Academic Edi o : Da id G. James
Recei ed: 18 July 2025
Re ised: 6 Oc obe 2025
Accep ed: 10 Oc obe 2025
Published: 20 Oc obe 2025
Ci a ion: Cos ache, C.; Rakosy, L.;
Rakosy, D. Long-Te m Phenological
Shi s in Bu e ly Species om
T ansyl ania, Romania—A Case
S udy. Insec s 2025,16, 1071. h ps://
doi.o g/10.3390/insec s16101071
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Licensee MDPI, Basel, Swi ze land.
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A icle
Long-Te m Phenological Shi s in Bu e ly Species om
T ansyl ania, Romania—A Case S udy
C is ina Cos ache 1, László Rakosy 2,3 and Deme a Rakosy 4,*
1Doc o al School o In eg a i e Biology, Facul y o Biology and Geology, Babes
,-Bolyai Uni e si y, S .
Republicii 44, 400015 Cluj-Napoca, Romania
2
Depa men o Taxonomy and Ecology, Babe
s
,
-Bolyai Uni e si y, S . Republicii 48,
400015 Cluj-Napoca, Romania
3Depa men o Fo es y and En i onmen al P o ec ion, ¸S e an cel Ma e Uni e si y, S . Uni e si 㸠ii 13,
720225 Sucea a, Romania
4Thünen Ins i u e o Biodi e si y, Bundesallee 65, 38116 B aunschweig, Ge many
*Co espondence: [email p o ec ed]
Simple Summa y
Clima echangecan signi ican lyimpac insec s, such as bu e lies, byshi ing hei geog aphic
anges, al e ing he numbe o gene a ions hey p oduce annually, o changing hei ligh
pe iods. To da e, mos e idence o hese e ec s comes om Wes e n and Cen al Eu ope,
whe e long- e m moni o ing p og ams ha e p o ided he necessa y da a o de ec clima e-
d i en ends. In con as , Eas e n Eu ope—o en conside ed a biodi e si y ha en due o he
ela i ely lowe a e o land-use change—has lacked such da a, making i di icul o assess
clima e change impac s in he egion. In his s udy, we u ilize an al e na i e da a sou ce:
his o ical museum collec ions combined wi h con empo a y eco ds and long- e m clima e
da a. This app oach allows us o in es iga e how he phenological cycles o 16 bu e ly
species wi h a ying li e his o y ai s ha e esponded o clima e change. Ou indings
e eal ha bu e ly species eme ging in sp ing now begin hei ligh pe iods app oxima ely
15 days ea lie , while hose ac i e in au umn ha e ex ended hei ligh pe iods by an a e age
o 23 days. These shi s in ligh pe iods may ha e signi ican ecological consequences,
pa icula ly h ough al e ed synch ony wi h hos plan s and o he c i ical esou ces.
Abs ac
Insec s can espond apidly o clima e change h ough popula ion luc ua ions, ange shi s,
al e ed ol inism, li e cycle changes, ligh pe iod adjus men s, beha iou al shi s, and
changes in habi a o ood p e e ence—o en a ying by egion due o local en i onmen-
al and an h opogenic ac o s. While he phenological cycles o diu nal lepidop e ans
ha e been ex ensi ely s udied in coun ies wi h la ge moni o ing ne wo ks, eas e n and
sou heas e n Eu ope emain unde - esea ched. This s udy p o ides he i s insigh s in o
phenological shi s in 16 bu e ly species in Cluj-Napoca (T ansyl ania, Romania) be ween
1921 and 2023, using a unique da ase combining his o ical and ecen eco ds. The species
s udied include sp ing-eme ging, mul i ol ine, and mig a o y bu e lies. Phenological
ends we e analyzed in ela ion o long- e m clima ic da a. Resul s show ha sp ing
species now eme ge app oxima ely 15 days ea lie , and au umn species ex end hei ligh
pe iods by up o 23 days. These changes co ela e wi h mul i-decadal ends in empe a u e
and p ecipi a ion. We also discuss changes in ol inism and mig a o y beha iou and he
po en ial impac s o clima e change on bu e ly popula ions in he s udy egion.
