Aculus crassulae, Knihinicki & Petanović & Cvrković & Varia, 2018

Knihinicki, Danuta K., Petanović, Radmila, Cvrković, Tatjana & Varia, Sonal, 2018, A new species of Aculus mite (Acari: Eriophyidae), a potential biocontrol agent for Australian swamp stonecrop, Crassula helmsii (Crassulaceae), Zootaxa 4497 (4), pp. 573-585 : 575-583

Aculus crassulae sp. nov. Knihinicki & Petanović

FIgS. 1–4

Description. FEMALE (N=11). FIgS. 1–2 . BODY 246 (196–251) [IDIOSOMA 234 (185–230)], WIDTH 79 (63–78), SPINDLEfORM IN SHAPE, ORANgE TO PINK IN COLOUR. Gnathosoma 21 (17–22), DOWNCURVED, DORSAL PEDIPALP gENUAL SETAE (d) 6 (4–7), PEDIPALP COXAL SETAE (ep) 6 (4–6), CHELICERAL STYLETS 22 (19–23). Prodorsal shield SUbTRIANgULAR 38 (37– 43), 70 (55–72) WIDE, WITH bROAD fRONTAL LObE, ROUNDED APICALLY, SHALLOW, bUT EXTENDINg OVER bASE Of gNATHOSOMA, ALMOST COVERINg SETAE ep. TUbERCLES Of SETAE (sc) ON REAR SHIELD MARgIN, WELL-SPACED, 27 (25–30) APART, PRODORSAL SETAE (sc) 14 (13–17), PROjECTINg bACKWARDS AND OUTWARDS. PRODORSAL SHIELD ORNAMENTATION WITHOUT LINES, bUT WITH NUMEROUS SMALL NODULES COVERINg WHOLE SURfACE AND LATERAL SIDES, OCCURRINg IN SHORT, LINEAR SEgMENTS ( AS VISIbLE IN SEM IMAgE, FIg. 2A ). Legs WITH ALL USUAL SETAE PRESENT. Leg I 41 (33–39; MEASURED fROM bASE Of TROCHANTER); fEMUR 9 (9–10), bASIVENTRAL fEMORAL SETA (bv) 14 (5–14); gENU 5 (5–6), ANTAXIAL gENUAL SETA (l ″) 31 (28–37); TIbIA 10 (9–10), PARAXIAL TIbIAL SETA (l ′) 6 (5–7); TARSUS 7.5 (7–8), PARAXIAL fASTIgIAL TARSAL SETA (ft ′) 17 (12–19), ANATAXIAL fASTIgIAL TARSAL SETA (ft ′ ′) 26 (20–26), VENTROMESAL SETA (u ′) 5 (4–6), TARSAL SOLENIDION (ω) 8 (7–8), DISTALLY ROUNDED WITH SMALL, DISTINCTIVE KNOb, TARSAL EMPODIUM (em) 6 (6–7), 4-RAYED WITH SECONDARY bRANCHES. Leg II 35 (30–36); fEMUR 8 (8– 10), bASIVENTRAL fEMORAL SETA (bv) 15 (13–15); gENU 5 (5–6), ANTAXIAL gENUAL SETA (l ″) 6 (4–7); TIbIA 9 (7–9); TARSUS 8 (7–8), PARAXIAL fASTIgIAL TARSAL SETA (ft ′) 7 (5–6), ANATAXIAL fASTIgIAL TARSAL SETA (ft ′ ′) 20 (18–22), VENTROMESAL SETA (u ′) 5 (4.5–5), TARSAL SOLENIDION (ω) 7.5 (7–8), DISTALLY ROUNDED WITH SMALL, DISTINCTIVE KNOb, TARSAL EMPODIUM (em) 6.5 (6– 6), 4-RAYED WITH SECONDARY bRANCHES. Coxigenital region WITH 9 (7–10) COXIgENITAL ANNULI. COXAE SPARSELY gRANULATED WITH SHORT DASHES, PROSTERNAL APODEME 12 (10–12), DISTINCT, fORKED ANTERIORLY. PROXIMAL SETAE ON COXISTERNUM I (1b) 7 (7–11), TUbERCLES 14 (12–14) APART; PROXIMAL SETAE ON COXISTERNUM II (1a) 14 (14–18), TUbERCLES 10 (9–10) APART; PROXIMAL SETAE ON COXISTERNUM III (2a) 33(15[bROKEN]–36), TUbERCLES 25 (22–28) APART. Opisthosoma WITH LATERAL DIffERENTIATION bETWEEN LARgER DORSAL ANNULI AND MORE NUMEROUS VENTRAL ANNULI, WITH SHORT, SHALLOW, MID-DORSAL RIDgE ON LAST 10–12 DORSAL ANNULI fROM REAR, 58 (53–59) DORSAL ANNULI, SMOOTH; 63 (55–63) VENTRAL ANNULI, WITH ELLIPTICAL MICROTUbERCLES. LATERAL SETA (c2) 38 64(51–64, N=6) APART ON ANNULUS 5 (4–6) fROM gENITALIA; VENTRAL SETA I (d) 55 (30–54) LONg ON ANNULUS 18 (16–19), TUbERCLES 45 (32–41) APART; VENTRAL SETA II (e) 15 (11–21), ON ANNULUS 35(34–37), TUbERCLES 25 (17–22) APART; VENTRAL SETA III (f) 23 (15–25) ON 5TH (5TH–6TH) ANNULUS fROM REAR, TUbERCLES 22 (22–24) APART. CAUDAL SETAE (h2) 45 (22–57). ACCESSORY SETA (h1) AbSENT. External genitalia 15 (13–15), 24 (22–25) WIDE, gENITAL COVERfLAP gRANULATED ANTERIORLY, WITH 12 (10–13) SHORT, MOSTLY ObLIqUE AND SOME LONgITUDINAL STRIATIONS IN A SINgLE ROW; PROXIMAL SETAE ON COXISTERNUM III (3a) 14 (10–20); TUbERCLES 18 (14–19) APART. Internal genitalia WITH ANTERIOR, TRANSVERSAL APODEME TRAPEZOIDAL, LONgITUDINAL bRIDgE RELATIVELY LONg, SPERMATHECAL TUbES DIRECTED LATERO-POSTERAD, SPERMATHECAE Egg-SHAPED, gLObOSE.

