The biology of the noctuid asclepiadis Schiff. (, ) in Sweden

JONAS TORERP

Fdrare, J.: The biology of the noctuid molh Schiff. (Lepidoptera, Noc- tuidae) in Sweden. [Biologin hos nattflyet Abrostola asclepiadis Schiff. (Lepidoptera, Noctuidae) i Sverige.l - Ent. Tidskr. I I 6 (4): I 79- I 86. Uppsala, Sweden I 995. ISSN 001 3-886x.

This article describes the biology, phenology and distribution of Abrostola asclepiadis Schiff. (Lepidoptera: Noctuidae) in Sweden, gathered during a long term study on its population ecology. Whereas larvae of other Abrostola spp. in the world are known to feed on plants among the Urticales, s\ch as spp., A. asclepiadrs uses Wncetoxicum hirundinariaMed. (Asclepiadaceae), a perennial plant with a number of toxic substances. My experimental data corroborates the view that l. asclepiadis is monophagous on its host plant. A. asclepiadis is a regionally uncommon and local species. This is most likely due to the patchy distribution ofits host plant. The moth has a high ability for dispersal and thus a good capacity of finding its host. Its distribution in Sweden follows the distribution of ( hirundinaria, viz. in eastern parts ofthe south and southcentral part ofthe country. However, in the southemmost province, Skine, where the host plant also occurs, the moth has never been found. This anomaly may be related to interhabitat distances in the province being too great for breeding populations to persist. Egg densities are often low and offspring mortality is high, generally more than 90 o/o. The main mortality agents are generalist predators, most notably ants. The impact of A. asclepiadis on its host plant is generally low or negligible.

Jonas Fdrare, Dept. of Entomologt, Swedish University of Agricultural Sciences, P. O. Box 7044, 5-750 07 Uppsala, Sweden.

Introduction The Abrostola Ochs. (Lepidoptera, Noctui- which feed on Urtica dioicaL., namely A. tripar- dae, ) consists ofabout 35 species and is tila Hufn. and A. triplasia L. (sensu Mikkola & represented in the Palearctic, Oriental, Nearctic Honey 1993). However, the third species, l. and Ethiopian regions. The genus is grouped in a asclepiadis Schiff., feeds on Wncetoxicum hirun- tribe (Abrostilini) together with one other genus, dinaria Med., belonging to the Asclepiadaceae. Mouralia, that occurs in the Neotropical region On the Swedish mainland it is the only leaf- (Kitching 1987). The tribe is considered primitive feeding species on this plant (except for in relation to other Plusiinae; e.g. larvae differ casual visits by larvae ofthe polyphagous noctuid from others in the subfamily by having thoracic Euplexia lucipara L. and brunnea legs on abdominal segments 3 and 4, most likely a Schiff. and the arctiid moth mendica plesiomorphic trait. Cl.). On the islands of Oland and Gotland also the Host plant affiliations are known only for a few tortricid moth Sparganothis pilleriana Schiff. Abrostola species, but according to presently avai- may be found on the plant (another tortricid moth, lable information, the genus generally seems to be Clepsis senecionana Htibn. has also been recorded associated with plants in the Urticales, often of the (8. Gustafsson, pers. comm.)). geuts Urtica. This applies to species in Japan Vincetoxicum hirundinaria is a perennial plant, (Ichinos6 1962), Europe (Skou l99l) and North that contains toxic compounds like the cardiac America (Eichlin & Cunningham 1978). In Scan- glucoside vincetoxin, and many alkaloids (Hoppe dinavia, there are three Abrostola species, two of 1975). The plant grows on cliffs, rocky outcrops

179 Jonas Fdrare Ent. Tidskr. ll6 (1995)

80 'I 00 1z', 14 160 18" zu- 22' 240 26 28

Fig. l. The range qf Wncetoxicum hirundinaria (solid line (cf Hultin 1971)) in Fennoscandia and Denmark. Empty circles denote isolated occurrences of the plant. The filled circles denote localities where Abrostola asclepiadis has been found. Marks include multiple records. Records on findings from Denmark and Finland according to Nordstrdm et al. (1969).

