C. Godin et G. Boivin, LEPIDOPTEROUS PESTS OF BRASSICA CROPS AND THEIR PARASITOIDS IN SOUTHWESTERN QUEBEC, Environmental entomology, 27(5), 1998, pp. 1157-1165
To evaluate the potential of using parasitoids against lepidopterous p
ests of Brassica oleracea (L.) in southwestern Quebec, we studied the
relative importance of parasitoids and diseases of lepidopterous pests
occurring on Brussels sprouts, and on early and late plantings of bro
ccoli and cabbage. During the 2-yr study (1993-1994), Plutella xyloste
lla (L.) and Artogeia rapae (L.) were the most important lepidopterous
species on early and late plantings, respectively. Late broccoli plan
tings were particularly infested by A. rapae. In total, 14 parasitoid
and 3 hyperparasitoid species were recovered (15 Hymenoptera, 2 Dipter
a). Plutella xylostella and A. rapae had the highest parasitism levels
, with 5 and 6 parasitoid species, respectively. Overall, parasitoids
accounted for 65 and 43%, and diseases accounted for 22 and 43% of the
mortality of P. xylostella and A. rapae, respectively. Arrangement of
the data into a parasitoid web showed that the most common parasitoid
species was the newly established Cotesia rubecula (Marshall). It was
the most important larval parasitoid of A. rapae and had the highest
hyperparasitism level (11%). Most parasitoid species were restricted t
o 1 host species, but all hyperparasitoid species were polyphagous and
parasitized only the most common parasitoid species. Natural control
by parasitoids and diseases was important only late in the season, and
restricted to maturing larvae and to pupae. Control would be improved
by focusing efforts earlier in the season, and on eggs and young larv
ae of the pests.