Scirtothrips perseae new species is described. It is a pest of avocado in southern California

Nakahara, Sueo

English

Hochschulschriftenserver - Universität Frankfurt am Main

INSECTA MUNDI, Vol. 11, No.2, June, 1997  189 Scirtothrips perseae (Thysanoptera: Thripidae), a new species infesting avocado in southern California Sueo Nakahara, Systematic Entomology Laboratory, PSI, Agricultural Research Service, USDA 10300 Baltimore Avenue, Beltsville, Maryland 20705-2350 Abstract: Scirtothrips perseae new species is described.  It is a pest of avocado in southern California. Key Words:  Scirtothrips, perseae n. sp., Thysanoptera, Thripidae, avocado, southern California During June of 1996,  an unknown species of Scirtothrips was discovered damaging fruits and foliage of avocado, Persea americana Mill., in Sat-icoy and Oxnard, Ventura County, California.  By July of 1997, infestations were found in avocado groves and backyard plantings in seven counties of southern California, from San Diego county adja-cent to  Mexico  and north  into San Luis Obispo county. Two native Scirtothrips species in California are infrequen  tly found on avocado trees. Although found on several other plants, S.  aceri Moulton apparen  tly breeds on oak leaf (Quercus spp.), and is not a pest.  The polyphagous S.  citri Moulton is a pest  of Citrus in California, bu t there is no evidence that it damages or breeds on avocado.  Individuals of Scirtothrips astrictus Mound and Marullo were recently found on avocado trees showing signs of damage at Cartago and Zarcero, Costa Rica.  The three species are further discussed and differenti-ated in the comments for the new species. All described species and specimens of several undescribed species in Scirtothirps were examined in  an  attempt  to  locate  the  origin  of  this  new species.  Although none matched the new species, several  similar specimens  were  examined from Mexico and Central America.  The species is  de-scribed here to provide a scientific name for biolog-ical and control studies now in progress. Scirtothrips perseae,  new species Suggested Common Name:  Avocado thrips Female (macropterous).  Body generally yel-low,  head with ocellar crescent red,  light brown shade present or absent from  interocellar area, area of eyes brown; pronotum with brown separate spots or spots coalesced, aligned diagonally posteri-orly  (Fig.  3);  mesonotum brown in anterior  112; metanotum with pale brown shade on  posterior part of metascutum and anterior part of metas-cutellum; abdominal tergites II-VIII with antecos-tal ridges completely brown, shaded light brown anteriorly and posteriorly of ridge,  submarginal brown spot on each side on tergites II-VII; a small brown spot on pleurite II; sternal antecostal ridges brown on IV-VII; forecoxa shaded pale brown, all femora light yellow with 2 or 3 pale brown spots dorsally,  proximal  1/2  of all  tibiae  shaded pale brown, distally yellow.  Forewings grayish brown, lighter distally,  scale completely grayish brown, veins with orange pigments.  Setae brown.  Anten-nal segment I pale as head, II-VIII brown except pale in pedicel, basal and subbasal area separated by brown ring on segment III, and subbasal ring on segments IV-V. Antenna (Fig.  1).  About 3 times longer than head; segments with convex sides, III and IV con-stricted distal of forked sense cones, base of VI  not pedicellate; forked sense cones on segments III-IV rather thick,  V-shaped, 24 !lm long,  about 3  ~lm thick near base;  inner simple  sense cone  on  VI arising at about midlength of segment, 35-37  ~lm long, extending distally to about midlength of  VIII. Head (Fig. 2).  About as long as pronotum, 1.5 times broader than long at occiput, slightly broader at eyes, cheeks rather straight or slightly converg-ing caudally posterior of small bulge just behind compound eye, occiput about 2/5 as long as eyes; posterior part of head with close-set transverse striae, interocular area and vertex with striae far apart or reticulated.  Compound eyes with 4 pig-mented facets in two transverse rows.  Diameter of ocellus  11-15 !lm.  Ocellar seta I anterior of fore ocellus, normally longer than other ocellar setae, seta II  anterolaterad of fore  ocellus  near mesal margin  of  eye,  seta  III  short,  posterior  of and separated by about diameter offore ocellus, inside ocellar triangle;  2 pairs of developed postocular setae between compound eyes.  Mouthcone conical, reaching posterior margin of prosternum; mandi-ble 100 (90-100) !lm long. Pronotum (Fig. 3).  1. 7  -1.8 times broader than long;  sculpture  close-set,  transversely  aligned. 