two-thirds its total length, which is characteristic of cecidomyiid pheromone-releasing behavior. 52,53 At the end of each observational period, we recorded whether midges died or did not call at all ('noncallers") during the experiment.…”

“…Due to limitations to moving individuals from the Swiss colony, as outlined in our permit (USDA APHIS permit number P526P-13-03136), we were unable to use Swiss midges in our field experiments. Both colonies were reared using 'Snow Crown' cauliflower in cages at approximately 25°C with relative humidity (RH) >30% under a 16L:8D photoperiod (see Hodgdon et al 47,48 ).…”

“…50 For the calling experiments, we collected females from the Ontario colony as they emerged from the soil during the peak emergence period for females, within the first 3 h after dawn. 48 For the mating experiments, we used a combination of newly emerging midges from the Swiss colony, as well as <24 h-old unmated males and females from single-female progenies reared individually in separate containers. Due to the genetics of sex determination in cecidomyiids, the majority of female swede midges (~80%, pers.…”

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

“…Current conventional management recommendations for swede midge are to use systemic neonicotinoids at transplant, followed by regular sprays of foliar insecticides for the remainder of the growing season ( Chen et al 2011 ; Hodgdon et al 2017 ), disrupting decades of effective IPM in Brassica systems ( Rodriguez Salamanca 2014 ). An alternative approach is to use an action threshold based on the capture of five males per pheromone trap per day with a minimum 7-d pesticide retreatment interval ( Hallett and Sears 2013 ).…”

“…This strategy reduces damage to acceptable levels in cabbage, but not cauliflower, possibly because cabbage heartleaves protect the developing meristem from feeding larvae ( Andaloro et al 1983 ). Also, organic growers are limited to using large-scale crop rotations ( Chen et al 2009 ) and/or covering crops with specialty insect netting ( Hodgdon et al 2017 ), both expensive strategies.…”