Keywo ds: his o ical da a; decline; Romania; clima e change; phenological cycles
Insec s 2025,16, 1071 h ps://doi.o g/10.3390/insec s16101071
Insec s 2025,16, 1071 2 o 17
1. In oduc ion
An inc easing numbe o scien i ic pape s a e being published om all co ne s o he
wo ld, add essing he subjec o clima e change and i s epe cussions o insec popula-
ions [
1
–
7
]. Insec s, such as Lepidop e a, exhibi high sensi i i y o clima e change, al hough
he deg ee and di ec ion o hei esponses may di e [
8
–
11
]. Some o he mos discussed
opics oday a e he impac o he annual inc ease in empe a u es, ea lie and pe sis en
d ough s, as well as wa me win e s on lepidop e a popula ions [
12
–
17
]. Nega i e impac s,
such as he o e all decline o biomass o lepidop e an popula ions o e en he ex inc ion
o ce ain species, has been demons a ed and b ough o he a en ion o he scien i ic
communi y and he gene al public epea edly o e he las 25 yea s [
12
–
14
,
18
]. Ye , posi i e
e ec s ha e also been obse ed [
8
,
11
]. Wi h changes in clima e p edic ed o exace ba e
o e he nex decades [
19
], he e is a g owing u gency o be e unde s and he impac o
clima e change on Lepidop e a, and o he insec g oups. Howe e , mos s udies o da e a e
cen ed a ound simila geog aphic loca ions and habi a s, mos ly Wes e n Eu ope [20–26]
(bu see [
27
–
30
]). Mo e esea ch is needed in unde s udied egions o highligh he impac
o clima e change on lepidop e an popula ions.
Phenological shi s in o ganisms se e as aluable bioindica o s o clima e
change [31,32]
.
This is also ue o Lepidop e a, which se e as aluable indica o s o s udying clima e
change due o hei sensi i i y o clima ic and en i onmen al a iables, apid esponses,
and ex ensi e his o y o esea ch [
23
,
26
,
33
,
34
]. As poikilo he mic o ganisms, which e ol ed
close ela ionships wi h plan s bo h as adul s and as la ae, Lepidop e a a e highly in-
luenced by a ia ions in empe a u e and p ecipi a ion [
7
,
35
]. In England, a 1–1.5
◦
C
inc ease in sp ing and summe empe a u es was co ela ed wi h phenological changes by
6–8 days be ween 1976 and 1998 [
17
]. In he Medi e anean Basin oo, a mean empe a u e
inc ease o 1–1.5
◦
C in speci ic sp ing o summe mon hs be ween 1988 and 2002 led o
ad ances in he i s appea ance da es o all assessed bu e ly species [
36
]. In con as ,
highe p ecipi a ion led o a delay in he li e cycles o bu e lies [
36
]. Simila pa e ns
ha e been obse ed ac oss Eu ope, and a e no es ic ed o bu e lies, bu also occu in
mo hs [21,37,38].
Despi e hese o e all consis en pa e ns, no all species espond o empe a u e
changes in he same way, wi h esponses a ying depending on hei e olu iona y his o y,
li e cycle ai s (o e win e ing s ages, ol inism, e c.), as well as he s a e o he habi a s hey
depend on and he ex end o he induced clima ic a ia ion [
8
]. Fo example, a s udy on
Edi h’s checke spo bu e ly (Euphyd yas edi ha) and he win e mo h (Ope oph e a b uma a),
showed ha species which e ol ed a less p ecise phenological ma ch wi h hei ood plan s
may be mo e s ongly a ec ed by clima e change [
39
]. In u n, o he s ha e ound ha bu -
e lies ha o e win e in he pupal s age a e mos a ec ed by empe a u e
changes [40,41]
.
Mode a e wa ming can also ini ially bene i ce ain species by speeding up hei de elop-
men and b oadening hei dis ibu ion [
42
]. Unusual luc ua ions in empe a u e, such as
unexpec edly high o low empe a u es, can also impac ligh du a ions and he numbe
o gene a ions, a phenomenon ha has been epo ed in he las 20–25 yea s [8,36].
In ecen yea s, esea che s om Wes e n Eu ope ha e published hei obse a ions
ega ding co ela ions be ween phenological shi s in he li e cycles o bu e lies and
clima e change [
9
,
23
,
43
]. They ha e obse ed an ex ension o he pe iod o ligh , wi h
ea lie occu ences a he beginning o he season and la e occu ences in he au umn.
