Operophtera brumata (L.) -- Geometridae
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This polyphagous defoliator of hardwoods is native to most of Europe and parts of Asia, where it is particularly frequent on fruit trees and oak. It was first recognized as an accidental introduction on the south shore of Nova Scotia in 1949 and eventually extended its range to the whole of this region together with small isolated parts of New Brunswick and Price Edward Island by 1958. Winter moth is also a serious pest of apples in Europe and of hazelnuts, cherries, and apples in Oregon (AliNiazee 1986, Croft & AliNiazee 1999).
In the first few years after its appearance in Nova Scotia, damage was evident in apple orchards, shade trees and oak forests. However, at this time hardwoods were not commercially exploited in the Province and so the winter moth was not considered a serious pest (Embree 1971). Consequently it was possible to initiate a biological control program rather than a program of insecticide eradication. The general research policy in the early 1950's was directed towards population dynamics of forest insect populations and thus the biological control program was initiated in 1954 with a view to population studies of the host and introduced parasitoids.
Prior to the introduction of parasitoids from Europe, the winter moth fluctuated erratically at high population densities. These fluctuations resulted from the coincidence of hatching of the overwintering eggs and bud burst in early spring (Embree 1965a,b). This same key mortality factor was also found to be responsible for changes in population levels of winter moth in Britain (Varley & Gradwell 1968).
Three tachinid and three ichneumonid parasitoids were obtained in sufficient quantity for introduction into Nova Scotia from Europe. The parasitoids were collected and shipped to Canada by staff of the Belleville Laboratory and the CIBC and field releases were made during the period 1954-62. These included releases of over 22,000 individuals of the tachinid Cyzenis albicans (Falk.) and a total of 2,261 individuals of the ichneumonid, Agrypon flaveolatum (Grav.), the only two species that became established. C. albicans is very fecund and oviposits microtype eggs around the edge of damaged foliage where they are ingested by late-instar host larvae. The egg hatch in the midgut of the host and the larvae bore through the gut wall to develop rapidly after the host has pupated. The tachinid pupates and overwinters within the host pupal case in the ground. The biology of A. flaveolatum is similar but its oviposits directly into the host larvae and has larger eggs and much lower fecundity.
Following the establishment of these two parasitoids, parasitism by C. albicans increased rapidly to 50% in 1960 and life table data showed that a considerable increase in prepupal mortality was responsible for the collapse of the winter moth population in the main study site (Embree 1965a,b). Parasitism by A. flaveolatum increased only following the initial decline of the host outbreak and while it may have enhanced the depression of the winter moth density, population models indicate that the efficiency of C. albicans alone is sufficient to account for successful biological control (Hassell 1980). However, a more recent analysis of the life table data from Nova Scotia and Britain (Roland, pers. comm.) indicates that the increased pupal mortality may have arisen only indirectly from the introduction of C. albicans. Increased parasitism by C. albicans is closely followed by an increase in the activity of soil predators, perhaps sustained on overwintering C. albicans puparia through late summer and early spring when prey are generally scarcer. Thus predation rather than parasitism may be more directly responsible for the observed increase in winter moth pupal mortality. Recent unpublished work in British Columbia indicates that staphylinid predators are especially important in regulation and that C. albicans puparia are avoided because they are too large for the predators.
More recently, between 1976 and 1978, winter moth has been noted in Oregon, Washington and British Columbia on various hardwood and fruit trees. Both C. albicans and A. flaveolatum were relocated to these areas between 1979 and 1982 and recoveries were made in many regions (Kimberling et al. 1986). However, it is too early to determine the success of these releases. But in contrast to the earlier program in Nova Scotia, the western program has been conducted at a time when research policy has moved away from population dynamics toward practical application of pest control and thus no detailed monitoring of the winter moth before and after parasitoid release has been made.
This program is often considered a good example of biological control in which, in contrast to earlier multiple introduction programs, selective introduction were made. These led to the establishment of a high host density specialist (Cyzenis), with high fecundity to bring about the collapse of an outbreak, and a low host density specialist (Agrypon), that has good searching ability to maintain the collapsed population at a low level of abundance. However, the main reason for the release of a smaller number of parasitoid species was the relatively meager size of collections in Europe, where winter moth abundance was not high at the time. Thus the only conscious selection process was of parasitoid species obtained in sufficient quantity for meaningful release (Mesnil 1967), although once the two established parasitoids were becoming effective in the early 1960's a decision was made to curtail releases of other species (Embree 1966). The end results were the successful establishment of two particularly suitable parasitoids and the program provides one of the best examples of the detailed evaluation of a biological control project. Also as was pointed out in earlier sections, the development of a detailed model in England prior to the importations tended to show very little regulatory impact by Cyzenis, which might have precluded its importation into North America.
