R I 3 R S X OD WLR Q V R I ' LIIH UH Q W & R Q WLQ H Q WV - BioOne · lis de diferentes regiones geográﬁcas se llevó a cabo lo que puede ayudar en la comprensión del fenotipo

Kumar et al: Taxonomic Traits and Preliminary Morphometrics of Scirtothrips dorsalis 941

SCIRTOTHRIPS DORSALIS (THYSANOPTERA: THRIPIDAE): SCANNING ELECTRON MICROGRAPHS OF KEY TAXONOMIC TRAITS AND A PRELIMINARY MORPHOMETRIC ANALYSIS OF THE GENERAL

MORPHOLOGY OF POPULATIONS OF DIFFERENT CONTINENTS

VIVEK KUMAR1*, DAKSHINA R. SEAL1, DAVID J. SCHUSTER2, CINDY MCKENZIE3, LANCE S. OSBORNE4,JAMES MARUNIAK5, AND SHOUAN ZHANG1

1Tropical Research and Education Center, UF/IFAS, 18905, SW 280 Street, Homestead, FL 33031

2Gulf Coast Research and Education Center, UF/IFAS, 14625 CR 672, Wimauma, FL 33598

3U.S. Horticultural Research Laboratory, 2001 South Rock Road, Fort Pierce, FL 34945

4Mid-Florida Research & Education Center, UF/IFAS, 2725 S. Binion Road, Apopka, FL 32703

5Department of Entomology & Nematology, UF/IFAS, P.O. Box 110620, Gainesville, FL 32611

ABSTRACT

The chilli thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) is an emerging pestof many economically important vegetable and ornamental crops grown in the UnitedStates. Accurate identification of this pest is a fundamental requirement in development ofeffective quarantine and management strategies. Using scanning electron microscopy, highresolution images of important taxonomic traits of this pest were produced, which will aidresearch, regulatory and extension personnel to identify this pest. High resolution imageswere obtained for identifying characters of S. dorsalis including tergites with antecostalridges; head with 3 pairs of ocellar setae, metanotum presenting longitudinal striations withmedially located pair of setae; veins of forewing presenting widely spaced setae; segmentVIII with complete posteromarginal comb of microtrichia; and sternites lacking discal setaebut covered with rows of microtrichia except in the antero-medial region. Further, a prelim-inary comparison of morphological traits of S. dorsalis populations from different geograph-ical regions was conducted, which can help in understanding the phenotype of this pest.Specimens of S. dorsalis were obtained from 5 distinct geographical regions: New Delhi, In-dia; Shizouka, Japan; Negev, Israel; St. Vincent and Florida in the United States. Fourteenmorphological characters of each population of S. dorsalis were measured and comparedamong the 5 populations. No significant differences were observed between the body lengthsof the various S. dorsalis populations, which ranged from 0.85 mm (Negev) to 0.98 mm (Flor-ida). When comparing 12 morphological characters, we found no significant differencesamong New Delhi, St. Vincent, Negev and Florida populations. However, when S. dorsalispopulations of these 4 regions were compared with Shizouka, significant differences were de-tected for either 2 or 5 morphological characters depending on the population, suggestingthe Japan population is more robust i.e., longer and wider mesothorax and metathorax, andwider abdomens. Also, the mean lengths of body size among different populations did notvary directly or inversely with latitude.

Key Words: chilli thrips identification, high resolution, morphometric analysis

RESUMEN

El trips de pimiento, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) es una plagaemergente de muchos cultivos horticolas y ornamentales de importancia económica en losEstados Unidos. La identificación exacta de esta plaga es un requisito fundamental en el de-sarrollo de cualquier estrategia eficaz de cuarentena y de gestión. Usando la imagen de mi-croscopio electrónico de barrido de alta resolución de esta plaga se produjo lo que se ayudade los productores y el personal de extensión para identificar esta plaga con gran facilidad.Además, una comparación de las características morfológicas de las poblaciones de S. dorsa-lis de diferentes regiones geográficas se llevó a cabo lo que puede ayudar en la comprensióndel fenotipo de esta plaga. Se obtuvieron especímenes de S. dorsalis de cinco regiones geo-gráficas distintas: Nueva Delhi, India; Shizouka, Japan; Negev, Israel; St. Vincent y la Flo-rida en los Estados Unidos. Se medido y se compararon catorce caracteres morfológicos decada población de S. dorsalis entre las cinco poblaciones. No se observaron diferencias signi-ficativas entre la longitud del cuerpo de las diferentes poblaciones de S. dorsalis, que variaentre 0.85 mm (Negev) a 0.98 mm (Florida). Al comparar los 12 caracteres morfológicos, no

