[Traduit par le journal]. Adults of the European skipper Thymelicus lineola, an insect pest of hay (Arthur 1966;. McNeil et al. 1975; Pengelley 1961), have been.
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NOTES
Plant-insect relationships between common milkweed Asclepias syriaca (Gentianales: Asclepiadacees) and the European skipper Thymelicus lineola (Lepidoptera: Hesperiidae)' DPpcrr-teme~ltdr biologir, U n i v ~ r s i t PL m ~ n l QrrPbec, , QrrP., Corlndcr GI K 7P4
Received February 7 , 1977 MCNEIL,J. N. 1977. Plant-insect relationships between common milkweed Asclrpicrs syr-icrctr (Gentianales: Asclepiadacees) and the European skipper Thym~licrrslit~eolo(Lepidoptera: Hesperiidae). Can. J. Bot. 55: 1553-1555. European skipper adults aggregate on common milkweed and their legs and (or) proboscis often become entangled in the flowers. Occasionally this results in the loss of legs or in the death of the insect. Normally the insects escape unharmed and frequently carry with them milkweed pollinia, attached to the extremity of their tarsi. Thus the European skipper, an insect pest, may act as a pollinating agent of a weed pest. the common milkweed. MCNEIL,J. N. 1977. Plant-insect relationships between common milkweed A.sclepicrs syr-icrccr (Gentianales: Asclepiadacees) and the European skipper Thynlrlicrrs l i ~ ~ e o l(Lepidoptera: n Hesperiidae). Can. J. Bot. 55: 1553-1555. Les adultes de I'hesperie des graminCes forment des rassemblements sur les fleurs de I'ascepiade commune ou ils sont souvent emprisonnes par les pattes et (ou) le proboscis. I1 en rCsulte parfois une perte des pattes ou la mort de I'insecte. Bien souvent, ceux qui reussisent 6 s'echapper des fleurs. portent a I'extrCmitt de leurs tarses des sacs de pollinies. En plus d'ktre insecte nuisible, I'hespCrie des graminCes joue Cgalement un r81e dans la pollinisation d'une plante nuisible, I'asclepiade commune. [Traduit par le journal]
Adults of the European skipper Thymelicus lineola, an insect pest of hay (Arthur 1966; McNeil et al. 1975; Pengelley 1961), have been recorded feeding on the following flowers: ox-eye daisy, Chrysanthemum leucanthemum L. (Mulligan and Kevan 1973; Pengelley 1961); tufted vetch, Vicia cracca L. (Mulligan and Kevan 1973); the lady-slipper orchid, Cypripediunz reginae Walt. (Arthur 1962); red clover, Trifolium pratense L., and white clover, T. repens L. (Rawson 1931); yellow sweet clover, Melilotus officinalis (L.) Desr. (Thomas 1952); sweet clover, Melilotus sp. (Pengelley 1961); Canada thistle, Cirsizrm aruense (L.) Scop. (Pengelley 1961 ; Shapiro 1971); dogbane, Apocynum sp. (Shapiro 1971); bird's-foot trefoil, Lotus corniculatus L. (Shapiro 1971); blueweed, Echium uulgare L. (Pengelley 1961); alfalfa, Medicago satiua L., and yarrow, Achillea millefolium L. (Thomas 1952); and common milkweed, Asclepias syriaca L. (Muller 1958; Rawson 1931). 'Contribution no. 190, Dtpartement de bioIogie, Universit6 Laval, QuCbec, QuC.
During my studies on the population dynamics of T. lineola in Quebec, I was particularly interested in the skipper-milkweed association. Extremely high butterfly densities were observed wherever milkweed was present (Fig. la). I observed, as did Rawson (1931), that skipper adults frequently became trapped either by their legs or by their proboscis (Fig. 16) as a result of the morphological structure of the milkweed flower. Rawson stated that adults were "caught by legs between the clefts of the glands on the pollen masses of the milkweed flower." I decided to determine if this entanglement resulted in significant adult mortality. I found that while a high percentage of adults became stuck by the legs and (or) proboscis, most were able to liberate themselves by vigorously flapping their wings and by moving their free legs. However, this action was not always without cost as on two different occasions I observed escaping adults leaving behind on flowers one or more of their legs (Fig. lc). While convinced that the actual adult mortality occurring as a direct result of becoming entangled was negligible, the patho-
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1554 CAN. J . BOT. VOL. 5 5 . 1977
NOTES
TABLE 1. Incidence of milkweed pollinia attached to the tarsi of the European skipper No. tarsi with pollinia
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...... .. . . ~, . . . . .. . . . . . .. .. .. .. .. . . . . . . . .
