J . E1'T()\I(11. S()C lil( l T COI.lI \IIlI.\ 73 (19761. D,·:(' :3 1. 1976 7

Literature Cited Il odl·k. I. 197:L Hi olog.v of Coccin ellid ae. Junk. The Hague. 260 p. Kapur. A.D. 1942. Bionomics of some Coccinellidae, predaceous on a phids and coccids in North India. lnd. J. Entomol. 4: 49-56. Kulman. H. :V1. 197 1. Parasitism of Anatis quindeei l11J)unl'tal a bv lIom alol)·lw.; krminalis. Ann. Entomol. Soc. Amer. 641 11:953-54. Leonard . 'VI. D. 193:1. A braconid parasit e of a Coccinelli d new in Puerto Hie o. ,J. F:con . 1·: n LO mol. :!1i:294 "Iiller. n. L . and W . L. Thompson. 1926. Life histories of Lady-beetle predaLOr s of the citrus iJphid. FloridiJ Entomol. 111: 40-46.57-:19. Miller. R. L. and W. L. Thompson. 1927. Life histories of Lady-beetle predators of t he citrus aphid. Florida Entomol. II : 1-18. \lueslwck. C. F. W .. K. V. Krombein and H. K. Townes. 19:) 1. Hvmenoptera of America "Iorlh of Mexico. U.S.D.A. agr. Monograph 2. 1~ 20 p. Peck. O. 1963. A catalogue of the Nearctic Chalcid oidae (I nsecta: H"menopteriJ I. Can. ~ : nt oll1o l. Suppl. 30. 1092 p.

PREDATION BY CARPENTER ANTS: A DETERRENT TO THE SPREAD OF

JUDITH H. MYERS AND BARBARA J. CAMPBELL Institute of Resource Ecology and Department of Plant Science University of British Colu mbia. Vancouver

ABSTRACT Cinnabar moth, an introduced biological cont rol agent for tansy ragwort. suffers heavy predation by carpenter ants in recently logged areas of Oregon. We suggest that t his mortality factor wi ll reduce the spread of Cin­ nabar moth, t hus preventing it from attacking a major seed source of tansy ragwort and reducing its potential as a biological control agent. Single larvae escape predation by ants more often than those in groups which suggests that carpenter ant predation may select for larval dispersal.

The Cinnabar moth, Tyria jacobaeae L. alienus. a predaceous ant. Further studies of 1Arctiidae). has been widely spread from its Lasius predation led Van der Meijden (1973) to native E urope because of its potential as a conclu de that this ant may limi t Ci nnabar biological control agent against the weed Tansy numbers in some sand dune areas of t he Neth­ ragwort, Senecio jacobaea L. The success of erlands. these in troductions has ranged from "never The following observations on predation by seen again" to "abundant and thriving" a fter ants were made as a by-product of experiments 15 years. At Abbotsford, B.C. the failure of the designed to investigate larval dispersal in the first releases was attributed to heavy predation Ci nnabar moth. by ground beetles 1Wilkinson , 1965). In the Gippsland vicinity of Victoria, Australia a Study Area and Methods mecopteran, Harpobittacus nigriceps. heavily The study was carried out in Linn County , predated a newly introduced Cinnabar popula­ Oregon which lies between t he western slope of tion and a nuclear polyhedral virus assured the t he Cascade Mountains and the eastern edge of failure of the attempted in troduction (Borne­ the Will amette Va lley. Larvae were collected missza, 1966). The causes for the lack of from the Silbernagel population which was success of other introductions are not known studied by Isaacson 11973). and were trans­ (Hawkes. 1968, Harris et al. 1975, fsaacson ported to an area about 10 miles to the south on 1973). Neal Creek Road. This area was logged within Van der Meijden (197 1) records an almost the last 10 years so that stumps and fallen logs perfect correlation between the log % mortality were abundant on the steep hillsides. Tansy of Cinnabar larvae and log density of Lasius ragwort is a common component of t he herb- 8 J. ENT()\IOL Soc BIUT CO!'U\1IlIA 73 (19761. DF:c 31. 1976

TABLE 1. Survival after 2 days of 3rd and 4th instar Cinn'abar larvae introduced to tansy ragwort plants in groups of approximately 20 individuals.

Percent Survival 0-10% 11 -25% 40% 65% 80-90% Frequency 8 ::l 2 1 3 Total Survival = 98/ 329=30%

aceous vegetation which has invaded this area, Results and moth populations occur sporadically along The disappearance rate of larvae from tansy the road. ragwort plants was exceedingly high (Table 11. We chose the particular site for the study Observations revealed that the reason for this because while abundant, large ragwort plants disappearance was the activity of carpenter occurred there, Cinnabar moth larvae were ants, Camponotlls sp., which nested in sur- lacking. We placed third and fourth instar rounding stumps. Ants were seen to attack and larvae on plants in groups of approximately 20 carry off the Cinnabar moth caterpillars but individuals, and recorded their movement from to verify t hat t he high rate of disappearance the central plant to surrounding plants. was due to ant predation we set up groups of TABLE 2. A comparison of Cinnabar larval survival on tansy ragwort plants to which ants had access and those which were ant-free. Larvae placed on plants in groups of 10.