942 Florida Entomologist 94(4) December 2011

se encontraron diferencias significativas entre las poblaciones de Nueva Delhi, San Vicente,Negev y de la Florida. Sin embargo, cuando se compararon las poblaciones de S. dorsalis deestas cuatro regiones con la poblacion de Shizouka, se detectaron diferencia significativas en2 o 5 caracteres morfológicos según la población, la cual indica que la población de Japón esmas robusta (es decir, el mesotórax y el metatórax son más largos y anchos, el abdomen esmás ancho). Además, el promedio de la longitud del cuerpo entre las poblaciones no varía enrelación directa o inversamente con la latitud geográfica.

Scirtothrips dorsalis Hood commonly knownas the Assam thrips, castor thrips, chilli thrips,berry thrips or yellow tea thrips (Dev 1964; Asaf-Ali et al. 1973; Seal & Klassen 2005; Masui 2007)is a highly polyphagous adventive pest speciesthat originated in south Asia. With liberalizationof trade in agricultural products and the historicgrowth in tourism during the past 3 decades, thistropical and subtropical pest has spread to allhabitable continents except Europe. S. dorsalishas been intercepted numerous times on variousflower, fruit and vegetable consignments im-ported into Europe, but failed to establish a dura-ble population on that continent (Vierbergen &Gagg 2009). Recently an incursion was also notedin a glasshouse of a botanical garden in theUnited Kingdom, but eradication measures weretaken and pest was controlled successfully (An-nie-Sophie Roy, pers. comm.). In the Americas, S.dorsalis gained its first foothold in Venezuela,where, since 2000, it has been causing damage tograpevine, Vitis vinifera L. (Vitaceae) (MacLeod &Collins 2006; Seal et al. 2010). Since 2003 whenSkarlinsy (2003) found S. dorsalis established inSt. Vincent, this species has been found widelydistributed in the Lesser Antilles and Puerto Rico(Ciomperlik & Seal 2004; Klassen & Seal 2008)and Surinam (Ciomperlik et al. 2005). In 2005 S.dorsalis was found established in Palm BeachCounty Florida on ‘Knockout’® rose (Rosa X‘Radrazz’) (Coolidge 2005), and in 3 counties ofTexas. Now S. dorsalis is established in 30 coun-ties in Florida and in 8 counties in Texas with con-firmations in Alabama and Louisiana in 2009 andNew York in 2010. In Florida, the pest becamerapidly distributed throughout the state by theretail trade in nursery plants. Osborne (2009)found this pest reproducing on more than 50plant species in Florida.

Detection of S. dorsalis larvae and adults infresh vegetation is difficult due to their thigmot-actic behavior and tiny stature (larvae < 1 mm;adults < 2 mm). Eggs are deposited within planttissues and may take a week for the larvae toemerge. Consequently, chances of transportationof S. dorsalis through state, regional, and inter-national trade of plant materials for all life stagesis high (Seal and Kumar 2010). S. dorsalis lifestages occur on meristems and other tender tis-sues of all above ground parts of the host plant.The feeding by this pest causes extensive areas tobe darkened with scars on various plant parts,

stunted growth of young leaves, reduced yield andunmarketable fruit.

Kuriyama et al. (1991) reported S. dorsalis tobe a weak flier, and that the most important routeof invasion into the greenhouse was by introduc-tion of infested pots and not aerial immigration.According to Meissner et al. (2005) the majorpathways of spread of this pest are air passengersand crew and their baggage, mail including maildelivered by express carriers, smuggled plantparts and windborne dispersal.