An ea lie ligh onse can lead o phenological misma ches be ween bu e lies and hei
ood plan s, which may no ha e synch onized hei phenological cycles acco dingly,
he eby a ec ing he su i al o bu e ly popula ions [
43
,
44
]. Howe e , an ex ended
ligh pe iod can allow many species o inc ease he numbe o gene a ions p oduced pe
yea [
43
]. Clima e-induced shi s in phenological pa e n can ha e seemingly bene icial
Insec s 2025,16, 1071 3 o 17
e ec s, wi h enhanced la e-season gene a ions con ibu ing o inc eases in he g ow h
a es o o e win e ing popula ions [
43
]. Howe e , hese la e gene a ions may no always
comple e hei de elopmen be o e win e , leading o “los gene a ions” [
43
]. Bu e ly
species ha e also been shown o ei he shi o expand hei anges no hwa ds o o highe
al i udes leading o changes in hei dis ibu ion a ea, bu po en ially also a decline in
species di e si y a mo e sou he n loca ions o lowe ele a ions [
15
,
26
,
45
,
46
]. These shi s
can dis up exis ing ecological ela ionships, as bu e lies may no ind sui able hos plan s
o mic ohabi a s in hei new a eas. Despi e some posi i e e ec s o clima e change, he
combined p essu es o clima e change and habi a al e a ion a e leading o signi ican
dec ease in bu e ly popula ion size [10,46–48].
Howe e , he pape s ha ha e appea ed on his opic a e concen a ed in coun ies
ha ha e a la ge amoun o da a, o en ob ained h ough ci izen science [
32
]. Bu wha is he
si ua ion in mos o he coun ies, whe e he numbe o olun ee s moni o ing bu e lies
and mo hs is low o e y low? I is o en sugges ed ha he si ua ion is be e in eas e n
and sou heas e n Eu opean coun ies. Pollu ion and habi a des uc ion a e mo e mode a e,
and insec declines a e much lowe han in cen al and wes e n Eu opean coun ies. In
eali y, howe e , he si ua ion in coun ies, such as Romania is no be e han in Cen al
Eu opean coun ies [
34
]. Due o he lack o ex ensi e da a p o ided by olun ee s h ough
ci izen science, he phenological esponse o insec s o clima e change in coun ies ha do
no bene i om a la ge moni o ing ne wo k is no known. Howe e , his o ical da a has
he po en ial o ill in his knowledge gap [
49
,
50
]. In he p esen s udy we in eg a ed all
exis ing da a— om his o ical collec ions o p esen day obse a ions—on bu e lies om
he mos s udied a ea in Romania, loca ed in T ansyl ania, a ound he ci y o Cluj-Napoca.
Ou aim was o analyze whe he bu e lies ha e unde gone changes in hei phenological
cycles, whe he hese changes di e among species and inally, whe he any shi s in he
phenological cycles could be explained by clima e change—de ined as shi s in empe a u e
a e ages, snow co e on he g ound, and p ecipi a ion.
2. Ma e ials and Me hods
2.1. S udy A ea and Pe iod
Long- e m da a on bu e ly popula ions is a e in Romania, mainly due o he lack
o na ional o egional bu e ly moni o ing p og ams. Howe e , some a eas o he coun-
y ha e bene i ed om decades o bu e ly sampling, leading o conside able his o ic
collec ions, no ye assessed o hei alue in examining long- e m popula ion ends in
bu e ly species. In he p esen s udy we ocused on one such a ea su ounding he ci y o
Cluj-Napoca (T ansyl ania).
T ansyl ania is Romania’s la ges p o ince, loca ed a he cen e o he coun y. I
includes pa s o he Ca pa hians and su ounding lowlands. I s a ied opog aphy and
land-use c ea e a mosaic o habi a s, ha suppo high bu e ly di e si y [
51
]. Long-
s anding low-in ensi y land-use has helped p ese e species- ich habi a s, hough ecen
ag icul u al in ensi ica ion and clima e change inc easingly h ea en local bu e ly popula-
ions. Cluj is one o he majo ci ies o T ansyl ania, loca ed in i s no h-wes e n egion.