Plants Without Ants Plants With Ants Original Number 49 40 Number After 2 Days 43 9 Percent Survival 86 23

larvae on plants with the base coated with Discussion "stickum" which prevented ants from crawling The relationship of the carpenter ant to the onto the plants. The comparative rates of dis­ Cinnabar larvae is an interesting one. The appearance of larvae on ant-free plants and Cinnabar larvae feed preferent ially at the tops those to which ants had access are compared in of the plants on the flower buds. Their feeding Table 2. activity re leases sap a nd t he carpe n ter a nLs will feed beside the caterpillars taking t he sap We observed that those Cinnabar larvae from the freshly cut surface. The t wo species which dispersed from the original plant had have been observed to coexist in this way. better short term survival than those which re- However, suddenly an ant may attack a cater- mained behind (Table 31. The effect of group pillar. The usual result is that the caterpillar size was further tested by comparing the sur- falls from the plant, sometimes taking its vival of single larvae to those in groups of 10. attacker with it . If other ants are nearby t hey While the survival of these individual larvae too will join in the attack. On one occasion wa s net as high as that of the natural dis- eight larvae lived two days on a plant that was persers (Table 3), it was almost double that of occasionally visited by ants. Suddenly t he larvae in groups of 10 (Table 2) ave! a 2 day attack began, and within one hour only t hree observation period. remained the others having been carried off TABLE :3. Survival after 2 days of Cinnabar larvae which dispersed nat uraliy from original tansy ragwort plants or were placed individually on plants.

Larvae Larvae Placed Dispersed On Individual Naturally Plants

Original Number 10 31 Number After 2 Days 9 13 Percent Survival 90 42 ,1. E:->Tm l{l l.. Soc Burr C() 1.II ~ IH 1.· \ 73 (1976). DI':C 3 1. 1976 9 by the carpenter ants. a situation in which dispersal of Cinnabar Tansy ragwort is common in Oregon on the larvae could be at a strong selective advantage. extensively logged slopes of the Cascades and The general interpretation has been that in of the Coastal mountains to the West. Although areas of high predation. survival of dispersing in many areas Cinnabar moths have become larvae will be low (Green. 1974). However. a l­ established (Nagel and Isaacson. 1974) the though larvae are exposed to predation while presence of carpenter ants in this environment traversing from one plant to another. aban­ will undoubtedly influence the success of the donment of the usual clumped distribution of natural spread of the moth to tansy ragwort Cinnabar moth larvae might make the areas. This wi ll interfere with the attempt to difference between success and failure of estab­ destroy t he source for tansy ragwort seed li shment. If there is a genetic component to which these areas provide. dispersal one might predict strong selection for Predation by carpenter ants gives rise to dispersal in these areas.

References Bornemissza. G. F . 1966. An attempt to control ragwort in Australia with the Cinnabar Moth. Callimorpha jacobaeae (L.) (Arctiidae: ). Australian J. of Zoology 14 : 201-243. Green. W. Q. 1974. An antagoni stic /host-plant system: The problem of persistence. Ph.D. t hesis. University of British Columbia. Hawkes. R. B. 1968. The Cinnabar moth, Tyria jacobaeae. for control of tansy ragwort. J. econ. Ent.61:499-501. Harris, P .. A. T. S. Wilkinson. M. E. Neary . L. S. Thompson, and D. Finnamore. 1975. Establish­ ment in Canada of the Cinnabar Moth. Tyria jacobaeal' (Lepidoptera: Arctiidae) for con­ t rolling t he weed Se nec io jaco baea. Can. E nt. 107 :913-9 17. Isaacson, D. L. 1973. A life table for the Cinnabar Moth, Tyria jacobaeae. in Oregon. Entomophaga 18: 29 1-303. Nagel. W . D. and D. L. Isaacson. 1974. Tyria jacobaeae and tansy ragwort in Western Oregon. J. econ. Ent. 67: 494-496. Van der Meijden. E. 1971. Sl' necio and Tyria (Callimorpha) in a Dutch dune area. A study on an interaction between a monophagous consumer and its host plant. Dynamics of Popula­ tions (P. J . den Boer and G. R. Gradwell, eds) (Oosterbeek, 1970): 390-404. ______. 1973. Experiments on dispersal. late-larval predation, and pupation in the Cinnabar Moth (Tyria jacobaeae L.) with a radio-active label (' 92 Ir). Neth. J. Zoo1. 23 : 403-445. Wilkinson. A. T. S. 1965. Releases of Cinnabar Moth, Hypocrita jacobaeae IL.) (Lepidoptera: Arctiidae) on tansy ragwort in British Columbia. Proc. E nt. Soc. Br. Columbia. 62: 10-1 3.