Genus Scirtothrips comprises more than 100species of thrips and S. dorsalis is one of the moststudied pests in the genus due to their economicimportance and global distribution. Due to thesmall size of thrips and morphological similari-ties, the identification of species in this genus is achallenge to non-experts. The morphologicaltraits of taxonomic importance for identificationof S. dorsalis are well defined in the literature.With slide mount images, Hoddle & Mound (2003)illustrated a taxonomic identification key of S.dorsalis along with 20 other Scirtothrips speciesin Australia. They noted that only 2 of the 21 spe-cies of Scirtothrips have microtrichial fields ex-tending fully across the sternites, i.e., S. aurantiiand S. dorsalis. In S. aurantii, the microtrichia al-most cover the entire surface of the sternites,whereas in S. dorsalis they are restricted to acomplete band across the posterior half of eachsternite. Thus, a clear and accurate taxonomiccharacterization is required to distinguish be-tween such species of Scirtothrips. The taxonomictraits of S. dorsalis illustrated by Skarlinsky(2004) and Hoddle (2009) illustrated with thripsslide mount images are very helpful. Neverthe-less, photographs taken at higher magnificationsand resolutions using advanced techniques likeScanning Electron Microscope (SEM) would beespecially helpful to research, regulatory and ex-tension personnel and, also, for teaching. The ac-curate and rapid identification of this invasiveand potentially devastating pest is essential toimplement effective plant quarantine and inte-grated control strategies.

A significant pathway of S. dorsalis into theCaribbean from south Asia was assumed to bepassengers whose ancestors had arrived from In-dia as indentured servants following the abolitionof slavery (Klassen et al. 2002). Many of thesefamilies are known to travel back and forth tovisit relatives in India. Thus, we conjectured that


the south Florida strain was derived from thepopulations in India. However, when we com-pared measurements of morphological features ofthe Florida 2009 strain to measurements of a pop-ulation in India reported by Raizada (1976), wenoted that the 5 characters (body length, anten-nal length, prothorax length, forewing length andhind wing length) out of 9 characters studied byRaizada was bigger in Florida (2009) strain. Onthe other hand, the Florida population of S. dor-salis was smaller compared with Indian popula-tion (1976) in 3 morphological characters, i.e.,head length, abdomen width and ovipositorlength. Thus, we felt there might be merit in mak-ing a preliminary comparison of the measure-ments of the morphological traits selected byRaizada with corresponding measurements oftraits of populations from different continentsand other widely separated locations.

The objectives of this study were a) to producehigh-resolution images of identifying charactersof S. dorsalis using SEM, and b) to determine ifcertain morphological characters of S. dorsalisadults differ significantly in size among popula-tions from different geographic regions of theworld.

MATERIALS AND METHODS

Sample Collection

Year of sample collection, geographical loca-tion (longitude and latitude), host plant, preser-vative, and sample source are reported in Table 1.Samples of S. dorsalis were obtained from 5widely separated locations: New Delhi, India(2008); Shizouka, Japan (2009); St. Vincent Is-land, West Indies (2006); Negev, Israel (2009);and Florida, USA (2009). The specimens fromNew Delhi, India reported by Raizada in 1976had been sampled from cotton (Gossypium hirsu-tum L.), castor (Ricinus Communis L.), pepper(Capsicum spp.) and other crops. Actual samplingtechnique depended on the individual sampler,but once adults were collected, they were immedi-ately placed in 70-95% ethanol and eventuallymailed to the Tropical Research and EducationCenter, UF/IFAS, Homestead, Florida, main-tained at -20 °C and later slide mounted for mor-phometric analysis.

Identification of Specimens

Thrips specimens were transferred to vialscontaining 75% alcohol for 10 min and then for5 min to a 10% KOH (potassium hydroxide so-lution) solution prepared in 50% ethanol. Whileplaced in KOH solution, the insect was gentlypounded in the abdominal region using a fineinsect pin to aid the removal of its abdominalcontents. For gradual dehydration, the speci- TA

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men was passed through a series of alcohol con-centrations starting from 65%, followed by 75%,85%, 90% and 95% for 5-8 min in each concen-tration. Each specimen was placed ventrally ona slide with a small drop of Hoyerís mountingmedia and covered with a glass cover slip. Theadult female thrips were identified and their

morphological traits were compared using taxo-nomic characteristics described by Hoddle andMound (2003), Skarlinsky (2004) and Hoddle etal. (2009) with a dissecting microscope at a min-imum of 10X magnification. Further, S. dorsalissamples collected from Florida were subjectedto morphological characterization using scan-ning electron microscopy to produce high qual-ity pictures, displaying features used for itsidentification.