Utbredningsgrdnsen fr)r tulkcirt mncetoxicum hirundinaria (heldragen linje) (jfr Hultdn I 97 I ) i Fennoskandien och Danmark. Tomma cirklar markerar isolerade fdrekomster ay vdxten. Fyllda cirklar markerqr find av tulkdrtsfly Abrostola asclepiadis. Markeringar inkluderar fall med mdnga rapporter frdn samma lokal. Fynd frdn Danmark och Finland enligt Nordstrc)m et al 1969. and wood margins from the Mediterranean region Material and methods eastwards to the Caucasian foothills and north- Flight dates and number ofcaptures for Abrostola wards through Europe to the countries surroun- asclepiadis in Sweden were obtained from enqui- ding the Baltic Sea. In Fennoscandia it has a ries sent to Swedish lepidopterologists and muse- patchy distribution along the Swedish Baltic Sea ums. The thus compiled dataset covered the pe- coast up to about 60o N, over the Aland islands to riod 1926 to 1990, with some later additions. southwestern mainland Finland (Fig. 1). On the Studies on larval development and feeding pre- Swedish islands of Oland, Gotland and the Danish ferences were performed in the laboratory. For the island of Bornholm the plant is abundant, often development studies ab ovo reared larvae, origi- occuring in large stands (Fig. l, cfSterner 1922, nating from parents from the provinces of Upp- Hult6n 1971). In Skine, the southernmost pro- land and Gotland were used. The parent moths had vince of Sweden, and in Denmark the host plant is been collected as larvae, allowed to pupate in the relatively scarce and the patches are separated by laboratory and were overwintered in a rearing long distances. cabinet (temperature around 3' C). During the The distribution ofl. asclepiadis in Fennoscan- mating trials, several males and females were kept dia follows that of the host plant, from Bomholm in a large cage, together with cut host plants. Eggs to the northern limit of the plant distribution (Fig. were collected daily and transferred to petri dishes l). However, no observations ofthe species have together with moist filter paper and leaves picked been made either in Skine or on the larger Danish from potted host plants, all originating from the islands. same patch outside Uppsala. Eggs were kept in

180 Ent. Tidskr. ll6 (1995) The biologt of Abrostola asclepiadis

I ul

t L. ,t \,,

c d

Fig. 2. Abrostola asclepiadis: a) adult moth (actual wingspan 32-36 mm), b) eggs on a Wncetoxicum hirundinaria leaf, c) a newly eclosed second instar larva (actual size approx. 7 mm), d) a fifth (last) instar larva (actual size 30- 40 mm). Pholo: J. Fdrare.

Abrostola asclepiadis: a) adult fidril (verklig vingbredd 32-36 mm) b) dgg pti tulkdrtsblad, c) nykldckt 2: a stadielarv (naturlig storlek c:a 7 mm), d) lemtestadielarv (sista larvstadiet, naturlig storlek 30-40 mm).

rearing cabinets at four constant temperatures used in an area meter (Delta TechnologiesrM) to from 15 to 30 oC. After hatching, fresh leaves calculate the leafarea consumed by each larva. were provided every second day in the beginning Data on the batch size were collected from a and every day later in development. All leaves random set of egg batches (Fdrare 1995). For the were photocopied before and after the larva had studies on feeding preferences, field collected eggs fed on them. The copied leaf images were then were used and kept as indicated above. Leaves l8r Jonas Fdrare Ent. Tidskr. 1 l6 (1995)

provided as food were picked from field collected 35

plants. 30 Field studies were conducted on the island of 25 Gotland in the Baltic Sea, in Uppsala (N 59'49', E 17" 39') in the province of Uppland, and in Tull- 2zo gam, south of Stockholm (N 58'58', E l7'35') in 8,u the province of S0dermanland. 10

Results and discussion 0 MAY JUNE JULY AUGUST SEPTEMBER Phenology and voltinism MONTH The adult moth (Fig. 2 a) is usually on the wing in Fig. j. Number ofcaptures ofAbrostola asclepiadis per June and July. No variation in flight date between four day intervals in the investigated samplefrom 1926- different parts ofthe distribution range (cfFig. 1) 1992. could be discerned from my data set. The mean flight date was around the first of July (Fig. 3). Flygdatum fdr tulkdrtsJly Abrostola asclepiadis, grup- However, sampling efforts varied between years perade i fyra dagars intervall i det undersdkta materia- letfrdn 1926-1992. and only a few years contain data from all parts of the distribution range, which makes a geographi- cal comparison diffrcult. My own observations of '160 egg laying during the years 1988-1994 around Uppsala suggest the same temporal distribution 140 during most years. 120 The developmental period of about six weeks . 100 from egg to pupa (see below) means that normally zF there will only be time to complete one generation 480 in Sweden per year. Even if eggs were laid already o 60 in early June, autumn weather would usually be too cool for successful larval development and 40 pupation of a second generation. However, there 20 are findings from I978 on the island of Oland that 0 suggest that a second generation may occur 0s1015202530 occasionally . Adult moths were caught as early as BATCH SIZE the beginning of June and as late as the second Fig. 4, Egg batch size for Abrostola asclepiadis. Data week of September (K. Tunsiiter, pers. comm.). from balches found around Tullgarn and Uppsala in Further south in Europe, more than one generation southeastern Sweden 1 990- I 994. frequently occurs. For instance, Hungarian collec- tors have observed two generations in central Eu- Kullstorleken hos tulkdrtsJly Abrostola asclepiadis. rope (Peter Andersson, pers. comm.). However, Datafrdn kullar pdtrdffade kring Tullgarn och Uppsala Hacker (1989) suggests that the Greek popula- I 990- I 994. tions of the moth are univoltine.