MALE (N=2). FIg 1 . MALE SHORTER THAN fEMALE, gENERALLY SIMILAR. BODY 181–191, 54–57 WIDE. Gnathosoma 15–16, d 5–6, ep 3, CHELICERAE 17–19; DOWN-CURVED. Prodorsal shield 34–37, 51–55 WIDE WITH bROAD fRONTAL LObE , ROUNDED APICALLY, SHALLOW, DESIgN RESEMbLINg fEMALE, sc 11–14, TUbERCLES 22–23 APART. Legs WITH ALL USUAL SETAE. Leg I 32, fEMUR 9–10, bv 7–9; gENU 5, l ″ 21–22; TIbIA 7, l ′ 4; TARSUS 6, ft ″ 16–20, ft ′ 12–14, u ′ 4–5, ω 6, DISTALLY ROUNDED WITH SMALL, DISTINCTIVE KNOb, em 6, 4-RAYED WITH SECONDARY bRANCHES. Leg II 30; fEMUR 8–9, bv 10–11; gENU 5, l ″ 5–6; TIbIA 6–7; TARSUS 7, ft ″ 14–15, ft ′ 6–7, u ′ 4–5, ω 6–7; em 6, 4- RAYED WITH SECONDARY bRANCHES. Coxigenital region AS SHOWN WITH 9 MICROTUbERCULATED ANNULI, 1b 6–8, TUbERCLES 11 APART; 1a 11–14, TUbERCLES 8 APART; 2a 19–20, TUbERCLES 21–24 APART . COXAE I AND II SPARSELY gRANULATED AS IN fEMALE , PROSTERNAL APODEME 8, DISTINCT, fORKED ANTERIORLY. Opisthosoma SIMILAR TO fEMALE, WITH AbOUT 52–54 DORSAL ANNULI AND 52–54 VENTRAL ANNULI, WITH SHORT, SHALLOW, MID-DORSAL RIDgE ON LAST 10 TO 12 DORSAL ANNULI fROM REAR; c 2 15–22, ON ANNULUS 4–5 (fROM gENITALIA); d 29–31 ON ANNULUS 16–17, TUbERCLES 29–31 APART; e 12 ON ANNULUS 31, TUbERCLES 17 APART; f 21–22 ON 5TH ANNULUS fROM REAR, TUbERCLES 18–20 APART; h2 37–39, h1 AbSENT. External genitalia 17–18 WIDE, EPIANDRUM TYPICALLY ORNAMENTED WITH SMALL gRANULES, 3a 11–12 AND TUbERCLES 12–13 APART.