Scanning Electron Microscopy

Adult S. dorsalis females from Florida werecollected in 30% ethanol and dehydrated in agraded series of 50%, 70%, 95%, and twice in100% ethanol for 30 min in each gradation. Sam-ples were kept in 100% ethanol overnight. On thenext d, samples were dried in 50% and 100% ofhexamethyldisilizane (HMDS:ethanol) for 30 mineach. Thereafter, samples were sputter coatedwith gold/palladium using the Hummer sputter-ing system (Anatech, USA) and subsequently ex-amined under a Hitachi S-4800 SEM operated at10-12 kV.

Fig. 1. Dorsal view of S. dorsalis adult presentingdark brown antecostal ridge (AR) on tergites.

Fig. 2. Eight segmented antenna with third and fourth segments each presenting a forked sensorium.


The following characters were used for posi-tive identification and morphological compari-son of S. dorsalis populations prior to morpho-metric analysis: Body of adult S. dorsalis is paleyellow in color bearing dark brown antecostalridge (AR) on tergites and sternites (Fig. 1).Head wider than long, bearing closely spacedlineation and a pair of eight segmented anten-nae with third and fourth segment each pre-sents a forked sensorium (Fig. 2). Of the threepairs of ocellar setae, the third pair, also knownas interocellar setae (IOS), arises between the 2hind ocelli (HO) (Fig. 3) and is nearly the samesize as the two pairs of post ocellar setae (POS)on the head. Pronotum presents closely spacedtransverse lineation (Fig. 4). Pronotal setae(anteroangular, anteromarginal and discal se-tae) are short and approximately equal inlength. Posteromarginal seta-II is broader and1.5 times longer than posteromarginal setae-Iand III. Posterior half of the metanotum pre-sents longitudinal striations; medially locatedmetanotal setae arise behind anterior margin,

campaniform sensilla are absent (Fig. 5).Forewings are distally light in color with pos-teromarginal straight cilia, on distal half, firstand second veins bear 3 and 2 widely spaced se-tae, respectively (Fig. 6). Abdominal tergites IIIto VI, each present a pair of small medially lo-cated setae (Fig. 7). The posteromarginal combon segment VIII is complete, tergite IX of fe-male presents medially located discal microtri-chia (Fig. 8). Discal setae absent on sternites,sternites covered with rows of microtrichia ex-cluding on the antero-medial region (Fig. 9),i.e., a complete band of microtrichia traversethe posterior half of each sternite.

Morphometric Measurements of Major Body Traits

We studied 14 morphological characters in 5populations of S. dorsalis and compared the re-sults with the measurements previously reportedby Raizada (1976). Raizada (1976) subjected 9characters of S. dorsalis adults to morphometricanalysis and in the present study; we added mea-

Fig. 3. Dorsal view of S. dorsalis head with ocellar triangle, interocellar setae (IOS), hind ocelli (HO) and pos-tocular setae (POS).


surements of the pro, meso, and meta thorax forcomparison. The objective of this study was tomake a preliminary determination of whethercertain morphological characters of S. dorsalisadults differ in size among populations from dif-ferent geographic regions of the world.

We selected 10 specimens from each of the 5populations for morphometric analysis. Thesources of these 5 populations are listed in Table 1.A single specimen of S. dorsalis was placed on eachslide with a drop of water: ethanol (50:50) to pro-tect the specimen from dehydrating. The specimenwas spread before measurements were taken.Fourteen morphological traits of 10 specimensfrom each region were quantified by measuring thelengths of the body, antennae, head, prothorax,mesothorax, metathorax, ovipositor, forewing andhind wing; and the widths of the head, abdomen,prothorax, mesothorax, and metathorax (Table 2)using an automontage advanced photography soft-ware program (Auto-Montage Pro software, ver-sion 5.02, Syncroscopy, Frederick, MD) and a LeicaMZ 12.5 stereomicroscope.

Statistical Analysis

Data on the measurement of various bodyparts of thrips pertaining to different geograph-ical regions were subjected to the square root (x+ 0.25) transformation to stabilize variance.Transformed data were analyzed using one-wayanalysis of variance (ANOVA, SAS InstituteInc. 2003). The differences among means oflength and width of body segments from differ-ent geographical regions were separated usingTukey’s HSD procedure (P < 0.05). Untrans-formed means and standard errors are reportedin Table 2.

RESULTS

Scanning Electron Microscopy

The results of the scanning electron micros-copy investigation are depicted in Figs. 2-9 anddescribed in the figure captions.

