Journal of Pest Science (2018) 91:551–563
Oviposition preference, larval distribution and impact of the swede
midge, Contarinia nasturtii, on growth and yield of canola
Jonathon L. Williams
· Rebecca H. Hallett
Received: 6 April 2017 / Revised: 27 August 2017 / Accepted: 16 September 2017 / Published online: 8 December 2017
© Springer-Verlag GmbH Germany, part of Springer Nature 2017
The swede midge (Contarinia nasturtii) has become a signiﬁcant economic pest of canola (Brassica napus L.) in Ontario
and an emergent pest in the Prairie provinces. Determining yield impacts of swede midge damage and the growth stage(s)
at which canola is most vulnerable or attractive to swede midge will contribute to the development of pest management
recommendations throughout the growth of the crop. In four experiments, canola plants were exposed to speciﬁc densi-
ties of adult swede midge and measures of oviposition, damage and yield were collected. There was a signiﬁcant positive
relationship between female density and total oviposition per plant with a very high capacity for larval numbers on canola;
up to ~ 4000. Given a choice of four growth stages, approximately 85% of oviposition occurred on seven-leaf and early bud
canola. Given no choice, the high total oviposition on 3-leaf and ﬂowering stages suggests that swede midge will oviposit
on less favorable canola growth stages, if no others are present. Damage sustained on primary racemes remained relatively
constant over time. However, damage ratings on secondary and tertiary racemes decreased over time in the highest treatment
densities, suggesting compensation by the plant. All yield measures, except seed weight per pod, signiﬁcantly decreased
with increasing female density on primary and/or secondary racemes. A density of ~ 0.6 females per plant resulted in 10%
reductions in the number of pods and seed weight produced on primary racemes. These results support recommendations
for insecticide applications at, or just prior to, the early bud stage.
Keywords Diptera · Cecidomyiidae · Brassica napus · Oviposition preference · Density-dependent eﬀects · Compensatory
Contarinia nasturtii is an invasive pest of brassicaceous
crops in North America.
Laboratory studies investigated the impacts of varying
densities of female swede midge on canola growth and
Canola plants at the seven-leaf and early bud stages were
preferred for oviposition.
All yield measures, except seed weight per pod, declined
with increasing female midge density.
Results are important for development of insecticide
application recommendations with respect to canola
stage and swede midge population densities.
The swede midge, Contarinia nasturtii (Kieﬀer) (Diptera:
Cecidomyiidae), is a small invasive ﬂy and pest of numerous
economically important crops in the Brassicaceae (Hallett
and Heal 2001). Since the ﬁrst North American record in
2000 on cole crops (Brassica oleracea L.), the swede midge
has become a signiﬁcant economic pest of canola (Brassica
napus L., B. rapa L. and B. juncea L.) in Ontario and an
emergent pest in the Prairie provinces of Canada (i.e., Sas-
katchewan, Manitoba and Alberta) (Hallett and Heal 2001;
CFIA 2009; OMAFRA 2011, 2013, 2014).
The swede midge causes damage to host plants dur-
ing its larval stage (Readshaw 1961; Hallett 2007). Adult
Communicated by J. Gross.
* Rebecca H. Hallett
School of Environmental Sciences, University of Guelph,
Guelph, ON N1G 2W1, Canada