NYMPH (N=1). FIg 3 . IN COMPARISON TO ADULTS, IMMATURES LACK THE fRONTAL LObE Of THE PRODORSAL SHIELD AND HAVE SUbEqUAL NUMbERS Of VENTRAL AND DORSAL OPISTHOSOMAL ANNULI (IMMATURE ANNULI NOT DORSO-VENTRALLY DIffERENTIATED). BODY 145, 50 WIDE; VERMIfORM IN SHAPE, TRANSLUCENT TO WHITISH IN COLOUR. Gnathosoma 14, d 4, ep 3, CHELICERAE 17.5. Prodorsal shield 33, 49 WIDE; SEMI-OVOID, ANTERIOR LObE LACKINg, ORNAMENTATION fAINT bUT RESEMbLINg ADULT WITH SIMILAR ARRANgEMENT Of NODULES, sc 6, TUbERCLES 19 APART . Legs. Leg I 25; fEMUR 6, bv 3; gENU 3, l ″ 7; TIbIA 5, l ′ 3; TARSUS 4, ft ″ 12, ft ′ 7, u ′ 4, ω 6, SIMILAR TO ADULT, em 5, 4 -RAYED. Leg II 20; fEMUR 6, bv 6; gENU 3, l ″ 5; TIbIA 4; TARSUS 5, ft ″ 11, ft ′ 4, u ′ 3, ω 5, SIMILAR TO ADULT, em 4.5, 4-RAYED. Coxigenital region WITH 1 b 4, TUbERCLES 10 APART ; 1a 6, TUbERCLES 6 APART; 2a 10, TUbERCLES 20 APART. COXAE SPARSELY gRANULATED. PROSTERNAL APODEME AbSENT. COXIgENITAL REgION WITH 8 MICROTUbERCULATED ANNULI. 3a 4, TUbERCLES 7 APART. Opisthosoma. APPEARANCE Of ANNULI SUbEqUAL, NOT DIffERENTIATED AS IN ADULT ; MICROTUbERCLES EVENLY PRESENT ON DORSAL ANNULI, SMALLER AND SPARSER ON VENTRAL ANNULI, EVENLY SPACED. WITH 51 DORSAL ANNULI AND 47 VENTRAL ANNULI. c2 20, ON ANNULUS 8 (fROM gENITAL TUbERCLES), 39 APART; d 12 ON ANNULUS 17, TUbERCLES 26 APART; e 12 ON ANNULUS 27, TUbERCLES 13 APART; f 14 ON 5TH ANNULUS fROM REAR, TUbERCLES 17 APART. h 2 10, 9 APART; h1 AbSENT.