Fig. 4. Pronotum of S. dorsalis presenting horizontal closely spaced sculpture lines.


Morphometric Measurements of Major Morphological Features of Scirtothrips dorsalis

No significant differences were detected be-tween the 5 S. dorsalis populations for 9 of themorphological characters measured in this study,i.e., body length, antennal length, length of head,width of head, length of prothorax, width of pro-thorax, length of ovipositor and lengths of theforewings and the hindwings (Table 2). However,statistically significant differences were detectedamong the 5 populations for mesothorax (lengthand width), metathorax (length and width) andwidth of abdomen.

New Delhi, India (2008) Population

The population from New Delhi did not differsignificantly from the Florida, St. Vincent or Ne-gev populations for any of the morphological char-acters under consideration. Significant differ-ences were detected between this population andthe population from Shizouka in that both the

metathorax length and abdomen width weresmaller in the New Delhi population (Table 3).

Florida, USA (2009) Population

The Florida population was not significantlydifferent from the populations of New Delhi orNegev for any of the 14 morphological charactersthat were measured (Table 3). The Florida popu-lation was characterized by a significantlysmaller metathorax than the St. Vincent popula-tion, but there were no significant differences be-tween these 2 populations for the other 13 charac-ters that were measured. Five morphologicalcharacters of the Florida population were signifi-cantly smaller than the Shizouka population.These differences were most significant with re-spect to the lengths and widths of the mesotho-rax, metathorax and width of abdomen (Table 3).

St. Vincent Island, West Indies (2006)

The St. Vincent population had a significantlylonger metathorax than the populations from

Fig. 5. Posterior half of the metanotum presents longitudinal striations; medially located metanotal setae arisebehind anterior margin, campaniform sensilla are absent.


Florida and Negev and a significantly narrowerabdomen compared with Negev and Shizoukapopulations.

Shizouka, Japan (2009) Population

The S. dorsalis population from Shizoukadiffered significantly from the other 4 popula-tions for 2 or 5 morphological characters, de-pending on the population, suggesting that theJapan population is more robust (i.e., mesotho-rax and metathorax are longer and wider, andabdomen is wider) (Table 3). The metathoraxwas longer and the abdomen was wider thanthe New Delhi population. Further, theShizouka population had a wider mesothrorax,metathrorax and abdomen, and longer meso-throrax and metathorax than the Florida popu-lation. The metathorax and abdomen ofShizouka were also wider than the St. Vincentpopulation. Furthermore, the Shizouka popula-tion mesothorax was wider and metathoraxlonger compared with the Negev population.

Negev, Israel (2009) Population

The population from Negev did not differ sta-tistically from the New Delhi (2008) and Florida(2009) populations in any of the morphologicaltraits under study, but differed significantly in 2features with St. Vincent (metathorax length andabdominal width) and Shizouka populations (me-sothorax width and metathorax length).

The mean lengths of the antennae of theNew Delhi (1976) population were numericallyvery similar to these of the Negev (2009) popu-lation, but shorter than those of all other popu-lations in this study. However, the differencesin the measurements of all the remaining traitsbetween the New Delhi (1976) and the otherpopulations in this study were numericallysmall.

DISCUSSION

Since its development in early 1950s, SEM isconsidered as an efficient morphological identifi-

Fig. 6. Shaded forewing of S. dorsalis is light in color distally with first and second vein presenting 3 and 2 widelyspaced setae, respectively.


cation tool with numerous advantages over tradi-tional microscopy including: i) it has a large depthof field, which allows greater part of a specimen tobe in focus at one time, ii) it has much higher res-olution than light microscope and iii) because ituses electromagnetism instead of lenses, speci-mens can be magnified to much higher levels andthe researcher has much more control in the de-gree of magnification of the specimen understudy(Schweitzer 2011). However, SEM’s use in thetaxonomic characterization of Thysanopteranshas been is limited. High-resolution pictures of S.dorsalis using SEM technique will help research,regulatory and extension personnel to identifythis pest with greater ease. SEM produced Figs.2-9 provide information about all of the majoridentification characters of this pest. Two mem-bers of genus Scirtothrips, S. aurantii and S. dor-salis are unusual in having sternites covered withmicrotrichia (Hoddle & Mound 2003; Hoddle et al.2009). Fig. 9 shows the band of microtrichia is

continuous only across the posterior half of the S.dorsalis sternite, a feature that differentiates thispest not only from S. surantii, but insofar as isknown, from all other species of Scirtothrips.

