BULLETIN DE L'INSTITUT ROYAL DES SC IENCES NATURE LL ES DE BELGIQUE BIOLOGJ E, 72-S UPPL.: 159- 164 , 20d2 BULLETIN VAN HET KONINKLJJK BELGISCH fNSTITUUT VOOR NATUURWETE SCI-lAPP EN BIOLOGJE, 72-SUPP L.: 159- 164, 2002 The invasion and spread of Lepidoptera in Britain D. AGASSIZ Abstract its spread at a smaller scale and analysing the response of its natural enemies. Shortly into the programme another A short hi story is given of the study of invasions of Lepidoptera into moth was found belonging to the same genus: Phy llono­ Britain with th e associated ecological th eory. The rate of spread was calculated for each of 29 spp. which showed a range fTom near zero to 'JICter platani (STDGR), which was discovered newly 10.3 krn/year. Data from the USA show a marked contrast, with a rate resident in London. Equivalent sampling of this species of spread greater by an order of magnitude. The reasons for this are was also undertaken. discussed, and it is suggested th at invasions fro m another continent are much Jess predictable and have the potential to spread at greater speed, Ecological the01y predicted that the insects should reaching hi gher density. In vaders from other continents are mentioned, spread radially outwards with uniform speed from the and the likelihood of these reaching Belgium is di scussed. point of introduction, given a homogeneous environment. The food plant used by the first species is Pyracantha Keywords: in vasions, Lepidoptera, ecology. which is widely planted in gardens and urban environ­ ments, enough to approach a uniform distribution. The food plant of the second species is Platanus, also intro­ Introduction duced into Britain but much less widely planted outside London and major towns. In 1990 the British Government realised that it was likely The presence (and density) or absence of both species that Genetically Modified Organisms (GMOs) would be were carefully monitored in each J 0 km square of the introduced into the country within the foreseeable future. National Grid throughout their known range for three They were anxious that ecological theory about the years and for at least 10 km beyond so that the boundaty spread of such organisms should be tested so that their of the range could be known exactly. The area was then spread could be predicted. There had been a recent symposium on this subject in Britain ananged by the Royal Society and the papers had been published (KORNBERG & WILLIAMS 1986). Much of the theory was also included in a book by Rob HENGE­ VELD (J 989) of the Netherlands. Such works took exam­ 120 • 110 - • leucographella ~ - ples from many different organisms, from mammals and ,. platani birds to diseases and human practices. For this reason an 100 • insect was considered as suitable an organism as any 90 80 other. 70 60 50 - The UK programme 40 • ~ 30 ~ It happened that at this time a small leaf-mining moth c5r 20 Phyllonatycter leucographella (ZELL.) had been found 10 newly established in Britain and its distribution at that 0 time had been carefully mapped by amateurs including 1986 1987 1988 1989 1990 1991 1992 1993 1994 myself. It was an ideal model to· monitor since it was Fig. 1 - The square root of area colonized by P. leucogra­ harml ess, established naturally of its own accord and phel/a (squares) and P. platani (diamonds). Range could easily be seen in the larva l stage. A three-year area was calcul ated as th e number of I 0 I 0 km programme was begun which invol ved monitoring the squares within whi ch the moth was recorded. The spread of the moth nationally, studying the dynamics of lines are fitted regressions. I I 160 D. AGASSIZ Fig. 2 - Records of Polycluysia moneta in Britain 1890-1900. calculated as the number of squares occupied. The results Of the 27 species investigated, a linear relationship be­ have been published (NASH et al. 1995) and show a tween the square root of range area and time was statis­ remarkable fit to the theory, P. leucographella advancing ·· tically significant in 22 cases, which is further strong at a uniform 10.3 km/year and P. platani at 8.6 km/year, evidence that invading species will normally advance measured by the simplest method of plotting the square with constant speed. What is of interest is that the range root of area [(areal'] against time (fig. 1). of speed with which the front advanced was small, ran­ ging from close to zero to I 0.3 km/year (table I). Indivi­ dual moths can fly much further than that in the course of Other research their lives, or even in one night or day, and one wonders why such a slow rate of progress is achieved. Although The British Isles