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Table 12
Phyllotreta spp.. 75
Several attacks by the parasitoid females on adults of P. strio/ata were observed on rape
plants in the plots during releases.
Flea beetles from the release sites were collected in 1979 and 1980 and reared in the
laboratory for evidence of parasitoid establishment. Numbers collected were 8502 P.
eruciferae, 261 P. strio/ata, and smaller numbers of other rape-infesting beetles in June
1979 from the 1978 release site; 3082 P. cruciferae and 674 P. siriolaia during July­
October 1979 from the 1979 release site; and 5039 P. siriolaia and 418 Psylliodes
punetlllata Melsh. in April 1980 from overwintering sites adjacent to the 1979 release
site. No M. hieolor emerged from these beetles.
Some adults of M. bicolor and M. sp Z were retained for laboratory studies (Table 12).
These studies showed that females of ,H. bicolor parasitized more P. striolClla than P.
cruciferae when equal numbers of the two hosts were present.
Imported parasitoids of Phyllolrela spp. used for laboratory studies
Species
Evaluation of Control Attempts
Recommendations
Microetonus hieolor Wesm.
Mieroelonus sp. Z
Year Origin
1977 Germany
1978 Austria
Switzerland
1979 Austria
1980 Austria
1977 Germany
1978 Switzerland
1979 Austria
1980 Austria
Number
Several factors have limited the probability of establishment. First, small numbers of
parasitoids were released. Second. scarcity ofthe preferred host. P. striolala. at Glenlea
may have limited oviposition by the females after release. Third. dispersal of the beetles
in autumn to overwintering sites and in spring in search of food, scattered the population
of parasitized beetles and thereby reduced the probability of female parasitoids that
emerged in the spring being fertilized. If M. hieolor has become established, the small
numbers released and scattering of the population would minimize our chances of
detecting establishment until the incidence of parasitism has increased substantially.
Larger colonies of M. bieolor (> 50() females per colony) should be released. Although
large numbers of parasitized flea beetles have been collected by the CIBC. only small
numbers of parasitoid adults have been reared and female colony size has never exceeded
100. There are two reasons for the small parasitoid colonies. First. many of the
immature parasitoids enter diapause and eventually die when the hosts are reared in
cages in Europe. Second. parasitoid emergence from cocoons obtained in Europe has
usually been less than 50%. The possibility that higher temperature and longer photoperiod
prevent diapause should be investigated. as well as the factors responsible for
poor survival of the parasitoid larvae and pupae in cocoons.
The possibility of obtaining additional candidate parasitoid species for release in
Canada should be investigated in discussions planned in 1981 between staff of the CIBC
and scientists from the USSR.
43
131
20
26
8
9
2
13
I