No major differences were observed in thebody lengths of S. dorsalis adults recently col-lected from the 5 regions. Mean body lengthsranged from 0.85 mm (Negev population) to 0.98mm (Florida population). The mean length ofadults collected from New Delhi, India in 2008was greater than that previously reported byRaizada (1976) (0.91 and 0.76 mm, respectively).The mean body length of the Florida (2009) popu-lation is 0.223 mm longer than that of the NewDelhi (1976) population. Likewise, the mean an-tennal length of the Florida (2009) S. dorsalis is0.026 mm longer than that of the New Delhi(1976) population. We speculate that these differ-ences may be attributed to a possible role of thefeeding and reproductive hosts in regulating bodysize of the pest.

Fig. 7. Abdominal tergites III to VI of S. dorsalis present small setae medially situated close to each other.


Insects are know to regulate their body sizein response to the temperature surroundingthem; which is associated with elevation andlatitude (Blanckenhorn & Demont 2004; Tan-towijoyoa & Hoffmann 2011). Studies suggestthat there can be positive correlations betweenelevation and latitude on the one hand and bodysize on the other; and this is commonly ob-served (Smith et al. 2000). On the other hand,no correlation, or even a negative correlation,may be observed between sizes of body traitsand elevation and latitude (Kubota et al. 2007;Hawkins & DeVries 1996). Variation in size canaffect fitness traits like development and repro-duction (Berger et al 2008; Tammaru et al.2002), somatic and sexual growth (Blancken-horn 2006; Fischer et al. 2003), thermoregula-tion (Bishop & Armbruster 1999) and dispersalability (Gutierrez & Menendez 1997). At hightemperatures, some populations of thrips spe-cies acquire a small and paler form, and at lowtemperatures, they tend to be large and dark incolor. However, results from our present study

did not show any significant impact of tempera-ture on body size of S. dorsalis collected fromthe 5 regions, but we have no detailed informa-tion on temperatures during the times of collec-tion.

According to Björkman et al. (2009) body sizewithin certain taxonomic groups tends to in-crease with latitude (Bergmann clines), whilein certain other groups insect body size de-creases (converse Bergmann clines), and in yetothers tends to stay relatively constant withlatitude. In this study, the populations werefrom the following latitudes: St. Vincent, WestIndies: 13.35 N; Homestead, Florida: 25.48 N;Delhi, India: 28.38 N; Negev, Israel: 34.67 N;and Shizouka, Japan: 36.00 N. On comparingthe measurements of individuals from 5 re-gions, we found that the body length of S. dor-salis in these samples did not vary either di-rectly or inversely with latitude (Table 2).

All of the specimens the recently collected atNew Delhi, Florida, St. Vincent and Negev werereared on pepper, but not at Shizouka, which

Fig. 8. The posteromarginal comb (row of microtrichia) on segment VIII is complete.


were reared on tea. Since tea was not a hostplant of the other 4 populations sampled in thisstudy, we could not determine if host plants di-rectly affect morphology. Nevertheless, theShizouka population differs significantly fromthe other populations by having a longer andwider mesothorax and metathorax and abdo-men that is wider, which is an essential mor-phological character of females that allowsthem to produce more eggs and have high fe-cundity and greater fitness (Benitez et al.2011). In a concurrent experiment conducted todetermine the effect of host plant on the growthof S. dorsalis, the pest was reared under identi-cal conditions at Homestead, Florida on 6 dif-

ferent hosts, i.e., ‘Jalapeño’ pepper (Capsicumannuum L.), ‘Pod Squad’ bean (Phaseolus vul-garis L.), ‘Black Beauty’ eggplant (Solanummelongena L.), ‘Butternut’ squash (Cucurbitamoschata [ex Duchesne Lam.] Duchesne exPoir.), ‘Solar Set’ tomato (Solanum lycopersi-cum L.) and ‘Knockout’ rose (Rosa chinensisJacq.) (Seal et al. 2010). Body lengths andwidths of different development stages (10 indi-viduals each) were measured, and no signifi-cant differences in body size of this pest was ob-served when S. dorsalis was reared on these 6different hosts indicating, that these host plantspecies did not differentially induce size alter-ations in S. dorsalis.