190 Discal and marginal setae except those on posterior margin  17(17-22),  5  or  6  setae  in  medial  row, longest 20(20-24) ~lm; posteromarginal setae rather short, B2 setae (Fig. 3b) 0.25-0.32 as long as prono-tum, 1.2-1.6 times longer than B 1 setae (Fig.  3a), 1.2-1.3  times longer than B3  setae (Fig.  3c),  B4 setae shortest.  Mesonotum.  Transversely sculp-tured,  striae  weak anteriorly;  median  setae far anterior of posterior margin, 20(23-25)  !lm  long. Metanotum.  Sculptured medially with longitudi-nally aligned elongate reticles followed posteriorly by wider reticles; median setae posterior of  anterior margin by 10(7-18) !lm, 20(17-30) !lm long; lateral setae 24(17-33)  ~lm long. Forewing.  Rather straight, apically pointed; fringe cilia wavy, 22(21-23); costal setae 26(27-29), 37(32-40) !lm  long at midlength, about as long as width of wing; forevein with groups of 3-4 and 4-6 setae in proximal 112,  distal 1/2 with 4 setae, occa-sionally 3 setae; hindvein with 3 setae; scale with 4 marginal and 1 discal seta. Abdomen.  Pair of median cliscal setae on terg-ites  II-VI  separated  usually  by  less  than  their length, on tergite IV 17 (15-17) !lm long, separated by 0.30(0.30 to 0.66) of their length, on V 18(17-20) !lm long, separated by  0.50(0.25 to about 1.00) of their length;  microtrichial field  on  each  side  of tergites III-VI with 3 dis cal setae, about 14 discal rows of microtrichia between D2-D3 setae; tergite VIII without median discal microtrichia (Fig.  4), posteromarginal comb complete, with about 41(35-42)  long microtrichia,  longest 20-22  !lm,  minute microtrichia between longer ones; tergite IX with-out median  discal  microtrichia,  B 1 setae longer than tergite X; tergite X shorter than IX,  Sternites with microtrichial band extending to  level of B2 setae; median sculpture lines and median posterior margin without microtrichia; ovipositor  185(175-198)  ~lm long. Male (macropterous).  Similar to females in color  except  abdomen  without brown  antecostal ridges or lateral spots. Most anatomical characters similar to  that of female, but smaller.  Head with interocellar area reticulated.  Forewing with 23-24 costal setae; fore vein with groups of 3-4 and 3-5 setae in proximal 11 2,  2-3 setae in distal 112;  hind vein with 3 setae, occasionally 4.  Abdominal tergite IX  with pair of drepanae curved mesally (cf. Fig. 5a); dorsal setae 3 pairs (cf.  Fig. 5b), aligned diagonally posterome-sad, median pair 54-62 !lm long, next laterad pair subequal to median pair, third laterad pair short-est. Volume 11, No.2, June, 1997, INSECTA MUNDI Measurements  of  holotype  and  female (paratypes) in !lm.  Body length 914-988compacted, 1082 (1044-1092) distended. Antenna: Totallength 237 (244-257); length and width of  segment I 17(17-20),23(22-24); II 35(35-40), 25(24-30); III 45(48-50), 20(20-22);  IV  42(45-48),  19(18-20);  V  37(35-40), 16(16-17); VI  42(42-48),  17(15-17);  VII  7(7),  7(7); VIII 12(11-12), 5(4-6). Length of head from  apex of vertex (91-96), length of compound eye 62(62-69), length of occiput posterior of compound eye  24(24),  width at com-pound eye 151 (146-163), width between compound eyes  62(54-69),  width  at  cheeks  146  (136-165). Length of  pronotum 98(100-104).  Forewing length 669(679-756), widthatmicllength37(37-40). Length of abdominal tergite IX 69(67-74), tergite X 45 (42-50).  Length of setae:  Ocellar setae I 21(17 -24), II 18(15-20), III 16(15-20); POi 22(17-22), POii 20(17-20); pronotal B 1 setae 20(17 -20), B2 setae 24-28(27-32), B3  setae 20(17-25), B4 setae about 11(10-12); abdominal tergite IX B 1 setae 67(57-64), B2 setae 62(62-64), tergite X Bl setae 59(62-70). Measurements of male paratypes in !lm.  Body length 783-865  long,  distended.  Antenna: total length 224-230 long; length of segment I 17,  II 35, III 42-48, IV 40, V35-1137, VI 37-38, VII 7, VIII 11. Forewing length 595; width at midlength 30. Larva.  Second instar larva generally white; head with pale anteromedian gray band running from vertex to venter between  bases of antennae; abdominal tergite IX with pale gray band from D 1 setae (Fig. 6a) to laterad ofD2 setae; tergite X with pale gray band  from D 1 setae laterad; legs partially gray and white. Antennal segment  I gray with apex white, II and III gray with bases and apices white, IV-VII gray. Sense cone on antennal segment IV about as long as segment  VII. Head not reticulated; with D  1, D3 and D5 setae apically pointed, D2 and D4 setae apically expanded; pronotum not reticulated; dor-sal setae apically pointed, except D6 setae thicker, longer and apically  expanded.  Forefemur with medio-dorsal setae pointed apically (Fig. 7a); mid-and hindfemur each with 1 subapical setae, thick-er, expanded apically.  