Norwegian Journal of Entomology Volume 49 No. 2 • 2002 Published by the Norwegian Entomological Society Oslo and Stavanger NORWEGIAN JOURNAL OF ENTOMOLOGY A continuation ofFauna Norvegica Serie B (1979-1998), Norwegian Journal ofEntomology (1975-1978) and Norsk entomologisk Tidsskrift (1921-1974). Published by The Norwegian Entomological Society (Norsk ento­ mologisk forening). Norwegian Journal ofEntomologypublishes original papers and reviews on taxonomy, faunistics, zoogeography, general and applied ecology ofinsects and related terrestrial arthropods. Short communications, e.g. one or two printed pages, are also considered. Manuscripts should be sent to the editor. Editor Lauritz Semme, Department ofBiology, University ofOslo, P.O.Box 1050 Blindern, N-0316 Oslo, Norway. E­ mail: [email protected]. Editorial secretary Lars Ove Hansen, Zoological Museum, University of Oslo, P.O.Box 1172, Blindern, N-0318 Oslo. E-mail: [email protected]. Editorial board Ame C. Nilssen, Tromse John O. 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Husk avsenderadresse. NEF web site: http://www.entomologi.no Front cover: Arctosa stigmosa (Thorell, 1875) (Araneae, Linyphiidae). Artist: Kjetil Aakra. Printed by: Reprografisk Industri AS, Oslo Norw. J. Entomol. 49, 77-80.2002 Discovery of the rare alate morph of Acyrthosiphon svalbardicum Heikinheimo (Homoptera; Aphididae): description and implications for species ecology lan D. Hodkinson, Stephen J. Coulson, Jeremy Bird & Nigel R. Webb Hodkinson, 1.0., Coulson, S.J., Bird, J.M. & Webb, N.R. 2002. Discovery ofthe rare alate morph of Acyrthosiphon svalbardicum Heikinheimo (Homoptera; Aphididae): description and implications for species ecology. Norw. J. Entomol. 49, 77-80. A single alate female ofthe endemic Svalbard aphid Acyrthosiphon svalbardicum is recorded from Storholmen in the Loven Islands, Kongsfjord, West Spitsbergen. This species has been studied inten­ sively but has hitherto been regarded as entirely apterous. The female is described in detail and the ecological implications ofthe discovery are discussed in the context ofprevious work, particularly in relation to the life cycle, dispersal and colonisation. Key words: Acyrthosiphon svalbardicum, Dryas, alate, dispersal, colonisation, induction. fan D. Hodkinson, Stephen J. Coulson and Jeremy M. Bird, School ofBiological & Earth Sciences, Liverpool John Moores University, Byrom St., Liverpool L3 3AF, u.K. [Contact: fan D. Hodkinson, E-mail [email protected]} Nigel R. Webb, NERC Centre for Ecology and Hydrology, Winfrith Technology Centre, Dorchester, Dorset, D T2 8ZD, u.K. BACKGROUND in warmer seasons but which allows A. svalbar­ dicum sporadically to exploit enhanced growing Acyrthosiphon svalbardicum Heikinheimo, 1968 conditions. It has been argued that the lack of is endemic to Spitsbergen, Svalbard. Its general winged forms, which severely limits dispersal, life history and ecology have been studied exten­ coupled with minimum day degree requirements sively on Kongsfjord adjacent to Ny-Alesund to complete the life cycle, restricts the spatial where it was known only from apterous forms distribution of A. svalbardicum populations to (Heikinheimo 1968; Strathdee et al. 1993c). A. microclimatically favourable sites adjacent to the svalbardicum feeds on Dryas octopetala and its fjord margins within the inner fjord. This is despite life cycle is highly unusual among highArctic in­ its host plant being more widely distributed sects in that it completes up to three generations (Strathdee & Bale 1995). during the short summer growing season. It over­ winters as eggs that hatch to give fundatrices, a During several years ofstudy A. svalbardicum was proportion of which give rise to apterous males exposed to many of the stimuli that induce the and females, which then mate and lay overwinter­ development ofalate forms in other aphids. These ing eggs (Strathdee et al. 1993b; 1995a;). This include raised temperature, crowding and cul­ represents the safe, reliable option that ensures turing on detatched sub-optimal host plants within continuity from year to year. However, the remai­ the laboratory (Strathdee 1993a,b; 1995b). Alate ning fundatrices produce a further generation of forms were never seen, either in the laboratory or viviparae, which then give rise to the males and field. Decreasing daylength, another possible fac­ females that produce additional overwintering tor, is also ruled out because of 24 h daylight eggs. This is the risky option that is only successful throughout the effective development period. 77 Hodkinson et al.: Alate morph ofAcyrthosiphon svalbardicum (Homoptera; Aphididae) In 2000 we discovered the apterous form of A. Measurements (in mm) svalbardicum on Midtholmen and Storholmen two Body length 1.74. Forewing length 2.44, antennal ofthe Loven Islands in Kongsford, lying about 3 length 1.22. Length of individual segments km from the mainland. This immediately raised 3,4,5,6a and 6b are 0.30, 0.20,0.21,0.13 and 0.25 the question of how a non-robust apterous aphid respectively. Length ofsiphunculus 0.26. Length could cross this marine barrier. The question was ofcaudal process 0.18. Length ofapical segment potentially answered in summer 200I when a ofrostrum 0.18. Length offemur - fore 0.43, mid single alate female was discovered in association 0.42, hind 0.51. Length of tibia - fore 0.69, mid with many apterous males and females in a late 0.64, hind 0.89. Length ofapical tarsal segment­ season Storholmen sample. The description ofthis fore 0.0104, mid 0.098, hind 0.0114. unique female is given below. It is interesting to note that we operated 28 yellow sticky traps conti­ Specimen examined nually throughout the 2001 season at sites adjacent 19 collected in water filled pitfall trap (1.0. Hod­ to areas whereA. svalbardicum was abundant but kinson) Svalbard, Spitsbergen, Storholmen in did not catch a single dispersing adult aphid. Kongsfjord 27 July 2001 in association with other apterous morphs. Specimen deposited in The Na­ tural History Museum (London). DESCRIPTION OF THE ALATE ADULT FEMALE OF A. SVALBARDICUM Detailed descriptions of the fundatrix, vivipara DISCUSSION ovipara and male morphs, together with species The discovery of an alate A. svalbardicum sug­ diagnostic features, were given in Strathdee et al. gests how the aphid might have dispersed to and (l993c). For comparison the description below between isolated islands and it again emphasises follows, as far as possible, the same format. Illu­ the remarkable adaptive flexibility contained with­ strations were prepared using SYNCROSCOPY in this aphid's genotype. However, it immediately Automontage and Montage Explorer packages to raises the question ofthe trigger mechanism that enhance images captured using a NC3CCD video induces the expression ofwings and the frequency camera mounted on a Nikon Optiphot 2 micro­ with which alates are produced. Recent work on scope from the specimen mounted in canada bal­ Acyrthosiphon pisum suggests that aphid distur­ sam on a slide. bance by predators and parasitoids can induce wing formation (Weisser et al. 1999, Sloggett & Morphological features Weisser 2002). Potential aphid parasitoids and Whole insect (Figure 1) slightly larger than the syrphid larvae were present among the samples other described morphs: note the anomaly in the in which the alate aphid was found. This raises branching sequence ofthe M vein ofthe left fore­ the interesting possibility that disturbance may wing. Antenna (Figure 2) with 5 large and 1-3 provide the mechanism that stimulates the aphid smaller placoid sensilla on segment 3 and a sub­ species to seek out potentially predator-free