. . .. .. .. . .. .. .. .. .. . .. .. . . . . . .. . ~.
No. adults
0
1
17
14
9
5
2
0
0
.
logical implications of a loss of one or more legs on factors such as longevity and oviposition were worth further consideration. T o determine the proportion of individual adults missing legs, I collected sweep-net samples of free-flying adults in an area where milkweed was present and heavily frequented. Only 3 of 47 individuals captured were missing one or more legs. However, another interesting aspect of this plant-insect interaction came to light. Thirty (63.8%) of insects captured had milkweed pollinia attached to the extremity of their tarsi (Fig. Id); the number of pollinia per insect varied considerably (Table 1). The sticky accessory gland of the pollinium may be in part responsible for the insect becoming stuck or else the pollinia are collected during the butterfly's efforts to escape. The presence of pollinia has no apparent effect on the movement of T. lineolal-I observed insects carrying pollinia flying normally between two patches of milkweed more than 1 km apart. Mulligan and Findlay (1970) demonstrated that A. syriaca does not set viable seeds when flowers are enclosed in pollination bags. This underlines the necessity for allogamous outcrossing of milkweed by insect pollinators, frequently Hymenoptera (Macior 1965). At least in Quebec, T. lineola, apart from being a serious insect pest, is an important pollinator of A . syriaca, a noxious weed in many of our agricultural ecosystems.
IjSS
Acknowledgments This research was supported by Conseil des Recherches et Services agricoles du Qutbec grant LS-74-567 and National Research Council of Canada grant A9551. ARTHUR,A. P. 1962. Adults of the European skipper, Tl~ytt~elic~trs li11eoltr (Ochs.) (Lepidoptera: Hesperiidae). trapped in flowers of the Snowy Lady's Slipper orchid. Proc. Entomol. Soc. Ont. 92: 190-191. 1966. The present status of the introduced skipper, Tllyrnelic~rslit~roltr(Ochs.) (Lepidoptera: Hesperiidae). in North America and possible methods of control. Can. Entomol. 98: 622426. MACIOR.L . W. 1965. Insect adaptation and behaviour in A.sc1epiir.s pollination. Bull. Torrey Bot. Club, 92: 114126. MCNEIL.J . N.. R. M. DUCHESNE. and A. C O M E A U . 1975. Known distribution of the European skipper, Thytnelicrrs litreoltr (Lepidoptera: Hesperiidae), in Quebec. Can. Entomol. 107: 1221-1225. J . 1958. Tlryttrelic~rrslirleoltr. a European skipper MULLER, (Hesperiidae) new for New Jersey. Lepid. News. 12: 174. . Reproductive M U L L I G AG. N , A.,and J . N. F I N D L A Y1970. systems end colonization in Canadian weeds. Can. J. Bot. 48: 859-860. MULLIGAN G., A,, and P. G. KEVAN.1973. Color brightness and other floral characteristics attracting insects to the blooms of some Canadian weeds. Can. J . Bot. 51: 1939-1952. PENGELLEY. D. H. 1961. Tl~yt1relicr(slit~eoltr (Ochs.) (Lepidoptera: Hesperiidae), a pest of hay and pasture grasses in southern Ontario. Proc. Entomol. Soc. Ont. 91: 189-197. RAWSON.G. W. 1931. The addition of a new skipper Adoptretr litlrolir (Ochs.) to the list of U.S. Lepidoptera. J . N.Y. Entomol. Soc. 79: 27-30. SHAPIRO. A. M. 1971. Range extension for the European litrt~oltr, in the Northwest (Lepiskipper. Tl~yitrc~licrrs doptera: Hesperiidae). J . N.Y. Entomol. Soc. 79: 27-30. THOMAS,E. S. 1952. A European skipper. Adopcietr litreoln. at Columbus. Ohio. Lepid. News. 6: 92-93.