The clima e o Cluj and i s su oundings is empe a e con inen al, wi h al i udes anging
be ween 350 and 800 m. The na u al meso- and mesoxe ophilous g asslands a e used as
pas u es o sheep and ca le o as ag icul u al land. The ew emaining deciduous o es s
a e domina ed by beech, ho nbeam and oak.
The egion o Cluj has a long his o y o lepidop e ological s udies (and he a ailabili y
o long- e m clima e da a), which allowed us o selec h ee ime pe iods o assessing he
long- e m impac o shi s in empe a u e and p ecipi a ion on he phenological cycles o
bu e lies. In he pe iod be o e he Second Wo ld Wa and a ew yea s a e (1920–1948),
Insec s 2025,16, 1071 4 o 17
se e al lepidop e ologis s we e ac i e in Cluj-Napoca (T ansyl ania), among which A. Os-
ogo ich [
52
] and S . Pe e i [
53
] we e he mos amous. These collec o s ha e con ibu ed
o ich lepidop e ological collec ions well p ese ed in he na u al his o y museums in
Cluj-Napoca (The Zoology Mueseum o he Babe¸s-Bolyai Uni e si y) and Bucha es (The
G igo e An ipa Na u al His o y Museum). F om hese collec ions 202 specimens we e in-
cluded in he s udy, specimens which ep esen ed he i s o las obse ed indi idual o he
selec ed species o a pa icula yea and no he en i e collec ion. Fo he pe iod 1965–1979
we used da a om p i a e collec ions and ield obse a ions o o he lepidop e ologis s
om Cluj, namely Ca ol Be e, An al Ko ig, Rudol Nemes and Vladimi Ma g Manoliu
(73 specimens). Finally, o he pe iod 1980–2023 we used ansec -based ield obse a ions
conduc ed by Vladimi Ma g Manoliu, Ma in Goia, and László Rákosy (250 obse a ions).
The ansec s co e he same gene al a ea, as he his o ical collec ions. The da a ob ained
om his o ical and p esen -day collec ions and obse a ions, was complemen ed wi h phe-
nological da a o bu e lies in he Cluj a ea ex ac ed om he li e a u e [
53
,
54
]. Al hough
ou ini ial aim was o analyze a cen u y o da a, he inabili y o e i y he accu acy o ea lie
collec ion eco ds and on limi a ions in he clima e eco ds led us o spli he s udy pe iod
in o wo main ime in e als 1921–1960 and 1973–2023.
2.2. Da a Acquisi ion
2.2.1. Bu e ly Da a
His o ical collec ions and con empo a y obse a ions we e used o de e mine he i s
annual eco ding da es o sp ing-eme ging bu e ly species, as well as he las annual
eco ding da es o mul i ol ine species wi h ex ended ligh pe iods, as documen ed in he
Cluj-Napoca a ea. F om he o al o 95 bu e ly species known o occu in he a ea [
51
,
54
]
we selec ed 16 species, based on da a a ailabili y, he pe iod o eme gence, he numbe
o gene a ions pe yea , leng h o he ligh pe iod and mig a o y beha iou . Fo species
which eme ge om he pupa in sp ing, 12 species we e selec ed: E ynnis ages (Linnaeus,
1758), Py gus mal ae (Linnaeus, 1758), Iphiclides podali ius (Linnaeus, 1758), Papilio machaon
(Linnaeus, 1758), Lep idea sinapis/ju e nica (Linnaeus, 1758), An hoca is ca damines (Linnaeus,
1758), Pie is napi (Linnaeus, 1758), Pie is apae (Linnaeus, 1758), Colias al aca iensis/hyale
(Ribbe, 1905), Glaucopsyche alexis (Poda, 1761), Plebejus a gus (Linnaeus, 1758), E ebia medusa
([Denis & Schi e mülle ], 1775). The i e bu e ly species wi h mul iple gene a ions pe
yea and a long ligh pe iod which ex ends owa ds au umn we e: Pie is apae (Linnaeus,
1758), Colias al aca iensis/hyale (Ribbe, 1905), Colias c oceus (Geo oy in Fou c oy, 1785),
Polyomma us ica us (Ro embu g, 1775) and Coenonympha pamphilus (Linnaeus, 1758). Finally,
a mig a o y species, Vanessa a alan a (Linnaeus, 1758) was chosen, which p e iously was
no known o o e win e as an adul in Romania, bu which is expec ed o do so unde
changing clima ic condi ions change. Each obse a ion was anno a ed wi h species name
(genus, species) and da e o obse a ion (day, mon h, yea ). To s anda dize he da a, only
he i s o he las da e he species was obse ed was selec ed, wi h a single eco d. An
o e iew o he sample size and he species conside ed is gi en in Table 1.
