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Pest Status
Background
Chapter 23
Thymelicus lineola (Ochsenheimer),
European Skipper (Lepidoptera:
Hesperiidae)
J.N. McNEIL
In the last review dealing with the European skipper. Thymelicus lineola (Ochs.), Arthur
(1971) reported that the distribution of this insect in Canada was limited to Ontario,
Quebec. New Brunswick. and Nova Scotia in the east. with one localized population at
Terrace, British Columbia. At that time economic losses caused by T. Iilleola had been
recorded in Grey and Hastings Counties. Ontario. The distribution of the skipper has
increased considerably and is now found in Prince Edward Island (Thompson 1974).
Newfoundland (Jackson 1978). and in Manitoba (Preston & Westwood 1981). Also the
population in British Columbia has now spread into the Lake Shuswap area (J. Proctor.
1982. personal communication).
Important hay losses have been recorded in Ontario (K. Bereza & W. Riley, 1978,
personal communication. Quebec (McNeil et al. 1975), and Prince Edward Island
(Thompson 1977). establishing it as a major pest species oftimothy in the more northerly
areas of its distribution. While the skipper is present throughout most northeastern
states (Arthur 1971) the only incidence where T. lineola has reached pest status occurred
in northern Michigan (R.F. Ruppel, 1977. personal communication).
Bacillus thurillgiellSis Berliner. has proven effective in controlling larval skipper populations
(Arthur & Angus 1965. Arthur 1968. McNeil et al. 1977) and is now recommended
by the Conseil des productions vegetales du Quebec (1 x 10 10 I.U./ha) if control measures
are required. It not only offers satisfactory foliage protection when compared with chemical
insecticides (Thompson 1977. Letendre & McNeil 1980), but also reduces the possible
impact on non-target species, such as bees.
The discovery of a nuclear polyhedrosis virus (NPV) affecting a high percentage of larval
populations around Normandin. Quebec (Smimoff 1974) stimulated research to evaluate its
potential as a biological control agent for T. lineola. Smimoff et al. (1976) and Duchesne
(1980) demonstrated the efficacy of this virus. however its action is much slower than B.
thurillgiellSis. Following an aerial application of B. thllringiellSis 1 x 10 10 I.U. at 18.71
l/ha. infected larvae were observed within 2 days and 100% mortality was obtained in 6
days (Fig. 2a). Defoliation levels at the time of harvest were 20%. the same a'i pre-treatment
levels. while in the controls defoliation averaged 90%. By comparison an aerial application
of the NPV. 5 x 10 6 polyhedra/ml at 18.71 l/ha. gave the same mortality but required
considerably more time (Fig. 2b). Also defoliation at harvest was 50%, and while being
lower than the 100% in the controls, was significantly higher than the pre-treatment level of
20%. Thus the virus has less potential than B. thllrillgiensis as a curative means of control,
but could be introduced as a preventative measure if populations are beginning to increase
but have not reached very high larval densities. This would be advantageous as the virus
persists in the population and has an effect over several years (Duchesne 1980). While few
other pathogens have been found infecting skipper larvae in Quebec. two entomopathogenic
fungi ZoophtJlOra radicans and Entomophthora egressa have been isolated from larvae
collected at Amqui in 1977 and 1978 (McNeil & MacLeod 1982).
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