LARVA (N=1). FIg. 4 . BODY 107, 52 WIDE; VERMIfORM IN SHAPE, TRANSLUCENT TO WHITISH IN COLOUR. Gnathosoma 17, d 4, CHELICERAE 14. Prodorsal shield 30, 44 WIDE; SEMI-OVOID, ANTERIOR LObE LACKINg, ORNAMENTATION fAINT bUT RESEMbLINg ADULT WITH SIMILAR ARRANgEMENT Of NODULES, sc 11, TUbERCLES 20 APART . Legs. Leg I 22; fEMUR 7, bv 12; gENU 4, l ″ 19; TIbIA 6, l ′ 6; TARSUS 5, ft ″ 14, ft ′ 9, ω 5, SIMILAR TO ADULT, em 4, 4 -RAYED. Leg II 21; fEMUR 6, bv 9; gENU 4, l ″ 21; TIbIA 4; TARSUS 4, ft ″ 13, ft ′ 9, u ′ 3, ω 6, SIMILAR TO ADULT, em 3, 4-RAYED. Coxigenital region WITH 1 b 8, TUbERCLES 9 APART ; 1a 12, TUbERCLES 7 APART; 2a 17, TUbERCLES 15 APART. COXAE SPARSELY gRANULATED. PROSTERNAL APODEME AbSENT. SETAE 3a 7, TUbERCLES 9 APART. Opisthosoma. APPEARANCE Of ANNULI SUbEqUAL, NOT DIffERENTIATED AS IN ADULT ; MICROTUbERCLES EVENLY PRESENT ON DORSAL ANNULI, SMALLER AND SPARSER ON VENTRAL ANNULI, EVENLY SPACED. WITH 42 DORSAL ANNULI AND 31 VENTRAL ANNULI. c2 17, ON ANNULUS 2 (fROM gENITAL TUbERCLES), 40 APART; d 28 ON ANNULUS 10, TUbERCLES 24 APART; e 11 ON ANNULUS 20, TUbERCLES 15 APART; f 16 ON 5TH ANNULUS fROM REAR, TUbERCLES 18 APART. h 2 29, 10 APART; h1 AbSENT.

DEUTOGYNE FEMALE. NOT ObSERVED.

Host plant. Crassula helmsii (KIRK) COCKAYNE : CRASSULACEAE . A PLANT SPECIES CONSIDERED NATIVE TO AUSTRALIA AND NEW ZEALAND.

Relationship with the host plant and field observations. CAUSINg DISTORTION AND fORMATION Of “bIg bUD” gALLS WHEREbY LEAVES fAIL TO OPEN AND EXPAND NORMALLY ( FIg. 5 ). LEAVES DEVELOP A DEEP MAgENTA COLOUR COMPARED TO HEALTHY gREEN SHOOTS. THE LEAVES CURL INWARDS TO fORM A gALL-LIKE STRUCTURE. UPON REACHINg MATURITY, THE MITES WERE ObSERVED OUTSIDE THE gALL IN READINESS fOR DISPERSAL. ONLY THE TERRESTRIAL OR EMERgENT gROWTH fORMS Of C. helmsii WERE fOUND TO bE INfESTED bY A. crassulae sp. nov. AND IT WAS NOT ObSERVED IN THE SUbMERgED PLANT fORM. ADDITIONAL RESEARCH (S. VARIA et al. UNPUbLISHED DATA 2017) SUggESTS THAT THE OPTIMAL TEMPERATURE fOR MITE DEVELOPMENT IS AbOVE 20 o C.

Type material. Holotype fEMALE (SINgLE SPECIMEN ON MICROSCOPE SLIDE PREPARATION) EX INSIDE bUD Of AUSTRALIAN SWAMP STONECROP, Crassula helmsii , LAKE COLAC, VICTORIA, S 38°19′43.07 " E 143°35′43.04″ , COLL. R. ADAIR, 20.IV.2013 (DEPOSITED IN ASCT). Paratypes ON 5 MICROSCOPE SLIDE PREPARATIONS ( SOME SLIDES HAVE MULTIPLE SPECIMENS) WITH SAME COLLECTION DATA AS HOLOTYPE; EX C. helmsii , CAUSINg bUD gALLS, IN qUARANTINE fACILITY , CABI, COLONY DERIVED fROM LAKE COLAC, VICTORIA AS IN HOLOTYPE, COLL . S. VARIA, 2013. OTHER SPECIMENS ALSO EXAMINED.

Etymology. THE SPECIES NAME crassulae IS A fEMININE NOUN IN gENITIVE AND REfLECTS THE NAME Of THE PLANT gENUS ON WHICH THE NEW SPECIES WAS fOUND.

Differential diagnosis and remarks. THE NEW SPECIES, A. crassulae , IS CHARACTERIZED bY THE fRONTAL LObE WHICH IS bROAD AND ROUNDED APICALLY, SHALLOW, bUT EXTENDINg OVER THE bASE Of THE gNATHOSOMA ALMOST COVERINg SETAE ep. THERE IS LATERAL DIffERENTIATION bETWEEN THE LARgER DORSAL ANNULI AND MORE NARROW AND NUMEROUS VENTRAL ANNULI. UNLIKE MOST OR ALL OTHER SPECIES IN THE gENUS Aculus , A. crassulae sp. nov. HAS A SHORT MID-DORSAL RIDgE AT THE END Of THE OPISTHOSOMA.