Oviposition Females oviposit underneath V. hirundinaria host plant shoots. Furthermore, small and shaded leaves (Fig. 2 b). In captivity, no individual female host plant patches receive higher egg densities has laid more than 255 eggs (pers. obs). In the than large and exposed ones (F

182 Ent. Tidskr. 116 (1995) The biology of Abrostola asclepiadis

a (cf Fig. 5 a). First and second instar larvae are active at all times during day and night. When 50 make holes in parls

CI 001 Z?, g o111todrt1.V 0t 08 il 6 0 6 001 srpordalcso'y I Ol o/ '/o /o /o % u o/o sercads q1o;4

wryocsn/'dss DJIAOSSDINJ unqlo o!tou!Puru!Ll

Dttoulpurutq 11 sodalcsV wntwDT D)totp o)tun unJtxola)uu

saroads 1ue16

'u8,(pytayow tDuu!) I 'snf1 nwwll y 1 uapouadolol tlro Co1Z tD^ uatnlondutal 'outo8utlpuoqaq uDllau ddn sapolap outo11n133.V rauD$p^ Dlllo pDlq pd oppgJddn ^o slpoldalcso 'y tfsltot11n1 qco o1ytod1t1 ololsotqy tgflasspu ttttugtB ao taatolalpolsolstgJsoq Quacoil t) pDu^aFa^O

'el:1/l aw8at ry31 aW puo ) o0Z sou. atryotadwat aqJ sruawput uaaiJaq l11ds atau spootg '(lxat aas) stuold tuatallrpto saaoal palslpoldalcso 'y puo oltltodttl'yJo aouol totsut tstgffo (o7) loarang 'J 'qo1

(SOOt) St I 'r{sprJ 'luA aluQl souof Ent. Tidskr. 1 l6 (1995) The biologt of Abrostola asclepiadis

Dispersal and colonizing ability have hatched eight Phryxe vulgaris Fall. (Diptera, Flight tests have revealed considerable dispersing Tachinidae), from larvae collected at the island of abilities. Some individuals flew for enough time Stora Karlsd, near Gotland, and two specimens of to cover more than 20 kilometers at low wind Microplitis sp. (Hymenoptera, Braconidae) from speeds (F6rare 1995). At Tullgam on the south- larvae collected around Uppsala. Predation on ol- eastern Swedish mainland, an A. asclepiadis po- der larvae also seems to be low. Whereas a Formi- pulation was shown to colonize and occupy ca ant can catch and carry larvae up to the third most of the patches in a 12 km2 area in seven instar, capture of a last instar larva requires the years (Fdrare 1995). Despite this, interpatch cooperation ofseveral ants (pers. obs.). distances may be too long in Skine to keep up Egg and larval predation thus are important fac- breeding populations (cf Harrison et al. 1988). tors in reducing the population size of A. ascle- Large populations can be found on the island of piadis (Forare 1995). Generally only a few of the Bomholm (e.g. Hoffmeyer 1949),less than 50 km larvae reach the final instar. Accordingly, seldom away from the coast, and A. asclepiadrs is proba- more than I % of the available foliage is ever con- bly capable of colonizing from that distance. sumed (Forare 1995), and hence A. asclepiadis Thus, I would not rule out the possibility that the will generally have a small or negligible effect on species has at some time colonized some of the its host plant population. Occasionally, however, patches, but that these attempts have failed due to very local defoliation may occur, where most unfavourable circumstances. leaves get consumed in portions ofpatches or on isolated plants. Similar observations of high larval densities at sites where the hostplant is scarce, Enemies have been made in Hungary (Ronkay, pers. Mortality of A. asclepiadls eggs seems mainly to comm.). be due to the action of generalist predators and Furthermore, predation of larvae seems to be parasitoids (Forare 1995). Egg mortality is usually weather dependent. A higher proportion oflarvae low, but can reach high levels in some years (Fci- survive in warm summers (Fcirare 1995). But in rare 1995). The main predators seem to be ants sun-exposed patches a summer that is too warm (Formica, Lasius and Myrmica spp.). The ants can also lead to plant wilting. Severe drought tear the eggs loose from the leaf surface. Chryso- occurs intermittently where the host plant grows pid larvae (Chrysopa spp.), anthocorid bugs on shallow soil. Under those circumstances very (Anthocoris sp.) and mites have on several few larvae will survive (Fdrare 1995). occasions been observed to suck out eggs, usually leaving the empty shell, but sometimes tearing it Conclusions loose while feeding and dropping it afterwards. A. asclepiadis is considered a rather uncommon No specialized egg parasitoids have been found on and local species by many insect collectors, and in A. asclepiadis. However, I have reared two spe- the literature the same view prevails (Hoffmeyer cies of parasitic wasps, one Trichogramma sp. 1949, Skou 1991). Apart from an outbreak on the (Trichogrammatidae) and one Telenomus sp. island of Usedom in the southern Baltic Sea in (Pteromalidae) from A. asclepiadrs eggs, from 1904 (Hoffrneyer 1949), there are no reports of both my study areas. The egg parasitoids usually high population densities. cause a mortality of a few percent. This pattem of abundance most likely stems Youngl. asclepiadis larvae (instars I and II) are from the patchy distribution of the host plant A. attacked by mainly the same predators as the eggs. asclepiadis adults have good dispersal abilities, Early larval mortality is high, very few larvae (usu- which probably explains that the species can be ally 0-5 %) from hatched eggs survive to the found throughout most of the range of V second or later instars (Ftirare 1995). Larger larvae hirundinaria, to its northern limit. Nevertheless, are also attacked by ants, but also by predacious colonized patches generally end up with low egg pentatomid bugs (Picromerus bidens (L.)) and pa- densities and the mortality of offspring is high, rasitoids. The latter, however, seem to be uncomm- mainly due to heavy predation by generalist pre- on (causing mortality of less than one percent) dators. Therefore, in most patches only a fraction judging from several hundred collected larvae. I of the available foliage is consumed.