have a remarkable history of biological this was a large data set, the shared characteristics of the recording, chiefly by amateurs. On account of this I was species may be quite strong. An analysis of the origin of able to extract data for a further 27 species of Lepidoptera the invading species showed that the majority came from which had successfully established and spread during the elsewhere in Europe, none from the Americas (although previous I 00 years up unti I 1991. I hope soon to extend there is one more recent arrival, Argyresthia cupressella, this data set for a further I 0 years. Most of the records of it is too early to say how it will spread) and only two or species were made by amateurs, often from moth traps or three from Australasia. other observations in their own gardens. An example of this are maps (fig. 2) showing the Some research has been undertaken in North America, records of the noctuid moth Polychrysia moneta (FABR.) notably by Doug FERGUSON who collected data on the for the ten years from its first record until 1900, there spread of moths introduced chiefly from Europe. Of these were sufficient records to draw a line around them on the there were quite a number. The same detail of recording is map to define the range area of the species at that time. not available in North America, but even so he calculated Data regarding the absence of species could not be ob­ the rate of spread which was of an order of magnitude tained with the same rigour as was possible with leaf greater than my studies in Britain had revealed. One can mining species, but it could often be implied where joke that everything in the USA is bigger, better and someone was recording on a regular basis. faster, but are there other factors to be considered? The British Isles are by definition islands and instead Some of these data have also been published (AGASSIZ of being able to expand in all directions, many species, 1996) so I wi ll confine myself to a single example: the beginning in the south east of England, have only a sector noctuid moth Lithophane leautieri was first found in of a circle to the no1th west into which they can move. Britain in 1951 . It is a European species whose larva Some attempts at disper~a l wi ll end up in the sea, but this feeds on cypress trees Chamaecyparis spp. etc. which can only have a partial reduction on the rate of progress. [t have been widely planted. The moth extended its range was not a factor in the spread of the Phyllonmy cter with the availabi li ty of food, moving northwards up the species mentioned above, which began their establish­ west coast of France before becoming established in the ment inland, not near the coast. south of Britain. From there it spread northwards with the Of more significance, surely, is the fact that the in­ front of its range advancing at a rate of 6 km/year (fig. 3). vaders of N01th America came fro m another continent, The invasion and spread of Lepidoptera in Britain 16 1 • • • •• • • • • • • • • • • •• .:i.. • ..•...... • •• ..•• ..• . • I • • • 1986 Fig. 3 - The spread of Lithophone leautieri. 162 D. AGASSIZ Table I - Rate of spread of Lepidoptera invading Britain. and the natural enemies of related species were not so prepared to react as to species with whi ch a balance had Species rate of spread been achieved over evolutionmy time. There are species (km/year) from North America which have become establi shed in Europe in recent decades. ln particular hvo leaf-mining Etainia decentella 3.05 moths feeding on Robinia, a tree introduced from the Americas. One was reported by VIDANO (1970) from Stigmella suberivora 2.20 northern Italy which by 1990 had reached as far as Hungary and Yugoslavia. The second was found near Psycho ides jilicivora 1.69 Baste in 1983 (WHITEBREAD 1990) and had spread into Austria, Switzerland, France, and Germany by 1990. I am Caloptilia rujipennella 7.33 not aware of any study to calculate the rate of spread, but . taking the furthest points of each and their distance from Phyllonmycter platani 8.63 the starting points, gives a rate of the order of 50 km/year. SIMB ERLOFF ( 1989) observed that more successful inva­ P. leucographella 10.30 sions had originated in Europe and had happened to the New World and Australia, and he argued that the bulk of Tachystola acroxantha 0.06 trade had been in that direction. It would be hard to argue that this is sti ll true, and one should consider the hypo­ Argolamprotes micella 3.89 thesis that evolution over the larger area of Eurasia had better equipped European species to make or resist inva­ Carpatolechia alburnella 3.72 sion.