WE COMPARED Aculus crassulae sp. nov. WITH THE ONLY OTHER Aculus SPECIES DESCRIbED fROM THE PLANT fAMILY CRASSULACEAE , I.E. Aculus cotyledonis ( KEIfER, 1939). THESE TWO SPECIES ARE SIMILAR IN THE NUMbER Of DORSAL ANNULI AND LENgTH Of THE sc SETAE. HOWEVER, THERE ARE SEVERAL MAjOR MORPHOLOgICAL DIffERENCES. THE NEW SPECIES CAN bE DISTINgUISHED bY HAVINg AN OPULENCE Of DISTINCTIVE NODULES COVERINg THE ENTIRE PRODORSAL SHIELD WHICH ARE PRESENT IN A SERIES Of SHORT, LINEAR SEgMENTS. IN CONTRAST, THE PRODORSAL SHIELD Of A. cotyledonis IS COMPRISED Of A STRONg NETWORK Of LINES AND IT HAS MUCH LONgER DORSAL SETAE. ADDITIONALLY, THE SPECIES DIffER fROM EACH OTHER IN THE NUMbER Of RAYS ON THE EMPODIA (4-RAYED IN A. crassulae sp. nov. AND 5-RAYED IN A. cotyledonis ). ALSO, UNLIKE OTHER CURRENTLY KNOWN SPECIES Of Aculus , THE DORSAL ANNULI IN THE NEW SPECIES fORM A CHARACTERISTIC, SHORT, SHALLOW, MID-DORSAL RIDgE AT THE POSTERIOR. THE DAMAgE SYMPTOMS ATTRIbUTED TO bOTH SPECIES ALSO DIffER. Aculus cotyledonis IS fOUND AT THE VERY bASE Of THE ROSETTE Of LEAfLETS Of THE HOST PLANT, D. caespitosa . IT bROWNS AND WRINKLES THE LEAf SURfACES, AND CAUSES AN UNEVEN WHITE SURfACE PULVERULENCE, WHILE THE NEW SPECIES CAUSES THE DISTORTION AND fORMATION Of “bIg bUD” gALLS ON C. helmsii WHEREbY LEAVES fAIL TO OPEN AND EXPAND NORMALLY.

Aculus crassulae sp. nov. IS ALSO SIMILAR TO Aculus haloragi ( LAMb, 1953) WHICH WAS fIRST DESCRIbED fROM NEW ZEALAND bY LAMb (1953) WITHIN THE gENUS Thamnacus . LATER, MANSON (1984) REDESCRIbED THE SPECIES AND REASSIgNED IT TO THE gENUS Aculops , CHANgINg THE NAME INTO haloragis . AMRINE AND STASNY (1994), AS WELL AS XUE AND ZHANg (2008), TREATED THIS SPECIES AS A MEMbER Of THE gENUS Aculus , PRObAbLY bECAUSE Of THE SHAPE Of THE SUbDORSAL SHIELD, AND RETURNED THE ORIgINAL SPECIES NAME Aculus haloragi . IT WAS LISTED AS CAUSINg DEfORMED INfLORESCENCES, LEAf AND bUD gALLS ON A RANgE Of Haloragis SPP. ( HALORAgACEAE ). Aculus crassulae sp. nov. AND A. haloragi INHAbIT PLANTS THAT bELONg TO THE SAME PLANT ORDER, SAXIfRAgALES . HENCE, IT WAS IMPORTANT TO COMPARE THEM fURTHER. THE ORIgINAL DESCRIPTIONS Of THE TWO SPECIES HAVE bEEN STUDIED AND A SUMMARY Of MEASUREMENTS ARE PRESENTED IN TAbLE 1. THE MAIN SIMILARITIES bETWEEN THE NEW SPECIES AND A. haloragi fROM NEW ZEALAND INCLUDE THE PRODORSAL SHIELD DESIgN AND ALSO THE fACT THAT IT HAS THE SAME NUMbER Of EMPODIAL RAYS. SOME SETAL LENgTHS ARE ALSO COMPARAbLE. HOWEVER, THERE ARE SOME MAjOR DIffERENCES SUCH AS A. crassulae sp. nov. HAVINg A MUCH LONgER bODY LENgTH AND A gREATER NUMbER Of DORSAL AND VENTRAL ANNULI THAN A. haloragi , AS WELL AS THE PRESENCE Of A SHORT MID- DORSAL RIDgE AT THE POSTERIOR END Of THE OPISTHOSOMA. IN THE ORIgINAL DESCRIPTION Of A. haloragi , LAMb (1953) MENTIONED THE PRESENCE Of A SHALLOW fURROW ON EITHER SIDE Of THE OPISTHOSOMA EXTENDINg TO THE CAUDA. HOWEVER, WHEN MANSON (1984) REDESCRIbED THAT SPECIES AfTER RE-EXAMININg LAMb’S TYPE MATERIAL, HE DID NOT ACCEPT LAMb’S ObSERVATION AND THIS IS PRObAbLY THE REASON WHY HE REMOVED IT fROM THE gENUS Thamnacus . NEITHER AUTHOR DESCRIbED OR ILLUSTRATED A SHORT, SHALLOW MID-DORSAL RIDgE EXTENDINg TOWARDS THE POSTERIOR Of THE OPISTHOSOMA. IN THE NEW SPECIES, A. crassulae , THIS CHARACTER IS EVIDENT IN SLIDE-MOUNTED SPECIMENS AND CAN CLEARLY bE SEEN IN THE SEM (SEE FIg. 2A ).