Table 1. O e iew o he assessed species and eco ds pe ime pe iod 1921–2023. No e ha only
hose eco ds we e conside ed which e lec ed he i s o las da e he species was obse ed (a single
eco d/species/yea ).
Species G oup To al
An hoca is ca damines Sp ing eme ging 14
Colias al aca iensis/hyale Sp ing eme ging 35
E ebia medusa Sp ing eme ging 41
Insec s 2025,16, 1071 5 o 17
Table 1. Con .
Species G oup To al
E ynnis ages Sp ing eme ging 39
Glaucopsyche alexis Sp ing eme ging 40
Iphiclides podali ius Sp ing eme ging 34
Lep idea sinapis Sp ing eme ging 44
Papilio machaon Sp ing eme ging 46
Pie is napi Sp ing eme ging 28
Pie is apae Sp ing eme ging 23
Plebejus a gus Sp ing eme ging 31
Py gus mal ae Sp ing eme ging 40
Coenonympha pamphilus Mul i oli in, long ligh pe iod 49
Colias c oceus Mul i oli in, long ligh pe iod 50
Colias al aca iensis/hyale Mul i oli in, long ligh pe iod 29
Pie is apae Mul i oli in, long ligh pe iod 16
Polyomma us icau s Mul i oli in, long ligh pe iod 54
Vanessa a alan a Mig a o y 13
To al 626
2.2.2. Clima e Da a
Fo bo h s udy pe iods, we used mon hly a e age da a o empe a u e (
◦
C) and o al
mon hly p ecipi a ion (L/m
2
), as hese wo clima ic pa ame e s a e essen ial o in luenc-
ing he eme gence da es o bu e lies [
55
], hei ligh du a ion as well as o e win e ing
pa e ns [36,40]
. Fo a mo e p ecise in e p e a ion o he obse ed phenological shi s in bu e -
ly species, we also used he snow co e da a, as snow co e impac s bo h he o e win e ing
la ae and adul s [
56
]. P ecipi a ion and empe a u e da a we e collec ed o he pe iod 1921
o 2023. While a e age annual da a was a ailable o he whole pe iod, he a e age mon hly
p ecipi a ion and empe a u e could only be assessed o he pe iod o 1973–2023. Snow co e
da a we e also a ailable only om 1973 o 2023. Fo he i s pe iod, spanning om 1921 o
1960, we ex ac ed da a om clima e ca alogues, while o he pe iod om 1973 o 2023, da a
we e ex ac ed om he p i a e a chi es p o ided by eques by he Na ional Me eo ological
Agency in Romania. The da a on clima e, spanning he pe iod om 1973 o 2023, we e colla ed
om a single me eo ological s a ion si ua ed in Cluj Coun y. The geog aphical loca ion o his
s a ion is speci ied by he coo dina es 46
◦
46
′
39.974
′′
N, 23
◦
34
′
16.699
′′
E, wi h an al i ude o
410 m, and i is loca ed 1.5 km no hwes o he ci y o Cluj-Napoca.
2.3. S a is ical Analyses
We used Py hon ( e sion 3.13) o p ocess and isualize he da a wi h he pandas,
ma plo lib, and seabo n lib a ies. We gene a ed Ke nel densi y es ima ion (KDE) plo s o
isualize changes in phenological pa e ns be ween 1921 and 2023 by o e laying species-
speci ic sca e poin s, colou -coded by genus. To illus a e he changes in phenological
cycles o bu e ly species we calcula ed de ia ions om he long- e m species-speci ic
a e age appea ance da e, isualized as ba plo s using ma plo lib.pyplo .ba (), wi h ea lie
and la e appea ances colou -coded acco dingly. We chose o agg ega e he da e on decades
o da apoin be ween 1973 and 2023 only o educe in e annual a iabili y and emphasize
long- e m clima ic and phenological ends. The educed ime span, ela i e o he Ke nel
Insec s 2025,16, 1071 6 o 17
Densi y Es ima ion (KDE) plo s, esul ed om an inadequa e sample size o he 1921–1973
pe iod. We op ed o a isual assessmen o pa e ns, a he han o mal signi icance es ing
due o he limi a ions in he quan i y and dis ibu ion o he da a.