Abdominal tergite IX with D2  setae apically expanded (Fig.  6b,  longer than apically pointed D 1 setae (Fig. 6a); tergite X with D 1 setae  acuminate, longer than acuminate D2 setae. First instar larva generally white.  Dorsal cha-etotaxy similar to  second instar larva except  1 medio-dorsal seta apically expanded on forefemur INSECTA MUNDI, Vol. 11, No.2, June, 1997 and D 1 setae on abdominal tergite X apically ex-panded. Type Material. Holotype  0  , 110  and 8d' paratypes, Oxnard, Ventura Co., California, Persea americana Mill.,  15-VIII-9G,  Penrose,  Asakawa, Bronson,  Laird  (9G-OGOOO)  (USNM).  Other paratypes from  California:  30,  2d',  10  larvae, Saticoy, Ventura Co., Persea americana, 24-VI-9G, T. Dimock and  C.  Gribble (452G89);  20, 1  d' , Irvine, Orange Co.,  14-VIII-9G, R.  Penrose, N.  Nisson (9G-OGOOl);  170, 2d', Highway 118, Ventura Co., Hass avocado, G-VII-97,  M.  Hoddle;  GO,  La Lorna Rd., Ventura Co.,  Hass avocado,  G-VII-97,  M.  Hoddle. Paratypes deposited in British Museum of Natural History,  London;  Bohart Museum, University of California, Davis; California Department of Food and Agriculture, Sacramento; Department of En  to-mology , University of California, Riverside; Florida Collection  of Arthropods,  Gainesville;  Forschun-ginstitut un Naturmuseum Senckenberg, Frank-furt am Main, Germnay; and U.S. National Muse-um of Natural History (USNM). Distribution:  California  (Los  Angeles,  Or-ange, Riverside, San Diego, San Luis Obispo, Santa Barbara and Ventura Counties). Collected from:  Per sea americana Mill. Etymology: Species is named after the gener-ic name of its recorded host, Persea. Economic Importance. This species feeds on avocado  foliage  and immature  fruits.  Lightly damaged immature fruits mature but the quality is reduced because of the scarring blemish on  the skin. Heavily scarred immature fruits do not devel-op.  The leaves become cup-shaped and bronzed. (M. Hoddle, pers. comm.). Comments.  In the Nearctic Region, this spe-cies is  similar to S.  aceri in coloration and most anatomical characters. The distinquishing charac-ters of S.  aceri are the short (5-7 ~lm) median setae on abdominal tergites III-VI whose bases are sepa-rated by more than :3 times their length, the intero-cellar area lacks sculpturing, and slight differences in coloration of basal an tennalsegments and brown maculation on the abdomen.  In contrast, the medi-an setae of S. perseae are 15-20 ~lln long on tergites III-VI and whose bases are separated at most by about their length but usually are closer, and the interocellar area is sculptured (Fig. 2).  Scirlolhrips citri has a pale yellow body without brown macula-tion.  It  usually has ,5-8 discal setae on each side of abdominal tergites III-VII  in contrast to  3 discal setae in S. perseae and S.  aceri.  The brown macu-lations of  S. as(n:c{,us from Costa Rica is similar but 191 more extensive than in S.  perseae.  It has ocellar seta III positioned between the posterior ocelli and a row of  median discal microtrichia is presen  t along the posterior margin of abdominal tergite VIII.  In S. perseae the ocellar seta III is positioned between the anterior and posterior ocelli,  and abdominal tergite VIII lacks discal microtrichia in the median area (Fig.  4). Acknowledgements I thank the following colleagues for reviewing the manuscript and providing useful suggestions: Raymond J. Gill, Department of Food and Agricul-ture, Sacramento, California; Laurence A. Mound, CSIRO, Canberra, Australia; and Steven W.  Lin-gafelter and Michael E. Schauff, Systematic Ento-mology Laboratory, Washington D.C.  I also thank Raymond J.  Gill and Mark Hoddle, University of California, Riverside for providing specimens.  In-formation on  distribution and damage symptoms were provided by Mark Hoddle, and Steve Peirce, California Avocado Commission.  The illustrations were prepared by  Linda H.  Lawrence, Scientific Illustrator, Systematic Entomology Laboratory. 192  Volume 11, No.2, June, 1997, INSECTA MUNDI 1  4 Figu  res 1-4. Scirtothrips perseae. Adult. 1. Antenna. 2. Head. 3. Pronotum; a. B 1 seta, b. B2 seta, c. B3 seta. 4. Abdominal tergite VIII.  Figu  re 5. Scirtothrips cu:eri.  Abdominal tergite IX and X; a. drepana, b. dorsal seta.  Figures 6-7. Scirtothrips perseae.  Larva. 6. Abdominal tergites IX and X; a. Dl seta, b. D2 seta.  7. Forefemora and part of tibia; a. middorsal seta.  Scale: =  0.1 mm. 

Scirtothrips perseae (Thysanoptera: Thripidae) : a new species infesting avocado in southern California

Abstract

Similar works

Full text

Available Versions

Hochschulschriftenserver - Universität Frankfurt am Main