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DNA barcoding. THE SEqUENCINg RESULTED IN A 606 bP LONg fRAgMENT Of THE MTCOI bARCODE REgION (SENSU HEbERT et al. 2004). BASE PAIR fREqUENCIES SHOWED THAT THE REgION IS AT-RICH (A: 0.210, C: 0.135, G: 0.162, T: 0.493).

PAIRWISE COMPARISON Of OVERLAPPINg MTCOI fRAgMENTS USED IN THIS STUDY INDICATED A HIgH LEVEL Of gENETIC DIVERgENCE bETWEEN THE ANALYZED POPULATION Of A. crassulae sp. nov. AND TWO CONgENERIC SPECIES A. amygdali AND A. ichnocarpi (22.6% AND 23.1%, RESPECTIVELY). THE DIVERgENCE RATES ARE IN CONgRUENCE WITH INTERSPECIfIC VARIATIONS IN OTHER MITE TAXONOMIC gROUPS ( STEVENS & HOgg 2006; LEWANDOWSKI et al. 2014; SKORACKA & DAbERT 2010; MARTIN et al. 2010; SKORACKA et al. 2013; CHETVERIKOV et al. 2012 & 2015; VIDOVIĆ et al. 2015; CVRKOVIĆ et al. 2016).

Figures

FIGURE 1. Schematic drawings of Aculus crassulae sp. nov. AD. Dorsal view of anterior body region; AL. Lateral view of anterior body region; CG. Female coxigenital region; DPM. Dorsal vew of posterior opisthosoma; em. Empodium; GM. Male genital region; IG. Internal female genitalia; LO. Lateral view of annuli; PM. Lateral view of posterior opisthosoma; ω. Solenidion.

FIGURE 2 A–D. Scanning electron micrographs of Aculus crassulae sp. nov. A. Two mites presented in dorsal view (showing mid-dorsal ridge towards posterior); B. Ventral view of female showing coxigenital region; C. Detailed view of male coxigenital region; D. Detailed view of tarsal empodium.

FIGURE 3. Semi-schematic drawing of Aculus crassulae sp. nov. DNY. Dorsal view of nymph.

FIGURE 4. Semi-schematic drawing of Aculus crassulae sp. nov. DL. Dorsal view of nymph.

FIGURE 5. Damage symptoms caused by Aculus crassulae sp. nov. A. Leaf stem of Crassula helmsii showing infected buds and B. Enlarged image of the mites inhabiting a deformed leaf bud. Scale bar = 5 mm -A; 2 mm -B.