Fo he pe iod 1921–1973 annual a e age empe a u e and p ecipi a ion was calcu-
la ed based on he a ailable da a. Fo he pe iod 1973–2023, a e age mon hly empe a u e
and p ecipi a ions we e analyzed using da a om he Cluj-Napoca me eo ological s a-
ion, me ged by decade as a hea map, using seabo n.hea map() o highligh seasonal and
long- e m wa ming ends. We combined da a on decades o show long- e m ends while
minimizing he sho - e m luc ua ions in wea he , local mic oclima e e ec s, and obse -
a ional inconsis encies o a clea isualiza ion o clima e change a he han episodic
wea he e en s. We ha e also analyzed he end and he impac o empe a u e on he snow
co e du a ion. In o de o obse e his ela ionship, a linea eg ession was pe o med
wi h scipy.s a s.lin eg ess(). The esul ing sca e plo was isualized using ma plo lib, wi h
poin s colou -coded o each decade and he coe icien o de e mina ion (R2).
3. Resul s
3.1. Species wi h Eme gence in Sp ing
F om he ele en bu e ly species which eme ge in sp ing, i e species exhibi ed
phenological shi s in mo e ecen eco ds (pos -1973), as e idenced by a concen a ed
clus e o obse a ions occu ing ea lie in he season (Figu e 1). The obse a ions o
he species P. napi,C. al aca iensis/hyale and L. sinapis/ju e nica, show a d as ic shi , wi h
peak obse a ions mo ing om May o Ap il and mid-Ma ch o e he same ime ame
(Figu e 2). Da a a e 1973 being mo e nume ous, he end change is mo e e iden o
he las 40 yea s. No all species, howe e , show clea phenological shi s be ween 1973
and 2023, wi h some species exhibi ing smalle o less consis en changes. Fo example:
P. mal ae and E. medusa show only mode a e shi s in hei phenological cycles (Figu e 2).
G. alexis and E. ages appea o show ela i ely s able eme gence imes, wi h peak i s
obse a ions emaining om la e Ap il o mid-May (Figu e 2).
Figu e 1. Phenological ends in he bu e ly species which eme ge in sp ing om 1921 o 2023.
Indi idual species a e ep esen ed by di e en colou s in he sca e plo and a e pa o he cumula i e
da a analyses o phenological shi s. Lines ep esen he KDE (ke nel densi y es ima ion) i h ough
he da a, ep esen ing a 2D dis ibu ion o he da a.
Insec s 2025,16, 1071 7 o 17
Figu e 2. De ia ion o i s obse a ion da es o he 11 sp ing eme ging species om he long- e m
mean o he i s obse a ion (N = sample size; A e age day = a e age day o i s eme gence). G een
ba s ep esen la e sigh ings = posi i e de ia ion; ed ba s ep esen ea lie sigh ings = nega i e
de ia ion. The ime in e al be ween 1973 and 2023 was spli by decades in o de o highligh
b eaking poin s in he obse ed ends.
3.2. Species wi h Mul iple Gene a ions and Long Fligh Pe iods
The i e species o bu e lies chosen o cap u e he possible shi in he phenological
cycles o mul i ol ine bu e lies, showed a eal p olonga ion o he ligh pe iod owa ds
he end o Oc obe and beginning o No embe . The shi seems o ha e s a ed a ound he
1970s–1980s and had a mo e p onounced shi in ecen yea s (a e he 2000s) (Figu e 3).
Insec s 2025,16, 1071 8 o 17
Fo C. c ocea,P. ica us and C. pamphilus, he ex ending o he ligh pe iod owa ds he end
o Oc obe is documen ed o he whole pe iod 1973–2023 (Figu e 4). P. apae ex ends i s
ligh pe iod by mo e han 35 days be ween 1973 and 2023 (Figu e 4). The mos p o ound
phenological shi is eco ded in he C. al aca iensis/hyale complex, which ex ended i s ligh
pe iod om mid-Sep embe o ea ly No embe be ween 1980 and 2023 (Figu e 4).
