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Pest Status
Background
Chapter 21
Phyllotreta spp., Flea Beetles (Coleoptera:
Chrysomelidae)
H.G. WYLIE, W.l. TURNOCK and L. BURGESS
Damage to rape crops in western Canada by flea beetles is caused primarily by adults of
two species, Phy/lotreta crllciferae (Goeze) and Phyl/otreta strio/ata (F.). A third flea
beetle, Psylliodes puncru/ata Melsh., occurs in virtually all seedling rape crops on the
prairies but by itself does not constitute a serious problem. Phyllolrela robusta Lee. and
Phyllolrela a/bionica (Lee.) occur occasionally on rape crops in Saskatchewan (Burgess
1977a) and three other described crucifer-feeding species in the genus Phyllotreta are
known to occur in that province (Burgess 1981b).
P. cruciferae was introduced on the west coast of North America in the early 1920s
(Milliron 1953) and was abundant on crucifers in the Prairie Provinces by the late 1930s
and early 1940s (Westdal & Romanow 1972). P. cruciferae has usually been the
dominant flea beetle in rape fields across the prairies, particularly in the more southerly
parts of the rape-growing area.
P. slrio/ala apparently was introduced to North America before 1801 (Chittenden
1923) and was present in Canada from the Atlantic provinces to British Columbia by the
early 1900s (Burgess 1977a). This species infests rape crops across the parkland
agricultural area from southern Manitoba to north of the Peace River in Alberta (Burgess
1977a). P. strio/ata has recently gained in relative importance as a pest in both Saskatchwan
and Alberta, being more abundant than P. cruciferae in some Saskatchewan rape
fields after 1976 (Burgess 1981a) and in some fields in central Alberta since 1979 (H.G.
Philip 1981 personal communication).
Flea beetle problems in rape crops have increased in severity in the past decade. In
Manitoba and Saskatchewan most fields of rape are threatened annually by these
insects. In Alberta, flea beetle problems have tended to be less acute than in Saskatchewan
and Manitoba, but in 1979 and 1980 heavy infestations were reported from
most rape-growing areas (H.G. Philip 1981 personal communication). The estimated
percentages of rape acreage treated with insecticides in 1979 were 75% in Manitoba,
59% in Saskatchewan, and 45% in Alberta (Turnock & Samborski 1980). Although yield
loss due to flea beetle damage is difficult to estimate. yield reductions of 15-50% have
occurred in untreated plots in insecticide trials (Turnock & Samborski 1980). The
combination of flea beetles and poor conditions for germination that occurred in 1975
and 1980 in Manitoba completely destroyed many fields of rape.
This is the first biological control programme set up against flea beetles of the genus
Phyllotreta. The programme was initiated because of the low level of natural control of
P. cruciferae and P. strio/ata and because these are introduced species. Studies in
Manitoba since 1975 confirmed only three native parasitoids of rape-infesting flea
beetles: a braconid. Microctonus \'ittatae Mues.; a mermithid; and an allantonematid.
Howardu/a sp. M. viltatae parasitizes adults of both P. cruciferae and P. strio/ala. but
the incidence of parasitism is usually less than 5%. Various factors limit the impact of
this braconid in Manitoba. including its short adult life and low oviposition rate. and
poor temporal synchronization with the host's population in mid-summer. Neither the
mermithid nor the allantonematid is sufficiently abundant to limit populations of the
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