For additional detail on biological control effort and biology of host and natural enemies, please also see the following (Silvestri 1941, McNay 1957, Graham 1958, Maybee 1958, 1959; Embree 1960, 1966; Wylie 1960, Cuming 1961, McGugan & Coppel 1962, Williamson 1962, 1963; Embree & Sisojevic 1965).
REFERENCES: [Additional references may be found at: MELVYL Library ]
AliNiazee, M. T. 1986. The European winter moth as a pest of filberts: Damage and chemical control. J. Ent. Soc. British Columbia 83: 6-12.
Croft, B. A. & M. T. AliNiazee. 1999. Biological control in deciduous tree fruit crops. In: Bellows, T. S. & T. W. Fisher (eds.), Handbook of Biological Control: Principles and Applications. Academic Press, San Diego, New York. 1046 p.
Cuming, F. G. 1961. The distribution, life history and economic importance of the winter moth, Operophtera brumata (L.) (Lepidoptera: Geometridae) in Nova Scotia. Canad. Ent. 93: 135-42.
Embree, D. G. 1960. Observations on the spread of Cyzenis albicans, an introduced parasite of the winter moth, Operophtera brumata (L.) in Nova Scotia. Canad. Ent. 92: 862-64.
Embree, D. G. 1965a. The bionomics and population density of Cyzenis albicans (Fall.) (Tachinidae: Diptera) in Nova Scotia. Canad. Ent. 97: 631-39.
Embree, D. G. 1965b. The population dynamics of the winter moth in Nova Scotia: 1954-62. Mem. Ent. Soc. Canad. No. 46. 57 p.
Embree, D. G. 1966. The role of introduced parasites in the control of the winter moth in Nova Scotia. Canad. Ent. 98: 1159-68.
Embree, D. G. 1971. The biological control of winter moth in Canada by introduced parasites. p. 217-26. In: C. B. Huffaker (ed.), Biological Control. Plenum Press, New York. 511 p.
Embree, D. G. & P. Sisojevic. 1965. The bionomics and population density of Cyzenis albicans (Fall.) (Tachinidae: Diptera) in Nova Scotia. Canad. Ent. 97: 631-39.
Graham, A. R. 1958. Recoveries of introduced species of parasites of the winter moth, Operophtera brumata (L.) in Nova Scotia. Canad. Ent. 90: 595-96.
Hassell, M. P. 1969. A population model for the interaction between Cyzenis albicans (Fall.) (Tachinidae) and Operophtera brumata (L.) (Geometridae) at Wytham, Berkshire. J. Anim. Ecol. 38: 567-76.
Hassell, M. P. 1980. Foraging strategies, population models and biological control: a case study. J. Anim. Ecol. 49: 603-28.
Kimberling, D. N., J. C. Miller & R. L. Penrose. 1986. Distribution and parasitism of winter moth, Operophtera brumata (Lepidoptera: Geometridae), in western Oregon. Environ. Ent. 15: 1042-46.
MacNay, C. G. 1957. Summary of parasite and predator liberations in Canada in 1957. Canad. Insect Pest Rev. 35: 291-98.
Maybee, G. E. 1958. Summary of parasite and predator liberations in Canada and of insect shipments from Canada in 1958. Canad. Insect Pest Rev. 36: 300-13.
McGugan, B. M. & H. C. Coppel. 1962. A review of the biological control attempts against insects and weeds in Canada. Pt. II. Biological control of forest insects, 1910-1958. Commonwealth Inst. Biol. Control Tech. Commun. 2: 35-127.
Mesnil, L. P. 1967. History of a success in biological control: the winter moth project in Canada. Tech. Bull. Comm. Inst. Biol. Contr. 8: 1-6.
Silvestri, F. 1941. Contribuzioni alla conoscenze degli insetti dannosi e dei loro simbionti. VI. La falena brumale o la brumale (Operophtera brumata L.). Bol. Lab. Ent. Agric., Portici 5: 61-119.
Varley, A. C. & G. R. Gradwell. 1968. Population models for the winter moth, p. 132-42. In: T. R. E. Southwood (ed.), Insect Abundance. Symp. Royal Ent. Soc. London 4.
Williamson, G. D. 1962. Summary of parasite and predator liberations in Canada and of insect shipments from Canada in 1962. Canad. Insect Pest Rev. 40: 147-58.
Williamson, G. D. 1963. Summary of parasite and predator liberations in Canada and insect shipments from Canada in 1963. Canad. Insect Pest Rev. 41: 137-51.
Wylie, H. G. 1960. Insect parasites of the winter moth, Operophtera brumata (L.) in Western Europe. Entomophaga 5: 111-29.