Figu e 3. Phenological ends in bu e ly species wi h mul iple gene a ions and long ligh pe iods
om 1921 o 2023. The indi idual species a e ep esen ed by di e en colou s in he sca e plo and
a e pa o he cumula i e da a analyzed o phenological shi s. Lines ep esen he KDE (ke nel
densi y es ima ion) i h ough he da a, ep esen ing a 2D dis ibu ion o he da a.
Figu e 4. De ia ion o las obse a ion da es o 5 species wi h mul iple gene a ions and long ligh
pe iods om he long- e m mean o he las obse a ion (N = sample size; A e age day = a e age
day o las obse a ion). G een ba s ep esen la e sigh ings = posi i e de ia ion; ed ba s ep esen
ea lie sigh ings = nega i e de ia ion. The ime in e al be ween 1973 and 2023 was spli by decades
in o de o highligh b eaking poin s in he obse ed ends.
Insec s 2025,16, 1071 9 o 17
3.3. Mig a o y Species
V. a alan a
was no p e iously known o o e win e no h o he Sou he n Ca pa hians.
Ea lie eco ds om T ansyl ania showed ha he i s indi iduals appea ed in collec ions
only a e he 15 h o 20 h o May. Al hough i had been suspec ed ha
V. a alan a
migh be
able o o e win e in he sou he n and sou heas e n pa s o he coun y, no conc e e e i-
dence suppo ed his assump ion. Howe e , o e he pas 15 yea s, sigh ings o
V. a alan a
in Cluj ha e become inc easingly common in Ap il and, in he las 5–6 yea s, e en as ea ly
as Ma ch. This sugges ed he possibili y ha he species was beginning o o e win e
in T ansyl ania, likely due o he egion’s inc easingly mild win e s. These assump ions
we e con i med when specimens we e obse ed as la e as mid-Decembe du ing unusually
wa m days o e he pas 4–5 yea s (Figu e 5).
Figu e 5. De ia ion o las obse a ion da es o he mig a o y species,
V. a alan a
om he long- e m
mean o he las obse a ion (N = sample size; A e age day = a e age day o las obse a ion). G een
ba s ep esen la e sigh ings = posi i e de ia ion; ed ba s ep esen ea lie sigh ings = nega i e
de ia ion. The ime in e al be ween 1973 and 2023 was spli by decades in o de o highligh
b eaking poin s in he obse ed ends.
3.4. Clima e
In o de o obse e he phenological shi s in bu e ly species, h ee majo clima ic
pa ame e s we e ex ac ed: he mon hly a e age p ecipi a ions, he a e age empe a u e,
and he snow co e o Cluj and i s su oundings. The eco ded annual p ecipi a ion
luc ua ed; howe e , he long- e m mean annual p ecipi a ion emained ela i ely cons an ,
wi h alues be ween
−
11.20 and 21.40 (Figu es 6a and 7a). A clea and consis en wa ming
end was obse ed when analyzing he mean annual mon hly empe a u es, wi h he
wa ming becoming mo e p onounced om app oxima ely 1980 onwa d (Figu e 6b). The
wa ming o he clima e becomes mo e e iden i only he summe mon hs a e assessed,
wi h a e age empe a u es inc easing signi ican ly, peaking in July and Augus be ween
2014 and 2023 a 20.9 ◦C and 21.0 ◦C (Figu e 7b).
In o de o co ela e he li e cycle changes in bu e ly species wi h he change in
clima ic condi ions in win e , we also ex ac ed he snow co e dynamics o he s udied
in e al (Figu e S1). This shows a clea nega i e linea end, wi h snow co e days
declining om app oxima ely 66 days in 1973–1984 o a ound 36 days in 2014–2023, as
a e age empe a u es inc eased by oughly 2
◦
C. The eg ession line highligh s his end,
wi h a high coe icien o de e mina ion (R
2
= 0.97), indica ing a obus co ela ion be ween
ising empe a u es and dec easing snow co e .
Insec s 2025,16, 1071 16 o 17
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