Fig. 9. Discal setae absent on sternites, posterior half of sternite presents a continuous band of microtrichia, butmicrotrichia are absent in the antero-medial region.


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The results from our study suggest that the Ja-pan population may have diverged the most fromthe ancestral population in south Asia. We specu-late that the Japan population is not ancestral topopulations in the Americas or Israel. It seemspossible that the population in India may be an-cestral to the populations in the New World andIsrael. This could have been facilitated by the ex-tensive movement of people between India and Is-rael, and India and the Caribbean. In addition, Is-rael has commercial horticultural ventures in theGreater Antilles. Thus, movement of S. dorsalisfrom India to Israel and subsequently to the Car-ibbean cannot be ruled out. It would be interest-ing to determine whether there are substantialgenetic or behavioral differences, and even barri-ers to reproduction, between the Shizouka andNew Delhi populations as well as between theShizouka and Florida populations.

We believe that by using the automontage sys-tem did not introduce inordinately large errorscause by failure to have each specimen perfectlywithin the horizontal plane. We repeated each mea-surement on 10 different individuals, and it is wellknown that small experimental errors tend to can-cel each other. Morphometric analysis is an efficienttool that is being utilized for identification, determi-nation of larval instar, and discrimination of crypticspecies of several insect species including leaf min-ers, bees, beetles, and aphids, (Dale 1985; Ellis & El-lis 2008; Favret 2009; Shiao 2004; Tantowijoyoa &Hoffmann 2011), but is rarely used for thrips. Thisis because thrips body size, and color are known tobe phenotypically plastic in response to changingenvironments, which can occur across both smalland large spatial scales (Sakimura 1969; Murai &Toda 2001; Mound 2005). It may be important to

collect live populations from different regions, rearthem under identical environmental conditions inorder to ascertain if the apparent stability of mor-phological traits has a genetic basis. Future re-search will concentrate on direct correlation of mor-phometric analyses with molecular analyses of co-horts to validate our hypothesis that the Japan pop-ulation is not ancestral to populations in the 4 otherregions.

ACKNOWLEDGMENTS

We express our heartfelt thanks to Phyllis Weintraub(Israel), Masui Shinichi (Japan) and M. L. Richards (St.Vincent) for providing samples of S. dorsalis. We thankLyle Buss for invaluable help in using the Automontageprogram, and Ian Maguire for improving the quality ofFigure 9. We thank Garima Kakkar, Megha Kalsi and sev-eral anonymous reviewers for their critically importantconstructive criticism and helpful comments. This studywas funded by a USDA-CSREES Special Grant for theProject: “Distribution of Scirtothrips dorsalis in the Carib-bean Region and the development of chemical and biolog-ical methods to manage this pest”. In addition financialsupport was provided by the Florida Agricultural Experi-ment Station and the University of Florida’s Center forTropical Agriculture.

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BENÕTEZ, H., VIDAL, M., BRIONES, R., AND JEREZ, V.2010. Sexual Dimorphism and Morphological Varia-tion in Populations of Ceroglossus chilensis(Eschscholtz, 1829) (Coleoptera: Carabidae). J. Ento-mol. Res. Soc. 12: 87-95.

TABLE 3. NUMBER OF TRAITS IN WHICH SIGNIFICANT QUANTITATIVE DIFFERENCES OCCURRED BETWEEN THE VARIOUSGEOGRAPHIC POPULATIONS OF SCIRTOTHRIPS DORSALIS WHEN COMPARED TWO AT ONE TIME, AND THE COR-RESPONDING TRAITS THAT WERE QUANTITATIVELY DIFFERENT.

India 2008 Florida 2009 St. Vincent 2006 Israel 2009 Japan 2009

India 2008 X 0 0 0 2 Metathorax L Abdomen W

Florida 2009 0 X 1 Metathorax L 0 5 Mesothorax L Mesothorax W Metathorax L Metathorax WAbdomen W

St. Vincent 2006 0 1 Metathorax L X 2 Metathorax L Abdomen W

2 Metathorax W Abdomen W

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X Mesothorax W Metathorax L

Japan 2009 2 Metathorax L Abdomen W

5 Mesothorax L Mesothorax W Metathorax L Metathorax WAbdomen W

2 Metathorax W Abdomen W

2 Mesothorax W Metathorax L


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