185 Jonas Fdrare Ent. Tidskr. ll6 (1995)

Acknowledgements culture of the Tokyo University of Agriculture and The author is indebted to many Swedish collectors for Technology 6: l-127. practical assistance and provision of collection data. Kitching, I. J. I 987. Spectacles and Silver Y's: a synthe- Special thanks go to Hikan Elmquist, Hans Meijlon, sis of the systematics, cladistics and biology of the Kjell Tunsiiteq Nils Ryrholm, Hans Hellberg, Nils Plusiinae (Lepidoptera: Noctuidae). - Bulletin of the Hyd6n and Ingvar Svensson. Christer Solbreck, Stig British museum (Natural History) 54(2):15-261 . Larsson, Christer Bj6rkman, Naomi Cappuccino and Mikkola, K. & Honey, M. R. 1993. The Nils Ryrholm provided valuable comments on the (Lepidoptera) described by Linnaeus. - Zool. J. Linn. manuscript. Richard Hopkins corrected my English. Soc.108:103-169. This work has been supported by grants from the The Nordstrdm, F., Kaaber, S., Opheim, M. & Sotavalta, O. Swedish Natural Science Research Council, The Natio- 1969. De fennoskandiska och danska nattflynas ut- nal Swedish Environmental Protection Board and the bredning. Lund (CWK Gleerup). Oscar and Lili Lamm foundation. Skou, P 1991. Nordens ugler, Danmarks Dyreliv bind 5. Stenstrup (Apollo Books). Stemer, R. 1922. The continental flora of south Sweden. - Geogr. arn. 4'.221-444. References Eichlin, T. D. & Cunningham, H. B. 1978. The Plusiinae (Lepidoptera: Noctuidae) of America north of Sammanfattning Mexico, emphasizing genitalic and larval morpho- Denna artikel beskriver biologin, fenologin och logy. - Technical Bulletin, United States Department utbredningen hos tulkdrtsflyet Abrostola ascle- of Agriculture, Agricultural Research Service. no piadrs Schiff. (Lepidoptera, Noctuidae) i Sverige. 1567:1-222. Medan larver av andra Abrostola-arter iir ktinda Ftirare, J. 1995. Population dynamics ofa monophagous viirdviixter inom insect living on a patchily distributed herb. Ph.D.- frin Urticales, sisom Urtica-ar- thesis, Swedish University of Agricultural Sciences, ter (briinnniisslor), lever A. asclepiadis pe tulkiirt Uppsala. (Vincetoxicum hirundinaria Med.; Asclepiada- Gullander, B. 1971. Nordens nattflyn. Stockholm (Nor- ceae), en perenn v6xt som inneh6ller minga gif- stedts ftirlag). tiga substanser. Mina ftidofors

Tids krift en P ar n as s i an a eft e rly s e s ! Ager nigon av ET:s liisare hiiften av tidskriften Pamassiana, tacksamt upplysningar om detta. (Parnassiana finns ej till- utgiven under perioden 1930-1939 (Neubrandenburg) av den genglig i nigot svenskt bibliotek.) svenske lepidopterologen Felix Bryk, eller kan i 6vrigt upp- Erikvon Mentzer Ornstigen 14, 183 50 Tiiby, tel. 08-758 29 71 lysa om fdrekomst av denna i Sverige? Undertecknad mottar

186